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Methods for Testing Transformer Differential Relays Applied to DeltaGrounded Wye Transformers Using SinglePhase Test Currents Presented at: Minnesota Power Systems Conference St. Paul, MN, USA November 11, 2015 Tom Ernst GE Digital Energy 4523 Jeremiah Rd. Cookeville, TN 38506 [email protected] Craig Talbot Minnesota Power 30 West Superior St. Duluth, MN 55802 [email protected] Abstract This paper provides an alternate method for testing transformer differential relays applied to deltagrounded wye transformers using singlephase test currents. The alternate method is based on the transformer threeline diagram and transformer nameplate. This alternate method simulates actual current flows in the transformer during singlelineground faults on the wye side and provides confirmation that the relay’s slope characteristics and phase shift settings are operating correctly. The alternate method is based on the transformer threeline diagram and provides verification that the relay’s settings are correct for the transformer application. Threephase testing is not possible with some test sets due in part by the limited number of current channels available and, in some applications, test sets can also be limited by the highcurrent values required for differential slope 2 region tests. Traditional methods of singlephase testing typically require the addition of √3 multipliers and other adjustments to account for zerosequence current removal, further increasing the magnitude of the test currents. Also, traditional tests (both 3phase and 1phase) use currents and phase shifts based on the relay settings. The alternate method improves both issues as only 2 channels are required of the test set and, since the test simulates real world, no multipliers are required. The alternate method uses two test currents that are always 180 degrees out of phase of each other for the differentially balanced condition regardless of the transformer phase shift lead or lag. As a result, the alternate method is especially useful for commission testing as it proves the transformer phase shift relay settings are correct for the transformer connection rather than testing the relay settings. Introduction Testing of transformer differential characteristics can be challenging. Threephase testing, while straight forward from a magnitude and phase relationship point of view, requires 6 highamperage test currents. For delta grd wye winding transformers, traditional singlephase testing requires nonobvious multipliers and does not simulate realworld fault conditions. This paper discusses an alternate method of singlephase testing that simulates realworld singlephase loading conditions without the need for phase shifts or current multipliers. This alternate method verifies the differential relay settings are appropriate for the installed transformer by using the installation drawings and transformer nameplate diagram to determine the test connections. Application examples of installations at Minnesota Power substations are used to demonstrate the method.

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  • MethodsforTestingTransformerDifferentialRelaysAppliedtoDeltaGroundedWyeTransformersUsingSinglePhaseTestCurrents

    Presentedat:MinnesotaPowerSystemsConference

    St.Paul,MN,USANovember11,2015

    TomErnstGEDigitalEnergy4523JeremiahRd.Cookeville,[email protected]

    CraigTalbotMinnesotaPower30WestSuperiorSt.Duluth,[email protected]

    AbstractThispaperprovidesanalternatemethodfortestingtransformerdifferentialrelaysappliedtodeltagroundedwyetransformersusingsinglephasetestcurrents.Thealternatemethodisbasedonthetransformerthreelinediagramandtransformernameplate.Thisalternatemethodsimulatesactualcurrentflowsinthetransformerduringsinglelinegroundfaultsonthewyesideandprovidesconfirmationthattherelaysslopecharacteristicsandphaseshiftsettingsareoperatingcorrectly.Thealternatemethodisbasedonthetransformerthreelinediagramandprovidesverificationthattherelayssettingsarecorrectforthetransformerapplication.Threephasetestingisnotpossiblewithsometestsetsdueinpartbythelimitednumberofcurrentchannelsavailableand,insomeapplications,testsetscanalsobelimitedbythehighcurrentvaluesrequiredfordifferentialslope2regiontests.Traditionalmethodsofsinglephasetestingtypicallyrequiretheadditionof3multipliersandotheradjustmentstoaccountforzerosequencecurrentremoval,furtherincreasingthemagnitudeofthetestcurrents.Also,traditionaltests(both3phaseand1phase)usecurrentsandphaseshiftsbasedontherelaysettings.Thealternatemethodimprovesbothissuesasonly2channelsarerequiredofthetestsetand,sincethetestsimulatesrealworld,nomultipliersarerequired.Thealternatemethodusestwotestcurrentsthatarealways180degreesoutofphaseofeachotherforthedifferentiallybalancedconditionregardlessofthetransformerphaseshiftleadorlag.Asaresult,thealternatemethodisespeciallyusefulforcommissiontestingasitprovesthetransformerphaseshiftrelaysettingsarecorrectforthetransformerconnectionratherthantestingtherelaysettings.Introduction

