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7/21/2019 Fernandez JO T 2011 http://slidepdf.com/reader/full/fernandez-jo-t-2011 1/61  The Virginia Tech Calibration System Javier O. Fernandez Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Electrical Engineering Virgilio A. Centeno, Chair Jaime De La Ree Lopez Richard W. Conners Keywords: calibration system, pmu calibration, pmu, phasor May 3, 2011 Blacksburg, VA Copyright 2011, Javier O. Fernandez

Fernandez JO T 2011

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Phasor measurement unit (PMU) applications on power grid monitoring systemshave been implemented since the early ninety’s. Large monitoring system networkperformance relies on the consistent measurements of PMUs across the system. This hasbecome a major challenge for designers since large networks use PMUs from variousmanufacturers who likely implement different synchrophasor technologies to perform thephasor estimations. The current synchrophasor standard, the IEEE C37.118-2005Synchrophasor Standard, covers adequately the steady-state characterization of PMUs butdoes not specify transient condition requirements. The North American SynchrophasorInitiative (NASPI) has developed a guide outlining the several tests required for dynamiccharacterization of PMUs. The National Institute of Standards and Technology (NIST)developed two PMU testing stands for steady-state conformance with the currentstandard and for dynamic performance testing. Since May 2010, Virginia Tech has beenworking closely with the NIST in developing a PMU testing system similar to the NISTdesigns for commercial testing of PMUs and research purposes, the Virginia TechCalibration System. This thesis focuses on assessing the system accuracy differencesbetween the designs, and the software interface modifications to adapt the new hardware.

Citation preview

Page 1: Fernandez JO T 2011

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The Virginia Tech Calibration System

Javier O Fernandez

Thesis submitted to the faculty of theVirginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science

InElectrical Engineering

Virgilio A Centeno ChairJaime De La Ree Lopez

Richard W Conners

Keywords calibration system pmu calibration pmu phasor

May 3 2011Blacksburg VA

Copyright 2011 Javier O Fernandez

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The Virginia Tech Calibration System

Javier O Fernandez

ABSTRACT

Phasor measurement unit (PMU) applications on power grid monitoring systems

have been implemented since the early ninetyrsquos Large monitoring system network

performance relies on the consistent measurements of PMUs across the system This has

become a major challenge for designers since large networks use PMUs from various

manufacturers who likely implement different synchrophasor technologies to perform the

phasor estimations The current synchrophasor standard the IEEE C37118-2005

Synchrophasor Standard covers adequately the steady-state characterization of PMUs but

does not specify transient condition requirements The North American Synchrophasor

Initiative (NASPI) has developed a guide outlining the several tests required for dynamic

characterization of PMUs The National Institute of Standards and Technology (NIST)

developed two PMU testing stands for steady-state conformance with the current

standard and for dynamic performance testing Since May 2010 Virginia Tech has been

working closely with the NIST in developing a PMU testing system similar to the NISTdesigns for commercial testing of PMUs and research purposes the Virginia Tech

Calibration System This thesis focuses on assessing the system accuracy differences

between the designs and the software interface modifications to adapt the new hardware

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iii

List of Figures v

List of Tables vi

List of Acronyms vii

1 Introduction 1

2 Literature Review 4

21 The IEEE 1344-1995 Synchrophasor Standard 4

22 The IEEE C37118-2005 Synchrophasor Standard 5

23 Need for a New Synchrophasor Standard 7

3 The Virginia Tech Calibration System Design 9

31 Requirements Decomposition 9

311 System Performance 9

3111 Time Source 11

3112 Data Acquisition 12 3113 Signal Processing 12

312 Parameter Testing 13

3121 Steady-State Testing 13

3122 Dynamic Testing 15

3123 Protocol Testing 15

313 Documentation 15

32 System Definition 15

321 System Description and High-level Architectural Depiction 16

33 Steady-state Design 17 331 Time Source 18

332 Signal Generation 18

333 Data Acquisition 19

334 Signal Processing 19

335 Clock Synchronization 20

336 Signal Attenuation 21

337 DUT interface 21

34 Dynamic Testing Design 22

341 Signal Generation 22

35 Calibration 23

4 Steady-state Testing 24

41 Accuracy and Time Alignment 24

411 Magnitude Accuracy 24

412 Phase Accuracy 27

413 Frequency Accuracy 31

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iv

5 Dynamic Testing 35

51 Step Change response 35

511 Dynamic Magnitude Response 37

512 Dynamic Phase Response 39

513 Dynamic Frequency Response 43

6 Conclusions and Recommendations 48

References 49

Appendix A NI PXI-6682 Timing Module Technical Specifications 51

Appendix B Omicron CMC 156 EP Technical Specifications 52

Appendix C NI PXIe-6356 Data Acquisition Module Technical Specifications 53

Appendix D NI PXI-6733 Analog Output Module Technical Specifications 54

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v

List of Figures

Figure 11 NIST phase measurement unit calibration system 3

Figure 12 Diagram of NIST dynamic test system 3 Figure 21 Convention for phasor representation 4

Figure 22 Convention for synchrophasor representation 5

Figure 23 Phasor measurement process with TVE error detection criteria 6

Figure 31 The Virginia Tech Calibration System requirements decomposition 9

Figure 32 The Virginia Tech Calibration System high level architectural depiction 16

Figure 33 Phase calibration of reference PMU with the 1PPS clock signal 23

Figure 41 MagTestRunNI VI front panel 25

Figure 42 MagTestRunNI VI block diagram 26

Figure 43 Voltage magnitude accuracy test results 27

Figure 44 PhaseTestRunNI VI front panel 28

Figure 45 PhaseTestRunNI VI block diagram 29 Figure 46 Phase accuracy test results 30

Figure 47 FreqTestRunNI VI front panel 32

Figure 48 FreqTestRunNI VI block diagram 33

Figure 49 Frequency accuracy test results 34

Figure 51 NI_DUT_Step_add VI block diagram 36

Figure 52 Run_Step_Test_on_DUTs_add VI front panel 37

Figure 53 Magnitude step change test signal 38

Figure 54 Magnitude step change test results 39

Figure 55 Phase step change test signal (-45˚) 40

Figure 56 Phases step change test signal (+45˚) 41

Figure 57 Phase step change test results (-45˚) 42

Figure 58 Phase step change test results (+45˚) 43

Figure 59 Frequency step change test signal (-2Hz) 44

Figure 510 Frequency step change test signal (+2Hz) 45

Figure 511 Frequency step change test results (-2Hz) 46

Figure 512 Frequency step change test results (+2Hz) 47

Figure B1 Omicron CMC 156 technical specifications 52

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vi

List of Tables

Table 21 Required PMU reporting rates 6

Table 31 Hardware modules used in the NIST designs 11 Table 32 Influence quantities and allowable error limits for compliance levels 0-1 14

Table 33 Major processing component descriptions in the Virginia Tech Calibration System 16

Table 34 Hardware used in the Virginia Tech Calibration System steady-state design 17

Table 35 Software interface VIs in the Virginia Tech Calibration System 17

Table 36 Time source module accuracy comparison with the NIST designs 18

Table 37 Signal generation module accuracy comparison with the NIST designs 19

Table 38 Data acquisition module accuracy comparison with the NIST designs 19

Table 39 Signal processing module accuracy comparison with the NIST designs 20

Table 310 Synchronization source accuracy comparison with the NIST designs 21

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design 22

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design 22

Table A1 NI PXI-6682H synchronization accuracy 51

Table C1 NI PXIe-6356 technical specifications 53

Table D1 NI PXI-6733 technical specifications 54

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The Virginia Tech Calibration System

Javier O Fernandez

ABSTRACT

Phasor measurement unit (PMU) applications on power grid monitoring systems

have been implemented since the early ninetyrsquos Large monitoring system network

performance relies on the consistent measurements of PMUs across the system This has

become a major challenge for designers since large networks use PMUs from various

manufacturers who likely implement different synchrophasor technologies to perform the

phasor estimations The current synchrophasor standard the IEEE C37118-2005

Synchrophasor Standard covers adequately the steady-state characterization of PMUs but

does not specify transient condition requirements The North American Synchrophasor

Initiative (NASPI) has developed a guide outlining the several tests required for dynamic

characterization of PMUs The National Institute of Standards and Technology (NIST)

developed two PMU testing stands for steady-state conformance with the current

standard and for dynamic performance testing Since May 2010 Virginia Tech has been

working closely with the NIST in developing a PMU testing system similar to the NISTdesigns for commercial testing of PMUs and research purposes the Virginia Tech

Calibration System This thesis focuses on assessing the system accuracy differences

between the designs and the software interface modifications to adapt the new hardware

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iii

List of Figures v

List of Tables vi

List of Acronyms vii

1 Introduction 1

2 Literature Review 4

21 The IEEE 1344-1995 Synchrophasor Standard 4

22 The IEEE C37118-2005 Synchrophasor Standard 5

23 Need for a New Synchrophasor Standard 7

3 The Virginia Tech Calibration System Design 9

31 Requirements Decomposition 9

311 System Performance 9

3111 Time Source 11

3112 Data Acquisition 12 3113 Signal Processing 12

312 Parameter Testing 13

3121 Steady-State Testing 13

3122 Dynamic Testing 15

3123 Protocol Testing 15

313 Documentation 15

32 System Definition 15

321 System Description and High-level Architectural Depiction 16

33 Steady-state Design 17 331 Time Source 18

332 Signal Generation 18

333 Data Acquisition 19

334 Signal Processing 19

335 Clock Synchronization 20

336 Signal Attenuation 21

337 DUT interface 21

34 Dynamic Testing Design 22

341 Signal Generation 22

35 Calibration 23

4 Steady-state Testing 24

41 Accuracy and Time Alignment 24

411 Magnitude Accuracy 24

412 Phase Accuracy 27

413 Frequency Accuracy 31

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iv

5 Dynamic Testing 35

51 Step Change response 35

511 Dynamic Magnitude Response 37

512 Dynamic Phase Response 39

513 Dynamic Frequency Response 43

6 Conclusions and Recommendations 48

References 49

Appendix A NI PXI-6682 Timing Module Technical Specifications 51

Appendix B Omicron CMC 156 EP Technical Specifications 52

Appendix C NI PXIe-6356 Data Acquisition Module Technical Specifications 53

Appendix D NI PXI-6733 Analog Output Module Technical Specifications 54

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v

List of Figures

Figure 11 NIST phase measurement unit calibration system 3

Figure 12 Diagram of NIST dynamic test system 3 Figure 21 Convention for phasor representation 4

