ELECTRICALDISTRIBUTIONSYSTEMSI. Introductiontothecourse:thiscourseisprovidedinaquestion&answerformatandisdividedinto5 chapters,itwillbecomeextremelyusefultoyou:

Ifyouwanttoknowtheparametersoftheinductionmotors,theireffectonthestartingand normalperformanceofthemachine. Ifyouwanttoanalyzeanexistinga.c.machineorevaluateanewoneforitssteadystateor transientstateincludingstartingandshortcircuit. Ifyouwanttoknowthemajorcomponentsinthepowerdistributionsystemsandhoweach componentisdefined. Ifyouwanttocalculatethelineandcableconstantsfromtheinformationfoundinstandard tables. Ifyouwanttoknowthedifferenttypesofbreakers,startersandswitchgearassemblies.Also,if youwanttoknowhowtheyaredefined. Ifyouwanttodothenecessarycalculationstosizetheloadbreaking/interrupting/disconnecting devicesfornormalandfaultconditions. Ifyouwanttoknowthetypesandsourcesofpowerlinedisturbances.Also,ifyouwanttoknow theeffectsofsuchdisturbancesonthemajorcomponentsofthepowersystemsandthemethods ofreducingthesedamagingeffects. Ifyouwanttoknowtheeffectsofusinglocalcapacitorsinincreasingthecircuitcapacityand howtosizecapacitorstoimprovethep.f.inmotorcircuits. Ifyouwanttoquantifytheeffectofdirectandindirectlightningstrokesonoverheaddistribution systems. Ifyouwanttoknowwhatarethedatathathavetobeavailableinordertoperformanyofthe followingstudies:TRV,stability,loadflow,fault/coordination,motorstarting,reliabilityand switchingtransients. Ifyoutoknowtheproceduretocalculatethefollowing:basicvaluesincludingbaseandp.u. values,loadflow,faultcurrent/voltagesensitivity,motorstarting,reliabilitystudiesforsimple radialsystems. Ifyouwanttoknowhowsteelproperties,switchboardinstruments,meters,relaysaredefined andwhatarethemajormodulesofPLCplusthebuildingblocksofanofficeautomation system. Ifyouwanttoknowthecalculationstobeperformedifamajorpowertransformeristobe protectedagainstshortcircuitsoroverloads. Ifyouwanttoknowwhataretheessentialprogramsanddataforthepowersystemsanalyst(or anyotherindividualinvolvedinelectricpowerdistributionandstudiesforthatmatter).

Contents: 1. A.C.Electricmachinesparameters&performance.

2. Overheadandundegrounddistributionsystemscomponents. 3. Switchgear,circuitbreakers,MCCandstarters. 4. Powerlinedisturbancesandpowerquality. 5. Powersystemsstudies. Lesson1:ACelectricmachinesparameters&performance. 1) Whataretheparametersoftheinductionmotorsandwhataretheteststobeperformedonsuch machinestobeabletoobtainthevaluesoftheseparameters? 2)Howcantheperformanceofaninductionmotorbeanalyzed? 3)Whataretheimportantcharacteristicsthatareusedindefiningsynchronousmachines(in general)andsynchronousgenerators(inparticular)?Sketchtheequivalentcircuitunderthe differentconditionsofoperation. 4)Whatarethedatarequiredfromtestingtocalculatetheparametersofsynchronousmotors? 5)Sketchtheequivalentcircuitofsinglephasetransformerandlisttherequiredtests(tobe performedontransformers)toobtainthevaluesoftheparametersoftheequivalentcircuit? 6)Asolvedproblemregardingtherunning&startingperformanceofaninductionmotor. 7)Asolvedproblemregardingthecharacteristicsofsynchronousmachines. 8)Asolvedproblemregardingtheparametersofsinglephasetransformers. 9)Asolvedproblemregardingthecharacteristicsof3windingtransformers. 10)Summarizethemethodsusedincalculatingtheparametersofsynchronousandinduction machines. Lessonsummary References 1)Whataretheparametersoftheinductionmotorsandwhataretheteststobe performedonsuchmachinestobeabletoobtainthevaluesoftheseparameters? Theparametersoftheinductionmotorsare:thestatorresistanceperphase,statorleakage reactance/phase,rotorresistance/phase,rotorleakagereactance/phase,mainfluxsusceptance andconductance/phase.Formotorsunderstartingconditionstheparametersarethesameas aboveexceptthevaluesoftherotorresistanceandreactance(referredtothestator)arehigher (duetoskineffect)andlower(duetotheskineffect&saturation),respectively.Theteststobe performedonsuchmachinestobeabletocalculatetheparametersofthemachinearetheno load(opencircuit)andlockedrotor(shortcircuit)underfullandreducedvoltage.Thereduced voltagetestisruntogettheunsaturatedreactancevalues(forrotor&stator).Thedatatobe collectedfromthenoloadtestare:Primaryvoltage,thenoloadcurrentandpowerat75C(or25 andcorrectedto75);fromthelockedrotor:thevoltage,currentandpowerat75C;fromthe lockedrotor(reducedvoltage):thevoltageandcurrent.Forthefirst2tests,thenominalmotor voltageisapplied,ifpossible.Fig.1showstheequivalentcircuitofaS.C.I.M.

R1:statorresistanceperphase,X1:statorleakagereactance/phase,R2':rotorresistance/phase referredtostator,s:slip,X2':rotorleakagereactancereferredtostator,Bm:mainflux susceptance,Gm:mainfluxconductance. 2)Howcantheperformanceofaninductionmotorbeanalyzed? Theperformanceofinductionmotorscanbeanalyzedbystudyingthefollowingpoints:heating ofwinding/iron,efficiencyofmotor,powerfactorofmachine,pullout(maximum)torque, startingtorque,startingcurrentsandtheeffectoftheparametersonsuchpoints.a)Heatingof windingandiron:toreducewindingheatingrotorandstatorresistanceshavetobesmall. Thoughforahighstartingtorque,therotorresistancehastobehigh.Toreduceironlosses,the mainfluxhastobelow.Notethatthemainfluxandrotorcurrentaffectthetorque. b)Efficiency:tohaveahighefficiencymotor,thewindings(copper)andironlosseshavetobe kepttotheminimumpossible. c)Powerfactor:toachieveahighpowerfactormachine,theleakagereactances(statorand rotor)havetobelowi.e.lowreactivecurrent.Tohaveahighpullouttorque,thefluxhastobe high. d)Maximum(pullout)torque:tohaveahighpullouttorqueininductionmotors,primary (stator)andsecondary(rotor)reactancesshouldbekepttoaminimum,therotorresistancewill onlydeterminetheslipofthemaximumtorque. e)InrushCurrent:reactances(andforsmallmotors,theresistances)oftherotorandstator windingshavetobehightohavealowinrushcurrent. f)Startingtorque:therotorwindingresistancehastobehightogetahighstartingtorque,this contravenestheefficiencyrequirement. Ascanbeseenfromtheabove,theparametersofinductionmachines(i.e.theirdesign)area compromisetoachievetheoptimumstarting,pulloutandrunningperformancesrequiredbythe differentapplications.Whenamotorisexistingandthefollowingdataareavailable:motorHP, terminalvoltage,frequency,numberofpoles,statorresistance,windagelosses,strayloadlosses andtheothermotorparameters(ortheresultsofthetests),thefollowingarecalculated:the

rotorcurrentreferredtostator(I2'),startingtorque(Tst)andthepowertransferredbythe rotatingfieldtotherotor(Prot.f)forstartingperformanceanalysis.Fortherunning performance:theslip(s),statorandrotorcurrents,thedevelopedtorqueandpower,the efficiencyandthepowertransferredbyrotatingfieldatratedmotorHPandatpullout conditionsorstatesarecalculated. 3)Whataretheimportantcharacteristicsthatareusedindefiningsynchronousmachines (ingeneral)andsynchronousgenerators(inparticular)?Sketchtheequivalentcircuit underthedifferentconditionsofoperation. Thecharacteristicsofsynchronousmachinesthatdefinesuchmachinesarethenoload,short circuit,airgapandpotiertriangle. Todefineagenerator,thefollowingcharacteristicstobeinvestigated:noloadandairgap,short circuitandPotiertriangle,loadcharacteristics,externalcharacteristics,regulationcurve,short circuitratioandthedeterminationofthedirectaxisreactance. a)Noloadandairgap(unsaturated)ch/cs:itisexpressedonagraphwiththeYaxis representingthearmature(stator)e.m.f.(electromotiveforce)orthepoleflux,withtheXaxis representingthefieldcurrent(If)orthefieldm.m.f.(magnetomotiveforceinAmpereturn).The airgapch/csisastraightlinepassingthroughtheoriginandthesecondpointistheE(rated statorvoltage)valueatalowfieldcurrent(unsaturatedconditions).Thenoloadcharacteristics underunsaturatedconditioncoincideswiththeairgapcharacteristicsuptoapoint.Atthe pointwhereEistheratedinducedinthearmaturebythefluxproducedfromtheresultantmmf (Mr)thecharacteristicslineisnonlinear(bendinward)saturatedcondition.Theresultantmmf willconstituteoftwoportions:thatparttodrivethefluxthroughtheairgapandtheotherpart todrivethefluxthroughtheironpartsofthemagneticpath.Fig.2belowshowstheairgap,no load&shortcircuitlinesvs.If. b)Shortcircuitcharacteristics(Potiertriangle):theS.C.ch/csrepresentsthearmaturecurrent (Ia)asafunctionofthefieldcurrent(If)orofthefieldmmf(MMF)withthearmature terminalsshortcircuited.Itistakenatsynchronousspeedofthegenerator.TheS.C.ch/csisa straightlinepassingthroughtheoriginandthesecondpointwillhavetheXaxisequaltothe fieldMMFandtheYaxisequalthearmaturecurrent.Potiertrianglewillhavethefollowing importantquantities:armaturereactionmmfandtheleakagereactance(impedance)ofthe armature.Thecosf=0loadcharacteristicsisconstructedfromthenoloadch/csandPotier triangle. c)Loadcharacteristics:itistheterminalvoltageVasfunctionoffieldcurrent(If)orfieldmmf (Mf)forconstantloadcurrent(Ia)andpowerfactor(p.f.).Atafixedloadcurrent,thefield currentisrequiredtosustainthenoloadvoltageanditincreaseswiththedecreaseofcosf,this mainlytocounteractthearmaturereaction.Potiertrianglecanbedeterminedfromthenoload ch/csandtwopointsonthecosf=0loadch/cs. d)Externalcharacteristics:itisexpressedastheterminalvoltage(V)asfunctionoftheload current(Ia)atconstantIfandp.f.Forlaggingcurrent,thevoltagedropincreasesasthepower factordecreasesandviceversaforleadingcurrent.

e)RegulationCurve:itdescribesthefieldcurrentasfunctionofeithertheloadcurrentwith constantp.f.orthep.f.atconstantcurrent(Ia)providedthattheterminalvoltageiskept constant.Thefieldcurrentincreaseswiththeincreaseinloadcurrent(p.f.isconstantletssayat 1or.8),thefieldmmfhastoincreasetocompensateforthearmaturereactionincrease. f)Shortcircuitratio:itistheratioofthefieldcurrentrequiredtoproduceratedvoltageonopen circuittothefieldcurrentrequiredtoproduceratedcurrentonshortcircuit.ThesaturatedS.C. ratioisobtainedfromthenoloadcurveandtheratedarmaturecurrent(fieldmmftoproduce ratedVdividedbythemmfproducingtheratedcurrent).TogettheunsaturatedS.C.ratio, dividetheMMFvaluethatproducestheratedVfromtheairgapstraightline(itistheextension ofthelinearairgaplinethatistakenfromthenoloadcurve)bytheMMFproducingtherated currentundershortcircuitcondition.AlargeSCRindicatesasmallarmaturereactionwhich meansthatthemachineislesssensitivetoloadvariations.AsmallSCRmeansthatthemachine ismoresensitivetoloadvariations. g)Determinationofdirectaxissynchronousreactance(Xd):itisobtainedfromthenoload linearportion(orairgapline)andS.C.characteristics.Thefieldcurrentinducesthenominal voltageontheairgapline.Whenthestatorisshortcircuitedandthefieldcurrentismaintained atthesamelevelaswiththeopencircuitcondition,theinducedemfinthestatoristhesameas withthenoloadconditionbutinthiscaseitisconsumedbythedropduetothesynchronous impedance.TheunsaturatedshortcircuitratioisusedtocalculateXd,Xd=1/SCR. Fig.2abelowshowstheequivalentcircuitofthesynchronousmachineunderthedifferent conditions.

Xs:statorleakagereactance,Xm:mainfluxreactance,Xf:fieldleakagereactance,Xd:damper leakagereactance.

4)Whatarethedatarequiredfromtestingtocalculatetheparametersofsynchronous motors? Theteststobeperformedonthesynchronousmachinesothattheparameterscanbecalculated are:theopencircuit(noload)characteristics,shortcircuitandtheairgapline.Fromthefirst test,twovaluesareobtained:thenominalstatorvoltatthefieldcurrentregistered;fromthe second:2pointsareobtained(4values):thenominalstatorcurrentanditscorrespondingfield currentandthestatorcurrent(Ia)atthefieldcurrentobtainedfromtheopencircuittest;from thefinaltest:thevoltageatthefieldcurrentequaltotheoneproducingthenominalcurrentin theprevioustest. 5)Sketchtheequivalentcircuitofsinglephasetransformerandlisttherequiredtests(to beperformedontransformers)toobtainthevaluesoftheparametersoftheequivalent circuit? Fig.3belowshowstheequivalentcircuitofasinglephasetransformer.Theteststobe performedontransformerssothattheparameters,whicharetheprimaryandsecondary windingsresistancesandreactancesplusthemainfluxsusceptanceandconductance,canbe calculatedare:thenoload(opencircuitedprimaryH.V.winding)testfromwhichtheopen circuitvoltonl.v.sideandthenoloadcurrentareobtained;theS.C.(l.v.windingshort circuited)fromwhich3valuesareregisteredtheS.C.lossesinW(orkw),theratedS.C. currentasseenfromtheprimarysideandthevoltagecirculatingsuchcurrent.Theprimary windingresistance(d.c.)shouldalsobemeasuredbyanohmmeterat25C.

