CapacitiveCurrentInterruptionwithHighVoltageAirbreakDisconnectors

PROEFSCHRIFT

terverkrijgingvandegraadvandoctoraandeTechnischeUniversiteitEindhoven,opgezagvanderectormagnificus,prof.dr.ir.C.J.vanDuijn,vooreen

commissieaangewezendoorhetCollegevoorPromotiesinhetopenbaarteverdedigenopwoensdag14maart2012om16.00uur

door

YajingChai

geborenteHubei,China

Ditproefschriftisgoedgekeurddoordepromotor:prof.dr.ir.R.P.P.SmeetsCopromotor:dr.P.A.A.F.WoutersThisprojectwasfundedbytheDutchMinistryofEconomicAffairs,AgricultureandInnovationinanIOPEMVTprogram.AcataloguerecordisavailablefromtheEindhovenUniversityofTechnologyLibrary.ISBN:9789038630977

ToMiloandRuirui

Promotor:prof.dr.ir. R.P.P. Smeets, Eindhoven University of Technology/KEMATesting,Inspections&CertificationCopromotor:dr.P.A.A.F.Wouters,EindhovenUniversityofTechnologyCorecommittee:prof.ir.L.vanderSluis,DelftUniversityofTechnologyprof.dring.V.Hinrichsen,DarmstadtUniversityofTechnologyprof.dr.E.Lomonova,EindhovenUniversityofTechnologyOthermembers:dr.D.F.Peelo,DFPeelo&Associatesprof.ir.W.L.Kling,EindhovenUniversityofTechnologyprof.dr.ir.A.C.P.M.Backx(chairman),EindhovenUniversityofTechnology

Summaryi

SummaryAs lowcost switching devices in high voltage electrical power supply systemdisconnectorsbasicallyhaveaninsulationfunctiononly.Nevertheless,theyhaveavery limited capability to interrupt current (below one Ampere), e.g. fromunloaded busbars or short overhead lines. The present study is a search forpossibilitiestoincreasethecurrentinterruptioncapabilitywithauxiliarydevicesinteracting with the switching arc. In this project the state of the art ofdisconnectorswitchingisinvestigatedandaninventoryispresentedofmodelsofthe free burning arc in air. A series of experiments were arranged at differentlaboratories.Theswitchingarcandtheinterruptionprocessarestudiedindetailthrough electrical andopticalmeasurements during the switchingprocess for adisconnector with (without) auxiliary devices under high voltage (0.5 30A,300kV)conditions.Threeoptionsforauxiliarydeviceswereinvestigated:(i)arccoolingbyforcedairflow;(ii)fastinterruptingbyhighvelocityopeningcontacts;(iii) reduction of arc energy by adding resistive elements. Finally, a qualitativedescription isprovidedon thephysicalnatureof thearcandhowtheevaluatedmethodsaffectthearccharacteristics.Allresultsareobtainedbyanalysisofhighresolutionmeasurementofarccurrent(includingallrelevanttransients),voltagesacrossthedisconnectorandhighspeedvideoobservation.Itwas found that, depending on the current to be interrupted, the interruptionprocessisgovernedbythedielectricand/orthermalprocesses.In thedielectric regime, the interrupted current is low (roughlybelow1A) andtheswitchingarcischaracterizedbyahighrateofrepetitionofinterruptionsandrestrikesthatonlyceaseafterasufficientgapspacinghasbeenreached.Therestrikesinteractseverelywiththecircuitryinwhichthedisconnectorisembedded,exciting transients in current and voltagewith frequenciesup to themegahertzrange.Highovervoltagescanbegenerated.Theirmagnitudescanbelimitedbyaproperchoiceofthecapacitanceatsupplysideofthedisconnector.Thearccircuitinteraction has been studied and relevant processes have been modelled andverifiedbyexperimentsinfullpowertestcircuits.In the thermal regime, the switching arc behaves less vehemently, interruptingandreignitingbasicallyoccurateverypowerfrequencycurrentzero.Becauseofthepresenceofsufficientthermalenergyintheswitchinggapalongthearcpath,the voltage to reignite the arc is limited, and the arccircuit interaction is lesspronounced.Thoughnotproducingverysevereovervoltages, thearcdurationislongerandthecurrentmaynotbeinterruptedateverycurrentzerocrossing.Theultimate thermal regime is reachedwhen thearc continues toexist afterpowerfrequencycurrentzerowithoutanyappreciablevoltagetoreignite.Thissituation