Figure 22 Convention for synchrophasor representation 5

Figure 23 Phasor measurement process with TVE error detection criteria 6

Figure 31 The Virginia Tech Calibration System requirements decomposition 9

Figure 32 The Virginia Tech Calibration System high level architectural depiction 16

Figure 33 Phase calibration of reference PMU with the 1PPS clock signal 23

Figure 41 MagTestRunNI VI front panel 25

Figure 42 MagTestRunNI VI block diagram 26

Figure 43 Voltage magnitude accuracy test results 27

Figure 44 PhaseTestRunNI VI front panel 28

Figure 45 PhaseTestRunNI VI block diagram 29 Figure 46 Phase accuracy test results 30

Figure 47 FreqTestRunNI VI front panel 32

Figure 48 FreqTestRunNI VI block diagram 33

Figure 49 Frequency accuracy test results 34

Figure 51 NI_DUT_Step_add VI block diagram 36

Figure 52 Run_Step_Test_on_DUTs_add VI front panel 37

Figure 53 Magnitude step change test signal 38

Figure 54 Magnitude step change test results 39

Figure 55 Phase step change test signal (-45˚) 40

Figure 56 Phases step change test signal (+45˚) 41

Figure 57 Phase step change test results (-45˚) 42

Figure 58 Phase step change test results (+45˚) 43

Figure 59 Frequency step change test signal (-2Hz) 44

Figure 510 Frequency step change test signal (+2Hz) 45

Figure 511 Frequency step change test results (-2Hz) 46

Figure 512 Frequency step change test results (+2Hz) 47

Figure B1 Omicron CMC 156 technical specifications 52

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vi

List of Tables

Table 21 Required PMU reporting rates 6

Table 31 Hardware modules used in the NIST designs 11 Table 32 Influence quantities and allowable error limits for compliance levels 0-1 14

Table 33 Major processing component descriptions in the Virginia Tech Calibration System 16

Table 34 Hardware used in the Virginia Tech Calibration System steady-state design 17

Table 35 Software interface VIs in the Virginia Tech Calibration System 17

Table 36 Time source module accuracy comparison with the NIST designs 18

Table 37 Signal generation module accuracy comparison with the NIST designs 19

Table 38 Data acquisition module accuracy comparison with the NIST designs 19

Table 39 Signal processing module accuracy comparison with the NIST designs 20

Table 310 Synchronization source accuracy comparison with the NIST designs 21

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design 22

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design 22

Table A1 NI PXI-6682H synchronization accuracy 51

Table C1 NI PXIe-6356 technical specifications 53

Table D1 NI PXI-6733 technical specifications 54

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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iii

List of Figures v

List of Tables vi

List of Acronyms vii

1 Introduction 1

2 Literature Review 4

21 The IEEE 1344-1995 Synchrophasor Standard 4

22 The IEEE C37118-2005 Synchrophasor Standard 5

23 Need for a New Synchrophasor Standard 7

3 The Virginia Tech Calibration System Design 9

31 Requirements Decomposition 9

311 System Performance 9

3111 Time Source 11

3112 Data Acquisition 12 3113 Signal Processing 12

312 Parameter Testing 13

3121 Steady-State Testing 13

3122 Dynamic Testing 15

3123 Protocol Testing 15

313 Documentation 15

32 System Definition 15

321 System Description and High-level Architectural Depiction 16

33 Steady-state Design 17 331 Time Source 18

332 Signal Generation 18

333 Data Acquisition 19

334 Signal Processing 19

335 Clock Synchronization 20

336 Signal Attenuation 21

337 DUT interface 21

34 Dynamic Testing Design 22

341 Signal Generation 22

35 Calibration 23

4 Steady-state Testing 24

41 Accuracy and Time Alignment 24

411 Magnitude Accuracy 24

412 Phase Accuracy 27

413 Frequency Accuracy 31

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iv

5 Dynamic Testing 35

51 Step Change response 35

511 Dynamic Magnitude Response 37

512 Dynamic Phase Response 39

513 Dynamic Frequency Response 43

6 Conclusions and Recommendations 48

References 49

Appendix A NI PXI-6682 Timing Module Technical Specifications 51

Appendix B Omicron CMC 156 EP Technical Specifications 52

Appendix C NI PXIe-6356 Data Acquisition Module Technical Specifications 53

Appendix D NI PXI-6733 Analog Output Module Technical Specifications 54

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v

List of Figures

Figure 11 NIST phase measurement unit calibration system 3

Figure 12 Diagram of NIST dynamic test system 3 Figure 21 Convention for phasor representation 4

Figure 22 Convention for synchrophasor representation 5

Figure 23 Phasor measurement process with TVE error detection criteria 6

Figure 31 The Virginia Tech Calibration System requirements decomposition 9

Figure 32 The Virginia Tech Calibration System high level architectural depiction 16

Figure 33 Phase calibration of reference PMU with the 1PPS clock signal 23

Figure 41 MagTestRunNI VI front panel 25

Figure 42 MagTestRunNI VI block diagram 26

Figure 43 Voltage magnitude accuracy test results 27

Figure 44 PhaseTestRunNI VI front panel 28

Figure 45 PhaseTestRunNI VI block diagram 29 Figure 46 Phase accuracy test results 30

Figure 47 FreqTestRunNI VI front panel 32

Figure 48 FreqTestRunNI VI block diagram 33

Figure 49 Frequency accuracy test results 34

Figure 51 NI_DUT_Step_add VI block diagram 36

Figure 52 Run_Step_Test_on_DUTs_add VI front panel 37

Figure 53 Magnitude step change test signal 38

Figure 54 Magnitude step change test results 39

Figure 55 Phase step change test signal (-45˚) 40

Figure 56 Phases step change test signal (+45˚) 41

Figure 57 Phase step change test results (-45˚) 42

Figure 58 Phase step change test results (+45˚) 43

Figure 59 Frequency step change test signal (-2Hz) 44

Figure 510 Frequency step change test signal (+2Hz) 45

Figure 511 Frequency step change test results (-2Hz) 46

Figure 512 Frequency step change test results (+2Hz) 47

Figure B1 Omicron CMC 156 technical specifications 52

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vi

List of Tables

Table 21 Required PMU reporting rates 6

Table 31 Hardware modules used in the NIST designs 11 Table 32 Influence quantities and allowable error limits for compliance levels 0-1 14

Table 33 Major processing component descriptions in the Virginia Tech Calibration System 16

Table 34 Hardware used in the Virginia Tech Calibration System steady-state design 17

Table 35 Software interface VIs in the Virginia Tech Calibration System 17

Table 36 Time source module accuracy comparison with the NIST designs 18

Table 37 Signal generation module accuracy comparison with the NIST designs 19

Table 38 Data acquisition module accuracy comparison with the NIST designs 19

Table 39 Signal processing module accuracy comparison with the NIST designs 20

Table 310 Synchronization source accuracy comparison with the NIST designs 21

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design 22

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design 22

Table A1 NI PXI-6682H synchronization accuracy 51

Table C1 NI PXIe-6356 technical specifications 53

Table D1 NI PXI-6733 technical specifications 54

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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iv

5 Dynamic Testing 35

51 Step Change response 35

511 Dynamic Magnitude Response 37

512 Dynamic Phase Response 39

513 Dynamic Frequency Response 43

6 Conclusions and Recommendations 48

References 49

Appendix A NI PXI-6682 Timing Module Technical Specifications 51

Appendix B Omicron CMC 156 EP Technical Specifications 52

Appendix C NI PXIe-6356 Data Acquisition Module Technical Specifications 53

Appendix D NI PXI-6733 Analog Output Module Technical Specifications 54

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v

List of Figures

Figure 11 NIST phase measurement unit calibration system 3

Figure 12 Diagram of NIST dynamic test system 3 Figure 21 Convention for phasor representation 4

Figure 22 Convention for synchrophasor representation 5

Figure 23 Phasor measurement process with TVE error detection criteria 6

Figure 31 The Virginia Tech Calibration System requirements decomposition 9

Figure 32 The Virginia Tech Calibration System high level architectural depiction 16

Figure 33 Phase calibration of reference PMU with the 1PPS clock signal 23

Figure 41 MagTestRunNI VI front panel 25

Figure 42 MagTestRunNI VI block diagram 26

Figure 43 Voltage magnitude accuracy test results 27

Figure 44 PhaseTestRunNI VI front panel 28

Figure 45 PhaseTestRunNI VI block diagram 29 Figure 46 Phase accuracy test results 30