R1:primarywindingresistance,X1:primarywindingleakagereactance,R2':secondary windingresistancereferredtotheprimarywinding,X2':secondarywindingreactancereferred totheprimary,Bm:mainfluxsusceptance,Gm:mainfluxconductance,r2':loadresistance referredtotheprimarywinding,x2':loadreactancereferredtotheprimary(inprimaryside terms). 6)A3phaseinductionmotor,3HP,440/220V,60HZ,4pole,1750rpm,hasthefollowing noloadtestresults:Vnl=440V,Inl=2.36A,Pnl=211W;lockedrotor(fullvoltage)results:

Ilr=29A,Vlr=440V,Plr=13.9KW;lockedrotor(reducedvoltage):Vlr1=76V,Ilr1=4.25A unsaturatedreactancecondition.Assumewindageloss=44W,strayloadloss=48W,skin effectfactors=1.3forrotorwindingresistance(referredtostator),.97forrotorreactance andstatorresistance/phase=2.26W.Determinethe6parametersoftheinductionmotor, itsstartingandrunningperformancedata,thetransientreactanceandthes.c.time constant,thes.c.currentafter1and2cyclesfromfaultinception.Calculatetheduration oftheinrushcurrentassumingJ=2lb.ft2fortherotatingparts. GIVEN:Vprim=440V,Ioc=2.36A,Poc=211W,Vlr=V1=440V,Ilr=29a,Plr=13.9KW, Vlrr=76V,Ilrr=4.25A,HP=3,r1@25C=2.26OHM,windageloss=44W,strayload loss=48W,skineffectforr2',x2'=1.3,0.97. SATURATEDREACTANCE: Zl=440/[(3).5(29)]=8.73W,Rl=13920/3(29)(29)=5.48W, X=[(8.73)2(5.48)2].5=6.8W,r1@75C=2.26[(234+75)/(234+25)]=2.69W, r2'=R1r1(@75C)=5.482.69=2.79W,X1=X2=X/2=3.4OHM. UNSATURATEDREACTANCE: Z=76/[(3.5)(4.25)]=10.3W,X=[(10.3)2(5.48)2].5=8.72W, X1=X/2=4.36OHM,Saturationfactor=4.36/3.4=1.3, includingforskineffect:r2'=2.79/1.3=2.14OHM, X2'=4.36/.97=4.5W,Xm=[(V1)(Ioc.X1)]/Ioc=[(440/3.5)(2.36)(4.36)]/2.36=103OHM, Ph+e=Poc3(Ioc)2(r1@75C)windagelosses=2113(2.36)2(2.69)44=122W. Assuming1/2theironlossesareduetothemainflux.Ph+e=122/2=61W Gm=Ph+e/3(E1)2={61}/{3[(440/3.5)(2.36)(4.36)]2}=3.43/10000MHO Rm=Gm.Xm2=[(3.43)/(10000)][103]2=3.66W STARTINGANDRUNNINGPERFORMANCE: Basevaluescalculations:Vb=440/3.5b=3x746/3x254=2.94A,Zb=254/2.94=86.5OHM. Pb=254x2.94=746W,Tb=7.04(3)(unitpower)/unitspeed=7.04x3x746/1800=8.8LB.ft. Parametersforstartingperformanceinp.u: r1=2.69/86.5=.0311,r2'=2.79/86.5=.0322,x1=x2'=3.4/86.5=.039(saturatedconditions). Parametersforrunningperformanceinp.u: r1=.0311,r2'=2.14/86.5=.0248,x1=4.36/86.5=.0504,x2'=4.5/86.5=.052(unsaturated). Parameterscommontoboth: Xm=103/86.5=1.19,Rm=3.66/86.5=.042p.u. Startingperformance:

r2'(1s)/s=0asatstandstills=1=(nsn)/ns

Z1=(r12+x12)=[(.03)2+(0.039)2]=0.05,tan1=x1/r1=51.4Z2'=[(.032)2+(.039)2]=.0506/_50.6 Zm=[(1.19)2+(.042)2]=1.19,tan11.19/.042=87.98 V1=I1.Z1+(I1)/[(1/Z2')+(Ym)] V1=I1[.05/_51.4+(1)/(1/.0506/_50.6)+(1/1.19/_87.98)];whereYm=1/Zm,V1=I1.Zeq, V1=1/_0 I1=V1/{.05/_51.4+{[(.0506)(1.19)/_138.58]/[.0506/_50.6+1.19/_87.98]}} I2'=I1[Zm/(Z2'+Zm)]=9.66/_50.4 Protfield=I2'2(r2'/s)=(9.66)2(.0322)=3p.u. Tst=3p.u.=3x8.8=26.4LB.ft RunningPerformance: s=.03,r2'(1s/s)=.8,Z1=.0593/_58.3,Z2'=.825/_3.6,Zm=1.19/_87.98, I1={1/_0}/{[.0593/_58.3]+[(.825/_3.6.1.19/_87.98)/(.825/_3.6+1.19/_87.98)]} Inputp.f.=cos38.2=.785 I2'=1.42/_38.2[1.19/_87.98/(.825/_3.6+1.19/_87.98)]=1.12/_5.74 Protfield=I2'2.(r2'/s)=(1.12)2(.0248/.03)=1.025p.u. Tdeveloped=1.025p.u.=1.025(8.8)=9.02LB.ft. MechanicallossTorque=7.04(strayloadloss+windage+mainfluxironloss)/ns(Torquebase) =7.04(48+44+61)/1800(8.8)=.068 Tnetdeveloped=1.025.068=.957p.u.x8.8=8.4LB.ft. Powerinput=3(1)(1.42)(cos38.2)=3.35p.u. Losses(statorcopper)=3(1.42)2(.0311)=.189p.u.

Losses(rotorcopper)=3(1.12)2x.0248=.093p.u. Noloadironlosses=122/746=.163p.u. Losses(strayload)=48/746=.064p.u. Losses(friction&windage)=.059p.u. Totallosses=.568p.u. Pdeveloped=3.35.568=2.78p.u.x746=2076W=2.78HP eff.=2.78/3.35=83% slip=3(1.12)2(.0248)/[3.35(.189+(.163/2))]=.03 snormal=3/2.78=.0324 spullout(@maxTorque)=[(1+(X1/Xm))(r2')/[X1+(1+(X1/Xm))X2'] =[(1.0+.0504/1.19)(.0248)/[.0504+(1.042)(.052)]=.246p.u.

r2'(1s/s)=0.0758(@s=.246),Z2'=r2'+r2'(1s/s)+jX2'={[r2'+r2'(1s/s)]2+X2'2}.5 =[(.0248+.0758)2+(.052)2].5=.113/_27.3tan1(.052)/(.0248+.0758)=27.3 I1=6.12/_41,I2'=5.85/_36,Protatingfield=I2'2(r2'/sp.o.)=3.44p.u. Tp.o.=3.44x8.8=30.2LB.ft. Tdeveloped(@3HP&s=.0324)=5250x3/1800(1.0324)=9.02Lb.ft StartingTorque/NormalTorque(rated)=3/1.025=2.92 PulloutTorque/ratedTorque=3.44/1.025=3.36 TransientAnalysis: Transientreactance=.0504+[(.052)(1.19)/(.052+1.19)]=X"=.1p.u. P.F.=.785,efficiency=83%,Ib=2.94A I1=3x746/.785(.83)(440)(1.732)=4.5A=1.53p.u. E1'=1[(.03+j.1)(1.53xcos38.2j1.53xsin38.2)]=.874p.u./_6 InitialS.C.current=.874/.1=8.74x2.94=25.7A To'=opencircuittransienttimeconstant=(X2+Xm)/2(pi)fr2,wherepi=3.141592654 T'=To'[X"/(X1+Xm)]=S.C.timeconstant IS.C.=InitialS.C.C.(et/T) To'=.052+1.19/2(pi)60(.0248)=.133sec. T'=.133(.1)/.124=.011sec. IS.C.(after1cyclei.e..0166sec.)=8.74(e.01666/.011)=2p.u. IS.C.(after2cycles)=8.74(.048)=.43p.u. StartingTime: Anapproximatesolutioniftheloadandmotorspeedtorquecurvesarenotavailableisas follows: t=J(rpm1rpm2)2(pi)/60gTn J=2lbft2,rpm1=1740,rpm2=0,g=32.2ft/sec,Tst=26.4,Trated(@ratedHP)=9.02 Tn=acceleratingtorquebetweenrpm2torpm1=Tst+Trated/2=(26.4+9.02)/2=17.7LB.ft. t=.7sec. 7)Asynchronousmachinerated45KVA,3phase,220Vl.l.,wastestedunderopencircuit (noload)andshortcircuit(lockedrotor),thefollowingweretheresults:OPENCIRCUIT: Vl.l.=220V,Ifield=2.84A,SHORTCIRCUIT:Iarm.1=118A(firstpoint),Ifield1=2.2A, Iarm.2=152A(secondpoint),Ifield2=2.84A,themachinewastestedatapowerfactor=0 fromshortcircuitedarmatureconditiontonoloadcondition.Thenoloadandairgap plustheshortcircuitcurvescanthusbeplotted(asshowninquestion3,fig.2above)and

thecharacteristicsofthemachinecanbeobtainedgraphically.Theairgaplineisplotted from:Ifield=2.2A,Vl.l.=202Vatratedarmaturecurrent=118A,assumes.c.loadlosses (3phaselosses)=1.8KW@25C,armatureresistance@25C=.0335W/phase,field resistance@25C=29.8W/phase.Calculatethesaturatedandunsaturatedreactance, theeffectivearmatureresistanceandthes.c.ratio.IfthismachinerunsasamotoratV= 230V,inputpowertoarmature=45KW,.8p.f.leadingcurrent,fieldcurrent=5.5A, thencalculatetheefficiencyofthemotor. Linetoneutralvoltage=202/1.732=116.7Vontheairgapline;forthesamefieldcurrentof 2.2a,ontheS.C.line,thearmaturecurrent=118amp. Thesaturatedreactance=Xs Theunsaturatedreactance=Xsairgap=116.7/118=.987OHM,ratioofunsaturatedreactanceto saturatedreactance=.987/.836=1.18 Shortcircuitratio=2.84/2.2=1.29(saturated),Xs(saturated)=1/1.29=.775p.u. Airgapfieldcurrentcorrespondingto220vlinelinearmaturevoltage=(220/202)(2.2)=2.39 A shortcircuitratio=2.39/2.2=1.086p.u.(unsaturated),Xs(unsaturated)=1/1.086=.92p.u. Thearmatureeffectiveresistance: S.C.loadloss/phase=1800/3=600W/ph. ra(eff)=600/(118)2=.043W/phase ra(eff)inp.u.=.04/(1)2=.04p.u. inp.u.:S.C.loadloss=1.8/45=.04p.u. ratioofa.c./d.c.resistance=.043/0335=1.28(skineffectandproximity) Note:armatureresistanceofm/csabovefewhundredsKVAislessthan0.01p.u. Forthem/coperatingasamotorwithleadingpowerfactor: Ia=45/(1.732)(.8)=141amp. Assumestrayloadlossof30%ofS.C.loadloss=.54KW Resistanceforcopperwindingofarmatureat75C=0.335[234+75/234+25]=.04OHM/ph Resistanceforcopperwindingoffieldat75C=29.8[(234+75)/(234+25)]=35.5OHM/ph ArmatureCulosses(assumera=.04or.035W/ph)=3Ia2ra=3(141)2(.04)=2.38KW FieldCulosses=(5.5)2(35.5)=1.07KWE=internalvoltageofmotor=VtIara= (230/1.732)(141)(.8+j.6)(.04)=128.4j3.4Vphase Vlinetoline=220Vatwhichcorelosses=1.2KW Totallosses=2.38+1.07+.56+1.2+.91=6.12KW Input=45+1.07=46.07KW Efficiency=1(6.12)/(46.07)=86.7%

8)Calculatetheequivalentcircuitparametersforthefollowingsinglephasetransformer. Theresultsoftheopencircuittest(H.V.wdgopen)are:Vo.c.=347V,Io.c.=18A,Po.c.= 980W.Theresultsfromtheshortcircuittest(L.V.wdgshorted)are:Vs.c.=70V,Is.c.= Irated,Ps.c.=1050W.The2windingtransformerratingsare:2400/347V,100KVA, primarywindingresistanceat25C=.24W.Also,calculatetheregulationandeffeciency atunityand.8p.f.fullloadcurrent. Transformerratio:2400/346V,Irated=(100)/2.4=41.6A Transformationratio=a=2400/346=7,Zsc=Vsc/Isc=70/41.6=1.68OHM Rsc=Psc/(Isc)2=1050/(41.6)2=.607OHM Xsc=[(1.68)2(.607)2].5=1.57OHMRsc(at75C)=.607[(234+75)/(234+25)]=.723OHM r1(at75C)=.24[234+75/234+25]=.28OHM r2'=Rscr1=.723.28=.44OHM X1=X2'=Xsc/2=.785OHM Fromopencircuittests:(L.V.wdg.excited): Ph+e=Po.c.(Io.c./a)2r1=980(18/7)2(.28)=978W E1=2400(Io.c./a)X1=2400(18/7)(.785)=2400V rm=gm(Xm)2=.00017(934)2=148OHM Zb=2400/41.6=57.7OHM,Zpu=1.68/57.7=.03pu Xpu=1.57/57.7=.027pu,Rpu=.0125p.u. Regulationandefficiency: Regulationat1p.f.:Reg.=(.0125)+(.027) 9)A3windingtransformer(primary,secondary,tertiary)singlephaserated7960V (1000KVA),2400V(500KVA)&2400V(500KVA).Theresultsofthes.c.testsareas follows: Test WDGExcited 1 2 1 1 WDGShortCircuited 2 3 AppliedVoltageValue 252 252 CurrentInExcitedWDG 62.7 62.7 Xm=2400/18/7=934OHM,gm=Ph+e/E12=.00017MHO

3 2 3 100 208 The3transformersareconnectedinaYDDconfigurationon13.8/2.4/2.4KV.Whenthetertiary windingsareshortcircuited(3phase),calculatethes.c.currentandthevoltageontheterminalsofthe secondarywindingsofthisbank.