iiSummary

mustbeavoidedbecausearcinggoesonuntilahigherlevelbreakerinterruptsthecurrent. Before this, the arc can reach far away from its roots and can greatlyreduceinsulationclearance.Themainfactorsinfluencingtheinterruptionperformancearethelevelofcurrenttobeinterrupted,thesystemvoltage,theratioofcapacitancesatbothsidesofthedisconnector and the gap length.These factors influence the energy supplied tothe arc upon restrike. This energy extends the arcing time by lowering thebreakdownvoltage.Ithasbeenobservedthatthearcinitsthermalmodealwaysreignitesinitsformertrajectory.Keytotheinterruptionprocessisthereductionofbreakdownvoltageinthispath,createdbyhotgasesremainingfromtheformerarc. The existing breakdown models are reviewed in order to understand theinfluenceofhightemperatureaironthebreakdownprocess.Basedon theobservedarcbehaviour,variousmethodshavebeenresearched toincreasetheinterruptioncapability.The most successful methods are those that remove the residual (partially)ionizedair from thearcpath.Experimentswere carriedout todemonstrate theeffectiveness of air flow directed into the arcs foot point. A substantial gain ininterruptioncapability isdemonstrated,butat thecostofgenerating reignitiontransients at a very rapid succession. Specifically, the experiments showed that7.5Acouldbeinterruptedsuccessfullyat90kVrmsvoltagewithashorterarcingduration(afactorof0.5wasobserved)thanwithoutairflow.Withapplicationofair flow, the frequencyof reignitionsoccurring, and thebreakdownvoltagearemuchhigherthanwithoutairflow.Anothermethod,theassistanceofanauxiliaryswitchabletoproduceaveryfastopening,wasalsosuccessful.Herein,thearcisforcedmechanically intoambientcoolair,thusavoidingaccumulationofthermalenergyinthearcpath.Specifically,itcaninterruptcurrentsupto7Aat100kVrmssafelyand9Aat90kVrmsintheexperiments with arcing time only a few tens of milliseconds instead of a fewseconds. The arc exhibits a "stiff" (linear) character instead of the "erratic"(randomlymoving)arcmodewithadisconnectoralone.Thismethodreducesthenumberofrestrikes.The possible influence of energy absorbing elements (resistors) is investigatedthrough circuit modelling, supported by some laboratory experiments. Othermethods, such as the application of series auxiliary interrupting elements(vacuum,SF6interrupterandablationassistedapproaches)havebeenevaluated.From the practical point of view, the auxiliary fastopening interrupter isrecommendedduetoitseconomic,simpleandeffectivemerits.Otherapproacheshave certain disadvantages. The method with air flow needs a complexconstructioninordertointroducethecompressedairflowintothedisconnector,

Summaryiiiand the hazard for nearby equipments from the overvoltages caused by theinterruption is greater.Themethodof inserted resistor requiresveryexpensivearrangement. Regarding the application of auxiliary interrupters, vacuuminterrupters have to be applied in considerable numbers in series and SF6interrupters have good performance but at very high cost. An ablation assistedapproachseemslesspromisingbecausetheleveloftheinterruptedcurrentistoolowtobeeffective.