Figure 47 FreqTestRunNI VI front panel 32

Figure 48 FreqTestRunNI VI block diagram 33

Figure 49 Frequency accuracy test results 34

Figure 51 NI_DUT_Step_add VI block diagram 36

Figure 52 Run_Step_Test_on_DUTs_add VI front panel 37

Figure 53 Magnitude step change test signal 38

Figure 54 Magnitude step change test results 39

Figure 55 Phase step change test signal (-45˚) 40

Figure 56 Phases step change test signal (+45˚) 41

Figure 57 Phase step change test results (-45˚) 42

Figure 58 Phase step change test results (+45˚) 43

Figure 59 Frequency step change test signal (-2Hz) 44

Figure 510 Frequency step change test signal (+2Hz) 45

Figure 511 Frequency step change test results (-2Hz) 46

Figure 512 Frequency step change test results (+2Hz) 47

Figure B1 Omicron CMC 156 technical specifications 52

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vi

List of Tables

Table 21 Required PMU reporting rates 6

Table 31 Hardware modules used in the NIST designs 11 Table 32 Influence quantities and allowable error limits for compliance levels 0-1 14

Table 33 Major processing component descriptions in the Virginia Tech Calibration System 16

Table 34 Hardware used in the Virginia Tech Calibration System steady-state design 17

Table 35 Software interface VIs in the Virginia Tech Calibration System 17

Table 36 Time source module accuracy comparison with the NIST designs 18

Table 37 Signal generation module accuracy comparison with the NIST designs 19

Table 38 Data acquisition module accuracy comparison with the NIST designs 19

Table 39 Signal processing module accuracy comparison with the NIST designs 20

Table 310 Synchronization source accuracy comparison with the NIST designs 21

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design 22

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design 22

Table A1 NI PXI-6682H synchronization accuracy 51

Table C1 NI PXIe-6356 technical specifications 53

Table D1 NI PXI-6733 technical specifications 54

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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v

List of Figures

Figure 11 NIST phase measurement unit calibration system 3

Figure 12 Diagram of NIST dynamic test system 3 Figure 21 Convention for phasor representation 4

Figure 22 Convention for synchrophasor representation 5

Figure 23 Phasor measurement process with TVE error detection criteria 6

Figure 31 The Virginia Tech Calibration System requirements decomposition 9

Figure 32 The Virginia Tech Calibration System high level architectural depiction 16

Figure 33 Phase calibration of reference PMU with the 1PPS clock signal 23

Figure 41 MagTestRunNI VI front panel 25

Figure 42 MagTestRunNI VI block diagram 26

Figure 43 Voltage magnitude accuracy test results 27

Figure 44 PhaseTestRunNI VI front panel 28

Figure 45 PhaseTestRunNI VI block diagram 29 Figure 46 Phase accuracy test results 30

Figure 47 FreqTestRunNI VI front panel 32

Figure 48 FreqTestRunNI VI block diagram 33

Figure 49 Frequency accuracy test results 34

Figure 51 NI_DUT_Step_add VI block diagram 36

Figure 52 Run_Step_Test_on_DUTs_add VI front panel 37

Figure 53 Magnitude step change test signal 38

Figure 54 Magnitude step change test results 39

Figure 55 Phase step change test signal (-45˚) 40

Figure 56 Phases step change test signal (+45˚) 41

Figure 57 Phase step change test results (-45˚) 42

Figure 58 Phase step change test results (+45˚) 43

Figure 59 Frequency step change test signal (-2Hz) 44

Figure 510 Frequency step change test signal (+2Hz) 45

Figure 511 Frequency step change test results (-2Hz) 46

Figure 512 Frequency step change test results (+2Hz) 47

Figure B1 Omicron CMC 156 technical specifications 52

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vi

List of Tables

Table 21 Required PMU reporting rates 6

Table 31 Hardware modules used in the NIST designs 11 Table 32 Influence quantities and allowable error limits for compliance levels 0-1 14

Table 33 Major processing component descriptions in the Virginia Tech Calibration System 16

Table 34 Hardware used in the Virginia Tech Calibration System steady-state design 17

Table 35 Software interface VIs in the Virginia Tech Calibration System 17

Table 36 Time source module accuracy comparison with the NIST designs 18

Table 37 Signal generation module accuracy comparison with the NIST designs 19

Table 38 Data acquisition module accuracy comparison with the NIST designs 19

Table 39 Signal processing module accuracy comparison with the NIST designs 20

Table 310 Synchronization source accuracy comparison with the NIST designs 21

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design 22

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design 22

Table A1 NI PXI-6682H synchronization accuracy 51

Table C1 NI PXIe-6356 technical specifications 53

Table D1 NI PXI-6733 technical specifications 54

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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vi

List of Tables

Table 21 Required PMU reporting rates 6

Table 31 Hardware modules used in the NIST designs 11 Table 32 Influence quantities and allowable error limits for compliance levels 0-1 14

Table 33 Major processing component descriptions in the Virginia Tech Calibration System 16

Table 34 Hardware used in the Virginia Tech Calibration System steady-state design 17

Table 35 Software interface VIs in the Virginia Tech Calibration System 17

Table 36 Time source module accuracy comparison with the NIST designs 18

Table 37 Signal generation module accuracy comparison with the NIST designs 19

Table 38 Data acquisition module accuracy comparison with the NIST designs 19

Table 39 Signal processing module accuracy comparison with the NIST designs 20

Table 310 Synchronization source accuracy comparison with the NIST designs 21

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design 22

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design 22

Table A1 NI PXI-6682H synchronization accuracy 51

Table C1 NI PXIe-6356 technical specifications 53

Table D1 NI PXI-6733 technical specifications 54

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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vii

List of Acronyms

PMU Phasor measurement unit

NASPI North American Synchrophasor InitiativeNIST National institute of standards and technology

WAMPAC Wide-area monitoring protection and control

DOE Department of Energy

PSTT Performance and Standards Task Team

WECC Western Electricity Coordinating Council

CERTS Consortium for Electric Reliability Technology Solutions

EIPP Eastern Interconnection Phasor Project

SOC Second of Century

TVE Total vector error

GPS Global Positioning System

NI National Instruments

DUT Device under testVI Virtual Instrument

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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1 INTRODUCTION

The Phasor Measurement Unit (PMU) also known as synchrophasor takes time

synchronized measurements of voltage and current signals on a power grid This device was first

developed by researchers at Virginia Tech in Blacksburg VA in the late 1980rsquos PMU devicesare commercialized as a stand-alone unit or the PMU function can be integrated into a protective

relay or other device

PMU applications on wide-area monitoring protection and control (WAMPAC) systems

have gained worldwide acceptance since its emergence as commercial devices in the power

industry market in early 1990rsquos Brazil and China are currently deploying large WAMPAC

systems to control their power grids [2 3] The US Department Of Energy (DOE) as a response

to the 1996 and 2003 blackouts has sponsored improvements in the control of power grids that

involve the use of PMU-based WAMPAC systems

WAMPAC systems integrate information from selected local networks to a remote

location to minimize the widespread effects of large disturbances Most large PMU

implementations on wide-area monitoring networks use devices from various manufacturers

which present a challenge to ensure consistent phasor readings as they likely use different

measurement technologies For such systems WAMPAC system performance relies on the PMU

conformance to the same synchrophasor standard

In December 2005 the IEEE C37118-2005 Synchrophasor Standard [1] to replace the

IEEE 1344-1995(R2001) Synchrophasor Standard [4] developed in March 2001 These

standards define the synchrophasor phasor measurements in power grids for interoperability and

interfacing with associated equipment The IEEE Standard for Synchrophasors for Power

Systems C37118-2005 [1] covers adequately the PMU characterization under steady-state

conditions but falls short under transient conditions Consistent dynamic performance among

PMUs is of great importance for most current phasor applications

In 2007 the North America efforts in phasor technology were combined and the North

American Synchro Phasor Initiative (NASPI) emerged with the intent to coordinate phasor

activities in the entire North American grid The increased role for industry collaborations of the

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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NASPI working group and task teams has already extended to a more global collaboration of

industry best practices while the DOE continues to support phasor research Today there are

seven task teams focusing on various aspects of phasor activities[5]

Amongst the task teams is the Performance and Standards Task Team (PSTT) The PSTTis chartered to coordinate and act as liaison to standardization efforts and to determine consistent

and satisfactory performance of synchronized measurement devices and systems by creating

guidelines and reports in accordance with best practices Many of the PSTT members are active

in many international industry activities which help the Task Team members to coordinate the

development of phasor-related standards both within the NASPI as well as outside of North

America[5]

The PSTT team developed two complementary documents to the IEEE C37118 PMU

Testing Guide [6] and SynchroPhasor Accuracy Characterization [7]

This Guide describes performance and interoperability tests and calibration procedures

for PMUs used in the electric power industry to monitor the condition of the electric power grid

Conformance tests with the IEEE C37118-2005 Synchrophasor Standard and extended test

procedures to address the dynamic performance requirements not specified in the IEEE C37118-

2005 Synchrophasor Standard are included [1] This considers performance standards established

by the Western Electricity Coordinating Council (WECC) [8] Laboratory PMU test and

calibration procedures described[6]

To promote better test and measurement procedures for PMU test and calibration the

National Institute of Standards and Technology (NIST) in US has established a

SynchroMetrology Laboratory in support of the Consortium for Electric Reliability Technology

Solutions (CERTS) which sponsors the NASPI (was EIPP) The laboratory is established to

develop test and calibration methods to combine traditional waveform parameter metrology with

procedures to reference these values to a synchronized timing source such as UTC[3]

The NIST SynchroMetrology Laboratory developed two calibration systems as shown in

