Chapter23ImprovementofsystemstabilitymarginsusingcoordinationcontrolofStaticVarCompensator(SVC)andThyristorControlledSeriesCapacitor(TCSC)

VenuYarlagadda,K.R.M.RaoandB.V.SankarRam

AbstractTheThyristorControlledSeriesCompensator(TCSC)andStaticVarCompensator(SVC)arevariableimpedanceFlexibleACTransmissionSystems(FACTS)Controllers.AcombinationoftheTCSCandtheSVCinstallationisproposedtoacquiresuperiorperformanceforthepowersystem.ThecoordinationbetweenthetwopiecesofequipmentisdesignedwiththeSVCtreatedasthesupplementoftheTCSC.WhenoperationoftheTCSCisconstrainedbytheinherentlimitationofequipment,suchasduetothefiring-anglelimitationofthethyristors,theadjustableSVCcansupplytheauxiliarysupporttoimprovetheoverallperformance.ThevoltageandanglestabilitymarginscanbegreatlyimprovedwiththecompatiblecontrolschemesoftheTCSCandtheSVC.

KeywordsTCSCÁSVCÁCo-ordinationcontrolofSVCandTCSCÁDesignof

smallscaleTCSCmodelÁVariableimpedanceFACTScontrollersÁSinglemachinetwobussystemÁVoltagestabilityÁP–VcurvesandP-dcurves

V.Yarlagadda(&)EEEDepartment,VNRVJIET,Hyderabad,Indiae-mail:venuyar@gmail.com

K.R.M.RaoEEEDepartment,MJCET,Hyderabad,India

B.V.SankarRamEEEDepartment,JNTUH,Hyderabad,India

V.V.Das(ed.),ProceedingsoftheThirdInternationalConferenceonTrendsinInformation,TelecommunicationandComputing,LectureNotesinElectricalEngineering150,DOI:10.1007/978-1-4614-3363-7_23,ÓSpringerScience+BusinessMediaNewYork2013

20723.1IntroductionVoltagestabilityimprovementdemandsdifferenttechniques,fixedcompensationandthevariablecompensation.FACTScontrollerswhicharethevariablecom-pensationdevicesarebeingusedformoreeffectiveresults.Inthispaper,thecoordinationcontrolofThyristorControlledSeriesCapacitor(TCSC)andStaticVarCompensator(SVC)isimplementedpracticallyinthelaboratory.TheTCSCisusedasanauxiliarycontrollerandSVCisusedastheMastercontrollerbywhichtheStabilityMarginshavebeenenhancedtremendouslywhichhasbeenprovedbytheP–VandP-dcurvesandbarcharts.

23.2PowerSystemStabilitySuccessfuloperationofapowersystemdependslargelyontheengineer’sabilitytoprovidereliableanduninterruptedservicetotheloads.Thereliabilityofthepowersupplyimpliesmuchmorethanmerelybeingavailable.Ideally,theloadsmustbefedatconstantvoltageandfrequencyatalltimes.Inpracticaltermsthismeansthatbothvoltageandfrequencymustbeheldwithinclosetolerancessothattheconsumers’equipmentmayoperatesatisfactorily.

23.3StabilityIndices23.3.1P-VCurveAsthepowertransferincreases,thevoltageatthereceivingenddecreases.Finally,thecriticalornosepointisreached.Itisthepointatwhichthesystemreactivepowerisoutofuse.Thecurvebetweenthevariationofbusvoltageswithoutputpower(P)iscalledasP–Vcurveor‘Nose’curve.PVcurvesareusedtodeterminetheloadingmarginofthepowersystem.Themarginbetweenthevoltagecollapsepointandthecurrentoperatingpointisusedasvoltagestabilitycriterion.

23.3.2P-dCurveTherelationbetweeninputpowerandtheloadangleiscalledpoweranglecharacteristics.Theequationisgivenby,P=EVsind/X.ThesteadystatestabilitylimitisEV/Xanditoccursat90°.

208V.Yarlagaddaetal.23.4ThyristorControlledSeriesCapacitorAcapacitivereactancecompensatorwhichconsistsofseriescapacitorbankshuntedbyathyristorcontrolledreactorinordertoprovideasmoothlyvariableseriescapacitivereactance.ATCSCisaseries-controlledcapacitivereactancethatcanprovidecontinuouscontrolofpowerontheaclineoverawiderange.Fromthesystemviewpoint,theprincipleofvariable-seriescompensationissimplytoincreasethefundamental-frequencyvoltageacrossanfixedcapacitor(FC)inaseriescompensatedlinethroughappropriatevariationofthefiringangle,a.AsimpleunderstandingofTCSCfunctioningcanbeobtainedbyanalyzingthebehaviorofavariableinductorconnectedinparallelwithanFC.Theequivalentimpedance,Zeq,ofthisLCcombinationisexpressedasTheimpedanceoftheFCalone,however,isgivenby—j(l/xC).IfxC-(l/xL)[0or,inotherwords,xL[(1/xC),thereactanceoftheFCislessthanthatoftheparallel-connectedvariablereactorandthatthiscombinationprovidesavariable-capacitivereactancearebothimplied.

23.5DesignofThyristorControlledSeriesCapacitorConsidertheLinereactanceofthetransmissionlineinperunitsystem.For50%compensation,thevalueofthecapacitorintheTCSCwillbe50%ofthelinereactance.Nowforcapacitivecompensation,thevalueofinductivereactancemustbegreaterthancapacitivereactance,thatis,Xl[Xc

Xtcsc¼XlÃXcðÞ=XlÀXcðÞð23:1Þ

TotalreactanceofthelinewithTCSCisX¼XlÀXtcscð23:2Þ

Qtcsc¼IcÃIcÃXcðÞÀItcrÃItcrÃXlðÞð23:3ÞThevariationofreactivepowerdemandwithloadvariationsareobtainedasNow,ifQdmin=minimumreactivepowerdemand,Qdmax=maximumreac-