Forprimarywinding:Vb=7960V,Ib=1000/7.96=125.4A Forsecondarywinding:Vb=2400V,Ib=1000/2.4=416A Forteritiarywinding:Vb=2400,Ib=416A Test 1 2 Zbetweenterminals 12 13 Vpu 252/7960=.0316 252/7960=.0316 Ipu 62.7/125=.5 62.7/125=.5 208/416=.5 Zpu=Vpu/Ipu .0632 .0632 .0832

3 23 100/2400=.0416 Z1=1/2[.0632+.0632.0832]=.0216pu Z2=1/2[.0832+.0632.0632]=.0416pu Z3=1/2[.0632+.0832.0632]=.0416pu

Isc=1/(.0216+.0416)=15.8p.u.(S.C.teritiary)=15.8x125.4=1984A V2=voltageonsecondarybuswhileteritiaryisshortcircuited=Is.c.xZ3IsecxZ2,Isecistheload current =15.8(.0416)1(.0416)=62.44.16=.5824p.u.TocalculatetheS.C.currentassumingabaseMVA=.5 MVA=500KVA: Znew=Zold[KVAnew/KVAold]p.u. Z3new=.5(.0416)=.0208,Z1new=.5(.0216)=.0108,Isc=1/.5(.0632)=1/(.0208+.0108)=31.6p.u., Ibase=500/7.96=62.8A,Isc=31.6(62.8)=1984A 10.Summarizethemethodsusedincalculatingtheparametersofsynchronousandinduction machines. Synchronousmachines: Positivesequence(synchronousparameters):Theairgap,noloadandshortcircuitcharacteristics:the machineisrunatsynchronousspeedintheproperdirection.Thethreephasearmatureterminalsare keptopenandlinetolinevoltagereadingsaretakenatdifferentfieldcurrent(arheostat)inthefield windingisusedtovarythefieldcurrent).Theexcitationisreducedtoaminimumandthe3phaseare shortedandthefieldreadingplusthecurrentflowinginoneofthelinesaretaken(todrawtheshort circuitunsaturatedcharacteristicslinepassingthroughtheorigin). Subtransientreactance:shortcircuitthefieldthroughanammeter,applyasinglephasevoltagetoany ofthethreelineterminals,rotatetherotorbyhand.Atthepositionindicatingmaximumfieldcurrentin thefieldammeter,halfthevoltameterreadinginthearmaturecircuitdividedbythearmaturecurrentin oneline(usinganammeterinoneofthelineterminals)isequalthesubtransientdirectaxisreactance. Attheminimumfieldcurrentreading,halfthearmaturevoltagedividedbythearmaturecurrentwill givethesubtransientreactanceintheqaxis. NegativeSequencereactance:thefieldisshortedonitself,twophasesareconnectedtoeachother throughanammeterandasinglephasevoltageisappliedtothisarmatureconfiguration.Thefieldis

rotatedatratedspeedandthevoltageappliedtothearmaturewillcorrespondtoapproximately circulatingtheratedmachinecurrent.Thenegativesequenceimpedance=V/1.7321(I).Thismethod canalsobeusedwithinductionm/cs. Zerosequenceimpedance:zerosequenceimpedanceismuchsmallerthanthepositiveandnegative andintheoryisclosetozero.Themachineisatstandstill,thefieldisopen,thesixterminalsofthe machineareavailableoutsidethemachineandthethreewindingsareconnectedinseries.Areduced voltageisappliedacrossthe3connectedwindingsandthezerosequenceimpedancewillbeequalto onethirdthevoltagereadonthevoltameterdividedbythecirculatedcurrentreadontheammeterin thearmaturecircuit. InductionMachine: Steadystatereactance:fromthethreetests,noload(opencircuit),lockedrotor(shortcircuit)full voltage(forsaturatedreactance)andlockedrotor(shortcircuit)reducedvoltage(forunsaturated reactance),theparametersareobtained. Transientreactance:iscalculatedfromtheparametersofthemachineobtainedfromtheabovetests.X" =[X2(Xm)/(X2+Xm)]+X1. SUMMARY: Inthischapter,theparametersandperformanceofa.c.electricmachineswerepresented.Thetests performedonsuchmachinestoobtaintheirparametersweregiven,theparametersandtheireffectson themachinesperformancewerecovered,too.Numericalexamplesweregiventoshowandclarifythe interrelationsbetweenthemachineparametersandtheperformance.Theinductionmachines parametersare:statorresistance&reactance,therotorresistanceandreactance,themainflux susceptanceandconductance.Theseparametersaffectthemachineduringstarting(inrushcurrent& startingtorque),atnominalload(fullloadcurrent&nominaltorque),andforthemaximum(pullout) machinetorque.They,also,affectthelosses(heatingofiron&winding),efficiencyandpowerfactor. Thecharacteristicsofsynchronousmachinesingeneralandgeneratorsinparticularpresentedinthis chapterwere:theairgapandnoload(armatureemforpolefluxvs.mmforfieldcurrent),shortcircuit (armaturecurrentvs.fieldcurrent),loadch/cs(terminalvoltagevs.fieldcurrentprovidedthattheload currentandthep.f.arekeptconstant),external(voltagevs.loadcurentwithconstantfieldcurrent& p.f.),regulation(fieldcurrentvs.loadcurrentwithconstantp.f.orfieldcurrentvs.p.f.withconstant loadcurrent,voltageiskeptconstantineithercase),shortcircuitratio(fieldcurrentproducingnominal voltageunderopencircuitconditionvs.fieldcurrentproducingratedcurrentunderarmatureshort circuitcondition)anddirectaxissynchronousreactancedetermination(whichisequalto1dividedby theSCR).Forthetransformers,2&3windingparameterswerepresentedandtheireffecton regulation/efficiencyof2windingstransformersandfor3windingsshortcircuitplusvoltage sensitivityoftheunfaultedbusweregivenandemphasizedbynumericalexamples. REFERENCES: 1. Greenwood,Allan"ElectricalTransientsinPowerSystems",Wiley. 2. Granger&Stevenson"PowerSystemAnalysis",McGrawHill.

3. Tuma,Jan"EngineeringMathematicsHandbook",McGrawHill. 4. Fitzgerald,Kingsley&Kusko"ElectricMachinery",McGrawHill. 5. Kheir,"AutomatingPowerSystemsAnalysis",Kheir Home page of VePi

Lesson2:Overheadandundergrounddistributionsystemscomponents. 1) HowwouldEPR(ethylenepropylenerubber)cables,upto35KV,beclassified? 2)HowwouldundergroundXLPE(crosslinkedpolyethylene)cablesclassified? 3)Whatarethedefiningparametersofcables? 4)Whatarethefactoryandsiteteststobeperformedoncables? 5)Whatarethedefiningparametersforlowvoltagesecondarycables? 6)Whatarethedifferenttypesoftransformersfoundindistributionsystems? 7)Whatarethedifferenttypesofoverheadswitches,padmountedswitchgearandthoseof lightninigarresters? 8)Whatarethestandardsthatgoverndistributiontransformers?Howaredistribution transformersdefined? 9)Howarewoodenandconcretepolesdefined? 10)Whatarethedifferentapplicationsofoilswitchesandwhataretheirdefiningparameters? 11)Howareoverheadairswitchesclassified? 12)Howarepadmountedswitchgeardefined? 13)Whataretheimportantparametersbywhichlightninigarrestersaredefined? 14)Howwouldcopperconductorsbedefined? 15)HowwouldACSR(aluminumconductorsteelreinforced)andASC(aluminumstranded

conductor)bedefined? 16)HowwouldAASC(aluminumalloystrandedconductor)andselfdampening/compact ACSRbedefined? 17)Whatarethedifferenttypesofcablesplicesandterminations? 18)Whatarethedifferenttypesofconnectorsandelbows? 19)Whatarethedesigntestsperformedontheseparableconnectors? 20)Whatarethedifferenttypesofinsulators,theirmaterialandcharacteristics? 21)WhatarethefunctionsofDAC(distributionautomationandcontrol)?Sketchthetypical undergrounddistributionarrangementsandtheoverheaddistributionsystem. 22)WhatarethemajorinformationobtainedfromadistributionsystemSCADA?Showablock diagramofthemajorcomponentsofaSCADA(systemsupervisorycontrol&dataacquisition). Sketchadiagramtoshowatypicalautomateddistributionsystemwithpowerand communicationlines. 23)WhatarethebasicmodulesinaPLC(programmablelogiccontroller)system?Sketcha frontplateof2ofthebasicmodules.Sketchablockdiagramshowingtheinterrelationofthe majormodules. 24)Asolvedproblemregardingconstantsofoverheadconductors? 25)Asolvedproblemregardingconstantsofundergroundcables? 26)Asolvedproblemregardingreflected&refractedpowersataconductor/cablejunction? 27)Asolvedproblemregardingpowertransformerprotection? Lessonsummary References 1)HowwouldEPR(ethylenepropylenerubber)cables,upto35KV,beclassified? TheclassificationofEPR(upto35KV)cablesisasfollows:thevoltageclass,theconductor material/size(whichisfunctionofthenormal/overload/shortcircuitcurrentvaluesandthe installationmethod/configuration),theinsulationthickness(whether100%or133%),jacketed orunjacketed,neutralsize(eitherfullor1/3rating),cableinconduitconfiguration/directburied orconcreteencasedconduits. 2)HowwouldundergroundXLPE(crosslinkedpolyethylene)cablesclassified? TheclassificationofXLPE(upto46KV)cablesisasfollows:thevoltageclass,theconductor material/size,insulationthickness,jacketedorunjacketed,neutral(concentricneutralandrating fullor1/3mainconductor)orshielded(Cutape),singleor3conductorcables,jackettype (whetherencapsulatedorsleeved),theuseofstrandfillorwaterblockingagentbetweenthe insulationandjacket. 3)Whatarethedefiningparametersofcables? Thedefiningparameterscanbeclassifiedbroadlyintodimensional,insulationmaterial propertiesandcurrentcarryingcapacity.Fordimensionalparameters,conductorsize/numberof strands/typeofstrands,diameteroverconductor,diameteroverinsulation,diameterover insulationscreen,numberandsizeofneutralconductorsortapedetails(thickness,width&lap type)anddiameteroverthejacketarethedefiningdata.Otherimportantdataare:weight/1000

ftlength,sizeofreelsandlength/reel.Theinsulation/jacketdefiningparametersare:beforeand afteragingtensilestrengthandelongation,hotcreepelongation/set,dielectricconstant, capacitance(SIC)duringandafterthestabilityperiod,insulationresistanceconstant,water absorptionproperties.Thelastsetofdefiningparametersarethecurrentlevelsatthenominal voltageunderthedifferentoperatingconditionswhicharefunctionof:thelayoutandproximity ofcurrentcarryingcables,themethodoflaying/pullingofcables,provisionoffutureadditional loadswiththeircorrespondingmaximumallowablevoltagedropandfinallythemaximum acceptabletemperaturerise&durationforthecableinsulatingmaterial. 4)Whatarethefactoryandsiteteststobeperformedoncables? Thedifferenttypesofteststhatareperformedoncablesatthefactoryare:partialdischarge,DC resistanceofcentralconductor,AChighvoltagedielectricwithstandability,DChighvoltage withstandability,insulationresistance,physicaldimensionsofcablecomponents,coldbend,low temperatureimpact,jacketintegrity,waterpenetrationandhightemperaturedriptestforthe strandfill(ifapplicable).Forconductorshieldthetestsare:volumeresistivity,elongationat rupture,voidandprotrusions,irregularitiesverification.Fortheinsulationare:tensilestrength (agedandunaged)/elongationatrupture(agedandunaged)/dissipationfactor(orpower factor)/hotcreep(elongationandset)/voidsandcontamination/solventextraction(ifapplicable). Fortheinsulationshieldare:volumeresistivity/elongationatrupture/voidandprotrusions irregularities/strippabilityatroomtemperatureandat25C/waterboiltest.Forthejacketare: tensilestrength,elongationatrupture(agedandunaged),absorptioncoefficient(ofwater),heat shockanddistortion.Onthecablethefollowingtestsmaybeperformed:structuralstabilityand insulationshrinkbackforcertaininsulationmaterials.Thetestsperformedonsiteare:visual inspection,size/ratingsverificationandD.C.withstandabilitytestsatvoltagelevelbelowthose usedinthefactory. 5)Whatarethedefiningparametersforlowvoltagesecondarycables? Thedefiningparametersforl.v.secondarycablesare:materialofphaseconductor,numberof strands,classofstrand,typeofconductor(ie.concentric,compactorcompressed),conductor size,insulationthickness,overalldiameterpercable,overalldiameterperassembly(ie.triplex orquadruplex),theneutralconductorsize(equaltothephaseorreduced),ifapplicable, insulationandjacketmaterials,jacketthicknessandtheweightperassemblyper1000ftlength. 6)Whatarethedifferenttypesoftransformersfoundindistributionsystems? Thedifferenttypesoftransformersfoundindistributionsystemsare:Power(upto10MVA) liquidfilled(oil),power(over10upto100MVA)oilfilledwithradiators/fans(oneor2sets), singlephasedistributiontransformers/oilfilled(withorwithoutradiators/fans)upto500KVA, threephasedistributiontransformers/oilfilled(withorwithoutradiators/fans)upto1.5MVA, drytypepowertransformers/3phase300KVAto2MVAorsiliconefilledorepoxyresin insulatedforindoorinstallations.Alloilfilledtransformersareinstalledoutdoorunlessa speciallayoutwithfireproof(resisting)materialandappropriatebarriersareused,thenindoor installationispossible.Distributiontransformerscanbeofthepolemounted,vaultor padmountedtype.Theprimaryvoltageofpowertransformerscanbeashighas750KV,though