Figures 11 and 12 one for testing PMU for compliance with the IEEE C37118-2005

Synchrophasor Standard [1] and the other for dynamic characterization on PMUs

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 11 NIST Phase Measurement Unit Calibration System [Stenbakken 2007] Illustrated

under ldquoFair Userdquo copyright guidelines

The purpose of developing the NIST Dynamic Test System includes the characterizationof commercial PMUs under dynamic power system conditions and the use of this data for the

development of new dynamic performance requirements for PMUs

Figure 12 Diagram of NIST Dynamic Test System [Stenbakken 2007] Illustrated under ldquoFair

Userdquo copyright guidelines

In this thesis project the NIST designs for steady-state calibration testing and dynamic

characterization of PMUs were implemented with new equipment the Virginia Tech Calibration

System This thesis provides an overview of the NIST designs and explains the required

modifications to integrate the new hardware

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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2 LITERATURE REVIEW

21 The IEEE 1344-1995 Synchrophasor Standard

This was the first PMU standard approved in December 1995 and reaffirmed in March

2005 It addresses synchronization of data sampling data-to-phasor conversions and formats for

timing input and phasor data output from a PMU [10]

The standard defined a precise method for time stamping data samples and phasor

measurements as shown in Figure 21 listed the requirements for the time synchronizing sources

and specified the allowed types of time input IRIG-B format 1 PPS and the high precision time

format

Figure 21 Convention for phasor representation [IEEE Standard for Synchrophasors for PowerSystems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

It approved the use of either synchronized or non-synchronized sampling requiring

phase-locked sampling for synchronized sampling systems or equivalent phasor measurements

for non-synchronizing sampling systems The standard also defined a resynchronization method

for external time and sampling sources

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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For steady state analysis it required that the phasor measurements followed the off-

nominal frequencies It also defined a convention for phasor representation independent from

window size The standard also requires phase compensations for delays internal to the PMU

It also defined the message format required for data reporting from the PMU organizedas data header and configuration frames and for commands received by the PMU

22 The IEEE C37118-2005 Synchrophasor Standard

This is the current PMU standard approved in December 2005 It addresses the definition

of a synchronized phasor time synchronization application of timetags method to verify

measurement compliance with the standard and message formats for communication with a

PMU [11]

This standard improved the time stamping method defined in the IEEE 1344-1995

Synchrophasor Standard [4] by redefining the phasor timetag as a group of three numbers a

second-of-century (SOC) count a fraction-of-second count and a time status value It also

allowed data format compatibility with other standards such as the IEC 61850 Standard

It defined the convention for phasor representation as an absolute phasor with a phase

locked to nominal frequency and synchronized to UTC time as shown in Figure 22

Figure 22 Convention for synchrophasor representation [IEEE Standard for Synchrophasors forPower Systems 2001] Illustrated under ldquoFair Userdquo copyright guidelines

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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This standard specified the required phasor reporting rates for 50 Hz and 60 Hz as shown

in Table 21 the actual used rate being selected by the user

Table 21 Required PMU reporting rates [IEEE Standard for Synchrophasors for Power Systems2006] Illustrated under ldquoFair Userdquo copyright guidelines

It defined the steady-state condition where the magnitude frequency and phase of the

test signal remained constant during the time of measurement

This standard introduced the concept of total vector error (TVE) for quantifying phasor

measurement errors as defined in Figure 23

Figure 23 Phasor measurement process with TVE error detection criteria [IEEE Standard forSynchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright guidelines

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The TVE is a comparison between a theoretical phasor X and an input phasor

measured by the PMU If a phase shift of ( is added to both X and the phasors would

rotate keeping the ratio between the magnitudes and the TVE constant

This standard also defined the error limits using the TVE concept for the recommended

steady-state compliance tests on the influence quantities shown in Table 32

The NIST developed the NIST PMU Calibration System for testing PMUs for

compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This steady-state

calibration test stand design is described in [9 11]

23 Need for a New Synchrophasor Standard

Some of the IEEE 1344-1995 Synchrophasor Standard [4] limitations were addressed in

the current standard The first standard defined the phasor requirements only at the zero

crossings or 1PPS second mark It did not specify any requirements for dynamic responses such

as measurement response time or accuracy under transient conditions The data format and the

serial type of interface required were not compatible with industry network communication

standards

The IEEE C37118-2005 Synchrophasor Standard [1] covers adequately most the steady-

state PMU characterization however there are limitations that will need to be addressed in the

new standard It does not specify frequency accuracy requirements Also lack of testing

procedures requirements in the current standard and unavailability of testing equipment are

major issues for PMU testing and calibration [5]

If the input frequency becomes off-nominal the mismatch induces a rotation between the

estimated phasor and the measured phasor causing the TVE to change inside the time window

Possible solutions are suggested in [12 13] including a modification to the standard to add a

TVE limit for the time window or a maximum frequency deviation for the compliance tests

Most importantly to support the increasing demand for high quality PMU applications on

large WAMS the current PMU standard needs to be further developed Future standards should

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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show a higher level of detail for dynamic PMU performance requirements testing procedures

and documentation that could guarantee homogeneous performance conformance among PMU

from different manufacturers

The NIST developed the NIST Dynamic Test System for testing PMU performance undertransient conditions and the use of this data for the development of new dynamic performance

requirements for PMUs This PMU dynamic characterization test stand design is described in [10

14 15]

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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3 THE VIRGINIA TECH CALIBRATION S YSTEM DESIGN

31 Requirements Decomposition

The requirements for the Virginia Tech Calibration System were based on the compliance

verification requirements specified in the IEEE C37118-2005 Synchrophasor Standard [1] and

dynamic PMU testing requirements This thesis provides the first and second level breakdown of

the requirement decomposition as shown in Figure 31 Each level was further developed with

the maturation of the design process and system concept

Figure 31 The Virginia Tech Calibration System requirements decomposition

311 System Performance

The IEEE C37118-2005 Synchrophasor Standard [1] specifies an accuracy for standard

test equipment of at least four times compared with the test requirement On the other hand the

PMU Testing Guide [6] increases this accuracy requirement to at least ten times the testing

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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specification and also defines an alternate setup where best available test equipment is used for

testing and calibrating the PMUs

A calibration device used to verify performance in accordance with this subclause shall

be traceable to national standards and have a ldquotest accuracy ratiordquo of at least four compared withthese test requirements (for example provide a TVE measurement within 025 where TVE is

1) In cases where there is no national standard available for establishing traceability a detailed

error analysis shall be performed to demonstrate compliance with these requirements[1]

In general the test equipment should be ten times more accurate than the test tolerance ie

the uncertainty of the test equipment should be less than one tenth the test tolerance Under these

conditions the error contribution from the test equipment can generally be ignored in the

evaluation of units under test [6]

There should generally be two setups

Full-featured calibration laboratory ndash used for testing and calibrating both the PMUs and

field test equipment This setup should be equipped with the best possible clock reference

waveform reconstruction (DA) measurement (AD) devices

Standard test equipment - should be ten times more accurate than the test tolerance

Standard test equipment is calibrated using the full-featured calibration laboratory setup

Different options may fall into this category It is important to note that some options may be

suitable for use in labs but some may be used in field Field testing may take place in a

substation control house or switchyard depending on which devices are to be tested

Primary test equipment consists of time reference sources and a multi-phase signal

generator It is suggested that the signal generator be capable of accepting large ldquoplayback filesrdquo

that store point on wave signals that control its output[6]

The NIST designs are full-featured calibration laboratory setups featuring extremely low

uncertainty signal generation data acquisition and signal processing equipment The hardware

modules used in the NIST designs are listed in Table 31

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Table 31 Hardware modules used in the NIST designs983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139830856608 983112983145983143983144 983120983154983141983139983145983155983145983151983150 C983151983157983150983156983141983154983124983145983149983141983154 983159983145983156983144 D983145983143983145983156983137983148 983113983119

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 (3) 983122983151983156983141983147 8100 983155983145983143983150983137983148 983139983137983148983145983138983154983137983156983151983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 983118983113 9831209831289831139830856733 983085 8 983139983144 983137983150983137983148983151983143 983151983157983156983152983157983156 16983085983138983145983156 1 983117983123983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139830856123 983085 8 983139983144 983137983150983137983148983151983143 983145983150983152983157983156 16983085983138983145983156 500 983147983123983155983139983144

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139830858196 20G983144983162 983120983141983150983156983145983157983149 983117 983120983128983113 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 983128983120

These modules are installed in NI PXI-1042 chassis featuring a PXI backplane capable of132Mbs data straming

The NIST PMU Calibration System is calibrated both on time accuracy and on waveform

accuracy It has been calibrated to have less than 0015 maximum magnitude uncertainty and

less than 0009 degree maximum angle uncertainty (less than 04 microsecond time uncertainty)

which means the test system has an uncertainty of less than 0015 TVE[3]

In our design we will be using the NIST software designs with new hardware The

minimum accuracy specification requirements for the new hardware equipment must be the same

as the NIST designs to guarantee at least the same performance

3111 Time Source

The current best available technology for obtaining and referencing UTC time is the

Global Positioning System (GPS) Originally developed for military applications the GPS

system is made up of a network of 24 satellites maintained by the US Department of Defense

referencing atomic clocks These clocks are extremely accurate time sources Factors that may

degrade GPS signal may include atmospheric disturbances such as ionosphere and troposphere

delays number of satellites visible orbital or ephemorsis errors and receiver clock errors[16]