ivSummary

Samenvattingv

SamenvattingScheidingsschakelaars, of kortweg "scheiders", zijn relatief eenvoudigeschakelaars inhoogspanningsnettendie inprincipeenkel een isolerende functiehebben.Nietteminbezittenzeeenzeerbeperktvermogenstromen(totca.1A)teonderbreken, zoals bijv. afkomstig van onbelaste railsystemen of kortehoogspanningslijnen. Deze studie bevat een onderzoek naar mogelijkheden hetstroomonderbrekendvermogenvanscheiderstevergrotenmethulpmiddelendiedirect ingrijpen inde schakelende lichtboog.Om tebeginnen isde standvandetechniekophetgebiedvanschakelenmetscheidersonderzochtenerwordteenoverzicht gegeven van het modelleren van vrij brandende lichtbogen in lucht.Tevensiseenserieexperimentenuitgevoerdindiverselaboratoria.Hierinzijndeschakelende lichtboog en het onderbrekingsproces in detail bestudeerd doormiddel van elektrische en optische metingen gedurende het schakelen onderhoogspanning (0.5 30A, 300kV) met en zonder hulpmiddelen. Drie mogelijkhulpmiddelen zijn onderzocht: (i) koeling van de lichtboog door beblazingmeteengeforceerdeluchtstroom;(ii)onderbrekingmetzeersnellecontactseparatiesnelheid; (iii) reductie van lichtboog energie door toevoeging van resistievecomponenten. Tot slot wordt een kwantitatieve beschrijving gegeven van delichtboog en hoe de boven beschreven methoden ingrijpen in diversekarakteristiekenvandelichtboog.Alle resultaten zijn verkregenmet behulp vanmetingenmet hoge resolutie vanlichtboog stroom en spanning (inclusief hun transinten) alsmede doorobservatiemetsnellevideotechnieken.Afhankelijk van de grootte van de te onderbreken stroom, wordt hetonderbrekingsprocesgekenmerktdoordilektrischeen/ofthermischeprocessen.Inhetdilektrischeregimeisdeteonderbrekenstroomklein(ruwwegbeneden1A) en de scheider lichtboog wordt gekenmerkt door een zeer snelleopeenvolgingvanonderbrekingenenherontstekingen.Ditprocesstoptwanneervoldoendecontactafstand isbereikt.Alsgevolgvandeherontstekingen isereenheftige wisselwerking met het elektrische circuit waar de scheider deel vanuitmaakt. Herontstekingen wekken daarbij transinten op in zowel stroom alsspanning met frequenties tot enkele megahertz. Hoge overspanningen kunnenhierbij optreden. De hoogte hiervan kanworden beperkt door een juiste keuzevan capaciteit aan de voedende zijde van de scheider. Dewisselwerking tussenlichtboog en circuit is bestudeerd; de relevante processen zijn gemodelleerd engetoetstmetexperimenteninhoogvermogenbeproevingscircuits.Inhet thermische regimegedraagtde lichtboog zichminderheftig, onderbreektde stroom en herontsteekt in principe pas op iedere nuldoorgang van denetfrequente stroom. Vanwege de aanwezigheid van voldoende thermische

viSamenvatting

energieinhetlichtboogpadtussendecontactenisdespanningnodigomdeboogte herontsteken beperkt en daarmee is de wisselwerking tussen lichtboog encircuit minder uitgesproken. Hoewel de overspanningen beperkt zijn, is delichtboogduur langer en wordt de stroom niet bij iedere netfrequentenuldoorgangonderbroken.Demeestuitgesprokenthermischeverschijningsvormis die waarin (bij verdere verhoging van de stroom) de lichtboog bij elkenuldoorgang herontsteekt zonder meetbare spanning. Deze situatie dientvermeden teworden omdat de lichtboog in deze situatie nietmeer dooft en destroom enkel nog door een vermogensschakelaar onderbroken kan worden.Hieraanvoorafgaandkande lichtboogveruitwaaierenende isolatieafstand totandere,onderspanningstaandedeleninhetstation(tezeer)verkleinen.Debelangrijkstefactorendiehetonderbrekingsprocesbenvloedenzijndehoogtevan de te onderbreken stroom, de netspanning, de verhouding van capaciteitenter weerszijden van de scheider en de momentane contactafstand. Dezeparameters bepalen de energie die aan de lichtboog wordt toegevoerd op hetmomentvanherontsteking.Dezeenergieverlengtdelichtboogduurdoordatdezededoorslagspanningreduceert.Uitwaarnemingblijktdatinhetthermischregimedelichtboogherontsteektinhetvoormaligelichtboogpad.Hieruitwordtafgeleiddat de essentie van het onderbrekingsproces de reductie van doorslagspanninglangs dit pad is. Deze reductie wordt veroorzaakt door hete gassen en restionisatieafkomstigvande(vorige)lichtboog.Voorhetbegrijpenvandeprocessendie leiden tot reductie van doorslagspanning bij temperatuur verhoging van deluchtzijndebestaandedoorslagmodellenbestudeerd.Op basis van de boven beschreven waarnemingen van het onderbrekingproceszijn diverse methoden onderzocht die kunnen leiden tot vergroting van hetstroomonderbrekendvermogenvanscheiders.Het meest succesvol zijn methoden die de gedeeltelijke geoniseerde luchtverwijderen uit het voormalige lichtboog pad. Experimenten zijn uitgevoerdwaarindeeffectiviteitbestudeerdwordtvanbeblazingvandevoetpuntenvandelichtboogmetkoude lucht.Eensignificanteverhogingvanstroomonderbrekendvermogen wordt inderdaad vastgesteld, echter ten koste van de generatie vanzeer snel opvolgende en hoge herontstekingen die steile spanningfrontengenereren.Deexperimententonenaandatbijeenfaseaardespanningvan90kVstromen tot ca. 7.5A succesvol onderbroken worden met een 50% korterelichtboogduurdanzonderbeblazing.Een andere methode bestaande uit het gebruik van zeer snel opendehulpcontacten om daarmee in zeer korte tijd een grote contactafstand terealiseren, blijkt eveneens succesvol. Op deze wijze worden de lichtboogvoetpunten zeer snel naar koele lucht getrokken waardoor een te grotethermischeenergiedichtheidvoorkomenwordt.Opdezemanierkunnenstromenvan 7A (bij 100kV) en 9A (bij 90kV) onderbroken worden, terwijl de