    Testingoftransformerdifferentialcharacteristicscanbechallenging.Threephasetesting,whilestraightforwardfromamagnitudeandphaserelationshippointofview,requires6highamperagetestcurrents.Fordeltagrdwyewindingtransformers,traditionalsinglephasetestingrequiresnonobviousmultipliersanddoesnotsimulaterealworldfaultconditions.Thispaperdiscussesanalternatemethodofsinglephasetestingthatsimulatesrealworldsinglephaseloadingconditionswithouttheneedforphaseshiftsorcurrentmultipliers.Thisalternatemethodverifiesthedifferentialrelaysettingsareappropriatefortheinstalledtransformerbyusingtheinstallationdrawingsandtransformernameplatediagramtodeterminethetestconnections.ApplicationexamplesofinstallationsatMinnesotaPowersubstationsareusedtodemonstratethemethod.

  • Traditional3PhaseTestingDifferentialpickuptestscanbeperformedusing3phasetestcurrents.Themagnitudeofthecurrentsrequiredforpickupistypicallylow(10%20%offullload)andonly3currentchannelsarerequiredfromthetestset.Formicroprocessorrelays,itisimportanttoconfirmthatallthreephasespickupwhenperforminga3phasetest.Slopecharacteristictestsrequiresimultaneousinjectionoftestcurrentsintoaminimumof2relaywindings.Themagnituderelationshipofthecurrentsbetweenthewindingsisbasedonthetransformerthreephasevoltageratio.Thephaseshiftbetweenthetestcurrentsisafunctionofthetransformerinternalandexternalconnections.Determiningthecorrectanglerequiresanexaminationofthesubstation3lineinstallationdrawingandthetransformernameplatediagram.Athoroughunderstandingof3phasepowerisalsorequiredsincetheexternalconnectionscanreversetheleadlagrelationshipofthewindingsifphasesA,BandCarenotconnectedtobushings1,2and3.Figure1showsaninstallationwithatypicaldeltagrdwyetransformerwithstandardIEEEphaseshift(secondarylagsprimaryby30).InthisinstallationtheinstalledphaserelationshipmatchesthetransformernameplatephaserelationshipsincephaseAisonbushings1,Bisonbushings2andCisonbushings3.The3phasetestcurrenttosimulatefullloadforthisinstallationarealsoshowninfigure1.

    Figure1:Typicaldeltagrdwyetransformerandassociated3phasetestcurrents

  • Figure2showsthesametransformerasfigure1buttheexternalconnectionsarerolledsuchthatphaseAisonbushings3,Bisonbushings2andCisonbushings1.Theresultinginstalledphaseshifthasthelowvoltagesideleadingthehighvoltagesideby30eventhoughthetransformernameplatedrawingshowsalaggingsecondaryvoltage.Notethatthetestcurrentsreflectthisleadingphaseangleshift.

    Figure2:Typicaldeltagrdwyetransformerwithrolledphasingandassociated3phasetestcurrentsFigure3showsthetestsetconnectionsfor3phasetestingofthetransformerinstallationshowninFigure1.Threephasedifferentialslopetestingrequires6testcurrentseachhavingdifferentphaseangles.Sometestsetscannotperform3phasedifferentialslopetestsbecauseofthelimitednumberofcurrentchannelsavailable.Additionally,sometestsetswith6currentchannelshavelimitedVAcapabilitywhenusingthe6channels;thisinturnlimitsthemagnitudeofthetestcurrents,especiallywhentestingtheregion2slopecharacteristic.

  • DifferentialRelay

    Figure3:3Phasetestingconnectionsforthefigure1transformerTraditional1PhaseTestingTraditionalsinglephasetestingoftransformerdifferentialrelays,asshowninfigure4,inherentlychecksthefunctionalityofeachphaseandrequiresonly2injectedcurrents.Byonlyusing2injectedcurrentsmostrelaytestsetscanperformthistypeoftesting.However,injectingsinglephasecurrentsfordifferentialslopetestingoftenrequiresmultipliersandphaseshiftsthatarenotobviousfromthesubstationandtransformer3linediagrams,especiallyfordeltagrdwyewindingtransformers.