Fluctuations in the GPS time signal may cause short term uncertainty of the GPS time

reference The use of a local receiver clock helps averaging fluctuations over time reducing the

errors in the time signals Since these built-in clocks are not as accurate as atomic clocks the

time signals may drift away from UTC time resulting in considerable offsets errors for our

application Two factors to consider when assessing suitable GPS receivers are the reception

quality of the GPS signal and the stability of the local built-in oscillator

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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A time error of 1 micros corresponds to a phase error of 0022deg for a 60 Hz system and 0018deg

for a 50 Hz system A phase error of 001 radian or 057deg will by itself cause 1 TVE This

corresponds to a maximum time error of plusmn 26 micros for a 60 Hz system and plusmn 31 micros for a 50 Hz

system[1]

3112 Data Acquisition

Phasor accuracy is limited by the data sampling as follows For a minimum error

requirement and a full-scale rating the AD converter needs the following

(31)

The factor radic2 scales the formula from RMS to bipolar peak values which is how AD

converters must be specified[4] Since the calibration system must have an accuracy of ten times

the 1 PMU requirement and the NIST designs use a full-scale of 3X-4X then

(32)

3113 Signal Processing

The NIST designs collect DUT phasor data computes the input test signal phasor and

compares them simultaneously The signal processing power is high but not sufficient to make

the system real-time The DUT data and input signals are buffered and used as needed for

required computations

The NIST designs are modular minimizing custom design for the sub-systems

minimizing costs Also allows for modular upgrades to meet new potential performance

requirements with minimum development time This involves developing module interfaces and

a clear division of software into functional tasks

The signal processing tasks are performed using NI Labview 85 software running on a

NI PXI-8196 embedded controller module using Windows XP operating system This design is

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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capable of handling phasor computations for reporting rates of up to 30 frames per second but

system limitations may be found at higher rates

Future synchrophasor standards may require higher PMU reporting rates for which the

NIST signal processing hardware may need to be upgraded to satisfy with the new processingrequirements or the software design modified to allow phasor computation and comparison

operations done entirely off-line

Given the large number of computations required to carry on the dynamic performance

tests a higher performance processor may be required for keeping the testing time relatively

short

312 Parameter TestingThe PMU testing is divided into steady-state and dynamic tests The IEEE C37118-2005

Synchrophasor Standard [1] defines each steady-state conformance test requirements and limits

The PMU Testing Guide [6] covers in more detail the steady-state tests and defines each

dynamic performance test and requirements

PMUrsquos usually must undertake factory acceptance tests commissioning tests and

maintenance tests Furthermore the PMU must also satisfy requirements tailored to its

application such as interoperability with other PMU system components common performancewith other units in the monitoring network high time synchronization and tagging accuracy The

steady-state and dynamic test requirements are defined for test signal injected at the PMUrsquos input

terminals[6]

3121 Steady-State Testing

The steady-state condition is defined per the standard as where the magnitude frequency

phase and all other influence quantities of the test signal are constant during the period of the

testing [1] The steady-state tests are performed to verify that the PMU accuracy is within theallowed limits when working under defined steady-state operating conditions The compliance

requirements shown in Table 32 specify the TVE level for signal frequency phasor magnitude

measurement phasor angle measurement harmonic distortion and out-of-band interference

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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All compliance tests are to be performed under steady-state conditions with reference

conditions and influence quantities as defined in Table 32 Effects of the influence quantities

shall be considered cumulative and the TVE shall not exceed the error listed for the given

compliance level under any combination of influence quantities shown in Table 32 To evaluate

compliance with this requirement the effects of the influence quantities may be separately

evaluated[6]

The steady-state tests proposed in the PSTT PMU Testing Guide [2] are divided into two

types conformance and functional performance tests The steady-state conformance tests are

required for compliance with the current synchrophasor standard magnitude accuracy test phase

accuracy test frequency accuracy test off-nominal frequency response test harmonic frequency

response test and out-of-band interference test The steady-state functional performance tests are

as follows rate of change of frequency accuracy test unbalanced magnitude response test

unbalanced phase response test and data reporting test

Table 32 Influence quantities and allowable error limits for compliance levels 0-1 [IEEEStandard for Synchrophasors for Power Systems 2006] Illustrated under ldquoFair Userdquo copyright

guidelines

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The NIST designs provides a set of automated tests for all PMU influence quantities

shown in Table 32 in steady-state as required for DUT compliance with the IEEE C37118-

2005 Synchrophasor Standard [1]

3122 Dynamic Testing

For dynamic tests the input signal varies during the period of the testing according to the

type of test being performed The PMU Testing Guide [6] suggests the following test to cover

PMU characterization under dynamic or transient conditions step change response for amplitude

phase and frequency along with frequency ramp and amplitude modulation

3123 Protocol Testing

This test is required to ensure interoperability among PMU devices across the monitoring

system It includes testing the message application entirely for all message types defined in itsframework for compliance with the IEEE C37118-2005 Synchrophasor Standard [1] This test

must be conducted prior to conformance and performance testing

313 Documentation

According to the IEEE C37118-2005 Synchrophasor Standard [1] documentation must

be provided by any vendor claiming compliance with the standard that shall include a statement

of the compliance level being achieved and demonstrating this performance In addition if the

verification system is based on an error analysis as called for previously this analysis shall be

provided as well[1]

In the NIST designs the test results are generated automatically by the signal processing

software The reports include all data pertaining to the corresponding test being conducted

graphs statistics and test parameters

32 System Definition

The Virginia Tech Calibration System is a steady-state and dynamic PMU calibration test

stand used for compliance verification with the IEEE C37118-2005 Synchrophasor Standard [1]

based on the NIST PMU Calibration System and NIST Dynamic Test System designs

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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321 System Description and High-level Architectural Depiction

The overall system involves providing the DUT interface the calibration test of the PMU

and the delivery of statistical data to determine PMU compliance with the synchrophasor

standard The major components and identified processes are listed in Table 33

Table 33 Major processing component descriptions in the Virginia Tech Calibration System983117983137983146983151983154 983120983154983151983139983141983155983155 983151983154 983107983151983149983152983151983150983141983150983156 983106983137983155983145983139 983108983141983155983139983154983145983152983156983145983151983150

983124983145983149983141 983123983151983157983154983139983141 983120983154983151983158983145983140983141 983156983145983149983141 983140983137983156983137 983137983150983140 983155983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983155983145983143983150983137983148983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150 983120983154983151983158983145983140983141 983120983117983125 3983085983152983144983137983155983141 983156983141983155983156 983159983137983158983141983142983151983154983149

983123983145983143983150983137983148 A983156983156983141983150983157983137983156983145983151983150 983113983150983152983157983156 983155983145983143983150983137983148 983139983151983150983140983145983156983145983151983150983145983150983143 983152983154983145983151983154 983156983151 983155983137983149983152983148983145983150983143 983152983154983151983139983141983155983155

983123983137983149983152983148983145983150983143 983137983150983140 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983120983144983137983155983151983154 983139983151983149983152983157983156983137983156983145983151983150 983137983150983140 D983125983124 983140983137983156983137 983139983151983149983152983137983154983145983155983151983150

D983125983124 983113983150983156983141983154983142983137983139983141 983120983154983151983158983145983140983141 983137983139983139983141983155983155 983156983151 983120983117983125 983157983150983140983141983154 983156983141983155983156

The high level architectural depiction and representation of the major components are

seen in Figure 32 The high level depiction shows the overall concept for the Virginia Tech

Calibration System and the major processes that are addressed in the design process

Figure 23 The Virginia Tech Calibration System high level architectural depiction

The NIST used the same approach for both the steady-state and dynamic PMU

calibration designs A National Instruments (NI) platform was used to develop a PMU capable oftaking phasor measurements with minimum uncertainty the NI PMU The test signals were

generated and fed to both the NI PMU and the PMU under test Then the measured phasor data

was compared in order to determine whether the device under test (DUT) passed the test

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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33 Steady-state Design

The National Instrument platform was selected for the PMU Calibration System design

The tests were developed using a graphical programming environment the NI Labview 85

development package The hardware modules described in Table 34 were installed in a rack

featuring a 10MHz timing and synchronization backplane with external clock input the NI PXIe-

1062Q chassis

Table 34 Hardware used in the Virginia Tech Calibration System steady-state designC983148983151983139983147 983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150983123983156983141983137983140983161983085983155983156983137983156983141 983119983149983145983139983154983151983150 C983117C 156 E983120 3983085983120983144983137983155983141 C983137983148983145983138983154983137983156983151983154

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in NI PXIe-1062Q chassis featuring a PXI express backplanecapable of 1GBs data streaming

Labview is divided into functional tasks called virtual instruments (VIs) Each VI has a

block diagram a front panel and a connection panel The front panel consists of controls and

indicators that allow the user to enter data and to get data from a running VI These controls can

also serve as interfaces to other VIs when dropped as a node onto the block diagram This

functionality allows the testing of VIs before being integrated as a subroutine into a larger

program

Labview is a dataflow programming language The execution order follows the structure

of a graphical block diagram where the developer connects VIs by drawing wires The VIs get

executed as soon as input data becomes available allowing parallel execution[17]

The signal processing software interfaces with all hardware modules through the different

interfaces shown in Table 35

Table 35 Software interface VIs in the Virginia Tech Calibration SystemD983125983124 983113983150983156983141983154983142983137983139983141 983122983157983150983135D983125983124983135983124C983120 983126983113 991251 983124C983120 983120983154983151983156983151983139983151983148

983124983145983149983141 983123983151983157983154983139983141 G983120983123983135983124983145983149983141983155983156983137983149983152983135983113983150983145983156 983126983113 991251 983118983113983085983123983161983150983139 D983154983145983158983141983154983155

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 3983120983135983126A983135C9831519831509831429831459831436213 983126983113 991251 983118983113983085DA983121983149983160 D983154983145983158983141983154983155