Samenvattingviilichtboogduur slechts enkele tientallen milliseconden bedraagt in plaats vanseconden bij toepassing van conventionele contacten. De uiterlijkeverschijningsvorm van de boog verandert hierbij van "dansend" (opwaartsbewegendmet veleuitstulpingen)naar "strak" (rechtlijnig brandend als kortsteverbinding tussende contacten).Het aantal herontstekingenblijft hiermeeookbeperkt.Ookdemogelijkeinvloedvanenergieabsorberendeelementen(weerstanden)isonderzochtmetmodellering,ondersteundmetenigelaboratoriumexperimenten.Alternatieven, zoals het gebruik van serie geschakelde onderbrekers (vacum,SF6onderbrekersenonderbrekinggebaseerdopablatie)zijngevalueerduitdeliteratuur.Ter vergroting van het stroom onderbrekend vermogenwordt vanuit praktischoogpuntdemethodemetdesnellehulpcontactenaanbevolenvanwegeprestatie,eenvoud en prijs. Andere methoden hebben duidelijke nadelen. Beblazing metlucht vereist een ingewikkelde constructie om gecomprimeerde lucht in denabijheidvandeschakelendecontactentebrengenenheeftalsbijkomendnadeeldegeneratievansteilespanningsfrontentijdensdeonderbreking.Hetaanbrengenvanweerstandenvereistdureaanpassingen.HulponderbrekersinvacumofSF6gasiseffectiefmaarkostbaarenconstructiefingewikkeldvanwegedehoogtevande spanning die serie schakeling van elementen vaak nodigmaakt. Oplossingenmet behulp van ablatie zijn minder kansrijk omdat de stroom hiervoorwaarschijnlijktelaagis.

viiiSamenvatting

Contentsix

Contents

SUMMARY..................................................................................................................................ISAMENVATTING.....................................................................................................................VCONTENTS..............................................................................................................................IXCHAPTER1...............................................................................................................................1HIGHVOLTAGEAIRBREAKDISCONNECTORS.............................................................1

1.1DEFINITIONOFDISCONNECTORS..................................................................................................11.2TYPEOFDISCONNECTORS..............................................................................................................11.3INTERRUPTINGCURRENTWITHDISCONNECTORS......................................................................31.4STANDARDIZATIONSTATUS...........................................................................................................41.5OBJECTIVEOFTHESIS.....................................................................................................................5

CHAPTER2...............................................................................................................................9LITERATUREREVIEW...........................................................................................................9

2.1AWARENESSOFTHECAPACITIVECURRENTINTERRUPTIONWITHDISCONNECTORS...........92.2FUNDAMENTALASPECTSOFCAPACITIVECURRENTINTERRUPTION....................................142.3TRANSIENTSCAUSEDBYCAPACITIVECURRENTINTERRUPTION..........................................162.4APPROACHESTOENHANCETHEINTERRUPTIONCAPABILITY...............................................172.5ARCMODELSRELATEDTOCURRENTINTERRUPTIONWITHADISCONNECTOR..................262.6CONCLUSION.................................................................................................................................29

CHAPTER3............................................................................................................................35BASICCIRCUITANALYSIS.................................................................................................35

3.1THEINTERRUPTIONPROCESS.....................................................................................................353.2THREECOMPONENTSANALYSIS................................................................................................373.3SIMULATIONOFRESTRIKES.......................................................................................................413.4RESTRIKETRANSIENTSINDISTRIBUTEDELEMENTLOADCIRCUITS...................................433.5CONCLUSION.................................................................................................................................45

CHAPTER4............................................................................................................................47EXPERIMENTALSETUP.....................................................................................................47

4.1HIGHVOLTAGESOURCE...............................................................................................................474.2MEASUREMENTSYSTEM..............................................................................................................514.3DISCONNECTORMAINBLADESOPENINGVELOCITY................................................................574.4CONCLUSION.................................................................................................................................59

xContents

CHAPTER5............................................................................................................................61CURRENTINTERRUPTIONMECHANISM.....................................................................61