  • Figure4:Traditional1phasetestconnections

    Alternate1PhaseMethodAnalternatemethodofusingsinglephasetestcurrentsisshowninfigures5and6.Thisconnectionisrelatedtothetransformerinternalandexternal3linediagramsandsimulatesrealworldloadandshortcircuitconditionswithouttheneedfornonobviousmultipliers.Differentiallybalancedsinglephasethroughcurrentforadeltagrdwyetransformerwith30degreelagsecondaryandtheassociatedtestconnectionsareshowninfigures5(a)and5(b)respectively.Thedifferentiallybalanced1phasethroughcurrentandassociatedtestconnectionsforadeltagrdwyetransformerwith30degreeleadsecondaryareshowninfigures6(a)and6(b)respectively.

  • Figure5(a):Differentiallybalanced1phasethroughcurrentfora30degreelagtransformer

  • Figure5(b):Differentiallybalanced1phasetestconnectionsfora30degreelagtransformer

  • X1X2X3

    X0

    H3 H2 H1

    X0X1

    X2

    X3

    H1

    H2H3

    Nameplate

    X0

    A(H3)Installed

    B(H2)C(H1)A(X3)

    B(X2)C(X1)

    A B C

    A B C

    115,00013,800/7970GY

    20MVA

    2000/5A

    200/5A

    [email protected]

    [email protected]

    [email protected]@180

    [email protected]

    TestCurrentstoRelay

    N1/N2=115/8

    Figure6(a):Differentiallybalanced1phasethroughcurrentfora30degreeleadtransformer

  • DifferentialRelay

    Figure6(b):Differentiallybalanced1phasetestconnectionsfora30degreeleadtransformerThetestcurrentmagnitudesandanglesshowninfigures5(b)and6(b)arecalculatedbasedonthedifferentiallybalancedthroughcurrentconditionsshowninfigures5(a)and6(a).Thecurrentscalculatedbyaproperlymodeledshortcircuitprogrammayalsobeappliedtosimulatetherelaysperformanceduringrealworldexternalfaultconditions.Eventhoughdeltagrdwyetransformerscreate3phaseangleshiftsof+/30degrees,thealternate1phasemethodtestcurrentsarealways180degreesapartfordifferentiallybalancedthroughcurrentconditions.Thesuccessofthealternatesinglephasetestclearlyindicatesifthetransformerphaseshiftsettingisenteredproperlyfortheinstallation.Figure7showsthetransformerdifferentialrelaycalculatedquantitiesforthetestshowninfigure5(b)wherethephaseshift(W2AngleWRT)settingisenteredcorrectly(30degrees).Notethatthedifferentialcurrentmagnitudeis0forallthreephasesandtherestraintcurrentmagnitudeis0.5perunitinphasesAandC,correctlyindicatingadifferentiallybalancedthroughcurrentcondition.

  • Figure7:DifferentiallybalancedthroughcurrentconditionwithcorrectphaseshiftsettingIfthephaseshiftsettingisenteredincorrectly(30degrees)andthetestcurrentsshowninfigure5(b)areentered,thetransformerdifferentialrelaycalculatedquantitiesclearlyshowaproblem(figure8):thedifferentialcurrentmagnitudesarenot0forphasesBandCandtherelaytrips.Oncethedifferentiallybalancedthroughcurrentconditionisestablishedcorrectly,asinfigure7,theangleofoneofthewindingcurrentscanberolleduntiltherelaytrips.Atthispoint,theslopecanbecalculatedbydividingthedifferentialcurrentmagnitudebytherestraintcurrentmagnitude.Figure9showstheresultsofthisslopetestshowingatripwithwinding2currentrolledfrom180to165.6degreesandacalculatedslope(S1)of:S1=0.13/0.50=0.26or26%.Thiscorrelateswellwiththeslope1settingof25%.Asimilartestcanberunwithlargertestcurrentstoverifytheslope2performance.

