CMC Test Universe AppNote Extending PTL Items for Distance Protection 2014 ENU

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© OMICRON Page 1 of 22

Application Note

Extending existing PTL items for distance protectionwith power swing blocking and tripping tests

Author Oliver Janke | [email protected]

Date Jan 09, 2014 (first version: Apr 19, 2011)

Related OMICRON ProductCMC, Test Universe

Application AreaProtection Systems

KeywordsPower Swing, NetSim, PTL

Versionv1.1

Document ID ANS_11007_ENU

Abstract

This document shows how to extend existing PTL items. The OMICRON Test Module NetSim will be usedfor testing the power swing blocking function during stable power swings and the tripping function duringunstable swings.


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© OMICRON 2014 Page 2 of 22

General information

OMICRON electronics GmbH including all international branch offices is henceforth referred to asOMICRON.

The product information, specifications, and technical data embodied in this application note represent thetechnical status at the time of writing and are subject to change without prior notice.

We have done our best to ensure that the information given in this application note is useful, accurate andentirely reliable. However, OMICRON does not assume responsibility for any inaccuracies which may bepresent.

OMICRON translates this application note from the source language English into a number of otherlanguages. Any translation of this document is done for local requirements, and in the event of a disputebetween the English and a non-English version, the English version of this note shall govern.

All rights including translation reserved. Reproduction of any kind, for example, photocopying, microfilming,optical character recognition and/or storage in electronic data processing systems, requires the explicitconsent of OMICRON. Reprinting, wholly or in part, is not permitted.

© OMICRON 2014. All rights reserved. This application note is a publication of OMICRON.


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Content

1 Safety instructions .......................................................................................................................... 4

2 Introduction ..................................................................................................................................... 5

3 The Emergence of Power Swings and their Detection .................................................................. 6

4 The OMICRON Protection Testing Library (PTL) ........................................................................... 8

4.1 The Structure of the XRIO Converter ........................................................................................ 8

4.2 Using the Import Filter ............................................................................................................... 8

5 Adding a NetSim Module for Power Swing Blocking ....... ........ ....... ....... ........ ....... ....... ........ ....... ... 9

6 Adding a NetSim Module for Power Swing Tripping ....................................................................15

7

Tips for Defining a Good Test Case ..............................................................................................17

8 Testing Power Swing Detection of ABB REL670 and Siemens 7SA631 ........... ........ ....... ....... .....18

8.1 Testing Power Swing Blocking of ABB REL670 ........................................................................18

8.2 Testing Power Swing Blocking and Tripping of Siemens 7SA631 .............................................19

List of Literature ...............................................................................................................................21


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1 Safety instructionsThis application note may only be used in combination with the relevant product manuals which contain allsafety instructions. The user is fully responsibility for any application that makes use of OMICRON products.

Instructions are always characterized by a symbol even if they are included to a safety instruction.

DANGER

Death or severe injury caused by high voltage or current if the respectiveprotective measures are not complied.

Carefully read and understand the content of this application note as well asthe manuals of the involved systems before starting its practical application.

Please contact OMICRON before you continue the process if you do notunderstand the safety instructions, operating instructions, or parts of it.

Follow each instruction mentioned there especially the safety instructionssince this is the only way to avoid danger that can occur when working athigh voltage or high current systems.

Furthermore, only use the involved equipment according to its intendedpurpose to guarantee a safe operation.

Existing national safety standards for accident prevention andenvironmental protection may supplement the equipment’s manual.

Only experienced and competent professionals that are trained for working in high voltage or high currentenvironments may perform this application note. Additional the following qualifications are required:

• authorized to work in environments of energy generation, transmission or distribution and familiar withthe approved operating practices in such environments.

• familiar with the five safety rules.

• good knowledge of the OMICRON CMC Test and Test Universe software.


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2 IntroductionThe OMICRON Protection Testing Library (PTL) provides predefined test plans (Protection TestingTemplates, PTTs) for testing a number of relays including distance protection devices. The respective PTLitem supports the test person in developing a high quality test for the main protection functions in a shorttime. But for different reasons power swing detection is not implemented in the PTL. The aim of thisapplication note is to demonstrate how the OMICRON Test Module NetSim can be added to an existing PTTto test this function. This is shown for the following three distance protection relays:

> AREVA P442> ABB REL670> SIEMENS 7SA631

NetSim will be used to simulate the transient processes in a power network during a power swing to analyzethe protection devices reaction. The whole protection system and not setting parameters is tested thereby.This kind of testing is called system testing. It proofs whether the IED (Intelligent Electronic Device) willprotect the electrical equipment in the specific case, or not.


