Introduction to Phasor Measurements Units (PMUs)

Wei-Jen Lee, Ph.D., PEDirector and ProfessorEnergy Systems Research CenterUniversity of Texas at Arlington

November 16, 2012

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Introduction

•Classical Definition of a Phasor▫A pure sinusoidal waveform can be

represented by a unique complex number known as a ‘phasor’. A sinusoidal signal

The phasor representation of this sinusoid is given by

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Introduction

•Classical Definition of a Phasor▫The RMS cosine-reference voltage and

current phasors are.

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Introduction

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(a) Sinusoidal signal (b) Phasor representation

•Classical Definition of a Phasor

Introduction

•Classical Definition of a Phasor▫If the sinusoid is not a pure sine wave, the

phasor is assumed to represent its fundamental frequency component.

▫The most commonly used method of calculating phasors from sampled data is that of Discrete Fourier Transform (DFT).

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Introduction

•Important of the Phasor Measurement

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sin* 21

L

TT

X

EEP

Introduction

•Important of the Phasor Measurement

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Introduction

•Modern EMS systems started from 1965▫Data refresh rate is around 2 to 5 seconds▫Measurement signals are not synchronized▫People relies upon power flow and state estimation to

estimate the angles among buses.▫It is an offline estimation and the results are not

reliable.

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Introduction

•Modern phasor measurement systems can trace origin to the development of the Symmetrical Component Distance Relay (SCDR) in the early 1970s.

• In early 1980s, measurement system started using GPS to synchronize the sampling clocks, which offering a common reference.

•The first experimental PMUs were developed at Virginia Tech in 1988, and Macrodyne built the first PMU in 1992.

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Introduction

•The modern PMUs use one pulse per second signals provided by the GPS satellite receivers.▫The accuracy of the GPS timing pulse is better than 1

µs.▫For a 60 Hz system corresponds to about 0.02 degrees.▫Current PMU records data at the rate of 30 samples per

second (This number can be adjusted).

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Introduction

•Functional block diagram of the elements in a PMU.

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PMU and Smart Grid Development

•The electrical power system is one of the most sophisticated man-made infrastructures.

•While the power system is a technological marvel, it is also reaching the limit of its ability to meet the nation's electricity needs.

•The modernization of the electricity infrastructure leads to the concept of smart grid.

•The smart grid as defined here is based upon the description found in the Energy Independence and Security Act 2007.

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PMU and Smart Grid Development

•The term “Smart Gird” refers to a modernization of the electricity delivery system so that it monitors, protect, and automatically optimizes the operation of its interconnected elements.

• In general, a comprehensive smart grid design should take holistic approaches and cover both top-down and bottom-up approaches.

•Many smart grid related activities have been carried out all over the world.

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Desired Features of Smart Grid

•Advanced monitoring, control, and demand management.

•Advanced components & operating concepts.•Robust modeling & simulation tools.•Seamless interconnection of low environmental impact

new generation technologies.•Standardized architecture & secure communication

standards.

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Potential Areas of Smart Grid Development and Applications

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PMU for Wide Area Monitoring and Control•Deployment of Phasor Measurement Unit (PMU)

▫ In 2007, the organization of U.S Department of Energy (DOE) and the North American Electric Reliability Corporation (NERC), along with involved electric utility companies and other organizations, formed the North American SynchroPhasor Initiative (NASPI)

▫With funding from The American Recovery and Reinvestment Act of 2009, several smart investment grant and demonstration projects have been awarded to advance the synchrophsor technology.

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PMU for Wide Area Monitoring and Control•Deployment of Phasor Measurement Unit (PMU)

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PMU for Wide Area Monitoring and Control•Potential PMU Applications

• Wide-Area Visualization and Monitoring;• Angle and Frequency Monitoring;• Interarea Oscillation Detection & Analysis;• Proximity to Voltage Collapse;• State Estimation;• Fast Frequency Regulation;• Transmission Fault Location Estimation;• Dynamic Model Validation.

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PMU for Wide Area Monitoring and Control•Though the above applications are from the view of

ISO, the PMUs-based applications also benefit generator owners and other market participants.

•PMUs are able to continuously record several different signals which are the requirements of ancillary services like spinning reserve, frequency control and voltage control.

•Once the infrastructure is permanently installed at the power plant, the online tests such as voltage step-change can be easily applied and recorded.

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Sample PMU Applications

•PMU applications in CAISO: Wide area visualization and monitoring

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Source: EPG

Sample PMU Applications

•Recording of Actual Event

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Sample PMU Applications

•Comparison between Actual response and Simulation Results

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WSCC (WECC) System Blackout on August 10, 1996

Sample PMU Applications

•State Estimation▫State estimation techniques were developed in 1970s

Obtain an approximation to averaged system state from scanned data (seconds to minutes)

It is referred as “Static State Estimates”.

▫PMUs enable synchronized phasor measurement bus voltages & currents. Make significant improvement on state estimation or state

measurement applications Install PMU in the system could be a smart move to improve the

accuracy and efficiency of state estimation.

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Sample PMU Applications

•PMU Based On-Line generator parameter identification system.

. . . . .

GPS

Ethernet

PMU

PMU

PMU

hp Workstation i2000

hp Workstation i2000

Phasor Data Concentrator

EMS Database

ApplicationsCommunication StandardsIEEE C37.118.2IEC 61850-90-5ICCP

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Sample PMU Applications

•PMU Based On-Line generator response and parameter identification system.

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Original System Reduced System

Sample PMU Applications

•PMU Based On-Line generator response and parameter identification system.• The Reliability Standards relate to generator model

verification are:• MOD-026-1 — Verification of Models and Data for Generator

Excitation System Functions• MOD-027-1 — Verification of Generator Unit Frequency Response

• Once these Reliability Standards are approved, the standards become mandatory and enforceable requirements

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Sample PMU Applications

•Fault Location in the Transmission Network.

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Relevant PMU Standards

•C37.111-1999▫A general transient data recording file format standard

•C37.118.1-2011▫Covers synchrophasor measurements for power systems▫Adds frequency & rate of change of frequency (ROCOF)

and dynamic operation •C37.118.2-2011

▫Defines real-time synchronized phasor measurement data exchange method

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Conclusion and Discussion

•PMU is a matured technology.• In addition to the original intended applications on

“Phasor Measurement”, PMUs offer attractive options for improving protection and control actions on modern power systems.

•Future power systems will have to face more stressful regimes; improved protection and control offered by the wide area measurement systems based on PMUs will become even more important.

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