5.1EXPERIMENTALOBSERVATIONS................................................................................................615.2ARCINTERRUPTIONCHARACTERISTICS....................................................................................695.3DISCONNECTORCONTACTSSPACING.........................................................................................755.4RESTRIKEVOLTAGE....................................................................................................................765.5ELECTRICALARCCHARACTERISTICS.........................................................................................805.6ENERGYINPUTINTOTHEARC....................................................................................................825.7TRANSIENTSUPONRESTRIKE...................................................................................................855.8CONCLUSION.................................................................................................................................885.9RECOMMENDATIONFORSTANDARDIZATION...........................................................................90

CHAPTER6............................................................................................................................91INTERRUPTIONWITHAIRFLOWASSISTANCE.........................................................91

6.1EXPERIMENTALSETUP................................................................................................................916.2EFFECTOFAIRFLOWONARCING...............................................................................................926.3INTERRUPTIONDATAANALYSIS.................................................................................................976.4CONCLUSION...............................................................................................................................103

CHAPTER7..........................................................................................................................107HIGHVELOCITYOPENINGAUXILIARYINTERRUPTER........................................107

7.1OPERATINGPRINCIPLE..............................................................................................................1077.2EXPERIMENTALSETUP..............................................................................................................1087.3OVERVIEWOFTHEEXPERIMENTALRESULTS........................................................................1097.4RESTRIKEVOLTAGE..................................................................................................................1147.5ENERGYINPUTINTOTHEARC..................................................................................................1177.6CONCLUSIONANDRECOMMENDATION...................................................................................120

CHAPTER8..........................................................................................................................123INTERRUPTIONWITHINSERTEDRESISTORS.........................................................123

8.1SERIESRESISTOR........................................................................................................................1238.2PARALLELRESISTOR..................................................................................................................1288.3DISCUSSION.................................................................................................................................130

CHAPTER9..........................................................................................................................133PREBREAKDOWNPHENOMENAINDISCONNECTORINTERRUPTION...........133

9.1CLASSICALMODELLINGOFBREAKDOWN................................................................................1339.2PREBREAKDOWNCURRENTINDISCONNECTORINTERRUPTION.......................................1379.3DISCUSSION.................................................................................................................................138

Contentsxi

CHAPTER10........................................................................................................................141CONCLUSIONSANDRECOMMENDATIONSFORFUTURERESEARCH...............141

10.1CONCLUSIONS...........................................................................................................................14110.2PROPOSEDFUTURERESEARCH..............................................................................................146

PUBLICATIONSRELATEDTOTHISWORK................................................................147NOMENCLATURE...............................................................................................................149ACKNOWLEDGEMENT.....................................................................................................153CURRICULUMVITAE........................................................................................................155

xiiContents

HighVoltageAirbreakDisconnectors1

Chapter1

HighVoltageAirbreakDisconnectors1.1DefinitionofdisconnectorsHigh voltage disconnectors are commonly used switching devices in powersubstations. According to the International Electrotechnical Vocabulary IEVnumber 4411405 [1], the definition of a disconnector (DS) is: "A mechanicalswitching device, which provides, in the open position, an isolating distance inaccordance with specified requirements". In IEEE standard C37.1001992 [2],insteadoftheterm"disconnector",theterms"disconnecting","disconnectswitch"or "isolator" are used, defined as "A mechanical switching device used forchangingtheconnectionsinacircuit,orforisolatingacircuitorequipmentfromthesourceofpower."Bothdefinitionsaresimilar.Theydefinethattheprinciplefunction ofDSs is to provide electrical and visible isolation from the system. Inaddition, theymust open and close reliably, carry current continuouslywithoutoverheating,andremainintheclosedpositionunderfaultcurrentconditions[3].Thedisconnectiongenerallycoverstwoaspects[4]: Disconnectionrelatedtoordinarydailyoperationofthesystem. Disconnection related to maintenance of transmission lines or substation

equipmentsuchastransformers,circuitbreakers,capacitorbanksandsoon.For power system, personnel safety practices normally require a visiblebreakasapointofisolation.AnopenDSmeetsthisrequirement.

1.2TypeofdisconnectorsDSs in Gas Insulated Substations are out of the scope of this thesis. Only highvoltageDSs in the atmospheric air are studied.TheHVairbreakDS comes inavariety of types and mounting arrangements. The most common fourconfigurations are: verticalbreak, centrebreak, doublebreak, and pantographtype. They can be mounted in various orientations, depending on the spaceofferedbythesubstation[3],[4].The verticalbreakDS is presented in Figure1.1 (left). This type ofDS is highlysuitableinicyenvironmentsthankstoitsrotatingbladesdesign.Itscontactdesignallows for application in installations where high fault current situations mayoccur.TheactivepartsofthistypeDSarethehingeendassembly,theblade,andthe jaw end assembly. The smaller of the two insulators at the left rotates andrives theblade to openor close. It is usually horizontallymounted as shown in