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3 The Emergence of Power Swings and their DetectionDuring the normal operation of the electrical power network the actual load always equals the generation.But caused by sudden load changes, switching operations or faults this balance can be disturbed. Becauseof the inertia of all connected electrical machines and the slow control of the generation of active powerthese events result in oscillations of voltages and currents. There are two possible scenarios:

1. The control devices are able to dampen the oscillations and the power system is equilibrated again. Wecall that a stable power swing.

2. One or more generators fall out of step and loose synchronism to the remaining network. This is called anunstable power swing.

During this process the installed distance protection relays measure impedances that can be similar to thoseduring three phase faults (see Figure 1) . If the impedance is within a tripping zone for a long enough time,

the protection device will trip the circuit breaker to disconnect the electrical equipment. During the first casetripping is not needed as no fault exists on the network and the disturbance will disappear by itself. To solvethe disturbance in the second case a few predefined connections within the network should break before thewhole network splits in separate subnetworks. To define these locations several considerations have to bemade. An activated power swing detection can prevent these non selective trips and thus possible blackoutslike the Northeast Blackout of 2003 in North America.

Figure 1: Impedance trajectory during power swings

But how does the IED distinguish between a stable power swing, an unstable one and a fault? While theimpedance change during a power swing is rather slow the impedance vector jumps directly into the trippingzone at a fault occurrence. At a stable power swing the measured impedance enters the zones from oneside, then turns around and leaves at the same side (see Figure 1) . During an unstable power swing theimpedance crosses the X axis completely and leaves the zones on the other side.

lineimpedance

stable power swing

unstable

power swingdetection zone


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The relay manufacturers developed different algorithms to decide which case is present. They all use one ormore of the following criteria:

> Power swing detection zone: As Figure 1 shows, a frame is drawn around the tripping zones orthe starting zones. If the impedance is calculated within this area for a given number ofmeasurement cycles, it is recognized as slowly changing and thus a power swing. Anotherpossibility is to determine the time the trajectory needs to move through this area. Position andsize of this frame are important parameters and can be set for some protection devices.

> Monotony: The movement direction in R and X is determined. During a power swing only onedirection is changing.

> Continuity: The measured impedance must be changing with at least a minimum value toensure, the trajectory is moving. Otherwise it cannot be a power swing.

> Regularity: The ratio of two successive changes of the measured impedances is below a limitvalue. This ensures that the trajectory moves with constant or slowly changing speed, but notperforming rapid changes.

> Out of step detection: It is proved from which side the trajectory enters and leaves the out ofstep detection zone (which can be the power swing detection zone or a similar one). Anothercriterion is the direction of the impedance movement when crossing the line angle. Dependingon the setting of the IED it trips immediately or after a given number of turns.

Furthermore other criteria and exceptions to the listed ones are possible.

There are two different power swing functions in modern numerical relays:

> Power swing blocking: The whole distance protection or only assigned zones are blocked whena power swing occurs.

> Power swing tripping: The relay trips after detecting an unstable power swing.


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4 The OMICRON Protection Testing Library (PTL)There are different sources for the PTL: It can be installed from the DVD or CDs that are shipped with theCMC test set or it can be downloaded from the OMICRON customer area ( www.omicron.at ). In both cases itis free of charge.

Each PTL item consists of several files:

> An *.xrio-file: This is the XRIO converter. It can be used as test object for every test module. After entering the actual relay settings, the converter calculates the characteristics for the mainprotection functions automatically.

> An *.occ-file: This is the PTT (Protection Test Template) and consists of several test modules totest the main functions of the corresponding protection device. A test for power swing blockingor tripping is always missing. The XRIO converter is already included as test object. Using thePTT is the fastest way of using the PTL as only the relay settings and little other informationhave to be entered in the test object.

> One or two *.pdf-files: These are the manuals for the PTL item. They contain importantinformation on how to use these files.

4.1 The Structure of the XRIO Converter

Each PTL XRIO converter is divided in five sections:

>

Relay Parameter Section: This is a copy of the relay settings software. The actual settings ofthe device have to be entered her either manually or with the help of an import filter (see chapter0) . Also the settings for the power swing detection are included, even if this function is notsupported by the PTT. They can be used to build a customized test for this function.

> Additional Information: This block contains few parameters which are needed to test thedevice but are not part of the relay settings.

> RIOplus: This part is used for calculations to convert the relay specific parameters to valuesvalid for the RIO block and OMICRON Test Universe test modules. It is only visible if theadvanced view of the XRIO editor is active.

