岑华蒙毕业设计外文翻译SVC与STATCOM在电力系统中应用的效益.docx

岑华蒙毕业设计外文翻译SVC与STATCOM在电力系统中应用的效益.docx

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岑华蒙毕业设计外文翻译SVC与STATCOM在电力系统中应用的效益

广西科技大学

毕业设计外文翻译

院别电气与信息工程学院

专业电气工程与自动化

班级电气101班

学号201000307027

姓名岑华蒙

指导教师周晓华

2013年12月28日

BenefitsofSVCandSTATCOMforElectric

UtilityApplication

Abstract--ExaminationofthebehaviorofSVCsandSTATCOMsinelectricpowersystemsispresented.Thepaperisbasedonanalyticalandsimulationanalysis,andconclusionscanbeusedaspowerindustryguidelines.

WeexplaintheprinciplestructuresofSVCsandSTATCOMs,themodelsfordynamicstudies,andtheimpactofthesedevicesonsteadystatevoltageandtransientvoltagestability.SensitivityanalysisisprovidedwhichshowstheimpactofSVCsandSTATCOMswithregardtonetworkstrength.Harmonicissues,spacerequirements,andpricediscussionsarealsobrieflyaddressed.

IndexTerms—DynamicCompensators,SVC,STATCOM,ShortCircuitCapacity,GainSensitivity,ShortTermVoltageStability,Harmonics

I.INTRODUCTION

SHUNT-connectedstaticvarcompensators（SVCs）areusedextensivelytocontroltheACvoltageintransmissionnetworks.Powerelectronicequipment,suchasthethyristorcontrolledreactor（TCR）andthethyristorswitchedcapacitor（TSC）havegainedasignificantmarket,primarilybecauseofwell-provenrobustnesstosupplydynamicreactivepowerwithfastresponsetimeandwithlowmaintenance.

Withtheadventofhighpowergateturn-offthyristorsandtransistordevices（GTO,IGBT,…）anewgenerationofpowerelectronicequipment,STATCOM,showsgreatpromiseforapplicationinpowersystems[3,4].

ThispaperaimstoexplainthebenefitsofSVCsandSTATCOMsforapplicationinutilitypowersystems.InstallationofalargenumberofSVCsandexperiencegainedfromrecentSTATCOMprojectsthroughouttheworldmotivatesustoclarifycertainaspectsofthesedevices.

II.BASICDESCRIPTION

ThissectionexplainsbrieflythebasicconfigurationofSVCsandSTATCOMs:

A.SVC

Thecompensatornormallyincludesathyristor-controlledreactor（TCR）,thyristor-switchedcapacitors（TSCs）andharmonicfilters.Itmightalsoincludemechanicallyswitchedshuntcapacitors（MSCs）,andthenthetermstaticvarsystemisused.Theharmonicfilters（fortheTCR-producedharmonics）arecapacitiveatfundamentalfrequency.TheTCRistypicallylargerthantheTSCblockssothatcontinuouscontrolisrealized.Otherpossibilitiesarefixedcapacitors（FCs）,andthyristorswitchedreactors（TSRs）.Usuallyadedicatedtransformerisused,withthecompensatorequipmentatmediumvoltage.Thetransmissionsidevoltageiscontrolled,andtheMvarratingsarereferredtothetransmissionside.

TheratingofanSVCcanbeoptimizedtomeettherequireddemand.Theratingcanbesymmetricorasymmetricwithrespecttoinductiveandcapacitivereactivepower.Asanexample,theratingcanbe200Mvarinductiveand200Mvarcapacitive,or100Mvarinductiveand200Mvarcapacitive.

B.STATCOM

Thevoltage-sourcedconverter（VSC）isthebasicelectronicpartofaSTATCOM,whichconvertsthedcvoltageintoathree-phasesetofoutputvoltageswithdesiredamplitude,frequency,andphase.

Therearedifferentmethodstorealizeavoltage-sourcedconverterforpowerutilityapplication.Basedonharmonicsandlossconsiderations,pulsewidthmodulation（PWM）ormultipleconvertersareused.

Inherently,STATCOMshaveasymmetricalratingwithrespecttoinductiveandcapacitivereactivepower.Forexample,theratingcanbe100Mvarinductiveand100Mvarcapacitive.Forasymmetricrating,STATCOMsneedacomplementaryreactivepowersource.ThiscanberealizedforexamplewithMSCs.

VII.THEFUNCTIONALRATINGCONCEPT

Traditionally,SVCsofacommondesignhavebeenusedtohandledifferenttypesofnetworkproblems.Thetrendtoday,however,istotailorSVCsfortheirintendeduse.ThisisimportantinordertomakeSVCscostefficient.

Forsteadystatevoltagesupport,i.e.,tofollowthedailyloadpattern,bulkreactivepowercombinedwithsteplesssmoothvoltagecontrolisdesired.VerniervoltageregulationcanbeprovidedbyaTCRrunninginparallelwithharmonicfilters.Thebulkreactivepowerisprovidedbymechanicallyswitchedcapacitorbanks（MSCs）orreactors（MSRs）governedbytheSVCcontroller.ThusSVCsservethepurposeofcontinuouslymaintainingasmoothvoltage,pilotingtheMSCswitching.

Ifthetaskistosupportasystemlimitedbypostcontingencyvoltageinstabilityorunacceptablevoltagelevels,alargeamountofquicklycontrollablereactivepowerisneededforashorttimeduration.AnSVCwithadditionalTSCsisanexcellentchoice.Postrecoveryvoltagesupportmayalsobenecessary—thisisthenpreferablyprovidedbyMSCsgovernedbytheSVC.

