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:

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).

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

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:

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.

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

Hence,AE=2.7/125Ohm.

DrawthecirclediagramaspertheguidelinesasshowninFig.A5.04.

FIG.A5.04