guidelines to relay settings for traction operation
DESCRIPTION
Traction Relay settings methodologyTwo phase system TrackingTRANSCRIPT
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APPENDIXV
GUIDELINESFORRELAYSETTINGSATTRACTIONSUBSTATIONSAND
SECTIONINGPOSTS
Thefollowingguidelinesmaybefollowedforcalculatingthesettingsofvariousprotectiverelaysattractionsubstationsandsectioningposts:
1.OhmImpedances
ThefollowingvaluesofOHEimpedancesmaybeusedforthepurposeofcalculatingrelaysettings:
i.SingletrackOHEwithoutreturnconductor 0.41/70Ohm/kmii.DoubletrackOHEwithoutRC 0.24/70Ohm/kmiii.SingletrackOHEwithRC 0.70/70Ohm/kmiv.DoubletrackOHEwithRC 0.43/70Ohm/km
v.Addboostertransformerimpedanceattherateof0.15Ohmperboostertransformer,wheretheseareprovided.
2.Feedingpost:Feederprotection
2.1Distanceprotectionusing'Mho'relay.TypeYCG14.
Atpresent,electromechanicaltype'Mho'relaysareusedforprotectionagainstcatenarytoearthfaults.Themaximumtorqueangleofthisrelayis75.Itsimpedancesettingmaybedecidedasfollows:
i.Inthecaseofsinglelinesections,theimpedancesettingoftherelaymaycorrespondto1.25timestheimpedanceoftheOHEfromthefeedingpostuptotheadjoiningfeedingpost.Thefactor1.25usedhereistocaterforerrorsintherelays,CT&PT.Followingrelationsmaybeusedforcalculatingtherelaysettings.
II.Inthecaseofdoublelinesections,thefollowingproceduremaybefollowed:
a)CalculatethesinglelineimpedanceoftheOHEfromthefeedingposttotheadjoiningfeedingpostsaythisisZ1.CalculateXfromthefollowingrelations:
b)Assumingsinglelineoperationfromthefeedingpost(FP)uptothesectioningpost(SP)&doublelineoperationfromSPtotheadjoiningFP,calculatetheOHEimpedancesaythisisZ2CalculateYfromthefollowingrelation:2
c)Assuminganoverloadof50%ofthetractiontransformerandthattheentirecurrentisfedthroughonefeedercircuitbreaker,criticalimpedancesettingoftherelay(toallowlineoperationatmaximumloads)iscalculatedfromthefollowingrelation:
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Say,criticalimpedancesettingisZ.Fortherelaynottooperateunderthesaidoverloadconditions,theimpedancesettingoftherelaymustbelowerthanZ.
d)TheimpedancesettingoftheMhorelayshouldbeaminimumofYandamaximumofX.ThesettingshouldalsonotexceedZ.Inotherwords,whenthevalueofZliesbetweenX&Y,therelaymaybesettoZ.IfZishigherthanX,thentherelaymaybesettoX.IfZislessthanY,thentherelayshouldbesettoYanditshouldbeunderstoodthattheassumedoverloadwillnotbepermittedbytherelay.NotethatthevaluesX,YandZarecalculatedalongthemaximumtorqueanglelineoftherelay.
iii.Therelaysettingsmaybecalculatedbyfollowingtheproceduregivenat(i)or(ii)aboveforthetwosidesofthefeedingpostseparately.However,thedistanceprotectionrelaysofboththefeedersshouldbesettohigherofthetwocalculatedvalues.Thisistoensurethatwhenonefeederbreakeristakenoutformaintenance,therelayshallbeabletoseethefaultsoneithersideoffeedingpost.
2.2Instantaneousovercurrentprotection.
Thisrelayprovidesprimaryprotectiontothecatenaryonearthfaultsinthevicinityofthefeedingpost.Thecurrentsettingoftherelaymaycorrespondtoabout200%ofthecontinuouscurrentratingofthetractiontransformer.Assumingthatafactorof1.25willaccountfortheCTandrelayerrorsandrelaytransientoverreach,therelaywillallowloadsofabout200/1.25,i.e.160%oftheratedloadcurrent.
2.3WrongphasecouplingprotectionusingoffsetMHOtypeYCG14(EnglishElectricmake).