Fortemporaryovervoltages,largeinductivereactivepowerisneededforashortperiodoftime.ThestandardTCRhassomeshort-timeovercurrentcapability.Thiscapacitycaneasilybeextendedbyloweringitssteadystateoperatingtemperatureandby“undersizing”thereactors.

A.EnhancedSVCs

TheSVCcharacteristicatdepressedvoltagecanbeefficientlyimprovedbyaddinganextraTSC.Thisbranchisintendedtooperateonlyduringundervoltageconditions.ItcanbeaddedwithoutintroducingadditionalcostinotherpartsoftheSVC.Mostimportantisthatthecurrentratingorthevoltagecapabilityofthepowertransformerdoesnotneedtobeincreased.Powertransformersallowlargeovercurrentduringlimitedtime（IEEEC57-115canbeusedasaguideforavailablecapacity）.Inmanycasesthreetimesoverloadincurrentfor10secondsisavailable.TheadditionalTSCratingistypicallyintherangeof50to100%oftheSVCrating.

B.SVCShortTermOverload

ThemaximumpowerfromanSVCatagivenvoltageisdeterminedbyitsreactance.Nooverloadcapacityisavailableunlessthereactanceislowered,e.g.,byaddingaTSC.Forovervoltages,however,theSVCreactanceisnolongerthelimitingfactor;insteadthecurrentincomponentsdefinesthelimit.Inmostcasesthethyristorssetthelimit.Thedesignismadesothatthethyristorsarerunningatamaximumallowedtemperatureatmaximumsteadystatesystemvoltage.Amargintodestructivetemperaturesisreservedinordertohandlefaultcases.TheForbes500kVstaticvarsystemnearDuluthMinnestoaUSAisaninterestingexampleofanEnhancedSVC[5].

VIII.HARMONICS

BothSVCsandSTATCOMsgenerateharmonics.TheTCRofanSVCisaharmoniccurrentsource.Networkharmonicvoltagesdistortionoccursasaresultofthecurrentsenteringthepowersystem.TheSTATCOMisaharmonicvoltagesource.NetworkvoltageharmonicdistortionoccursasaresultofvoltagedivisionbetweentheSTATCOMphaseimpedanceandthenetworkimpedance.

ThemajorharmonicgenerationinSVCsisatlowfrequencies;abovethe15thharmonicthecontributionisnormallysmall.Atlowerfrequenciesthegenerationislargeandfiltersareneeded.SVCsnormallyhaveatleast5thand7thharmonicfilters.Thefilterratingisintherangeof25–50%oftheTCRsize.

STATCOMswithPWMoperationhavetheirmajorharmonicgenerationathigherfrequencies.ThemajorcontributionsareatoddmultiplesofthePWMswitchfrequency;atevenmultiplesthelevelsarelower.Theharmonicgenerationdecayswithincreasingfrequency.STATCOMsmightalsogenerateharmonicsinthesamespectraastheconventionalSVCs.Themagnitudesdependonconvertertopologyandthemodulationandswitchingfrequencyused.InmostcasesSTATCOMsaswellasSVCsrequireharmonicfilters.

IX.FOOTPRINT

MoreandmorefrequentlythefootprintavailableforprospectiveSTATCOMsorSVCsisrestricted.Thetrendis,asinmanyotherfields,morecapacityonlessspace.Requirementsforextremelytightdesigns,however,resultinhighercosts.IngeneralthefootprintissueseemsnottohindertheutilizationofSTATCOMsorSVCs,butoccasionally,STATCOMhasbeenpreferredbasedonanticipatedsmallerfootprint.

WhencomparingSVCswithSTATCOMs,itistemptingtoassumethatthelatterwillfitwithinamuchsmallerfootprint,asthepassivereactiveelements（aircorereactorsandhighvoltagecapacitorbanks）are“replaced”withsemiconductorassemblies.Intheauthors’opinion,thisassumptionhoweverremainstobepracticallyproved.ThemainreasonforthisisthatthevoltagesourcedconverterconceptsappliedinSTATCOMstodatehavebeenbuiltwithseveral（evenasmanyaseight）inverterbridgesinparallel.Thisdesignphilosophyimpliesmanycurrentpaths,highfaultcurrentsandcomplexmagneticinterfacesbetweentheconvertersandthegrid.Allinall,notallSTATCOMscomeoutasdownsizedcomparedtoSVCs.AlsothehigherlossesintheSTATCOMwillrequiresubstantiallylargercoolingequipment.However,astheSTATCOMtechnologyevolves,includingtheuseofverycompactinverterassemblieswithseriesconnectedsemiconductordevices,andwithpulsewidthmodulation,thereisadefinitepotentialfordownsizing.

InthecaseofSVCs,theindustryhasalongproductdevelopmentwhere,whennecessary,measureshavebeentakentodownsizetheinstallation.Suchmeasuresincludeelevateddesignofapparatuses,stackingofcomponents（reactorsandcapacitors）,verticalorientationofbusbarsanduseofnon-magneticmaterialinnearbystructures.Inafewextremecasesironcorereactorshavebeenutilizedinordertoallowinstallationinverytightpremises.InadditionthedevelopmentofmuchhigherpowerdensityinhighpowerthyristorsandcapacitorscontributestophysicallysmallerSVCs.

X.LIFECYCLEOREVALUATEDCOSTS

Itistheauthors’experiencethattheinvestmentcostofSVCsistodaysubstantiallylowerthanofcomparableSTATCOMs.AsSTATCOMsprovidesimprovedperformance,itwillbethechoiceinthecaseswherethiscanbejustified,suchas