2Chapter1

Figure1.1. (left)AthreephaseverticalbreakDSmountedhorizontally inaclosedposition(CourtesyofHAPAMB.V.);(right)centrebreakDSinaclosedposition(CourtesyofSiemens).Figure 1.1 (left). It can also be vertically mounted, i.e. the blade is verticallyoriented in closed position. The verticalbreak DS requires minimum phasespacing.AnexampleofacentrebreakDSisillustratedinFigure1.1(right).ThistypeDSisused mainly in locations with low overhead clearances. However, it requireslarger phase spacing than a verticalbreak DS. The active parts consist of twoblades, disconnecting at the centre. Both insulators rotate in a vertical plane toopenorclosetheDS.AdoublebreakDSisavariationofacentrebreaktypeandisshowninFigure1.2(left). The active parts are two jaw assemblies, one at each end, and a rotatingblade.ThecentreinsulatorrotatestoopenorclosetheDS.Theycanbeinstalledinminimum overhead clearance locations and require minimum phase spacing.Their field of application includes icy environments due to the rotating bladesdesignandinstallationsinhighfaultcurrent locationsduetothecontactdesign.This design provides for two gaps per phase, allowing to interrupt significantlyhighercurrentthanthesinglebreaktypeDSs[3],[4].Thisisbecausethesystemvoltageisdistributedacrosstwogaps.ThepantographDStype,showninFigure1.2(right),isusedworldwide(butonlyoccasionally in North America) for Extra High Voltage application, 345800kV.Theactivepartsconsistofafixedcontactsarrangementattachedtothebusbaratthetop,ascissortypebladeandahingeassemblyatthebottom.Thesmalleroneof the two insulators rotates to open or close the DS. This type DS normallyprovides transitions from high to low busbars, together with providing visibleseparationatthesametime.Thismethodrequirestheleastspace.

HighVoltageAirbreakDisconnectors3

Figure 1.2. (left)DoublebreakDS in an open position; (right) pantographDS in a closedposition(CourtesyofHAPAMB.V).1.3InterruptingcurrentwithdisconnectorsDisconnectors disconnect unloaded circuits in order to accomplish visibleisolation. However, they are operated under energized conditions and willtherefore interruptsomecurrent.Themagnitudeof thiscurrentdependsonthespecificsituations.AlthoughDSsdonothaveanycurrentinterruptionrating,theydo have a certain interrupting capability, but it is limited due to their slowlymovingcontacts.OvertheyearsDSshavebeenappliedto interrupttransformerexcitation currents, capacitive currents from short lengths of bus, cable oroverhead line and small load currents. In this case, very small current isinterruptedagainstfullsystemrecoveryvoltage(RV).Anothermajorapplicationis bus transfer switching. In this case, often the full load current has to betransferredintoaparallelpath.BecauseofmanydifferentconditionsunderwhichtheDSsmustinterruptcurrents,nointerruptingratingsareassigned[5].Themainapplicationswhereacurrentistobeinterruptedare[4]: TransformermagnetizingcurrentIt isalsocalledexcitationcurrent.Thecurrentisusually lessthan2A,oftenlessthan 1A at 100% excitation voltage, for todays transformers. The current isgenerally described in terms of an equivalent RMS value derived from the corelossmeasurementbythemanufacturer. CapacitivecurrentThis current, also called charging current, arises from connected short busbars,short unloaded transmission line, instrument transformers and other elementshavingstraycapacitance.Theyactasacapacitiveload.ThetypicalrangeofthesecurrentsforstationairbreakequipmentisshowninTable1.1[6].

4Chapter1

Table1.1Typicalcapacitivecurrentrangeinoutdoorsubstations(50Hz).