themostcommonare345KV,220KV,115KV,fordistributiontransformersashighas72KV thoughthemostcommonare34.5,25KV(27.6KV),15KV. 7)Whatarethedifferenttypesofoverheadswitches,padmountedswitchgearandthoseof lightninigarresters? Thedifferenttypesofoverheadswitchesare:eithersingleorthreephase,eithermanually operatedorelectric/manualoperated,eitherlocalcontrolorremote/localcontrol,oilinsulated orairorSF6.Thedifferenttypesofpadmountedswitchgearare:eithermanuallyor manually/motoroperated,controlledlocallyorlocally/remotely,airoroilorSF6/vacuum insulated,protectivedevicesareeitherfusesorelectronicdevices.Theconfigurationwill, generally,havefourcompartmentswithanycombinationoffuseorinterrupter,switch,solidor emptycompartment.Thedifferenttypesoflightningarrestersare:station,intermediate, distribution(heavyduty,normalorlightduty)andmayberiserpoletype. 8)Whatarethestandardsthatgoverndistributiontransformers?Howaredistribution transformersdefined? Thestandardsthatgoverndistributiontransformersare:CSA"Singlephase&threephase distributiontransformers"Std.C2,CSA"Drytypetransformers"C9,CSA"Guideforloading Drytypedistributionandpowertransformers"C9.1andCSA"Insulatingoil"C50.The distributiontransformersaredefinedasfollows:thevoltageratings(insulationclasslevelof primaryh.v.winding,theprimaryandsecondarywindingsratedvoltage),shortcircuit capabilityforafaultonthebushingsofthetransformer(currentvalueanditscorresponding duration),dielectrictestvalues(appliedvoltagefor1minute,fullwaveandchoppedBILand timetoflashoverforthechopped),outdoortransformerbushingsratings(definedbytheir insulationclass,60HZ1minute/dry,10second/wetdielectricwithstandability,thefullwaveand choppedBIL),audiblesoundlevelsandinducedvoltagetests. 9)Howarewoodenandconcretepolesdefined? Thewoodenpolesaredefinedasfollows:theclass(1to74500LBto1200minimumhorizontal breakingloadwhenapplied2ft.frompoletop),theminimumcircumferenceatpoletoplevel (27"to15"),lengthofpole(25to110ft,generally),minimumcircumferenceatthegroundlevel (distancefrombutt),thewoodspecies(WesternRedCedar,SouthernYellowPine,DouglasFir, WesternLarch),thetreatmentagainstattackfromfungiandinsects(eg.creosoteoil,ammonical copperfattyacid,pentachlorphenolorchromatedcopperarsenates)andtheweightperpole. Theconcretepolesaredefinedaccordingly:ultimateload(classAtoJ,600LBto4500LB, respectively),thelength,themanufacturingprocess(regularorprestressedclass),thesteel reinforcingrods(cage)tensilestrength,thediameter,theracewaydiameter,spacingand diameterofholesinthepole,groundingbars(galvanizedorcoated)surfacetreatment. 10)Whatarethedifferentapplicationsofoilswitchesandwhataretheirdefining parameters? Thedifferentapplicationsofoverheadoilswitchesinutilitydistributionsystemsare:general purposeforinductiveandresistiveloads&capacitor(capacitivecurrentswitching).The definingparametersare:theratedmaximumvoltage,thebasicimpulselevel,thedielectric

withstand,continuouscurrent,inductiveloadswitching,capacitiveswitchingcurrent,making current,momentarycurrent,shorttimecurrentrating;forthecontrolcircuit:nominalandrange ofoperatingvoltage,tripcoilcurrent.Theweight,dimensions,oilvolumeandspeedof operationfortheswitcharealsoimportantdefiningdata.Theothertwodevicesthatmayuseoil astheswitchingmediumarethesectionalizesandreclosers. 11)Howareoverheadairswitchesclassified? Thefollowingistheclassificationoftheairinsulatedswitchesaccordingtotheirbreakingtype: sidebreakswitches,verticalbreakanddoublebreak.Thedifferenttypesofmountingsforsuch switchesare:upright,vertical,triangular,tieredoutboardmountingandpedestal.Theinsulators oftheswitchmaybeepoxyorporcelain,thebaseisinsulatedorsteel. 12)Howarepadmountedswitchgeardefined? Padmountedswitchgearcanbedefined(specified)accordingly:theinsulatingmaterialusedi.e. airinsulated,oilorgas,thenominalvoltageclass,maximumoperatingvoltage,thebasic impulselevel,thecurrentratingsforthedifferentsidesi.e.continuouscurrent,loadinterruption (resistive,inductiveincludingnoloadtransformermagnetizingandcapacitiveincludingcable charging),momentary,faultclose,thedimensionsofthegear,theopeningforthecableentry, propertiesofsteelwork(likethicknessgauge,surfacetreatmentandfinish),theweightandthe assemblyvoltagewithstandabilitytests(A.C.andD.C.).Thespeedofoperation(currenttime curves)forthefusesorprotectivedeviceshadtobespecified. 13)Whataretheimportantparametersbywhichlightningarrestersaredefined? TheimportantparametersbywhichL.A.aredefinedare:dutycyclevoltage,impulsetestcrest voltage,powerfrequencyvoltage(dryandwetforoutdoorinstallations),impulsecurrent rating,maximumcontinuousoperatingvoltage,switchingsurgescapability,highcurrent/short timeandlowcurrent/longdurationrating,materialofhousing,designofinternalsie.gappedor gaplesselements(nonlinearresistancematerial). 14)Howwouldcopperconductorsbedefined? Theconstructionofcopperconductorsisdefinedasfollows:crosssectionarea,classof conductor(indicationofdegreeofflexibility),numberofwires,diameterofwire,tensile strength,elongation,diameterofconductor,type(concentriclays,compactorcompressed)and weightper1000ft. 15)HowwouldACSR(aluminumconductorsteelreinforced)andASC(aluminum strandedconductor)bedefined? Thedefiningparametersforaluminiumconductorsteelreinforceddesignsare:theAlarea,the totalconductorarea,steel/Alarearatio,numberofAlwires,diameterofAlwire,areaofsteel wire,diameterofsteelwire,diameterofcore(steel),diameterofconductor,tensilestrength, AWGsize,totalconductorweightper1000ft.andtheratioofAlweighttothetotalweight.The definingparametersforaluminiumstrandedconductorsare:thealuminumconductorarea,the quantity(number)ofAlwires,diameterofeachwire,thediameteroftheconductor,thetensile strength,theelongationandthetotalweightofconductorper1000ft. 16)HowwouldAASC(aluminumalloystrandedconductor)andselfdampening/compact

ACSRbedefined? ThedefiningparametersforAluminiumalloystrandedconductorsare:Alalloyareaandthe equivalentAlarea,numberofAlalloywire,diameterperwire,overalldiameterofconductor, AWG/KCMIL,weight/1000ft,tensilestrengthandelongation.Thedefiningparametersforself dampeningconductorsandcompactACSRare:aluminiumarea,totalconductorarea,steeltoAl area(ratio),numberofAlwires,numberofsteelwires,core(steel)diameter,overallconductor diameter,conductorweight/1000ftlength,ratioofAlweighttototalweight,tensilestrength andelongation. 17)Whatarethedifferenttypesofcablesplicesandterminations? Thedifferenttypesofcablesplicesare:tapped,heatshrinkableandcoldshrinkable.Themajor componentsofaspliceare:cableadapters,splicehousing,conductorcontact,conductiveinsert, retainingrings/tube,interferencefitandgroundingeye.Thedifferenttypesofcable terminationsare:thefullytaped,mouldedstressconeandtape,onepiecemouldedcable termination,porcelainterminators,heatshrinkablesandpotheads. 18)Whatarethedifferenttypesofconnectorsandelbows? Thedifferenttypesofconnectorsare:themechanical(forAland/orCuconductors),the compression,thewedge(toconnectmainconductorstotaps),hotlineclamps(themain overheadtoequipmentconnection)andthestirrups(wedgedorbolted).Thetwotypesof separableconnectors(elbows)arethedeadbreakandloadbreak.Themajorcomponentsof elbowsare:theconnector,themouldedinsulatingbody,cableadapter,thetestpoint,thesemi conducingshield,semiconductinginsert,groundingtabsthepullingeye,theprobe(forload break,itisfieldreplaceablewithabelativematerialarcfollower). 19)Whatarethedesigntestsperformedontheseparableconnectors? Thedesigntestsperformedontheelbowsare:partialdischargeinceptionandextinctionlevels (corona),withstandpowerfrequencyvoltagecapability(a.c.andd.c.),impulsevoltage withstandlevel,shorttimecurrentrating,switchingtest,faultclosurerating,currentcyclingfor insulatedanduninsulatedconnectors,cablepulloutfromelbow(connector),operatingforce, pullingeyeoperation,testpointcappullingtest,shieldingtest,interchangeability,accelerated thermalandsealinglife,testpointcapacitance(voltagepresenceindication)test. 20)Whatarethedifferenttypesofinsulators,theirmaterialandcharacteristics? Thedifferenttypesofinsulatorsare:thepin,thesuspensionandthepost(verticaland horizontal).Thedifferentinsulatorsmaterialsare:porcelain,glass,fibreglass,polymerand silicone.Thepropertiesofinsulatorscanbebroadlyclassifiedinto:mechanical,electrical, environmentalandmaintenance.Themechanicalcanfurtherbeclassifiedinto:differentloads theinsulatorsissubjectedtoduetoweightsofsupportedcomponents,shortcircuit,ice,etc. (normal,design,cyclic,torsional,overloadsexceptional),safetyfactors,singleormultiple insulatorassembliesandagingeffectonstrengthofinsulator.Theelectricalparametersdefining theinsulatorsare:BIL,powerfrequencywithstandability(dry,wetandflashoverlevel),leakage distance,powerarcseffect,performanceundersteepfrontvoltagewave,clearancesand performanceundercontamination.Theenvironmentalcharacteristicscanbefurtherbrokedown

into:insulatorageingunderultravioletraysanddryarcing,typeofcontamination,radio interferencevoltage,washingrequirements,corrosiveenvironmentsandtemperaturerange. 21)WhatarethefunctionsofDAC(distributionautomationandcontrol)?Sketchthe typicalundergrounddistributionarrangementsandtheoverheaddistributionsystem. Distributionautomationandcontrolfunctionscanbeclassifiedinto:loadmanagement,real timeoperationalmanagementandremotemetering.Thefirstfunctionmaybesubclassifiedinto: discretionaryloadswitching,peakloadpricing,loadsheddingandcoldloadpickup.The secondfunctionissubclassifiedinto:loadreconfiguration,voltageregulation,transformerload management,feederloadmanagement,capacitorcontrol,faultindication/location/isolation, systemanalysis/studies,state/conditionmonitoringandremoteconnect/disconnectofservices. Fig.4showstheundergroundarrangementsandfig.5showsthetypicaloverheadsystem.

22)WhatarethemajorinformationobtainedfromadistributionsystemSCADA?Showa blockdiagramofthemajorcomponentsofaSCADA(systemsupervisorycontrol&data acquisition).Sketchadiagramtoshowatypicalautomateddistributionsystemwithpower andcommunicationlines. ThemajorinformationobtainedfromaSCADAinapowerdistributionsystemare:indications (eg.statechangelikeopeningorclosingofcircuitbreakers,loadbreakswitches,reclosures, disconnects,operationofarelayorfaultindicators)ofeventsoralarms,levels(eg.oillevel,tap changerposition,readingfrompressuregauges),pulses(eg.energymetercounters), measurands(eg.current,voltage,powerreading,temperatureofoilorwindings,leakage current).Fig.6showsatypicalSCADAandfig.7showsasinglelineforanautomatedsystem.

23)WhatarethebasicmodulesinaPLC(programmablelogiccontroller)system?Sketch afrontplateof2ofthebasicmodules.Sketchablockdiagramshowingtheinterrelationof themajormodules. ThebasicmodulesofaPLCsystemare:theprocessor,theinput/output(theycanfurtherbe classifiedintodigitalandanalog),processcontrol(proportional/integral/derivative),stepper motor,interfacemodules(theycanbefurtherclassifiedinto:localandremote,localandremote transfer,network,networktransfer,multimedianetworkinterface,peripheraldevices(they includeloader/monitor,processcontrolstations,CRTprogrammers,handheldprogrammers, tapeloader).Fig.8showsthefrontplatesofthelocalandremoteinterfaceunits,fig.9showsa typicalblockdiagramincludingtheracks,interface/input/output/networkinterfacemodules.