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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331 Time Source

The time source is used as a reference for time stamping the test signal and for triggering

the sampling module

The NIST designs included an interface for the GPS module using the NI DAQmxfunction library the GPS_Timestamp_Initvi This VI configured the clock-synchronization of

the NI PXI-6608 timing module with an external GPS receiver unit via IRIG-B and outputted a

timestamp upon the 1-PPS rising edge GPS signal This event triggered a timing clock

maintained by the data acquisition module built-in sampling clock used for time stamping each

PMU phasor frame at the rate selected for the test

The Virginia Tech Calibration System design includes a GPS-based time source the NI

PXI-6682H timing module The new interface was based on the GPS_Timestamp_Initvi and

modified using a library of functions for controlling NI timing modules the NI-Sync driver

software This VI was simplified to directly request the GPS module through the backplane for

a timestamp upon the 1-PPS rising edge GPS signal

The time source module selected for the Virginia Tech design has slightly less accuracy

than the NIST designs as shown in Table 36 corresponding to an additional phase error in the

Virginia Tech Calibration System of 0000748deg for a 60 Hz system and 0000612deg for a 50 Hz

system The Symetricom xLI GPS accuracy specifications were obtained from [18] Detailed

specifications of the NI PXI-6682H GPS module are shown in Appendix A

Table 36 Time source module accuracy comparison with the NIST designs983123983129983117E983124983122983113C983119983117 983160983116983113 G983120983123 983118983113 9831209831289831139830856682983112

1983120983120983123 98321730983150983155 983122983117983123 100983150983155 983152983141983137983147 98321747983150983155 983122983117983123 100983150983155 983152983141983137983147 983085

332 Signal Generation

The NIST designs included three Rotek 8100 signal calibrator units for steady-state

signal generation and an IRIG-B interface VI the Rotek Calibrator library

In the Virginia Tech Calibration System the steady-state signals were generated using a

high precision three-phase calibrator the Omicron CMC 156 EP Its interface featured the step

and ramp signal generation for all the signal influence quantities required on the steady-state

testing the Omicron QuickCMC interface

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The signal generation hardware selected for the Virginia Tech Calibration System has the

same accuracy under typical conditions as the NIST designs as shown in Table 37 Additional

detailed specifications for the Omicron CMC 156 are shown in Appendix B

Table 37 Signal generation module accuracy comparison with the NIST designs983122983151983156983141983147 8100 983119983149983145983139983154983151983150 C983117C 156

983126983151983148983156983137983143983141 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

C983157983154983154983141983150983156 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 001 983151983142 983126983151983148983156983137983143983141 983123983141983156983156983145983150983143 =

333 Data Acquisition

The NIST designs included the NI PXI-6123 data acquisition module featuring eight

analog input channels The voltage and current were measured for each phase using only six

input channels from the card The current feedbacks from the current transducers were a voltage

proportional to the current levels Its software interface the 3P_VA_Config_6123_d VI used the NI DAQmx function library to set up the analog input card measuring range sampling rate and

trigger for selected channels

The Virginia Tech Calibration System included the NI PXIe-6356 data acquisition

module featuring eight analog input channels Its interface uses the 3P_VA_Config_6123_d VI

with modified input parameters to match the new hardware

The signal generation hardware selected for the Virginia Tech Calibration System asshown in Table 38 is capable of a higher sampling rate which improves the accuracy of the

phasor estimation Additional detailed specifications for the NI PXIe-6356 data acquisition

module are shown in Appendix C

Table 38 Data acquisition module accuracy comparison with the NIST designs983118983113 9831209831289831139830856123 983118983113 9831209831289831139831419830856356

ADC 983154983141983155983151983148983157983156983145983151983150 16 983138983145983156 16 983138983145983156 =

983123983137983149983152983148983145983150983143 983154983137983156983141 500 983147983123983155 125 983117983123983155 +

334 Signal Processing

The NIST designs included a NI PXI-8196 20Ghz Pentium M PXI Embedded Controller

and a set of VIs to perform the PMU function and phasor estimation and to compare it with the

DUT phasor data the Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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In the Virginia Tech Calibration System the signal processing tasks were performed by a

high-performance processor-based embedded controller the NI PXIe-8108 controller module

The Run_NI2New_C and the RT_NI_DUT_Compare_eSAVE VIs were used for the signal

processing tasks

The NI PXIe-8108 includes a dual-core processor capable of executing two computing

tasks simultaneously This is a major advantage over single-core embedded controllers such as

the NI PXI-8196 when executing Labview multi-threaded applications like the Run_NI2New_C

and the RT_NI_DUT_Compare_eSAVE VIs

National Instruments claims a performance improvement of up to one hundred percent on

multi-threaded applications between the NI PXI-8196 and the NI PXI-8105 one of the first dual-

core embedded controller systems [20] Using SYSmark benchmarking software NI PXIe-8108

controllers demonstrate an overall performance improvement of one hundred and nine percent

over the PXI-8105 controllers [21 22] Therefore the VT Calibration system signal processor

performance is over two hundred per cent higher than the one used in the NIST designs as

shown in Table 39

Table 39 Signal processing module accuracy comparison with the NIST designs983118983113 9831209831289831139830858196 983118983113 9831209831289831139831419830858108

983120983154983151983139983141983155983155983151983154983124983161983152983141

983113983150983156983141983148 983120983141983150983156983145983157983149 983117 760 983113983150983156983141983148 C983151983154983141 2 D983157983151 9831249400 +

335 Clock Synchronization

The NIST designs included the Symmetricom XLi GPS 10MHz frequency output as the

clock synchronization source for the data acquisition and signal generation modules

In the Virginia Tech Calibration System an DUT B 1084B featuring a 10MHz frequency

output is used as the clock synchronization source No software interface was required for this

module since it connected directly to the NI chassis clock input via a coaxial cable

The clock synchronization source hardware selected for the Virginia Tech Calibration

System is slightly more accurate than the NIST designs as shown in Table 310 The

Symetricom xLI GPS accuracy specifications were obtained from [18] However the NIST

designs use the same GPS module as a time and clock synchronization source while the Virginia

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Tech design uses two GPS modules The Arbiter 1084B has a UTC synchronization accuracy of

forty nanoseconds RMS and hundred nanoseconds peak as specified in [23] The accuracy of

both GPS modules combined is eighty seven nanoseconds corresponding to an additional phase

error in the Virginia Tech Calibration System of 0001254deg for a 60 Hz system and 0001026deg

for a 50 Hz system

Table 310 Synchronization source accuracy comparison with the NIST designs

983123983129983117983117E983124983122983113C983119983117 983128983116983145 G983120983123 A983154983138983145983156983141983154 1084B

983125983150983148983151983139983147983141983140

983119983155983139983145983148983148983137983156983151983154

983155983156983137983138983145983148983145983156983161

983126C983124C983128983119 5983160109830857

DC983128983119 1983160109830857

+

A983148983148983137983150

D983141983158983145983137983156983145983151983150

983155983156983137983138983145983148983145983156983161

1983160109830859 983152983141983154 983155983141983139 59831601098308510 983152983141983154 983155983141983139 +

336 Signal Attenuation

The NIST designs included a Jamb CT two hundred to one NIST built two-stage current

transducers and twenty to one or two hundred to one resistive attenuators with Vishay low

temperature coefficient resistors with capacitor tuning voltage attenuators

The Virginia Tech Calibration System used a twenty to one voltage divider for voltage

attenuation and high precision current shunt resistors for current attenuation The phase error

introduced by the different signal attenuation implementations was properly compensated bysetting a phase correction factor in the NI PMU

337 DUT interface

The NIST and the Virginia Tech Calibration System designs included a software

interface using TCP and UDP protocols to exchange data with the DUT the Run_DUT_TCP and

the Run_DUT_UDP VIs

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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34 Dynamic Testing Design

The dynamic testing design is similar to the steady-state design with the exception of the

signal generation component as shown in Table 311 The Omicron CMC 156 EP is not capable

of producing the test signals required for the dynamic tests

Table 311 Hardware used in the Virginia Tech Calibration System dynamic design983123983161983150983139983144983154983151983150983145983162983137983156983145983151983150 983123983151983157983154983139983141 D983125983124 B 1084B G983120983123 983123983137983156983141983148983148983145983156983141 C983148983151983139983147

983124983145983149983141 983123983151983157983154983139983141 983118983113 9831209831289831139831419830856682983112 G983120983123 C983148983151983139983147 983137983150983140 983124983145983149983141983154

983123983145983143983150983137983148 G983141983150983141983154983137983156983145983151983150D983161983150983137983149983145983139983118983113 9831209831289831139830856733 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983151983157983156983152983157983156

(3) C983154983151983159983150 983120983123983085400 983120983151983159983141983154 A983149983152983148983145983142983145983141983154983155

D983137983156983137 A983139983153983157983145983155983145983156983145983151983150 983118983113 9831209831289831139831419830856356 983085 8 983139983144983137983150983150983141983148 983137983150983137983148983151983143 983145983150983152983157983156

983123983145983143983150983137983148 983120983154983151983139983141983155983155983145983150983143 983118983113 9831209831289831139831419830858108 253G983144983162 D983157983137983148983085C983151983154983141 983120983128983113 983141983160983152983154983141983155983155 E983149983138983141983140983140983141983140 C983151983150983156983154983151983148983148983141983154 983127983145983150 7

These modules are installed in a NI PXIe-1062Q chassis featuring a PXI express backplane

capable of 1GBs data streaming341 Signal Generation

The NIST Dynamic Test System design included the NI PXI-6733 analog output module

and a set of Rotek 8100 amplifiers for dynamic test signal generation

The Virginia Tech Calibrator System uses the NI PXI-6733 analog output module and

three Crown PS-400 power amplifiers The test signals are created in software by the different