LoopcurrentLoopsarecreatedwhen theDScommutesor transferscurrent fromonecircuit,suchasabusbaror transmission line, toaparallel circuit.The loopcurrent canreach up to the full load current in practice. This current has to be switchedagainstaverylowvoltage(thevoltageacrosstheparallelpath)[4].1.4StandardizationstatusA small current interruption capability of the DSs has been recognized by bothIEEE and IEC standards. In the IEC standard [7], apart from the definition andbasicfunctionoftheDS,thecurrentinterruptingcapabilityisaddressedinthreenotes:NOTE1: Adisconnector is capableofopeningand closinga circuitwheneithernegligiblecurrentisbrokenormade,orwhennosignificantchangeinthevoltageacrosstheterminalsofeachofthepolesofthedisconnectoroccurs.NOTE 2: "Negligible current" implies currents such as the capacitive currents of bushings,busbars,connections,veryshortlengthsofcable,currentsofpermanentlyconnectedgradingimpedancesofcircuitbreakersandcurrentsofvoltagetransformersanddividers.Forratedvoltagesof420kVandbelow,a currentnot exceeding0.5A isanegligible current for thepurposeof thisdefinition; forratedvoltageabove420kVandcurrentsexceeding0.5A, themanufacturershouldbeconsulted.NOTE3:Foradisconnectorhavingaratedvoltageof52kVandabove,aratedabilityofbustransfercurrentswitchingmaybeassigned.SimilarlyintheIEEEstandard[8],thefollowingnoteismade:NOTE:Itisrequiredtocarrynormalloadcurrentcontinuously,andalsoabnormalorshortcircuit currents for short intervalsas specified. It isalso required to open or close circuitseitherwhennegligiblecurrentisbrokenormade,orwhennosignificantchangeinthevoltageacrosstheterminalsofeachoftheswitchpolesoccurs.An earlier version of the IEEE standard did include the following note andindicatedthethreetypesofcurrentwithoutexplanation[9].

Equipment Capacitivecurrent(A)72.5kV 145kV 245kV 300kV 420kV 550kVCT 0.04 0.04 0.04 0.05 0.08 0.1CVT(4F) 0.05 0.11 0.18 0.22 0.3 0.4Busbars/m 1.7104 0.32103 0.54103 0.66103 0.84103 1.1103

HighVoltageAirbreakDisconnectors5

NOTE:Adisconnectingswitchandahorngapswitchhavenointerruptingrating.However,itisrecognizedthattheymayberequiredtointerruptthechargingcurrentofadjacentbuses,supports and bushings. Under certain conditions, theymay interrupt other relatively lowcurrents,suchas:

1. Transformermagnetizingcurrent.2. Chargingcurrentsof linesdependingon length,voltage, insulationandother local

conditions.3. Smallloadcurrents.

Apartfromtheaboverecognition,therearenostandardsorrequiredratingsforthe current interruption by DSs. Both standards only refer to the currentcapability of the DS, and both use the word "negligible" to qualify the smallcurrent.Bothpointoutthepotentialcurrenttypesandthepossiblesource,whichcausesthesesmallcurrents.ThedifferencebetweenthetwostandardsisthattheIEC standard defines the meaning of "negligible current" and quantifies thecorrespondingcurrentlevels,whereastheIEEEstandarddoesnot.Reference[6]gave the typical range of these currents for station airbreak equipment from72.5kV to 1200kV. This is the newest IEC technical report, released in 2009,whichdescribes thecapacitivecurrentswitchingduty forhighvoltageairbreakDSsforratedvoltagesabove52kVandprovidesguidanceonlaboratorytestingtodemonstrate the switching capability. This is also the first time to provide ananalysisoftheswitchingdutyandtodefinetestingprocedures.1.5ObjectiveofthesisAmong these three main applications of current interruption using DSs, loopcurrent interruption has been investigated in detail in [4]. As compared toinductivecurrent(excitationcurrent)andresistivecurrentswitching,acapacitivecurrent is a more challenging to interrupt because of the trapped chargeremainingontheloadtobeswitched(Chapters3,5).IntheIEEEstandard[8],theessentialdifferencebetweencapacitivecurrentandexcitationcurrent ispointedoutas:"This type of capacitive interruption is similar to excitation current interruption inwhichthere is a succession of interruptions near zero current, each followed by restrikes. Thedifference between the two types of interruptions is that for each capacitive currentinterruption,a charge ismore likely tobe retainedby the capacitivedevice.Eachof thesetrappedchargescreatesanadditivebiasvoltagethatincreasestheprobabilityofrestrikingacross the open gap of the switch 1/2cycle laterwhen the source voltage has reversed itspolarity.Consequently, longerarcreacheshavebeenexperiencedwhenswitchingcapacitivecurrentsthanwhenswitchingexcitationcurrents."CertainlycomparedwithswitchingonthecapacitivecurrentwithDSs,switchingoff(interrupting)capacitivecurrentisamoreseveretask.