> Template Controller: This block is needed for the PTT. Only visible in advanced view.> RIO: This block contains the resulting characteristics for most of the protection functions.

Nothing must be changed here, as the formulas for the automatic calculation would be

destroyed. In case of a distance protection the RIO function Distance contains the zones. Theywill be used for testing the power swing detection.

4.2 Using the Import Filter

With the help of one of the OMICRON import filters the manual entry of settings may be omitted. Differentimport filter for different manufacturers are available. With the import filter and the specific relay parametersoftware export file, it is possible to import the relay settings automatically into the XRIO converter. Even ifthe PTTs are normally not supporting power swing detection, the relay import filter will also work for thesesettings.


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5 Adding a NetSim Module for Power Swing BlockingIn the following the PTT for AREVA P441, P442 and P444 is used as an example. After installing this PTLitem the PTT is opened and the settings of the relay are entered in the converter.

For testing the power swing blocking function a NetSim module is inserted after the last distance protectiontest, which is the SOTF (switch on to fault) test. At first the correct Test Case at the menu Parameters mustbe selected (see Figure 2) . There are three different power swing cases:

> Synchronous: A stable power swing is simulated. This one is selected here.> Asynchronous, Multiple Turns: An unstable power swing is simulated with multiple pole slips.> Asynchronous, With Fault: An unstable power swing is simulated with multiple pole slips.

Additionally a fault occurs at a predefined time.

The impedance view (Figure 3) shows, that the module is automatically using the impedance characteristicdata of the converter. Also the three trajectories of the phase to phase impedances are drawn. With thedefault test settings entered in the test view (Figure 4) tabs the impedances will never reach the trip zonesand thus no power swing blocking can be tested. Therefore the according settings have to be adapted first.Some further understanding of the data of the actual network and the physics behind the power swing isneeded.

Figure 2: Selection of the Test Case


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Figure 3: Impedance view

Most of the parameters which have to be entered in the Test View do not correspond to the settings of theprotection function. Instead these are data about the network the IED is used on. By means of these datathe module will simulate the transient signals which occur during a power swing on this network. Not thesettings of the relay are tested, but its behavior under realistic conditions. Unfortunately some of the needednetwork data are often not available in practice. Furthermore most of the networks have a variety ofswitching states. This leads to many different combinations of test settings that have to be tested. But withsome considerations a good test case can be found. If there is no claim laid to test with real network data,there is still the possibility to test the protection function with the standard values.

So let's go through the test views tabs and see, which effect on the test the individual settings have.

Fault

In this tab a Prefault and a Postfault time can be set. 100 ms are enough for both. The next two settings aremuch more important for the test:

The Slip angle specifies the maximum asynchronicity. ±180° are the theoretical limits for a stable powerswing. If the angle became even more, the machine would fall out of step, as its maximum torque wasexceeded. Less slip angle means less power swing and results in higher impedances. By entering themaximum of -180° it is achieved that the relay measures impedances within the tripping zones. The negativelimit is chosen as this will create a power swing coming from the right what looks like a big load to the IED.The protection device will thus be tested whether it is still working fine in such a difficult situation.


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Figure 4: Test View with entered Fault settings

The Slip time defines the duration of the power swing. If this time is too short the trajectory might move tofast and leave the tripping zones before the distance protection tripped. 500ms are a good value but after allsettings were entered it must be checked, that the trajectory stays within a tripping zone for a long enoughtime.

Line

Here the LinkToXRIO function is used to define the lines parameters (see Figure 5) . For the selected modeZ and k the corresponding values are stored in the RIO block of the converter (see Figure 6) . As they are

secondary values, this option must be selected in the View menu before linking otherwise they areinterpreted as primary values. The value for the grounding factor must be checked, as some PTL convertersuse a grounding factor of zero and recalculate all zones to loop impedances. In that case the link must bedone to the corresponding parameter in the Relay Parameter Section . Changing the Mode might be needed.

Figure 5: Line settings


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Figure 6: Linking the line settings

Sources

These data are characterizing the network. A user defined block called "System Data" is added to the XRIOconverter for some calculations (see Figure 8) .

The Voltage and Frequency in this tab (Figure 7) can be linked to the nominal values in the RIO Device block.

Delta V and Delta phi are both zero for the moment. Chapter 7 explains how these values can be used to

move the trajectory of the impedances.For the impedance magnitudes and angles a user defined XRIO block shall be used. This block must beadded to the XRIO converter like shown in Figure 8 and is used to calculate the source impedances

, from the short circuit power , of the two connected sources. To calculate the parametersZ1 source 1 and 2 equation (1) is implemented as a formula in XRIO.