TheimpedancesettingoftheEnglishElectricmakeYCG14relayisgivenbyK1K2(K3+K4),whereK1&K2areplugboardsettingsandK3&K4arepotentiometersetting(ReferRelayCatalogue).Themaximumtorqueangleoftherelayis125andforwardoffsetisabout10%ofK1K2.TheWPCrelayatthatsubstationwherethe25kVvoltageislaggingwithrespecttothevoltageatthesubstation,withwhichithasbeenwronglycoupledwilloperate:
TheimpedancesettingoftheWPCrelaysatTSS1maybedeterminedgraphicallyfollowingtheproceduregivenbelow(referFig.A5.01):
a.DrawlinesA'A,AB&BB'asshown.
where,
AistheoriginofRXdiagram
A'A=SourceimpedanceatTSS1asseenonthe25kVside.Theimpedanceanglemaybetakenas85(Thisincludestransformerandtransmissionlineimpedances).
AB=MinimumOHEimpedancebetweenTSS1andTSS2.Theimpedanceanglemaybetakenas70.(Foradoublelinesection,thiscorrespondstothedoublelineimpedanceofthesection,whereasforasinglelinesectionthiscorrespondstothesinglelineimpedanceofthesection).
BB'=SourceimpedanceatTSS2asseenonthe25kVside.Theimpedanceanglemaybetakenas85.(Thisincludestransformerandtransmissionlineimpedances).
b.JoinA'withB'.ConstructarightanglebisectortoA'B'andlocatepointsP&QonthebisectorlinesuchthattheanglessubtendedatthesepointsbyA'B'are120and60respectively.P&QaretheWPCpointsforCaseI(referFig.A5.01).
c.DrawlinesAC&CC',where
AC=MaximumOHEimpedancebetweenTSSlandTSS3.Theimpedanceanglemaybetakenas70.(ThiscorrespondstothesinglelineOHEimpedancebetweenTSS1andTSS3irrespectiveofsingleline/doublelinesection).
CC=SourceimpedanceatTSS3asseenonthe25kVside.Theimpedanceanglemaybetaken85.(Thisincludestransformerandtransmissionlineimpedances).
d.JoinA'withC'.ConstructarightanglebisectortothelineA'C'.LocatepointsR&StherightanglebisectorsuchthattheanglessubtendedbyA'Care120and60respectively.RandSaretheWPCpointsforCaseII(referFig.A5.01).
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e.DrawlineAOatanangleof125withtheRaxis.Thislineisthemaximumtorqueanglelinefortherelay.
f.DrawacirclewithcentreonthemaximumtorqueanglelinesuchthatthepointsP,Q,R&Sarejustenclosedbythecircle.ThecirclecutsthemaximumtorqueanglelineatDandE.Theoffset'AE'willbeequalto0.1xK1xK2xPTratio/CTratio.AsK1andK2arenotknownexactly,guessmaybemadeinitially.Step(f)mayberepeatedaftergoingthroughstep(g)..
g.MeasureAD,sayitis'Z1'.
Now,thedesiredimpedancesettingoftherelayatTSS1,sayZ2
Thefactor1.25usedhereistocaterforerrorsintheCT,PT&relay.ValuesofK1,K2,K3,&K4maybesuitablyselectedtogettheimpedancesettingZ.ForwardoffsetAEmaybecheckedtobearound0.1xK1xK2xPTratio/CTratio.Iftheoffsetisdifferent,thecircledrawnat(f)mayberedrawntosatisfythisrequirement.
DETERMINATIONOFTHESETTINGOFWRONGPHASECOUPLINGRELAY
FIG.A5.01
h.TheimpedancesettingsofwrongphasecouplingrelayfortwosidesoftheTSS1maybecalculatedindividuallyfollowingtheaboveprocedure.ThehigherofthetwovaluesmaybeadoptedforboththeWPCrelaysatTSS1.
3.Tractionsubstation:Transformerprotection:
LowVoltageside(25kVside)
I.Restrictedearthfaultrelay
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Thecurrentsettingofthisrelaymaycorrespondto10%oftheratedcurrentoftractionpowertransformer.
II.IDMTovercurrentrelay.
Thefunctionofthisrelayistoactasbackupprotectiontothefeederprotectionrelays.Thereachoftherelayshouldbeasmuchaspossible.However,topermitoverloadingofthetractionpowertransformerofthetractionsubstation,thecurrentsettingoftherelaymaybeselectedtocorrespondto150%oftheratedcurrentofthetractionpowertransformer.
ThetimemultipliersettingoftheIDMTrelaymaybeselectedsuchthattherelayoperationtimeis0.4to0.5sec.foranearthfaultonthe25kVbus.
3.2HighVoltageside(220kv/132kV/110kV/66kVside)
i.Restrictedearthfaultrelay
Thecurrentsettingoftherelaymaycorrespondto10%oftheratedcurrentoftractionpowertransformer.
ii.IDMTovercurrentrelaywithinstantaneousovercurrentelement
Theinstantaneouselementmaybesettocorrespondtoacurrentof1.25timesthefaultcurrent,foranearthfaultonthe25kVbusatthetractionsubstation.Thepurposeofsuchsettingistoavoidoperationofthisrelayfor25kVbusfaultsatthetractionsubstation.