24)Foranoverheadconductorwithsize=556.5MCM,aluminumcorewith19strands andoperatingvoltageof25KV,calculatethereactanceat60c/sand50HZper1000ft,the resistance(AL1350)per1000ft,thecapacitance,chargingcurrent/1000ftandsurge impedance. Given:Conductordetails:556.5MCM/19strands/Al1359. Nominalvoltage:25KV,frequency:60&50c/s,length1000ft,conductordiameter:.855" (fromtables),area:.437inch2(fromtablesor7.854(1000)(556.5)/(10+7)=.437in.2) L=(2)/(10+7)[ln(d/r')]H/m=(2/10+7)ln12(2)/.855(.7788)(at1ftspacing)

L=7.17(1000)/3.28(10+6)=2185/10000000H/1000ft. XL=2pi60L=.082OHM@60c/sandXL=.068OHM@50c/s,wherepi=3.141592654 R=.0927microOHMft(1000)/.437/(12)(12)=.0305ignoringskineffect,takingintoaccount

approximateskineffectthenR=.0305(1.15)=.035OHM

C=1/(10+9)(18)(lnd/r)F/m=1/(10+9)(18)(ln12/.855/2)=.0166/10+9 C=.0166(1000)/3.28(10+9)F/1000ft=5.08(109)farad/1000ft XC=1/2pifC=5.22(10+5)OHM, chargingcurrent=25000/1.732(5.2)(10+5)=.028amp/1000ft

Z=surgeimpedanceundertheseconditions=(L/C).5)=207OHM 25)ForanundergroundXLPEcable,size=250MCM,aluminum1350corewith37 strandsandoperatingon25KVsystem,calculatethereactanceat60&50HZper1000ft, resistanceper1000ft,capacitance,surgeimpedance,chargingcurrent/1000ft,speedof propagationofthewaveandtheinsulationresistance. Given:cabledata:250MCM,XLPE,AL1350,37strands,25KV,1000ftlength,conductor dia.:.575in,area=.196in2),dia.overinsulation:1.16",e=3.5,whereeisthedielectric constant L=(2/10+7)[ln12(2)/(.575)(.7788)=2427/(10+7)H/1000ftat1ftspacing XL=.092OHM@60c/sand.076OHM@50c/s R/1000ft=.0927(1000)(144)/.196=.068OHM(1.15)=.078OHM

C=3.5/)10+9)(18)(ln1.16/.575)=.277/(10)F/m(1000)/3.28=84/(10+9)F/1000ft Latinsulationneutralorsheath=2ln1.16/.575(.7788)/(10+7)=2(107)H/m Chargingcurrentfor1000ftcablelength=(25000/1.732)(31578)=.46amp. Z=surgeimpedance=(L/C).5)=27OHM,XC=1/2piC60=31578OHM/1000ft v=speedofpropagation=(1)/(LC).5)=1.34(10+8)m/sec. Volumetricinsulationresistance=(ra)(ln1.16/.575)/(2pl)(12)(2.54),whereraistheresistivity orspecificresistanceofthedielectric assumera=6(10+14),Rvolumetric=6(10+14)(.7)/191511=2193MegaOHM/1000ft. 26)Iftheoverheadconductorandtheundergroundcableofproblems24&25are connectedinseriesandavoltagewaveof25KVistravellingthroughtheoverheadportion, calculatethereflectedandrefractedpowersatthejunctionpoint. Zline=207,Zcable=27,KV=25 reflactedvoltage=(27207)25/1.732(207+27)=11.1KV refractedvoltage=(2)(27)(25)/1.732(207+27)=3.33KV refractedpower=3(Vph)(Vph)/Zcable=3(3.33)(3.33)/27=1232KW reflectedpower=3(11.1)(11.1)/207=1785KW 27)Providethedifferentialandgasaccumulation/suddenreleaseprotectiontoa100MVA powertransformer,220/25KVwith+/16%tapchanger.Assumethattheavailablerelays haveapickupsettingbetween2050%ofrelayratingwithanadjustableslopeof2050% andanotherwithfixedslopeandrestrainedpickupbetween20and50%and

unrestrainedpickupof8,13,20xrelaynominalcurrent.Thepressuregasrelayshavetwo settings,forthetrip5.217.2KPaandforthealarm200400CC.Thetapchangergas pressuretripcanbesetbetween35390KPa. Iexcitation=5%offullloadprimary,C.T.error=2.5%,relayrating=5A,C.T.primary current=1.5xfullloadcurrentoftransformer. Iprimary=100(1000)/(220)(1.732)=262A Isecondary=262x220/25=2300A Usinga1200/800/200:5AC.T.ontheprimaryside(theC.Tsaredeltaconnected),3500:5A C.T.onsecondaryside(theC.Tsarewyeconnected)ofthepowertransformer.Turnsratioof C.T.onprimarywinding=800/5=160,onsecondary=3500/5=700.Relaycurrentdueto primaryC.T.atf.l.=(262/160)1.732=2.8amp,relaycurrentduetosecondaryC.T.atf.l.= 2300/700=3.28amp,relaycurrentratio=3.28/2.8=1.17.Mismatchatmidpointchangerand fullload=17%. At220+16%=255KVtap,maintainingsecondaryvoltageat25KV,primaryfullloadcurrent =100(1000)/255(1.732)=226amp,relaycurrent=226/160(1.732)=2.45amp.,voltageof25 KVonthesecondarywhileprimary=22016%=185KVprimaryfullloadcurrent= 100(1000)/185(1.732)=312amp.,relaycurrent=312/160(1.732)=3.4A Mismatchfor+16%=3.28/2.45,mismatchfor16%=3.28/3.4whichare34%and4%, respectively.Themaximummismatch=34%,add6%assafetymargin.Thustheslope adjustment=40%(rangeis20to50%).Thepickuplevelunderfullloadcurrent= inacccuracies+escitingcurrent+allowanceforthelimitedrestraintatemergencyloadthrough currents=2.5(5/100)+(1.732)(5(262)/160)(100)+(3.282.45)=.125+.14+.83=1.1amp,the pickupsetting=40%(5)=2A(range20to50%). Theunrestrainedinstantaneoustripingcurrent=13x5=65amp.secondaryrelaycurrent. VERIFICATIONS:

Assuminga100MVAbaseand220/25KVbase,Ibase(@primaryside)=100/1.732)(220)= 262amp.,Ibase(@secondaryside)=2300amp. Assuminganinfinitesource,11%impedancetransformer,a3phasefaultonthesecondaryof thetransformerbeyondthedifferentialprotectionzonewillproduce9p.u.faultcurrent(1/.11), Iprimary=2358amp.,Isec.=20700amp.Thecurrentfromtheprimarysideintotherelay= (1.732)2358/16025.5amp.,fromthesecondaryside=20700//700=29.6amp.Amismatchof 29.6/25.5=16%. Assumingthetapchangertobeat220KV+16%=255KVandtheimpedance=14%,theshort circuitfaultcurrentofa3phasefault=1/.14=7.16p.u.,fullloadprimarycurrent=232amp., SCContheprimaryside=1661A,SCConthesecondaryside=16468A,relaycurrentfrom primaryside=1661(1.732)/160=18A,relaycurrentfromthesecondaryside=16468/700= 23.5,themismatch=30%. Assumingthetapchangerat220KV16%=185KVandtheimpedance=8%,a3phasefault

current=1/.08=12.5p.u.,primarycurrent=312A,SCConprimaryside=3900A,SCCon secondaryside=28750A,relaycurrentfromprim.side=42.2A,relaycurrentfromsec.side= 41.1A,mismatch=3% GASRELAYS: Maintankalarm=200cc,maintanktrip=17KPaabovestaticheadatrelaylevel,tapchangertrip= 100KPa. SUMMARY: Inthischapter,thedefiningparameters,classifications,testsandtypicalconfigurationsofdistribution systemscomponentswerepresented.ThegeneralpropertiesofmediumvoltageEPR&XLPEcables weregivenplusfactory&sitetests.Forlowvoltagesecondarycables,thedefiningparameterswere listed.Fortransformers,abroadclassificationwasgiven.ThedefiningparametersandtheCSA standardsthatgoverntheratings,design,manufacturingandtestingofdistributiontransformerswere presented.Othercomponentsfoundinoverheadandundergrounddistributionsystemswerecovered fromtheirtypesanddefiningparameterspointofview.Thesecomponentsare:lightningarresters, conductors,terminations,splices,connectors,elbowsandinsulators.Distributionsystemsautomation andSCADAwerepresentedbycoveringthefunctionsanddatacollectedfromsuchsystems.Typical systemsweregiventoclarifythistopic.ThemajormodulesfoundinatypicalPLC(programmable logiccontrollers)installationwerepresented.Thenumericalexamplesattheendofthischaptershowed howthelineandcableconstants(inductance,capacitance,resistance,inductive/capacitivereactances, surgeimpedance,chargingcurrentandpropagationspeed)andtheeffectofthesurgeimpedanceon travellingwavesarecalculated.Theyalsodemonstratedamethodtoselect/adjust/verifythesettingsof relays(differential&gas)usedintheprotectionofpowertransformers. REFERENCES: 1. 2. 3. 4. 5. 6. 7. Wildi,T"Electrotechnique",LesPressesdel'UniversitLaval. CSA,"CanadianElectricityCode",Part1,stdC22.1. CSA,"Singlephase&threephasedistributiontransformers",stdC2. Gonen"Electricpowerdistributionsystemsengineering",McGrawHill. Kurtz,"Thelineman's&cableman'sHandbook",McGrawHill. Perry,"ChemicalEngineershandbook",McGrawHill. ICEAS66524,"Crosslinkedthermosettingpolyethyleneinsulatedwire&cableforthe transmission&distributionofelectricalenergy". 8. ASTM2.03,"Nonferrousmetalproductselectricalconductors. 9. Brady,"Materialshandbook",McgrawHill. 10.Kheir,"ComputerProgrammingforPowerSystemAnalysts",Kheir.

Home page of VePi

Lesson3:Switchgear,circuitbreakers,MCCSandcontactors. 1) Whatarethedefiningparametersforlowvoltagecircuitbreakers? 2)Whatarethedefiningparametersformediumvoltagecircuitbreakers? 3)Whatarethedifferenttypesofinterruptingmediausedinm.v.c.b.?Whatarethecommon propertiesforsuchquenchingmedia? 4)Whatarethedifferenttypesofswitchgearassembliesandwhatarethesubclassificationof eachtype?Whatarethestandardsgoverningswitchgearassemblies&circuitbreakers?What arethetypesofbatteriesfoundinsuchequipment?Giveabriefdescriptionofeachtype. 5)Whatarethedefiningparametersforlowvoltagealternatingcurrentmagnetic contactors/starters? 6)Whatarethedefiningparametersofl.v.combinationstarters? 7)Whatarethedefiningparametersforfullvoltage2speedstarters? 8)Whatarethedefiningparametersoflowvoltage,reducedvoltagestarterunits? 9)Whatwouldatabledefiningthemotorprotectioncircuitbreakershaveasheadings? 10)Whatwouldatabledefiningmotorprotectionfuseshaveasheadings? 11)Whataretheheadingsofatabledefiningm.v.controllers? 12)Whatarethegeneralpropertiesofconstructionalandstainlesssteels? 13)Whatarethedifferenttypesofswitchboardinstrumentsandthedifferentmechanisms?What arethedefiningparametersforsuchdevices? 14)WhatarethedefiningparametersforKWH,KVARandsolidstatemeters?

15)Whatarethedifferentconstructionsofprotectiverelays?Givethedefiningparametersfor thedifferenttypesofthefollowingrelays:overcurrent,over/undervoltage,differentialand distance. 16)Asolvedproblemregardingthesizingofthebreakingdevicesofaswitchgearassembly. Lessonsummary References 1)Whatarethedefiningparametersforlowvoltagecircuitbreakers? Thedefiningparametersoflowvoltagecircuitbreakersare:theratedvoltage,thecircuitbreaker currentrating,symmetricalinterruptingcapacity(withinstantaneousanddelayedintegral protectiverelays),closeandlatchratingforasecond,thesensorscurrentratio,thefunctions ofprotectionontheintegralovercurrentprotectivedevice,electrically/manuallyoperatedor manuallyonly,theweightanddimensionsofcircuitbreakers,theindicatorsoftheintegral protectivedevice(ifavailable).Forelectricallyoperatedbreakers,therangeofoperating voltagesandcurrentsplusthenominalvaluesforthesolenoids/motors/tripcoilsareimportant parameters,too. 2)Whatarethedefiningparametersformediumvoltagecircuitbreakers? Thedefiningparametersofmediumvoltagecircuitbreakersare:thevoltageratings(nominal, maximumandminimum),the3phaseMVAbreakerrating,theratedcurrent,theKfactor (Max./Min.ratio),symmetricalinterruptingratings(atmaximum,nominalandminimum voltage)inKA,theasymmetricalfactor,theshorttimerating,thecloseandlatch,theinsulation level(powerfrequency,impulselevel),theweight,thedimensions,theinterruptingmedium,the TRVcapability,anyarcingmediummonitoringdevices,circuitbreakerclosingtime,tripping time,interruptingtime,springchargingtime,thecontrolvoltages(nominalandrange),the springchargingcurrent,closecoilcurrentrequirement,thetripcoilcurrentratingandsurges switchingcapabilities. 3)Whatarethedifferenttypesofinterruptingmediausedinm.v.c.b.?Whatarethe commonpropertiesforsuchquenchingmedia? Theinterruptingmediausedinmediumvoltagecircuitbreakersare:air,oilSF6andvacuum. Thegeneralpropertiesoffluidsusedinarcextinguishingchambersinm.v.c.b.are:high dielectricstrengthofthegasorliquid,thermallyandchemicallystable,noninflammable,high thermalconductivity,lowdissociationtemperature,shortthermaltimeconstant,shouldnot produceconductingmaterialduringarcing.Gasesusedsofarinm.v.c.b.canbeclassifiedinto simple(air)orelectronegative(SF6). 4)Whatarethedifferenttypesofswitchgearassembliesandwhatarethesubclassification ofeachtype?Whatarethestandardsgoverningswitchgearassemblies&circuitbreakers? Whatarethetypesofbatteriesfoundinsuchequipment?Giveabriefdescriptionofeach type. Thedifferenttypesforswitchgearassembliesare:indoorandoutdoor.Thesubclassificationfor theindooris:standard,sprinklerproof,arcproof,dustproof,seismicproof,metalclad constructionvs.metalenclosed,enclosurewithorwithoutadriphood;fortheoutdooris:walk