, = . · ,

,·

· ,

· , (1)

In this equation , is the primary nominal line to line voltage. The four variables above and below theright fraction line are the primary and secondary values of the installed current transformers or voltagetransformers. They are needed to convert the impedance value to a secondary value.

The results can be linked to the NetSim settings Zmag for source 1 and source 2. The angles can beentered either directly in NetSim or as seen in Figure 7 and Figure 8 also linked to XRIO. In the converterthe angle is calculated from an R/X ratio of 10%, which is an approximation that can be made if the exactvalues are not known. For this example 5000 MVA are used for both sources.

The grounding factor magnitudes and angles can normally be chosen as one and zero, if the exact valuesare unknown.


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Figure 7: The sources definition

Figure 8: The user defined block System Data in XRIO

Outputs

The primary and secondary values for the current transformers and voltage transformers can be linked to thecorresponding values in the RIO Device block (see Figure 9) . This has only to be done for the location (A orB) at which the relay is installed.

Figure 9: The output configuration


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After all settings have been entered the impedance view shows the resulting power swing (see Figure 10) . As a next step, the trajectories are proved to remain in a tripping zone long enough to evoke a trip. As thetrajectories move into Z1 (T Z1 = 0 s) this zone will probably cause the trip. Depending on the movementspeed theoretically every other zone could trip first. To test the power swing blocking function at least onezone must be found that would surely trip, if the function did not work probably. Therefore the cursors are

moved on the time axis to find the points where the trajectories enter and leave the zone. It is even moreexact not to take the borders of the zone but to use the tolerance lines. Now the time deviation can be read,which is about 110 ms what is enough for the relay to trip. The proper operation of the power swing blockingfunction can be tested with this power swing. If the time was too short the Slip Time (Fault settings) can beincreased.

Figure 10: Measuring the time the trajectory of the resulting power swing is within zone 1

After configuring the trip signal in the local hardware configuration three measurements for the phaseselective trip times can be defined. These time measurements start with the beginning of the power swingand end with the trip signal for phase A, B or C. When testing the power swing blocking function, no trip is

expected at all, that's why no nominal values are entered. Therefore the assessment must be donemanually. The test was OK if no trip occurred. The Measurement View after a successful test is shown inFigure 11.

Figure 11: Measurement View


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6 Adding a NetSim Module for Power Swing TrippingTo test the power swing tripping function of the relay another NetSim module must be added, wherePower Swing / Asynchronous / Multiple Turns is selected as test case. The settings are very similar to thosefrom the power swing blocking test:

Power Swing

A Slip frequency (see Figure 12) of 1 Hz causes a slow enough movement through the impedance plane, topossible cause a trip. The duration of each turn will be is 1 s and the trajectory will again move from right toleft through the impedance plane.

As the example relay is configured to block during the first turn and trip if a second one occurs, theNumber of turns should at least be two.

Figure 12: The Power Swing settings

Line, Sources and Outputs

These settings are exactly the same as for the power swing blocking test and can be seen in Figure 5, Figure 7 and Figure 9.

The resulting impedance trajectory is shown in Figure 13. The time within zone 1 can be determined asabout 110 ms, what is long enough.


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Figure 13: The resulting out of step power swing

Again measurements for the trip times are defined. Unlike during the power swing blocking test trips are nowexpected in all three phases. Defining a nominal time is not possible, as it depends on the moment the relayrecognizes, that the power swing is an unstable one, which in turn depends on the algorithm of the IED. Thistask is something completely different to measuring the trip time of a zone. The assessment again has to bedone manually. Figure 14 shows the result of this measurement: A trip time above 1 s signifies that the relaytripped as supposed during the second turn. This can be verified with help of the signal view. Figure 15clearly shows that all three trip signals occur during the second power swing. This is exactly how the IED

was meant to react. Thus the power swing tripping function could successfully be tested that way.

Figure 14: Measurement for the trip time


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Figure 15: Signal view of an unstable power swing

7 Tips for Defining a Good Test Case A good test case for a stable power swing is one with the turning point of the trajectory inside of zone 1. Thiswill ensure that the relay will trip if the power swing blocking function did not work probably.

If the real network data (i.e. the source impedances) are unknown, default values have to be used or

assumptions must be done.

If the resulting turning point is outside of all tripping zones there is a possibility to move it within theimpedance plane: By changing the value for Delta V (see Figure 7) the transfer of reactive power on the linecan be modeled. With Delta phi the active power transfer can be changed. This results in a movement of theturning point like shown in Figure 16. A change of reactive power results in a movement in direction of theline angle, a change of active power in a movement in 90° turned to it.