    TRANSFORMER SETTINGS AND CTs Nomber of Windings: 2 DIFF / RSTR CHARACTERISTIC

    W1 W2 W3 W4 W5 W6 DIFFERENTIAL- RESTRAINT GRAPHRated(MVA) 20 20 0 0 0 0 Diff. min. PKP 0.10 Slope1 25.0Nom. (kV) 115 13.8 230 13.8 0.48 69 Kneepoint 1 2.00Connection DELTA WYE WYE WYE WYE WYE Kneepoint 2 3.00 Slope2 50.0Grounding NO YES NO NO YES YESAngle WRT 0 -30 0 0 0 0 Pre-calculated graph points >>Pre-calculated ratio of the point from the CT primary 200 2000 2000 8000 3000 1000 Id/Ir, (%) Ph A Ph B Ph C characteristic, corresponding to the same CT sec. tap 5 5 5 5 5 5 25.0 25.0 25.0 restraint as per the actual Id/Ir ratio. The trip Inom. Prim. 100.4 836.7 0.0 0.0 0.0 0.0 occurs, when the actual Id/Ir ratio,(%) is biggerInom.Sec. 2.510 2.092 0.000 0.000 0.000 0.000 than the pre-calculated Id/Ir ratio, (%)Rotations ABC 1 ACTUAL VALUES TEST CURRENTS Magnitude Ref. Winding #: 1

    IA IB ICW1 DIFFERENTIAL CURRENTSMagnitude 2.50 0.00 2.50 Iad Ibd IcdAngle 0.0 0.0 180.0 Magnitude 0.00 0.00 0.00W2 Angle -180.0 -180.0 0.0Magnitude 3.61 0.00 0.00Angle 180.0 0.0 0.0 RESTRAINT CURRENTSW3 Iar Ibr IcrMagnitude 0.00 0.00 0.00 Magnitude 0.50 0.00 0.50Angle 0.0 0.0 0.0W4 Actual Differential/Restraint RatioMagnitude 0.00 0.00 0.00 Actual ph A % ph B % ph C %Angle 0.0 0.0 0.0 Id/Ir ratio 0.0 100.0 0.0W5Magnitude 0.00 0.00 0.00 DIFF. OPERATIONAngle 0.0 0.0 0.0 NO TRIPW6 Ia Ib IcMagnitude 0.00 0.00 0.00 No trip No trip No tripAngle 0.0 0.0 0.0

    Select Magnitude Ref. Winding:

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    11

    12

    0 1 2 3 4 5 6 7 8 9 10 11 12

    I diff, pu

    I restr, pu

    Operating Characteristic

    Slope characteristics Iad Ibd Icd

  • Figure8:Differentiallybalancedthroughcurrentconditionwithincorrectphaseshiftsetting

    Figure9:Slopeverificationtestwithwinding2testcurrentanglerolledtopointoftrip

    TRANSFORMER SETTINGS AND CTs Nomber of Windings: 2 DIFF / RSTR CHARACTERISTIC

    W1 W2 W3 W4 W5 W6 DIFFERENTIAL- RESTRAINT GRAPHRated(MVA) 20 20 0 0 0 0 Diff. min. PKP 0.10 Slope1 25.0Nom. (kV) 115 13.8 230 13.8 0.48 69 Kneepoint 1 2.00Connection DELTA WYE WYE WYE WYE WYE Kneepoint 2 3.00 Slope2 50.0Grounding NO YES NO NO YES YESAngle WRT 0 30 0 0 0 0 Pre-calculated graph points >>Pre-calculated ratio of the point from the CT primary 200 2000 2000 8000 3000 1000 Id/Ir, (%) Ph A Ph B Ph C characteristic, corresponding to the same CT sec. tap 5 5 5 5 5 5 25.0 25.0 25.0 restraint as per the actual Id/Ir ratio. The trip Inom. Prim. 100.4 836.7 0.0 0.0 0.0 0.0 occurs, when the actual Id/Ir ratio,(%) is biggerInom.Sec. 2.510 2.092 0.000 0.000 0.000 0.000 than the pre-calculated Id/Ir ratio, (%)Rotations ABC 1 ACTUAL VALUES TEST CURRENTS Magnitude Ref. Winding #: 1