in,walkinwithworkingarea,walkindoublerow,nonwalkinwithorwithoutworkingarea, enclosureforcable/busentryortransformerthroat,enclosurewiththermalinsulation/isle heatersandfinallyindoorcubicledesigninstalledinanoutdoorhouse. Thestandardsthatgoverncircuitbreakers/switchgeardesigntestingandapplicationare:ANSI C37seriesincluding.09"TestprocedureforA.C.highvoltagecircuitbreakersratedona symmetricalcurrentbasis",.04"RatingstructureforA.C.highvoltagecircuitbreakersratedon asymmetricalcurrentbasis",.06"PreferredratingsandrelatedrequiredcapabilitiesforA.C. highvoltagecircuitbreakersratedonasymmetricalcurrentbasis",.20"Switchgear assemblies",IEC56"HighvoltageA.C.circuitbreakers",IEC60series"Highvoltagetest techniques",IEC694"Commonclausesforhighvoltageswitchgearandcontrolgear", C22.2#31"switchgearassemblies"andCAN3C13"Instrumenttransformers.". Thedifferenttypesofstationarybatteriesusedinconjunctionwiththeseequipmentare:lead acidandnickelcadmium.Thefirsthasthreepossibilitiesofpositiveplateswhichare:the pasted,multitubularandplantetype.Thenegativeplateswillbeofthepastedtype,thegridfor theplanteandmultitubularismadeofleadantimonyandthatforthepastedismadeofeither leadantimonyorleadcalcium.Theactivematerialinthe+veplateisleadoxideandintheve plateisspongelead.Theelectrolyteisasolutionofdilutedsulphuricacidwithspecificgravity ofapproximately1.2.Forthenickelcadbatteries,theplatesmaybeofthepocketorthesintered type.Theactivematerial(nickelhydratedforthe+veplateandcadmiumspongefortheve)is placedinnickelplatedsteelholders.Theelectrolyteisasolutionofpotassiumhydroxidediluted inwaterwithaspecificgravityof1.16to1.19at25C. 5)Whatarethedefiningparametersforlowvoltagealternatingcurrentmagnetic contactors/starters? Thedefiningratingsforlowvoltagealternatingcurrentmagneticcontactors/startersare:the NEMAsize,thevoltagerating,themaximumHPforsinglephaseandthreephasemotors(for bothnonplugging/nonjoggingandplugging/joggingapplications),thecontinuouscurrentrating ofthecontactor/starter,theservicelimit,transformerswitchingcapabilityratingforsingleand threephaseapplications,thecapacitiveswitchingcapability(involtandKVAR),the dimensions,theweights,theoverloadprotectiveelementtypeandrating. 6)Whatarethedefiningparametersofl.v.combinationstarters? Thedefiningparametersoflowfullvoltagecombinationstarterunits:thestartersize,the maximummotorHPatthedifferentstandardvoltages(200v,230,460and575v),whetherthe unitisreversingornonreversing,thefuseorcircuitbreakersize(usedasaprotectionagainst shortcircuitorprotection/loadbreakdevice),thesizeoftheunitininchesorspacefactor,the weightoftheunit,methodofattachmenttoriserbusbarsofMCC(boltonorplugin)andsize plustypeofmotoroverloadprotectionelement/relay. 7)Whatarethedefiningparametersforfullvoltage2speedstarters? Thedefiningparametersforfullvoltage2speedstarterunitsare:thestartersize,theHP (maximum)atthedifferentnominalvoltages,thecircuitbreakerorfusesizefortheshortcircuit protection,thedimensionininchesorspacefactorforthe1windingand2windingmotor

starterunit,unitweight,methodofattachmenttoMCCandthetypeplussizeofo/cprotection device. 8)Whatarethedefiningparametersoflowvoltage,reducedvoltagestarterunits? Thedefiningparametersoflowvoltagereducevoltagestarterunits(applicabletopartwinding andautotransformerunits):thestartersize,themaximummotorHPatthedifferentrated voltages,thecircuitbreakerorfuserating,thedimensionsorspacefactorfortheunits,the weight,thesizeplustypeoftheo/lelement,theinstallationmethodintheMCC. 9)Whatwouldatabledefiningthemotorprotectioncircuitbreakershaveasheadings? Thetablewillhavethefollowingheadings:3phasemotorHP,themotorfullloadcurrentatthe differentnominalvoltages,thecircuitbreakercontinuouscurrent,thedifferentadjustments(eg. 7x/11x/13x),theweightanddimension,theadjustablerange. 10)Whatwouldatabledefiningmotorprotectionfuseshaveasheadings? Thefusesformotorprotectiontablewillhavethefollowing:themaximummotorHPrating,the motorfullloadcurrentrating,thefusesizeforthedifferentvoltageclasses,thefusetype(50KA interruptingfuse,HRC200KAI.c.,codefuse10KAorsizeLover600a200KA),thefuse weight. 11)Whataretheheadingsofatabledefiningm.v.controllers? Thetableforamediumvoltagecontroller(contactorandfuse)willhavethefollowingheadings: thecontactormaximumcontinuouscurrent,theinterruptingcapacity(atthespecifiedKV),the designation,thevoltageratingandrange,theinterruptingcapacityofthefuse(inKAandMVA @theratedvoltage),themaximumHPmotorratingforthemotordesign/p.f./voltage/controller currentrating,thedielectricwithstandvoltage,thecontrollertype(fullvoltage,reversingvs nonreversing,reducedvoltageautotransformervsreactor).Them.v.fusesforcontrollerscan bedefinedwhenthefollowingvaluesaregiven:themotorlockedrotorcurrent,motorfullload currentxservicefactor,themaximumcontinuouscurrentratingofthefuseinsidethe compartment,thefusesize,thepeakcurrentletthroughcharacteristics. 12)Whatarethegeneralpropertiesofconstructionalandstainlesssteels? Themechanicalpropertiesofconstructionalsteelsare:theASTMdesignations,thethickness range,yieldpoint,elongationasapercentofthelength(eg.in8inches),tensilestrengthand weldability.Thoseforstainlesssteelare:A1SIdesignation,condition,.2%yieldpoint, elongationin2incheslength,tensilestrengthandareareduction. 13)Whatarethedifferenttypesofswitchboardinstrumentsandthedifferent mechanisms?Whatarethedefiningparametersforsuchdevices? Thedifferenttypesofswitchboardinstruments:voltmeters,wattmeters(singlephaseand polyphase),varmeters,powerfactormeters,frequencymeters,ammeters.Thedifferent mechanismsare:tautbandsuspension,repulsionvane,electrodynamic,D'Arsonval/zenerdiode. Thedefiningparameters:impedance,inputresistance,inductance,voltampere/W/RVA/p.f.of mechanism(burden),mechanismtype(selfcontainedortransformer),instrumenttransformer ratio,scaleandunits/scaledivision. 14)WhatarethedefiningparametersforKWH,KVARandsolidstatemeters?

ThedefiningparametersofKWHmetersare:typeofmeterandnumberofelements,connection method,weight/dimension,burdendataforeachtype/elementsnumber(phase,potentialcircuit andcurrentcircuit),KVAattachmentdata(meter,volt,scale/multiplier,amprange),disk constantWH/diskrevolution,registerratio.ThoseforKVARare:burden(potentialandcurrent circuits),weightanddimensions(forthedifferentdesigns),temperaturerise,ratingsand enclosuresforthedifferenttypes/numbersofelements.Thoseforsolidstatemetersare: potentialinputratings(inputvoltage,impedance,burden,overloadcapability,currentinput ratings(burden,inputcurrentandimpedance,overload),weight&dimensions,controlpower requirements,communicationcapability(protocol,baudrate,standards),measuredparameters (measurands). 15)Whatarethedifferentconstructionsofprotectiverelays?Givethedefining parametersforthedifferenttypesofthefollowingrelays:overcurrent,over/undervoltage, differentialanddistance. Relayscanbeclassifiedbasedontheirconstructionintoelectromechanical(magneticinduction, magneticattraction,thermalandD'Arsonval),solidstateandmicroprocessor/digitalbased. Thedefiningparametersforelectromechanicalbasedo/crelaysare:weightanddimensions, typeofrelaytimecurrentcharacteristicscurves(inversedefiniteminimumtime,shorttime, veryinverse,extremelyinverse),currenttaprange,timedialrange,operatingtime,burdenand thermalratings(continuouscurrent,1sec.ratingandpowerfactor,attapsetting,at3timestap, at10timestapandat20timestap).Thoseforo/csolidstaterelaysare:weightanddimensions, currentrating,frequency,d.c.supplyvoltageandburden,burdenonC.T.,settingrangeforthe instantaneousandtimedelayfunctions,timemultipliersetting,operatingtimesfortimedelay andinstantaneousfunctions.Theparametersforthemicroprocessorbasedare:weightand dimensions,ratedcurrent,settingrange,ratedcurrentforthegroundfaultunitandthesetting range,operatingtimes,burden,overloadcapacity,controlpowervoltageandburden,resetting timesandcontactsratings. Thedefiningparametersfortheover/undervoltageelectromechanicalrelaysare:theweightand dimensions,thecontinuousinputvoltagerating,theshorttime(eg.2minute)voltagerating,the taps'range,burden,timedialrange.Those,forthesolidstateare:weightanddimension,input voltageratings,pickuprange,dropoutsettingrange,timedelaysetting(pickupanddropout), control(auxiliary)supplyvoltageandrange. Thedefiningparametersforaelectromechanicaldifferentialrelaysare:theweightand dimensions,theapplicationi.e.transformerdifferentialormotororgeneratordifferential protection,numberofphasesi.e.singleorthreephase,numberofoperateandrestraintcircuits, minimumtripcurrent,burden,operatingtime,typei.e.fixedorvariablepercentage(biased) relay,currentinputs. Thedefiningparametersforsolidstatepercentage(biased)relayswithinstantaneoustripping andharmonicsrestraint:weightanddimensionsincludinginterposingrelays(ifany),the currentsinput,overloadcapacity,frequency,interposingC.T.ratio(ifany),burden,operating current,restraintcurrentsettings,unrestrainedcurrentsettingrange,operatetime,resetratio,

orderofharmonicsrestrainedi.e.2ndor5th,auxiliarypowervoltageandpowerconsumption, burdenofoperatingandrestraintcircuits. Thedefiningparametersfortheelectromechanicaldistancerelaysare:theweightand dimensions,characteristicstypei.e.impedance/reactance/admittance/angleimpedance (OHM)/offsetMHO/modifiedimpedance/complex/elliptical/quadrilateral,relayreach,taps, variationinreachandmaximumtorqueangleovertherangeoftaps,burdenoninstrument transformers.Thoseforsolidstaterelays,theparametersare:weightanddimensions,input circuits,burden,controlvoltageandconsumption,characteristicstorque(angle),resetratio. 16)Aunitsubstationisconnectedtotheutilitylinethrougha25KVcircuitbreakerwhich feedsa5MVAtransformer,5%impedance3phase,25KV/600v.Thelowvoltagewinding ofthetransformerisconnectedthrougha600vmainbreakertoalowvoltageswitchgear. Theswitchgearhas3circuitbreakersfeedingeacha400HPmotor,.25reactance,1800 RPM.Afourthcircuitbreakerisfeedinga750KVA,4.5%impedance600/208vandthe lastbreakerinthislineupfeedstheother600/347vloads(2MVA).Forafault(LLL)on themainbus,calculatethefaultcurrentwithandwithoutmotorcontributionandgivethe contributionofeachmotor.Calculatealsothemotorbreakerfaultcurrentforafaulton themotorterminals.Assumeoninfinitesource.Givethebreakers'sizeonthelowvoltage sideoftransformer,giveatypicalunitsubstationlayout.

MVAbase=5,KVbase(primarysideofpowertransformer)=25,KVbase(secondaryside)=.6, Ibase=5(1000)/1.732(.6)=4811amp=fullloadcurrent.Fullloadcurrentonprimaryside= 4811(600)/25000=115amp.Faultcurrentfor3phasefaultonmainbus=1/.05=20p.u.= 20(4811)=96KA(fromsuplyside).