These two parameters can now be used to move the turning point from outside of the tripping characteristicto the inside. Of course only realistic values should be used, that correspond to a power transfer that canhappen in reality. Nevertheless this function can still be tested by using unrealistic test values that do not

represent the connected network.


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Figure 16: Movement of the turning point depending on the power transport

8 Testing Power Swing Detection of ABB REL670 and Siemens 7SA631Up to this point this application note describes how to test the power swing blocking and tripping of the

AREVA P442 relay. This chapter is therefore devoted to using the existing OMICRON NetSim modules totest the same protection function in other relay types. This will be done with very few changes as noparameter test but a system test was performed. Even if the line parameters and zone reaches will be thesame for these examples the distance characteristics will differ from relay to relay.

8.1 Testing Power Swing Blocking of ABB REL670

In the example settings of this IED only power swing blocking is included. A test for power swing tripping isnot needed.

The first step is to prepare the XRIO converter. As some settings of the NetSim module are linked to theSystem Data block, this block must be copied to the REL670 converter. Therefore the Organize function(XRIO editor advanced view) is used: The P442 converter is imported in the right window. Then theSystem Data block is marked and moved to the appropriate place in the REL670 converter.

Now the NetSim module for power swing blocking is copied to the REL670 PTT. It will automatically use thealready imported System Data block of the converter. Depending on the wiring the local hardwareconfiguration might have to be adapted. Also the measurements are changed as only one general trip signalexists in this example. As the parameters for the line are different to those in the P442 converter they haveto be adapted as seen in Figure 17. In the REL670 settings no grounding factor k is defined. That's why adifferent Mode is chosen and the values are now linked to the R and X values of the positive and negativesequence parameters of the line. These values are found in the settings for the fault locator. Please note,that they are primary values and therefore the module must be configured to view primary values whilelinking.

line an le


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Figure 17: Defining the line for testing ABB REL670

The resulting impedance trajectory is shown in Figure 18. After checking its residence time in zone 1 themodule is ready for testing.

Figure 18: Power swing blocking test for ABB REL670

8.2 Testing Power Swing Blocking and Tripping of Siemens 7SA631

In the example settings for this relay power swing blocking and tripping are activated. It is configured to havephase selective trip signals. Therefore both NetSim modules from the Areva P442 test can be copied to theSiemens 7SA631 PTT. But before that the System Data block must be added to the converter like in theprevious chapter. The modules will now automatically use these values and also the distance characteristicof the RIO block. Again the links for the line settings must be adapted to the new settings: Like in Figure 19 a


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different mode must be selected. The R and X values can be taken from the RIOplus block underProtectedObject . The two ratios RE/R and XE/X are linked to the RIO distance function.

For testing power swing tripping the number of turns is changed, as the IED is meant to trip during the first

pole slip. Figure 20 shows the resulting trajectory. After checking its residence time within zone 1 the testcan be started.

Figure 19: Line settings for Siemens 7SA631

Figure 20: Testing of power swing tripping of Siemens 7SA631


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List of Literature

[1] Michael Albert, Eugenio Carvalheira, Oliver Janke: PTL: A solid basis for building customized lineprotection test standards, OMICRON IPTS 2009 (www.omicron.at)

[2] Dr. Peter Meinhardt, OMICRON electronics GmbH: Testing approaches for power swing blockingfunction, OMICRON IPTS 2009 (www.omicron.at)

[3] Dr. Fred Steinhauser, OMICRON electronics GmbH: Testing of the Power Swing Blocking inDistance Relays

[4] Dr. Yuchen Lu, Dr. Juergen Holbach, Laurie Martuscello, P.E., Edward Krizauskas, P.E.: Tests ofDistance Relay Performance on Stable and Unstable Power Swings Using Simulated Data of the

August 14th 2003 System Disturbance

[5] Jörg Blumschein, Matthias Kereit, Yilmaz Yelgin, SIEMENS: Erhöhung der Netzstabilität durchzuverlässige Pendelerkennung, Tagungsbeitrag 4.1 OMICRON Anwendertagung 2009(www.omicron.at)

[6] MiCOM P441/P442/P444 Numerical Distance Protection, Technical Manual

[7] Technical reference manual Line distance protection IED REL 670

[8] SIPROTEC DISTANZSCHUTZ 7SA6 M ANUAL


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CMC Test Universe AppNote Extending PTL Items for Distance Protection 2014 ENU