    IA IB ICW1 DIFFERENTIAL CURRENTSMagnitude 2.50 0.00 2.50 Iad Ibd IcdAngle 0.0 0.0 180.0 Magnitude 0.00 0.50 0.50W2 Angle -180.0 0.0 -180.0Magnitude 3.61 0.00 0.00Angle 180.0 0.0 0.0 RESTRAINT CURRENTSW3 Iar Ibr IcrMagnitude 0.00 0.00 0.00 Magnitude 0.50 0.50 0.50Angle 0.0 0.0 0.0W4 Actual Differential/Restraint RatioMagnitude 0.00 0.00 0.00 Actual ph A % ph B % ph C %Angle 0.0 0.0 0.0 Id/Ir ratio 0.0 100.0 100.0W5Magnitude 0.00 0.00 0.00 DIFF. OPERATIONAngle 0.0 0.0 0.0 TRIPW6 Ia Ib IcMagnitude 0.00 0.00 0.00 No trip Trip TripAngle 0.0 0.0 0.0

    Select Magnitude Ref. Winding:

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    11

    12

    0 1 2 3 4 5 6 7 8 9 10 11 12

    I diff, pu

    I restr, pu

    Operating Characteristic

    Slope characteristics Iad Ibd Icd

    TRANSFORMER SETTINGS AND CTs Nomber of Windings: 2 DIFF / RSTR CHARACTERISTIC

    W1 W2 W3 W4 W5 W6 DIFFERENTIAL- RESTRAINT GRAPHRated(MVA) 20 20 0 0 0 0 Diff. min. PKP 0.10 Slope1 25.0Nom. (kV) 115 13.8 230 13.8 0.48 69 Kneepoint 1 2.00Connection DELTA WYE WYE WYE WYE WYE Kneepoint 2 3.00 Slope2 50.0Grounding NO YES NO NO YES YESAngle WRT 0 -30 0 0 0 0 Pre-calculated graph points >>Pre-calculated ratio of the point from the CT primary 200 2000 2000 8000 3000 1000 Id/Ir, (%) Ph A Ph B Ph C characteristic, corresponding to the same CT sec. tap 5 5 5 5 5 5 25.0 25.0 25.0 restraint as per the actual Id/Ir ratio. The trip Inom. Prim. 100.4 836.7 0.0 0.0 0.0 0.0 occurs, when the actual Id/Ir ratio,(%) is biggerInom.Sec. 2.510 2.092 0.000 0.000 0.000 0.000 than the pre-calculated Id/Ir ratio, (%)Rotations ABC 1 ACTUAL VALUES TEST CURRENTS Magnitude Ref. Winding #: 1

    IA IB ICW1 DIFFERENTIAL CURRENTSMagnitude 2.50 0.00 2.50 Iad Ibd IcdAngle 0.0 0.0 180.0 Magnitude 0.13 0.00 0.13W2 Angle -277.1 -194.4 -97.1Magnitude 3.61 0.00 0.00Angle 165.6 0.0 0.0 RESTRAINT CURRENTSW3 Iar Ibr IcrMagnitude 0.00 0.00 0.00 Magnitude 0.50 0.00 0.50Angle 0.0 0.0 0.0W4 Actual Differential/Restraint RatioMagnitude 0.00 0.00 0.00 Actual ph A % ph B % ph C %Angle 0.0 0.0 0.0 Id/Ir ratio 25.1 100.0 25.1W5Magnitude 0.00 0.00 0.00 DIFF. OPERATIONAngle 0.0 0.0 0.0 TRIPW6 Ia Ib IcMagnitude 0.00 0.00 0.00 Trip No trip TripAngle 0.0 0.0 0.0

    Select Magnitude Ref. Winding:

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    11

    12

    0 1 2 3 4 5 6 7 8 9 10 11 12

    I diff, pu

    I restr, pu

    Operating Characteristic

    Slope characteristics Iad Ibd Icd

  • Sincethealternatemethodisasinglephasetest,itisnecessarytorepeatthetestforeachphaseforatotalof3connectionsforeachwindingpair.Tables1and2showtestconnectionsrequiredfora2windingdeltagrdwyetransformerwith30degreelag(figures5(a)&(b))andlead(figures6(a)&(b))connectionsrespectively.Table1:Testconnectionsfora2winding30degreelagdeltawyeconnectiontransformerTestID Winding1(delta)connections Winding2(wye)connectionsA InonA&outonC AB InonB&outonA BC InonC&outonB C