Xmotor=.25(5000/350)=3.5p.u.(assumingmotorp.f.=.85) 3motorscotributionfora3phasefaultonmainbus=1/1.16=.85p.u.=.85(4811=4089amp. Totalfaultcurrent=96+4=100KA Contributionpermotor=.283(4811)=1370amp. ForLLLfaultonmotorterminals,thefaultcurrentthroughthemotorbreaker=2(1.37)+96= 98.7KA. Motorfullloadcurrent=400(746)/1.732(.85)(.9)(600)=375amp.(assumingamotorefficiency of.9) F.L.currentto750KVAtransformer=750(1000)/1.732(600)=722amp. F.L.currenttothe2MVAload=2000/1.732(.6)=1924amp. Forthemainlowvoltagecircuitbreaker: Continuouscurent(framesize)=5000amp.,I.C.=120KA Forthemotorscircuitbreakers(fusedorcurrentlimiting): Continuouscurrent=800Amp,I.C.=100KA,Sensorsratio+400/5amp. Forthe750KVAtransformer(fusedorcurrentlimiting): Continuouscurrent=1600amp.,I.C.=100KA,Sensor=800/5amp. Forthe2MVAload(fusedorcurrentlimiting): Continuouscurrent=2000amp.,I.C.=100KA,Sensor=2000/5amp. Fig.11showsthetypicallayout.

SUMMARY:

Inthischapter,circuitbreakers,switchgearassemblies,startersandcontrollerswerepresented fromthedefinition,standardsandbriefdescriptionpointsofview.Forlowvoltagecircuit breakers,thecoverageincludedtheratingsofthepowerandelectriccontrolcircuits.For mediumvoltagecircuitbreakersandswitchgearassemblies,thecoverageincludedthebreakers interruptingmedia,breakersratings,governingstandards,differenttypesofswitchgear assembliesandtypesofstationarybatteriesfoundinsuchassemblies.Forl.v.starters,the coverageincludedthedefiningparametersforthefollowingdevices:contactors,combination starters(fullvoltage/singlespeed,fullvoltage/twospeed,autotransformer/partwindingreduced voltage),motorprotectionfusesandmagneticelementonlycircuitbreakers).Formedium voltagestarters,thecoverageincludedthecontactorsandfusedefiningparameters.Certain relatedmiscellaneoustopicswerealsocoveredbrieflylikethegeneralpropertiesof constructional&stainlesssteel,switchboardinstrumentstypes&mechanisms,metersdefining parametersandrelaystypes&definingparameters. Thenumericalexampleattheendofthisunitclarifiedtheselectionofbreakersina hypotheticalunitsubstationincludingthecontinuouscurrent,interruptingcapacityandsensors ratioforeachbreaker. References: 1. Wildi,T."Electrotechnique",LesPressesdel'UniversitLaval. 2. IEEE"Recommendedpracticeforprotection&coordinationofindustrial&commercialpower systems"std242. 3. CSA"Switchgearassemblies"stdC22.2no.31. 4. CSA"Instrumenttransformers"stdCAN3C13. 5. Wadhwa,C."Electricalpowersystems",Wiley. 6. Kheir"Computerprogrammingforpowersystemsanalysts",Kheir. Home page of VePi

Lesson4:Powerlinedisturbances. 1) Whatarethedisturbancesfoundinpowersystems? 2)Whatarethesourcesofdisturbancesinpowersystems?Sketch4examplesforthesourcesof disturbances. 3)Whataretheeffectsofsuchdisturbancesonthemajorelementsofpowersystems? 4)Whataretheindicatorsofthequalityofpowerinaplant? 5)Whatarethemethodsusedtoreducethesedisturbances?Sketchtwoofthedevicesusedin reducingthesteadystatedisturbances.Whatarethemajorstandardsthatarepowerquality related? 6)Whatarethemajorhardwarecomponentsinanofficeautomationsystem?Whatarethe majorresponsibilitiesofanoperatingsystem?Whatarethedifferenttypeslocalareanetworks andwhatarethedifferenttypesoftransmissionmediausedwithLANs. 7)Asolvedproblemregardingtheeffectofapplyingcapacitorsinimprovingthepowerfactorof acircuit. 8)Asolvedproblemregardingthequantificationoflightningstrokes. Lessonsummary References 1)Whatarethedisturbancesfoundinpowersystems? Disturbancesfoundinpowerlinescanbeclassifiedintosteadystateandtransients.Steadystate canfurtherbeclassifiedintoharmonicsandvoltagenotching.Thetransientsdisturbancescan befurtherclassifiedinto:brownouts(undervoltage),overvoltage,sags,surges,frequency variations,powerlinenoise,radiofrequencyinterference. 2)Whatarethesourcesofdisturbancesinpowersystems?Sketch4examplesforthe

sourcesofdisturbances. Thesourcesofsteadystateand/ortransientdisturbancesoriginatefromoutsidethepremisesas wellfrominside.Thesourcescanbeclassifiedbroadlyintoenvironmental(eg.lightning), operational(eg.switching),failure(eg.arcinggrounds)conditions.Thesourcesofsteadystate disturbancescanbearcfurnaces,welders,saturablereactors,rectifiers,thyristorcontrolled loads,variablevoltage/frequencydrives,uninterruptablepowersupply,magnetizingcurrents. Thesourcesfortransientdisturbancescanbeinductive/capacitiveloadsswitching,photocopiers, airconditioners,motors(switchingstartingandstopping),ballasts,lightswitches.Fig.12 shows4examplesforsourcesofdisturbancesinpowersystems.

3)Whataretheeffectsofsuchdisturbancesonthemajorelementsofpowersystems? Theeffectsthatthesteadystatedisturbanceshaveonthemajorelectricalequipmentare: _Motorandgenerators:atharmonicfrequencies,copperandironlossesincreaseand consequentlytheinsulationtemperature.Atextremeconditions,generatorscanhuntandmotors aresubjectedtopulsatingtorques. _Transformers:operatingundersustainedovervoltageconditionsmeansmorecopperandiron losses,thusoverheating.Duetothenonlinearcharacteristicsoftheironcore,overexcitingthe transformerwillcausethesteadystateexcitingcurrenttoincreasesignificantly(itisthepoint ontheflatportionofthevoltage/excitingcurrentcurveofthecore).Thiscurrentisreachin third&fifthharmonics,thushormonicsareinjectedintothesystem. _Powercables:overvoltageswillstresstheinsulation.Duetoresonanceconditions(betweenthe cablecapacitanceandloadinductance)fromotherthanfundamental(highharmonicsorder), thecablemaybesubjectedtoahighresonantvoltagewhichmaystartspartialdischargeinthe voidsfoundintheinsulatingmaterialThepartialdischargemayeventuallyleadstothefailure ofthecable.Harmonicsmaycausehigherskineffectthusoverheatingofconductorandthe insulationwilloperatecontinuouslyunderhighertemperatures. _Capacitors:atresonancefrequency,higherthenratedvoltagemaybeimposedontheunitand higherthanratedcurrentmayflowthroughthecapacitorblowingfusesoroverheatingtheunit. _Switchgearandmotorcontrolcentres:overheatingduetoincreasedlossesmaycausea reductionintheinsulationlife. _Protectiverelaying:nuisancetrippingornotrippingofelectromechanicalrelays(duetotorque ofharmoniccomponents),maloperationofnoneRMSsensing(peak)solidstaterelays.

_Metersandinstruments:positiveandnegativeerrorsarepossibleinelectromechanicalmeter readings. _Electronicequipment:misoperationorerraticoperationofmicroprocessorbasedandsolid statedeviceswhenhighharmonicsandvoltagenotchingarepresentinthecircuitsfeedingsuch devices. _Circuitbreakers:harmonicscancausethebreakerinsulationtobestressedduetoovervoltage andcurrentcarryingpartstobeoperatedathigherthannormaltemperatures.Thismayleadto failureofcircuitbreakerswhileintheclosedoropenedposition. _Communications:whencommunicationlinesareincloseproximitytohighharmonicscontent powerlines,interferencemayoccurwithdataandsignalstransmittedonthecommunication lines,sparioussystemresponsesatthereceivingendmayoccur. _Otherdeviceslikeballastsmayfail,clocksandpagingsystemsmaymalfunction. Theeffectsoftransientsare: _Motors:mayfailifsubjectedtoprolongedperiodofundervoltages,overvoltageswillstressthe insulationandeventuallywillcausetheinsulationtofail. _Heatersandlighting:Overvoltagewillcausethedevicetorunhotandifleftforalongperiod itmayburnitselfout. _Electronicdevicesaresusceptibletonoiseandspikes.Failureinpowersupplies/boardsand burningofchipswillbetheresult. _Transformers:overvoltageforprolongedtimeswillstresstheinsulation(andmayeventually causeafailure)andwillincreasetheharmonic(higherorder)levelinthesystem.Spikesmay causeaninsulationfailure. _Supervisorycontrolequipment:maymalfunctionfromelectromagneticinterference. 4)Whataretheindicatorsofthequalityofpowerinaplant? Theindicatorsofthequalityofpowerintheplantare: _Thelengthoffeedertowhichtheserviceisconnected.Itisimportanattoknowwhetherthe lineisanoverheadoranundergroundoneoramixofboth,ifthelastwhatistheproportionality ofoverheadtothetotalfeederlength.Ifitisanoverheadline,thedegreeofexposuretotrees, lightninig,trafficandcontaminantsmayindicatethequalityofpowertobeexpected.Onthe otherhand,ifundergroundcablesareusedthe,methodoflaying/pullingcablesmaygivean indicationofthequality.Theoperationphilosophyoftheutilityincludingfault indication/isolation/restoration,maintenanceproceduresandcablesfaulthandlingmayalso indicatetheaveragenumberoffailuresandthedurationperfailureforthefeeder. _Utilityphilosophyregardingtheuseofreclosures,sectionalizes,voltageregulators,lightning arresters,capacitorsandtheadjustmentsofovercurrentrelaysonthefeeders/reclosersandfuse sizing.Certaincomponentsimprovethequalitybutothersmayjeoperdizeitortheavailability ofthepowersource. _Thetotalnumberoffeedersconnectedtothetransformerstationbusundernormaland emergencysituationsasafaultonanyfeederwillaffectthevoltageonthestationbus. _Thesitehasanyequipmentthatwouldpumpdirtypowerintothesystem.Theknowledgeof

theequipmentconnectedtothesamefeederthatmaycauseharmonics,spikes,sags,etc.....tobe injectedintothesystemorsuperimposedonthenormalvoltageisimportanttoknowifpower qualityisanisue. 5)Whatarethemethodsusedtoreducethesedisturbances?Sketchtwoofthedevicesused inreducingthesteadystatedisturbances.Whatarethemajorstandardsthatarepower qualityrelated? Themitigationmethodstoproducetheeffectsofsuchdisturbancesare: Forsteadystatedisturbances:shuntfilters,seriesfilters,zerosequencefilter,phase multiplication,harmonicsinjection,thedesignofthepowersystem,reactorsorisolation transformer,reducingsystemimpedance.Fig.13showstwotypesofsuchdevices. Fortransientsdisturbances:builtinfilters,dedicatedlines/isolatedgrounds,regulation transformers,isolationtransformers,saturatedtransformers,ferroresonanttransformers,ultra isolationferroresonanttransformers,lineconditioners,clampingdevices,standbypower sources,uninterruptablepowersupplies(UPS). Thestandardsthatarerelatedtopowerqualityare:ANSI/IEEE519"Recommendedpractices andrequirementsforharmoniccontrolinelectricalpowersystems"(formerlyGuidefor harmoniccontrolandreactivecompensationatstaticpowerconverter),IEC1004series "Electromagneticcompatability"andANSI62series"SurgearrestersforA.C.powercircuits" plusCSA233series"SurgearrestersforA.C.systems".

6)Whatarethemajorhardwarecomponentsinanofficeautomationsystem?Whatare themajorresponsibilitiesofanoperatingsystem?Whatarethedifferenttypeslocalarea networksandwhatarethedifferenttypesoftransmissipnmediausedwithLANs. Themajorhardwarecomponentsare:themotherboard,microprocessor(CPU),diskdrives, monitorsandadapters(theyincludemonochromedisplayandadapter,colourgraphics, enhancedcolourdisplay,videographicsarray,supervideographicscards),keyboards,plotters, printers,modemsandotherinputdeviceslikemouse,joystickandinterfaces(forSCADA systemsorfromPLCsystems).Theoperatingsystemisresponsibleforinitializingthesystem, performingstartuptests,openingandcopyingthenecessaryfilesintomemory,givingcontrol totheuserandsoftwarerunundertheoperatingsystem.Localareanetworkstypesare: contentiontype,reservationorroundrobinoringeneralcanbeclassifiedintodistributedor centralizedcontrol.Thetransmissionmediamaybeanyofthefollowing:twistedpaircopper cable,coaxialcable,fiberopticsorlineofsight. 7)A20HPmotor,575v,3phase,.75p.f.,.85efficiency,calculatethecapacitorratingto improvethepowerfactorto.95,theincreaseincurrentflowthroughthemotorcircuitto otherconnectedloadsprovidedthattheapparentpowerremainsthesameinbothcases. MotorKWat.75p.f.=20(.746)=14.9KW KVAat.75p.f.=19.866,KVAR=[KVA2KW2].5=13.14 MotorKWat.95p.f.=14.9KW,KVA=14.9/.95=15.68

KVAR2=[15.68214.92].5=4.88 KVAR1KVAR2=13.144.88=8.26KVAR=capacitorrating.