ThecurrentsettingoftheIDMTrelaymaybesuchthatithasmaximumreachbutpermitsoverloadingoftractiontransformer.Thesettingmay,therefore,beselectedtocorrespondto150%oftheratedcurrentoftractionpowertransformer.TohavetimegradingwiththeIDMTrelayonthe25kVside,thetimemultipliersettingmaybeselectedsuchthattherelayoperatingtimeis0.8to0.9sec.forearthfaultonthe25kVbusatthetractionsubstation.
iii.Biaseddifferentialrelay(typeDDT)
Thethreesettingsoftherelaymaybeselectedasfollows:
a)Thepercentagebiassettingshouldbesochosenthattherelayremainsinoperativeondifferentialcurrentsresultingfrom(1)tapchangingontractiontransformer,(2)mismatchinCTratiosand(3)differenceinCTsaturationlevelsunderthroughfaultconditions.Percentagemismatchresultingfromfactors(1)and(2)maybecalculatedfromactualdataandanallowanceof7.5to15%maybemadeforfactor(3).
b)Theoperatingcurrentsettingmaybetakenas40%.Ifmaloperationsoftherelayareobservedonthroughfaultsandmagnetisinginrush(switchinginofpowertransformer),ahighersettingmaybeconsidered.
c)Thetimemultipliersettingmaybetakenas1.Ifmaloperationsoftherelayarenotedonmagnetisinginrushbutnotonthroughfaults,thenthetimemultipliersettingmaybeincreased.
4.Sectioningposts
4.1Undervoltageprotection.
incaseofextendedfeed,thebridginginterrupterattheSPisinclosedcondition.AnundervoltagerelayisprovidedtoopenthisinterrupterwhentheOHEvoltagefallsbelowasatisfactoryoperatingvalue.
Theundervoltagerelaymaybesettooperatebetween19and20kVdependingonlocalconditions.
SAMPLECALCULATIONSFORRELAYSETTINGS
EXAMPLE1
Thefollowingtractionsubstationdetailsareassumedhere:
1.1TractionPowerTransformer:
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2.Feedingpost:Feederprotection:
2.1DistanceprotectionusingMho,relay,YCC14.
TheOHEsectiondetailsassumedherearegiveninFig.A5.02.
FIG.A5.02
ThecalculationsgivenbelowareforthesettingofCB1.ThevaluesofZ1X,Z2,Y,Zgivenintheguidelinesarecalculatedas:
ABTspacingof2.66kmisassumedabove,giving6BTsineachline.TheimpedanceangleoftheBTisassumedherethesameastheOHE,I.e.70
SincethevalueofZliesbetweenX&Y.thecalculatedsettingforCB1=17.18Ohm.Similarly,calculatethesettingforCB2.and.saythesettingcalculatedforCB2shouldbe=18.0Ohm.
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Nowfollowingtheguidelinesgiveninpara2.1(iii).boththeMho'relayofCB1andCB2shouldbesetat18.0Ohms.
2.2Instantaneousovercurrentprotections.
Thecurrentsettinghastocorrespondto200%ofthecontinuouscurrentratingofthetractiontransformer,i.e.1000Amps,ontheprimarysideand10Amps,onthesecondarysideofCT.Hencetherelayhastobesetto10Amps.Iftheratedcurrentoftherelayis5Amps.,thiscorrespondsto200%settingoftherelay.
2.3WrongphasecouplingprotectionusingoffsetMHORelaytype
YCG14(Fig.A5.03)
Assumptionmadeinthesamplecalculation
i)3ph.FaultlevelofTSS1&TSS2is1000MVAandTSS3is1500MVA.
ii)Tractiontransformerimpedanceis12%at13.5MVA,27kVBase.
iii)DoublelinesectionwithoutB.T.&R.C.
iv)DistancebetweenTSS1&TSS2Is60km.
v)DistancebetweenTSS2&TSS3is60km.
vi)OHEimpedanceangle=70
vii)Sourceimpedance(Transmissionline&TractionTransformer)angleis85
viii)Max.TorqueAngleoftheYCG14WPCrelay:125.
ix)C.T.Ratio=500A/5A
x)P.T.Ratio=25000V/110V.
3PhaseFaultlevelofTSS1&TSS2on132kVside.=1000MVA
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Hence,AE=2.7/125Ohm.
DrawthecirclediagramaspertheguidelinesasshowninFig.A5.04.
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FIG.A5.04