VIs running the dynamic tests Additional detailed specifications for the NI PXI-6733 analog

module are shown in Appendix D

The amplifier module used in the Virginia Tech Calibration System is less accurate than

the NIST Dynamic Test System design as shown in Table 312 however this should not introduce

additional error in the tests since the test signals are fed to both the NI PMU and the DUT The

Rotek 8100 accuracy specifications were obtained from [24] The Crown PS-400 accuracy

specifications were obtained from [25]

Table 312 Dynamic signal generation accuracy comparison with the NIST Dynamic TestSystem design983122983151983156983141983147 8100 C983154983151983159983150 983120983123983085400

983120983151983159983141983154

A983139983139983157983154983137983139983161001 01 983085

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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35 Calibration

The Virginia Tech Calibration System is compensated for phase errors introduced in the

NI PMU measurements by various delay sources such as the wiring between the modules

current transducers phase shifts etc

Figure 45 Phase calibration of reference PMU with the 1PPS clock signal [PMU System

Testing and Calibration Guide 2007] Illustrated under ldquoFair Userdquo copyright guidelines

Calibration involves reading the phase errors in the NI PMU measurement from input

signals with known phase angles and then adding the phase compensations in the software The

signal source is clock synchronized to UTC time and phase shifted so the positive zero crossing

of Phase A is aligned with the 1PPS the NI PMU should read -90 degrees if properly calibrated

The signal source is readjusted to align the 1PPS with the negative zero crossing of Phase A the

NI PMU should read +90 degrees A high precision oscilloscope is set to trigger on the 1PPS

rising edge as shown in Figure 33 The signal source must generate a high frequency outputduring calibration to be able align the test signal with the 1PPS[6]

Once the phase delays are determined they can be manually inputted into the front panel

of the NI PMU the Run_NI2New_C VI or through the calibration program the TimeDelayTest

VI

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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4 STEADY-STATE TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess steady-state

performance of a PMU DUT A

41 Accuracy and Time Alignment

This section shows the tests performed to assess accuracy and time alignment of PMUs

The accuracy and time alignment tests include magnitude phase angle and frequency tests

The RT_NI_DUT_Compare_eSave VI is executed simultaneously with the

corresponding VIs used to run the different accuracy tests It starts the NI PMU via the

Run_NI2New_C VI and connects to the DUT via the Run_DUT_TCP VI to gather the data and

perform the phasor comparisons and to send the errors to the DisplayErrorsLVM4 VI This

program displays the errors and saves the data to NI DIAdem files The NI DIAdem is a software

tool used for data archiving and analysis

411 Magnitude Accuracy

The MagTestRunNI VI is used to run the voltage and current magnitude accuracy tests

For the voltage magnitude accuracy test this program executes the

RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of 10 to 120 in

steps of 5 of nominal voltage with an adjustable delay in between the steps Each magnitude

step is maintained for one minute until the test is completed The phasor data comparison results

between the NI PMU and the DUT are analyzed and the minimum maximum and mean TVE

values are sent to the DisplayErrorsLVM4 VI The current level is kept constant during the test

In the current magnitude accuracy test the current levels are stepped and the voltage

level is kept constant

The steady-state generator is updated in between the magnitude steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 42 shows the MagTestRunNI VI Block Diagram The Error_Stats VIs compute

the TVE statistics of the phasor data comparison between the PMUs later shown in Figures 43

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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44 and 45 The Error_Stats_Vector computes other frequency statistical errors The

Update_Mag VI in the NIST PMU Calibration System design was an IRIG-B interface with the

signal generator module It updated the test signal magnitude levels automatically during the test

using Rotek drivers This function is not available in the Virginia Tech Calibrator System

because Labview drivers for the Omicron CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the MagTestRunNI VI Front

Panel lower left corner shown in Figure 41

Figure 43 shows the magnitude accuracy test results performed on DUT A

Figure 41 MagTestRunNI VI front panel

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 42 MagTestRunNI VI block diagram

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 43 Voltage magnitude accuracy test results

412 Phase Accuracy

The PhaseTestRunNI VI is used to run the phase accuracy tests This program executes

the RT_NI_DUT_Compare_eSave VI with test signal magnitude parameters of -180˚ to 180˚ in

steps of 10˚ with an adjustable delay in between the steps Each phase step is maintained for one

minute until the test is completed The phasor data comparison results between the NI PMU and

the DUT are analyzed and the minimum maximum and mean TVE values are sent to the

DisplayErrorsLVM4 VI

The steady-state generator is updated in between the phase steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 45 shows the PhaseTestRunNI VI Block Diagram The Update_Phase VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

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P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

It updated the test signal phase automatically during the test using Rotek drivers This function is

not available in the Virginia Tech Calibrator System because Labview drivers for the Omicron

CMC 156 EP have not been developed yet

The magnitude accuracy test parameters are inputted in the PhaseTestRunNI VI FrontPanel lower left corner shown in Figure 44

Figure 46 shows the phase accuracy test results performed on DUT A

Figure 44 PhaseTestRunNI VI front panel

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 45 PhaseTestRunNI VI block diagram

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

7212019 Fernandez JO T 2011

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Figure 51 NI_DUT_Step_add VI block diagram

7212019 Fernandez JO T 2011

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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P a g e | 38

The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 46 Phase accuracy test results

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413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

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P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 38: Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

413 Frequency Accuracy

The FreqTestRunNI VI is used to run the frequency magnitude accuracy tests This

program executes the RT_NI_DUT_Compare_eSave VI with test signal frequency parameters of

54 to 66Hz in steps of 01Hz with an adjustable delay in between the steps Each frequency step

is maintained for one minute until the test is completed For 50Hz systems the test signal

frequency parameters are 44 to 56 Hz

The steady-state generator is updated in between the frequency steps to generate the

corresponding test signal levels using the Omicron QuickCMC interface

Figure 48 shows the FreqTestRunNI VI Block Diagram The Update_Freq_2 VI in the

NIST PMU Calibration System design was an IRIG-B interface with the signal generator module

It updated the test signal frequency levels automatically during the test using Rotek drivers This

function is not available in the Virginia Tech Calibrator System because Labview drivers for the

Omicron CMC 156 EP have not been developed yet

The frequency accuracy test parameters are inputted in the FreqTestRunNI VI Front

Panel lower left corner shown in Figure 47

Figures 49 shows the frequency test results performed on DUT A

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 47 FreqTestRunNI VI front panel

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 51 NI_DUT_Step_add VI block diagram

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

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P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 48 FreqTestRunNI VI block diagram

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Figure 49 Frequency accuracy test results

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 51 NI_DUT_Step_add VI block diagram

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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P a g e | 38

The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 55 Phase step change test signal (-45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 56 Phases step change test signal (+45˚)

7212019 Fernandez JO T 2011

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Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

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P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

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P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

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P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 41: Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 49 Frequency accuracy test results

7212019 Fernandez JO T 2011

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P a g e | 35

The Virginia Tech Calibration System copy 2011 Javier Fernandez

5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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5 D YNAMIC TESTING

This chapter shows the results of test performed by the Virginia Tech Calibration System

and explain the interaction between the hardware and the software used to assess the dynamic

performance of a PMU DUT A

51 Step Change response

This section shows the tests performed for determining performance of PMUs in response

to step changes The step change response tests include magnitude phase angle and frequency

tests

The Run_Step_Test_on_DUTs_add VI is used to run the step change response tests It

uses the concept of interleaving phasors developed in [15] Each test is executed using the

NI_DUT_Step_add VI The error data is sent to the DisplayampStore VI This program displays

the errors and saves the data to NI DIAdem files

The NI_DUT_Step_add VI Block diagram is shown in Figure 51 The Run_NI_Add VI

generates the test signals and starts the NI PMU The Collect_data VI gathers and aligns the

phasor data according to their time stamps The Analyze_Data VI performs the phasor

comparisons

The Run_DUT_TCP_add VI is executed simultaneously with the

Run_Step_Test_on_DUTs_add VI to start the DUT

The test parameters are inputted in the Run_Step_Test_on_DUTs_add VI Front Panel

shown in Figure 52

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

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Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

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APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

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P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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Figure 51 NI_DUT_Step_add VI block diagram

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Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

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P a g e | 38

The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

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Figure 55 Phase step change test signal (-45˚)

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Figure 56 Phases step change test signal (+45˚)

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Figure 57 Phase step change test results (-45˚)

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Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

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Figure 59 Frequency step change test signal (-2Hz)

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Figure 510 Frequency step change test signal (+2Hz)

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Figure 511 Frequency step change test results (-2Hz)

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Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

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P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 44: Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 52 Run_Step_Test_on_DUTs_add VI front panel

511 Dynamic Magnitude Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic magnitude step changeresponse test for voltage and current For the voltage this program executes the

NI_DUT_Step_add VI with an amplitude step change of 20 of nominal voltage The current

level is kept constant The test signal is shown in Figure 53

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4561

P a g e | 38

The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

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P a g e | 40

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 55 Phase step change test signal (-45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 56 Phases step change test signal (+45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

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P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 45: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4561

P a g e | 38

The Virginia Tech Calibration System copy 2011 Javier Fernandez

For the current magnitude step change test the current is stepped and voltage is kept

constant The Crown PS-400 power amplifier was not capable of producing the current signals It

often became unstable and tripped when stepping the current

Figure 54 shows the magnitude step change response test results performed on DUT A

Figure 53 Magnitude step change test signal

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4661

P a g e | 39

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4761

P a g e | 40

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 55 Phase step change test signal (-45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4861