KW=[19.86624.882].5=19.25KW Theadditionalpowerthatmaybetransferredduetothelocalcapacitor= 19.2514.9=4.35KW Atunityp.f.theadditionalcurrent=4.35/(575)(3)/(1.732)=4.36amp. Motorf.l.currentat.95p.f.=20(.746)/(1.732)(.95)(.85)575=18.5amp. 8)Ashortoverheadlinerated25KVnominalandissupportedonwoodenpolesat40ft fromgroundwith400KVdryBIL.Calculatethestrokecurrentthatwillcausethislineto flashoveriftheindirectlightningstrikehits20ftfromthephaseconductor.Calculatethe distancebetweenthelightningarresterssothata20KAlightningstrikeof8/20secwill notcausethelinetoflashover.RepeattheinterL.A.distanceifthewaveshapeassumes 4/10s. V=20.h.k.Ia/y;whereVisthevoltagethatwillcauseaflashover=400KV,k=1.2,histhe heightofconductorfromgroundlevel=40ft,yisthedistanceofthestrokefromtheconductor, Iaisthestrokecurrent. Ia=400(20)/20(1.2)(40)=8.33KA Assumea200ohmlinesurge(characteristics)impedance,voltagebuildupatpointofhitting= Z(I)/2=200(20)/2=2000KVpeak Thevoltagerisestopeakvaluein8s.Thustherateofriseofthiswave= 2000/8=250KV/s. Theinsulationlevelof400KVisreachedin400/250=1.6s. Thedistancebetweenarresters=1.6(.9)(984)/2=700ft Thedistancefor4/10swave=350ft SUMMARY: Inthischapterthelinedisturbanceswerepresented.Thetypes,sources,effectsonthe equipmentinthepowersystemsandthemetigationmethodsofsteadystateandtransient disturbancesweregiven.Theindicatorsthatmaybeusedinevaluatingoranalyzingthequality ofpowertobeexpectedatanylocationwerelisted.Thestandardsthatgovernthedesignofthe equipmentinordertominimizetheirdangereouseffectsofpumpingharmonicsorcausing voltagenotcheswerelisted.Thestandardsthatgoverntheprotectingdevicesthatwouldprotect theequipmentfromtheeffectsofsuchdisturbanceswerealsogiven.Also,themajorelements ofanofficeautomationsystemwerepresented.Theseelementscangeneratedirtypowerorbe affected(itselectroniccomponents&devices)fromdirtypowergeneratedelsewhereinthe interconnectedpowersystem.Thefirstofthelasttwonumericalexamplesshowedtheeffectof theapplicationoflocalcapacitorswithmotors.Capacitorswillimprovethep.f.andwill increasethecapacityofthefeedercircuit.Thesecondnumericalexamplequantifiedinasimple mannertheeffectofandtheflashoverlevelsofindirectanddirectlightninigstrokes. References:

1. Greenwood,Allan"Electricaltransientsinpowersystems",Wiley. 2. Wadhwa,C.L."Electricalpowersystems",Wiley. 3. IEEE"Recommendedpracticeforpowersystemanalysis",std399. Home page of VePi

Lesson5:Powersystemsstudies. 1) Whatarethegeneralrequirementsforanypowersystemsstudy? 2)WhatarethedatarequiredtoperformTRVcalculations? 3)Whatarethedatarequiredtoperformastabilitystudy? 4)Whatarethedatarequiredtoperformfaultcalculations?Toperformacoordinationstudy, whataretherequireddata? 5)Whatarethedatarequiredtoperformloadflowstudies?Whataretheiterativemethodsthat maybeusedinthecalculations? 6)Whataretherequireddataforswitchingtransientsstudies? 7)Whatarethedifferenttypesofmotorstartingstudies?Whatarethereequireddatatoperform suchstudies? 8)Whatarethemajorcomponentsinanindustrialsystemreliabilitystudy?Whatarethe requireddatatoperformsuchstudiesandwhatistheoutcome? 9)Whatarethecomponentsofadistributionutilitysystem?Whataretherequireddataandwhat istheoutcomeofsuchstudies? 10)Whatarethegeneraldatarequiredtoperformsteadystateandtransientstatestability calculations? 11)Whatarethebuildingblocksofanelectricalpowersystemsstudiesinformationsystem? 12)Asolvedproblemregardingtheprinciplecalculationsinvolvedwhenanalyzingapower distributionsystem. 13)Whataretheessentialcomputerprogramsforthepowersystemsanalyst? Lessonsummary References 1)Whatarethegeneralrequirementsforanypowersystemsstudy? Thegeneralrequirementsthatarecommonforallpowersystemsstudyare:thesingleline diagramfortheplant(orpartof)understudy,therating/type/makeforallsystemelements withinthestudyboundaries,anyavailabletestreportsormanualsandtheelementary (schematic)orconnection(wiring)diagrams. 2)WhatarethedatarequiredtoperformTRVcalculations? ThedatarequiredtoperformaTRVstudyare:theeffectiveinductancesandcapacitancesatthe TRVfrequencies(fromthenominalvoltagefrequency)forbushings,buses,powerand instrumenttransformersnearthecircuitbreakertobeswitched;thenumberoflinesorcables connectedtothebusatthetimeoffault,theirequivalentsurgeimpedance,length,termination andinterconnection;thetypeoffault,magnitudeoffaultcurrentandthevaluescontributed fromthelocalsources. 3)Whatarethedatarequiredtoperformastabilitystudy? Thedatarequiredtoperformastabilitystudyare: _Systemdata:impedanceoflines,cables,reactorsandanyotherseriescomponents;KVA

rating,impedance,voltageratings,ratio,windingconnection,availabletaps,typeoftapchanger controlandtapstepsize;shortcircuitcapacityofutilitysupply,KVARofcapacitorbanks (majorones);descriptionofnormalandemergency(contingency)switchingarrangements. _Loaddata:realandreactiveloadsonallsignificantloadbusesinthesystem. _Rotatingmachinedata:mechanicalandelectricalpowerratings,inertiaconstantofallrotating parts,speed,active/reactivepower(forgenerators)orspeed/torquecharacteristics(ifmotor),no load/airgapandlockedrotorcharacteristicscurves,reactancesandtimeconstants, damping/excitation/governor/steamsystems(ifapplicable)limitsandtimeconstraintsformajor synchronousmachines.Forminorsynchronousmachines,thefollowingdatawouldberequired: mechanical/electricalpowerratings,inertiaspeedanddirectaxissynchronousreactance.For majorinductionmachines,therequireddataare:mechanical/electricalratings,inertia,load speedtorquecurves,positiveandnegativesequencecircuitdataanddescriptionofmotor startingarrangements.Forminorinductionmachinetherequireddataarethe electrical/mechanicalpowerthesequenceequivalentimpedancecircuitandstarting arrangements(ifany). _Typeofdisturbancestobestudiedforexample:initialswitchingstatus,faultconditions,other switchingoperations.Thelimitsofacceptablevoltage,currentsandpowerswingsarealso importantforsuchstudies.Protectiverelaysdata,settingandoperatingtimes/includingclearing timeofswitchingdevicesarealsorequiredtocomparewiththestudyoutcometoverifythe transientstabilitystateforthespecificoperation(condition). 4)Whatarethedatarequiredtoperformfaultcalculations?Toperformacoordination study,whataretherequireddata? Thedatarequiredtoperformfaultcalculationsare:thepositive/negative/zerosequence impedancesofthesystemunderstudy,toachievethisrequirementthefollowingdatahavetobe available:size,lengthandmethodoflayingforallcablesinthesystemunderstudy,the overheadconductorssize,typeandconfiguration,transformersKVA/impedance(withits base)/tapchangerlimitsandstepsize/impedancepertapstep/primaryandsecondary voltage/methodofneutralgroundingandpertinentdata,fortheinductionorsynchronous motors:therating/subtransientreactance/transientreactance/speed/XtoRratio,thecurrent limitingreactors(ifany). Forthecoordinationstudythefollowingdataareessential:therelayscurrenttime characteristicscurves,fusestotalclearingtimecurrent/minimummeltingtimecurrent characteristicscurves,totalavailable3phaseshortcircuitcurrentinthesystem,damagecurves forcables/transformers,inrushcurrentstoinductionmotorsandtheirdurations,inrushcurrent fortransformersandduration,relaysburdendata,instrumenttransformers saturation/excitation/accuracy/ratio/tapsnumberandratiosdata. 5)Whatarethedatarequiredtoperformloadflowstudies?Whataretheiterative methodsthatmaybeusedinthecalculations? Thepertinentdatarequiredforloadflowstudiesare:forgenerators:active(real)powerandthe maintained(constant)voltage,forloads:therealandreactivepower(scheduledandconstant

overtheperiodofthestudy),fortheslackbus:thevoltageandphaseangleatthebus(bothare keptconstantovertheperiodofthestudy),theadmittancematrixofthemodellednetwork(this willincludetheadmittanceofinterconnectingpowerlinesandtheshuntbranches),forthe transformers:ratings,tapstepsandnumber(ifapplicable). Anyofthefollowingiterativemethodsmaybeused:GaussSeidel,NewtonRaphsonorFast decoupledmethod. 6)Whataretherequireddataforswitchingtransientsstudies? Therequireddataforswitchingtransientsstudiesare: _Utilityinformation:seriesresistanceandreactance,zerosequenceand+vesequenceparallel capacitance,minimumandmaximumavailableandfutureshortcircuitlevels,maximumand minimumvoltagesandoperationdescription/reclosingprocedure. _Transformersdata:ratings,connections,windingsarrangementdetails,tapchangersdetails, (steps,limits),leakagereactanceandresistance(+veandzerosequence),noloadvoltagevs excitingcurrent,basevoltage/current,neutralgroundingdetails. _Capacitordata:MVARormicrofarad,voltagerating,connections,neutralgroundingdetails, switchingdevicedetails,tunningreactorsdata(ifapplicable). _Cablesandconductors:length,size,arrangement,conduitdetails,insulation/shield/sheath details. _Surgearresters:location,ratings. _Groundingresistors:ratingsimpedance. _Reactors:ratings,impedance(foralltaps). _Rotatingmachines:regulatortype(ifapplicable)andsubtransient/transientreactances. _Operatingmodes:sequenceandconditionofeachoperationofswitchingdevices,actionof protectiveschemeagainstovervoltageandundervoltage. 7)Whatarethedifferenttypesofmotorstartingstudies?Whatarethereequireddatato performsuchstudies? Thedifferenttypesofmotorstartingstudiesare:voltagedrop(snapshot),detailedvoltage profile(timedependentbusvoltageanalysis)andmotortorque/accelerationtimeanalysis. Thedatarequiredmayvaryfunctionofthedegreeofthedetail(thedepth)ofthestudy:utility andgeneratorimpedances,transformersimpedance,cablessizes/number/material/conduit type/reactance/resistance,overheadconductorssizes/type/quantity/material/resistanceand reactance,loadtype(constantimpedanceorapparentpowerorcurrent)/powerfactor/load factor/inrushcharacteristics,loadandmotorrotatingpartsinertia,inertiaofmechanical couplingoranygearing,speedtorquecharacteristicsofbothmotorandload,speedvscurrent andpowerfactorcurves. 8)Whatarethemajorcomponentsinanindustrialsystemreliabilitystudy?Whatarethe requireddatatoperformsuchstudiesandwhatistheoutcome? Themajorcomponentsthatmaybeincludedinareliabilitystudyforanindustrialsystemare: m.v.circuitbreakers,m.v.disconnectswitches,powerordistributiontransformers,underground cablesandcablesplices,cableterminations,lowvoltagecircuitbreakers,lowvoltageand

mediumvoltageswitchgearassemblies(withinsulatedoruninsulatedbus)andutilityservice. Thedatarequiredtoperformareliabilitystudyare:thefailurerates(failuresperyear)andhours ofdowntime/failureforeachequipmentorcomponentincludedinthestudy.Theoutputhasto beanumberproportionaltotheforcednumberofhoursofdowntimeperyearforthesystem understudy. 9)Whatarethecomponentsofadistributionutilitysystem?Whataretherequireddata andwhatistheoutcomeofsuchstudies? Themajorcomponentsthatcanbeconsideredinadistribution,utility,systemare:thepower transformerinthetransformerstation,thehighvoltagedisconnectswitch,themediumvoltage circuitbreakersandswitchgearassemblies,theinsulators,thecableterminations,theoverhead conductors/undergroundcablesandsplices,thepadmountedswitchgearandthedistribution transformers.Thedatarequiredtoperformareliabilitystudyforsuchasystemare:thenumber oftaps(branches)offthemainfeeder,thenumberofsegmentsperlineortap,thelengthper segment,theexposurefactorpersegment,theconductorfactorpersegment,theupstream device(fuse,breaker,recloser,sectionalizer)factorforeachsegmentandtheweightednumber ofcustomersinterruptedwhenthesegmentfails.Also,thefollowingdataarerequired:number offailuresperyearandnumberofhoursperfailureforeachcomponentsinthesystemincluding theoverheadandundergrounddistributionnetwork.Theoutputwillhavetwotypesofnumbers oneproportionaltotheannualinterruptiontimeandthesecondproportionaltocustomerhours ofinterruption. 10)Whatarethegeneraldatarequiredtoperformsteadystateandtransientstate stabilitycalculations? Forasteadystatestability(i.e.beforeafaultconditionorswitchingoperation,forexample),the datarequiredare:thevoltageatbothbusesthathavethepowerflowinginbetween,the impedanceofthelineandtheangledifferencebetweenthetransmittingandreceivingbuses. Thefollowingdatawouldberequiredtoperformatransientstatestabilitystudy: _Duringswitchingorfaults:poweroutofgenerator,selfconductanceofbuses,transfer admittancebetweenalltheconnectedbuses,angulardisplacementofeachtwoadjacentbuses (machinesorinfinitebus),resistanceandreactancebetweeneachtwoconnectedbuses,the generatorconstants(ifapplicable). _Postfaultclearing:thesamedataasforduringthefaultcondition. 11)Whatarethebuildingblocksofanelectricalpowersystemsstudiesinformation system? Theinformationsystemthatisusedtoperformpowersystemsstudiesmusthave(butnotlimited to):reliabilitydata(failuresandhours/failurefordifferentequipment,typicalreactancevalues forinductionandsynchronousmachines,resistanceandreactancevaluesofCopperand Aluminumconductors,reactancevaluesoftypical3phasecablecircuitsindifferentconduit materials,X/R