    Table2:Testconnectionsfora2winding30degreeleaddeltawyeconnectiontransformerTestID Winding1(delta)connections Winding2(wye)connectionsA InonA&outonB AB InonB&outonC BC InonC&outonA C

    Thetraditionalsinglephasetestmethodrequiresinjectingtestcurrentswithmagnitudesandanglesnotobviousfromthesubstationandtransformerdrawingswhilethealternatemethodcurrentmagnitudesandanglesarevisuallyrelatedtotheinstalled3linediagramandtheinternalturnsratio(N1/N2)ofthetransformer.However,acloseinspectionshowsthata3multiplierisimpliedduetotherelationshipbetweenthetransformer3phasevoltageratioandtheinternalturnsratio.Asaresult,thetestcurrentsforthealternatemethodarestilllargerthanthoserequiredfor3phasetesting.Forthisreason,itmaystillbedifficultforsometestsetstodeliverhightestcurrentstoverifytheregion2slope.Itshouldbepossibletodevelopanautomatedtestplanforthealternatesinglephasemethodwhichwouldselectthetestoutputsfromtable1ortable2dependingonthephaseshiftsetting.Assuch,themethodcouldbeusedformaintenancetesting.However,themethodisuniquelysuitedforcommissiontestingwherethecoreactivityofthemethodistodeterminethetestconnectionsbasedonanexaminationoftheinstallationdrawingswiththeultimategoalofverifyingthatthephaseshiftsettingiscorrectfortheinstallation.ApplicationExamplesTwoapplicationexamplesatMinnesotaPowersubstationsareincludedbelow.Thefirstexampleisadistributionsubstationwherethedistributionvoltagelagsthetransmissionvoltage.Thesecondexampleisanotherdistributionsubstationinadifferentdivisionwherethedistributionvoltageleadsthetransmissionvoltage.Inbothcases,IEEEstandardphaseshifttransformerswereinstalled(XsidelagstheHsideby30).AnanalysisofatransformerdifferentialrelayoperationcausedbyanincorrectphaseshiftsettingisalsoincludedintheApplicationExamplessection.

  • LaggingexampleInthisexample,thedistributionvoltage(34.5kV)lagsthetransmissionvoltage(115kV)by30.Figure10showsthetransformernameplatediagramandfigure11showsthesubstation3linediagramofthetransformerinstallationwitharrowsshowingdifferentiallybalancedsinglephaseloading.SinceABCphasesareconnectedtobushings123respectively,theinstallationphasordiagrammatchesthetransformernameplatephasordiagram.

    Figure10:Transformernameplateforexample1

  • MinnesotaPowerusesacalculationsheettodocumentthebasisoftheirrelaysettingsandtodefinethecommissionteststobeperformed.Thecommissiontestingdefinitionsfortheexample1transformerdifferentialslopecharacteristicareshowninfigure12.Youwillnotethatthetestconnectionsmatchwiththoseshowninfigure5(b)andTable1fora30laginstallation.

    X0

    A(H1)

    B(H2)C(H3)A(X1)

    B(X2)C(X3)

    1200/5MR300/5Tap

    1200/5MR1200/5Tap

    197A

    1137A

    [email protected]

    [email protected]

    N1/N2=115/19.9

    Figure11:3lineinstallationdiagramforexample1withdifferentiallybalanced1phaseload

  • Figure12:Testingdefinitionsforexample1transformerdifferentialslopecharacteristicLeadingExampleInthisexample,thedistributionvoltage(13.8kV)leadsthetransmissionvoltage(115kV)by30.Figure13showsthetransformernameplatediagramandfigure14showsthesubstation3linediagramofthetransformerinstallationwitharrowsshowingdifferentiallybalanced1phaseloading.SinceABCphasesareconnectedtobushings321respectively,theinstallationphasordiagramisshifted60fromthetransformernameplatephasordiagramtoshowa30leadrelationship.