P a g e | 41

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 56 Phases step change test signal (+45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4961

P a g e | 42

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5061

P a g e | 43

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5161

P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

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P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

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P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

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P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 46: Fernandez JO T 2011

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 54 Magnitude step change test results

512 Dynamic Phase Response

The Run_Step_Test_on_DUTs_add VI is used to run the dynamic phase step change

response test This program executes the NI_DUT_Step_add VI with phase step changes of plusmn15˚

and plusmn45˚ The test signals for the plusmn45˚ phase step change test are shown in Figures 55 and 56

Figures 57 and 58 show the plusmn45˚phase step change response test results performed on

DUT A

7212019 Fernandez JO T 2011

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P a g e | 40

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 55 Phase step change test signal (-45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 56 Phases step change test signal (+45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5161

P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5261

P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 47: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4761

P a g e | 40

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 55 Phase step change test signal (-45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4861

P a g e | 41

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 56 Phases step change test signal (+45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4961

P a g e | 42

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5061

P a g e | 43

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5161

P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5261

P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 48: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4861

P a g e | 41

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 56 Phases step change test signal (+45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4961

P a g e | 42

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5061

P a g e | 43

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5161

P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5261

P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 49: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 4961

P a g e | 42

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 57 Phase step change test results (-45˚)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5061

P a g e | 43

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5161

P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5261

P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 50: Fernandez JO T 2011

7212019 Fernandez JO T 2011

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P a g e | 43

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 58 Phase step change test results (+45˚)

513 Dynamic Frequency Response

The Run_Step_Test_on_DUTs_add VI is used to run the frequency phase step change

response test This program executes the NI_DUT_Step_add VI with frequency step changes of

plusmn1Hz plusmn2Hz and plusmn3Hz The test signals for the plusmn2Hz frequency step change test are shown in

Figures 59 and 510

Figures 511 and 512 show the plusmn2Hz frequency step change response test results

performed on DUT A

7212019 Fernandez JO T 2011

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P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5261

P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 51: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5161

P a g e | 44

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 59 Frequency step change test signal (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5261

P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 52: Fernandez JO T 2011

7212019 Fernandez JO T 2011

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P a g e | 45

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 510 Frequency step change test signal (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5361

P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 53: Fernandez JO T 2011

7212019 Fernandez JO T 2011

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P a g e | 46

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 511 Frequency step change test results (-2Hz)

7212019 Fernandez JO T 2011

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P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 54: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5461

P a g e | 47

The Virginia Tech Calibration System copy 2011 Javier Fernandez

Figure 512 Frequency step change test results (+2Hz)

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 55: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5561

P a g e | 48

The Virginia Tech Calibration System copy 2011 Javier Fernandez

6 CONCLUSIONS AND RECOMMENDATIONS

A test stand for steady-state and dynamic characterization of PMUs based on the NIST

PMU Calibration System and the NIST Dynamic Test System was developed at Virginia Tech

the Virginia Tech Calibration System

The hardware requirements were specified in order to meet and improve the performance

of the NIST designs within the project budget The NI platform was selected for the data

acquisition dynamic signal generation and data processing functions in order to implement the

NIST design software

The hardware modules were installed and tested using NI tools prior to integration with

the NIST software The different software module interfaces were modified to adapt the newhardware drivers The software modifications performed in the Virginia Tech Calibration System

do not affect the overall performance of the system

A GPS based synchronization scheme was implemented across the hardware modules to

guarantee minimum phase errors in the NI PMU measurements The time and clock

synchronization implementation have added an additional phase error of 0001254deg for a 60 Hz

system and 0001026deg for a 50 Hz system

The amplifiers used in the dynamic design were not capable of producing the test signals

required to conduct the current varying tests This limitation is believed to be caused by

deteriorations due to aging as the Crown PS-400 power amplifiers used in the dynamic design

were manufactured in the late eightyrsquos A set of high performance amplifiers may be required to

perform the complete set of dynamic performance tests

After reviewing the hardware differences and software modifications the Virginia Tech

Calibration System performance compares very close to the NIST design The steady-state anddynamic tests shown in chapters 4 and 5 of this thesis were supervised by the NIST showing

successful functioning of the Virginia Tech Calibration System

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 56: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5661

P a g e | 49

The Virginia Tech Calibration System copy 2011 Javier Fernandez

REFERENCES

1 IEEE Standard for Synchrophasors for Power Systems IEEE Standard C37118-2005

March 20062 Moraes R et al Deploying a large-scale PMU system for the Brazilian interconnected

power system Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2008) p 143-149

3 Hu Y D Novosel and R Quanta Technol NC Progresses in PMU testing and

calibration Electric Utility Deregulation and Restructuring and Power Technologies2008 DRPT 2008 (6-9 April 2009) p 150-155

4 IEEE Standard for Synchrophasors for Power Systems IEEE Standard 1344-

1995(R2001) March 20015 Huang Z et al Performance Evaluation of Phasor Measurement Systems Power

Engineering Society General Meeting 2008 IEEE6 PMU System Testing and Calibration Guide Technical Report for the North American

Synchrophasor Initiative Performance and Standard Task Team team leader G

Stenbakken7 Synchrophasor Measurement Accuracy Characterization Technical Report for the NorthAmerican Synchrophasor Initiative Performance and Standard Task Team team leader GStenbakken

8 Bill Mittelstadt J Kehler and S Kothepalli WECC Plan for Dynamic Performance and

Disturbance Monitoring WECC Disturbance Monitoring Work Group 20009 Stenbakken G and T Nelson Static Calibration and Dynamic Characterization of

PMUs at NIST Power amp Energy Society General Meeting 2007 IEEE10 Stenbakken GN and M Zhou Dynamic Phasor Measurement Unit Test System IEEE

Power Engineering Society General Meeting11 Stenbakken G and T Nelson NIST support of phasor measurements to increase

reliability of the North American electric power grid Power amp Energy Society GeneralMeeting 2006 IEEE12 Donolo M and VA Centeno Accuracy Limits for Synchrophasor Measurements and

the IEEE Standard IEEE Transactions on Power Delivery (Jan 2008)13 Phadke AG and B Kasztenny Synchronized Phasor and Frequency Measurement

Under Transient Conditions IEEE Transactions on Power Delivery 24(1)14 Stenbakken G et al Reference Values for Synamic Calibration of PMUs Hawaii

International Conference of System Sciences Proceedings of the 41st Annual (7-10 Jan2008) p 171-171

15 J Ren M Kezunovic and G Stenbakken Characterizing dynamic behavior of PMUs

using step signals European Transactions on Electric Power 2011

16 Wang L et al An Evaluation of Network Time Protocol for Clock Synchronization inWide Area Measurements Power amp Energy Society General Meeting 2008 IEEE

17 National Instruments Labview User Manual April 2003

18 Symmetricom XLi Time and Frequency System Symmetricom XLi datasheet Oct 200519 National Instruments NI PXI-81958196 User Manual NI PXI-8105 datasheet March

2005

20 National Instruments 20 GHz Dual-Core Embedded Controller for PXI NI PXI-8105

datasheet March 2006

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

P a g e | 53

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6161

P a g e | 54

APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

Page 57: Fernandez JO T 2011

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5761

P a g e | 50

The Virginia Tech Calibration System copy 2011 Javier Fernandez

21 National Instruments 216 GHz Dual-Core Embedded Controller for PXI and PXI

Express NI PXI-8106 and NI PXIe-8106 datasheet Jan 200722 National Instruments 253 GHz Dual-Core Embedded Controller for PXI Express NI

PXIe-8108 datasheet Sep 2008

23 Arbiter Systems Model 1084ABC GPS Satellite Clock Arbiter 1084B datasheet Dec

201024 Rotek The Rotek Model 8100 Rotek 8100 datasheet Jan 2004

25 Omicron CMS 156 3 Phase Voltage and Current Amplifier CMS 156 technical data

July 201026 National Instruments NI PXI-6682 and PXI-6682H Timing and Synchronization Modules

for PXI NI PXI-6682 Series User Manual March 2009

27 Omicron CMC 156 EP 3 Phase Voltage + 3 Phase Current Test Set CMC 156 EP

technical data Sep 201028 National Instruments NI 63566358 Specifications NI PXIe-63566358 technical data

Aug 201029 National Instruments NI 67316733 Specifications NI PXI-67316733 technical data

June 2007

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5861

P a g e | 51

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 5961

P a g e | 52

The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

7212019 Fernandez JO T 2011

httpslidepdfcomreaderfullfernandez-jo-t-2011 6061

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX A NI PXI-6682 TIMING MODULE TECHNICAL

SPECIFICATIONS

Table A1 lists the synchronization accuracy that the PXI-6682H offers while operating

in various modes[26]

Table A1 NI PXI-6682H synchronization accuracy

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX B OMICRON CMC 156 EP TECHNICAL

SPECIFICATIONS

Figure B1 shows the Omicron CMC 156 technical specifications for voltage and current

generation[27]

Figure B1 Omicron CMC 156 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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The Virginia Tech Calibration System copy 2011 Javier Fernandez

APPENDIX C NI PXIE-6356 DATA ACQUISITION MODULE

TECHNICAL SPECIFICATIONS

Table C1 shows the NI PXIe-6356 for analog input obtained from [28]

Table C1 NI PXIe-6356 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications

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APPENDIX D NI PXI-6733 ANALOG OUTPUT MODULE

TECHNICAL SPECIFICATIONS

Table D1 shows the NI PXI-6733 for analog output obtained from [29]

Table D1 NI PXI-6733 technical specifications