    Test 3.a: Restraint slope verification:

    Test ValuesI mag. I ang. Connection:

    A-phase 3.28 0 In on A-Ph Wdg 1 (+) and out on C-Ph Wdg 1 (+) with A-Ph Wdg 1 (-) jumpered to C-Ph Wdg 1 (-)B-phase 4.73 180 A-Ph Wdg 2 (+), role angle until 87R assertsC-phase 0.00 0 no connection

    Note point where 87R asserts. IOP/IRT should equal Slope at trip point.Repeat for B-Phase:

    Test ValuesI mag. I ang. Connection:

    A-phase 3.28 0 In on B-Ph Wdg 1 (+) and out on A-Ph Wdg 1 (+) with B-Ph Wdg 1 (-) jumpered to A-Ph Wdg 1 (-)B-phase 4.73 180 B-Ph Wdg 2 (+), role angle until 87R assertsC-phase 0.00 0 no connection

    Note point where 87R asserts. IOP/IRT should equal Slope at trip point.Repeat for C-Phase:

    Test ValuesI mag. I ang. Connection:

    A-phase 3.28 0 In on C-Ph Wdg 1 (+) and out on B-Ph Wdg 1 (+) with C-Ph Wdg 1 (-) jumpered to B-Ph Wdg 1 (-)B-phase 4.73 180 C-Ph Wdg 2 (+), role angle until 87R assertsC-phase 0.00 0 no connection

    Note point where 87R asserts. IOP/IRT should equal Slope at trip point.Monitor 87R bits. Use MET DIF to view operate current (IOP) and Restraint currents (IRT). Initially IOP = 0 and IRT = 1.0.

    Monitor 87R bits. Use MET DIF to view operate current (IOP) and Restraint currents (IRT). Initially IOP = 0 and IRT = 1.0.

    Monitor 87R bits. Use MET DIF to view operate current (IOP) and Restraint currents (IRT). Initially IOP = 0 and IRT = 1.0.

  • Figure13:Transformernameplateforexample2Thecommissiontestingdefinitionsfortheexample2transformerdifferentialslopecharacteristicareshowninfigure15.Youwillnotethatthetestconnectionsmatchwiththoseshowninfigure6(b)andTable2fora30leadinstallation.

  • 160A

    [email protected]

    [email protected]

    2240A

    X0

    A(H3)

    B(H2)C(H1)A(X3)

    B(X2)C(X1)

    ABC

    600/5MR400/5Tap

    2000/5SR

    N1/N2=115/8.2

    Figure14:3lineinstallationdiagramforexample2withdifferentiallybalanced1phaseload

  • Figure15:Testingdefinitionsforexample2transformerdifferentialslopecharacteristicTransformerDifferentialRelayIncorrectOperationAnalysisExampleFigure16showsatransformerthroughfaulteventthattherelayincorrectlyinterruptedasaninzonedifferentialfaultandissuedatrip.TRHA,TRHB,andTRHCarehighsidetransformercurrents.TRLA,TRLB,andTRLCarelowsidetransformercurrentsand1TA,1TB,and1TCarelowsidemainbreakercurrents.Thisisa2windingdeltagrdwyetransformer.Thelowside(TRL_)currentsareusedforovercurrentbackupandthedifferentialelementsusethehighside(TRH_)andlowsidemainbreaker(1T_)currents.Duetoconstructionconstraints,thetransformerwasnotfullyloadedbeforetheBphasetogroundfeederfaultoccurred.Theloadcurrentsonthetransformerwerebelowtheminimumpickupoftherelaydifferentialelements.Duringthetripinvestigationitwasdeterminedthattherelaysettingforphaseanglecompensationforthelowvoltagesideofthetransformerwascompensatedforalaggingrelationship.Inthisinstallation,phasesABCareconnectedtobushing321resultinginthelowsideleadingthehighsideby30.Thistypeofconnectioncanbeseeninfigure4.Thealternatemethodoftestingwasnotusedforcommissioningofthistransformerdifferentialrelay.Forthisapplication,ifthetestconnectionsshowninfigures6(a)and6(b)andtable2wereused,thephaseanglecompensationsettingserrormayhavebeenidentifiedandathroughfaulttripofthedifferentialrelaymayhavebeenavoided.

    Test 3.a: Restraint slope verification:

    Test ValuesI mag. I ang. Connection:

    A-phase 2.00 0 In on A-Ph Wdg 1 (+) and out on B-Ph Wdg 1 (+) with A-Ph Wdg 1 (-) jumpered to B-Ph Wdg 1 (-)B-phase 5.60 180 A-Ph Wdg 2 (+), role angle until 87R assertsC-phase 0.00 0 no connection

    Use Differential and Restraint in Actual Values to view Differential current and Restraint current for A phase and B phase. C phase differentialand restraint currents should be 0 if the winding compensation factor (Angle WRT) is correct. Repeat for B-Phase:

    Test ValuesI mag. I ang. Connection:

    A-phase 2.00 0 In on B-Ph Wdg 1 (+) and out on C-Ph Wdg 1 (+) with B-Ph Wdg 1 (-) jumpered to C-Ph Wdg 1 (-)B-phase 5.60 180 B-Ph Wdg 2 (+), role angle until 87R assertsC-phase 0.00 0 no connection

    Use Differential and Restraint in Actual Values to view Differential current and Restraint current for B phase and C phase. A phase differentialand restraint currents should be 0 if the winding compensation factor (Angle WRT) is correct. Repeat for C-Phase:

    Test ValuesI mag. I ang. Connection:

    A-phase 2.00 0 In on C-Ph Wdg 1 (+) and out on A-Ph Wdg 1 (+) with C-Ph Wdg 1 (-) jumpered to A-Ph Wdg 1 (-)B-phase 5.60 180 C-Ph Wdg 2 (+), role angle until 87R assertsC-phase 0.00 0 no connection

    Use Differential and Restraint in Actual Values to view Differential current and Restraint current for C phase and A phase. B phase differentialand restraint currents should be 0 if the winding compensation factor (Angle WRT) is correct.

    Monitor 87R bits and view the operate current (IOP) and restraint current (IRT).

    Monitor 87R bits and view the operate current (IOP) and restraint current (IRT).

    Monitor 87R bits and view the operate current (IOP) and restraint current (IRT).

  • Figure16:TransformerthroughfaultwithincorrectphaseshiftrelaysettingsConclusionThreephasetestingoftransformerdifferentialrelaycharacteristicsrequiresathoroughunderstandingof3phasepowertodeterminetheappropriatephaseshiftandatestsetwith6highamperagetestcurrentoutputs.Traditionalsinglephasetestingrequiresnonobviousmultipliersfordeltagrdwyewindingtransformersanddoesnotsimulaterealworldfaultconditions.Thealternatemethodofsinglephasetestingdiscussedinthispapersimulatesrealworlddifferentiallybalancedsinglephaseloadingconditionsthatreflecttheinstallation3lineandtransformernameplatediagrams.Whilethismethodcanbeusedformaintenancetesting,itismostideallysuitedforcommissiontestingwherethegoalistoassurethesettingsarecorrectfortheinstallation.BiographiesTomErnstisaP&CTechnicalApplicationEngineerfortheNorthAmericanCommercialteam.HehasbeenwithGEsince2011supportingtheGridAutomationProtectionandControlPortfolio.PriortojoiningGE,TomhasbeenwithMinnesotaPowerasaSupervisingEngineer,DeltaEngineeringInternationalasaManagerofElectricalEngineering,HDREngineeringasaManagerofElectricalEngineeringandNorthernStatesPowerasaSupervisingEngineer.HereceivedhisBachelorofScienceinElectricalEngineeringfromtheUniversityofMinnesotain1978andhisMasterofScienceinPowerSystemsfromMichiganTechnologicalUniversityin2008.HeisaregisteredProfessionalEngineerintheStateofMinnesota.CraigTalbotisaSupervisingEngineerfortheRelayandMaintenanceEngineeringDepartmentatMinnesotaPower.HejoinedMinnesotaPowerin2011asaRelayandMaintenanceEngineer.PriortojoiningMinnesotaPowerheworkedatL&SElectricInc.asaFieldEngineer.HereceivedhisBachelorofScienceinElectricalEngineeringfromMontanaStateUniversityin2002.CraigisaregisteredProfessionalEngineerintheStateofMinnesota.