6Chapter1

Itwasmentioned that a socalled "negligible current" doesnot exceed0.5A forratedvoltagesof420kVandbelow.Inthepast,thecurrentinterruptingcapabilityof airbreakDSs therefore has been taken as 0.5A or less. However, at presentwith the fast development of power networks, users requirement for smallcapacitive current interruption using airbreak DSs is frequently higher due tocomplexity of the network or financial reasons. The subject of this thesis"InterruptionofcapacitivecurrentbyHVairbreakdisconnectors"addressesthechallengingtaskofinterruptingrelativelylargecapacitivecurrents(uptofewtensofamperes).CapacitivecurrentinterruptionwithaDSconsistsmicroscopicallyofasuccessionof interactiveeventsbetweenthepowercircuitandtheACarcwitharepetitivesequence of interruptions, reignitions/restrikes. The arc reestablishment ischaracterized in terms of oscillations and transients of current and voltage,recovery voltage. The interruption process is characterized in terms of arcduration, arc reach (perpendicular distance of outermost arc position to a lineconnecting the contacts), arc type (repetitive or continuous), arc brightness,energyinputintothearc,andsoforth.Thisdissertationwillparticularlyfocuson: TheprinciplemechanismofthecapacitivecurrentinterruptionusingHVair

breakDSs.It includesthetransientvoltageandcurrent,energyinputofthecircuit,restrikevoltage,etc.

Thephenomenaoftheswitchingarc,includingdifferentfeatures,suchasarc

voltage,arccurrentandotherphysicalcharacteristicssuchasarcbrightness,arc length,arcduration,arcreach,archeight,basedontheanalysisofdatafromopticalandelectricalexperiments.

Influencing factors on the transient and arc phenomena,which include the

ratioofthesourceandloadsidecapacitances,powersupplyvoltage,currentleveltobeinterruptedandrestrikevoltagefromtheelectricalside.Fromthephysical side, the influencesof (forced)arc coolingand (forced)elongationareanalyzedexperimentally.

Thebreakdownvoltageandtheprebreakdownmechanismintheairduring

thenumerousreignitionsandrestrikes. Approachestoenhancetheinterruptioncapability.

i. Anairflowsystemassistingarcquenchingii. Auxiliaryhighvelocitycontactsiii. Insertionofresistorsintothecircuitiv. Otherapproaches(discussiononly)

HighVoltageAirbreakDisconnectors7

The research is carried out based on experiments in different laboratories.Development and preliminary experiments are done at the high voltagelaboratoryofEindhovenUniversityofTechnology.FullscaletestsareperformedatKEMAHighPowerLaboratoriesinArnhemandPrague.ThetestobjectDSsaresuppliedbyHAPAMB.V.,theNetherlands.References[1] IEVnumber4411405,[online].

Available:http://std.iec.ch/iev/iev.nsf/display?openform&ievref=4411405.[2] IEEE StandardDefinitions for Power Switchgear, IEEE Standard C37.1001992, Oct.

1992.[3] J.D.McDonald,ElectricPowerSubstationsEngineering,London:CRCpress,2007.[4] D. F. Peelo, "Current interruption using high voltage airbreak disconnectors", Ph.D.

dissertation,Dept.ElectricalEngineering,EindhovenUniv.ofTechnology,Eindhoven,2004.

[5] IEEE Guide to Current Interruptionwith HornGap Air Switches, American NationalStandard(ANSI)IEEEStandardC37.36b1990,Jul.1990.

[6] IECTechnicalReport IEC/TR62271305, "Highvoltage switchgear and controlgearPart 305: Capacitive current switching capability of airinsulated disconnectors forratedvoltagesabove52kV",Nov.2009.

[7] IEC Standard on "High voltage switchgear and control gearPart 102: Alternatingcurrentdisconnectorsandearthingswitches",IEC62271102,Dec.2001.

[8] IEEEStandardDefinitionsandRequirements forHighVoltageair switches, insulators,andbussupports, American National Standard (ANSI) IEEE Standard C37.3Oh1978,Jun.1978.

[9] AmericanNationalStandardDefinitionsandRequirementsforHighvoltageAirSwitches,Insulators, and Bus Supports, American National Standard (ANSI) IEEE StandardC37.301971,Apr.1971.

8Chapter1

LiteratureReview9

Chapter2

LiteratureReviewFromthehugenumberofpublicationsondevicesappliedinpowersystems,thereappearstoexistonlyalimitedamountofpapersonairbreakDSs.Especially,onlyafewofthemareactuallyconcernedwiththephenomenarelatedtofairlysmallcapacitive current interruption with DSs in high voltage systems. The reviewpresented in this chapter is based on selected papers (partly) related tointerruptionofsmallcapacitivecurrent.Inparticularthischapterwillinvolvefivetopics: EngineeringguidelinesoncurrentinterruptionwithairbreakDSs. Fundamental aspects of capacitive current interruptionwith a standalone

DS(i.e.withoutanyauxiliarydevicestoaidinterruption). TransientscausedbyDSswitching. ApproachestoimprovecapacitivecurrentinterruptingcapabilityoftheDS. Possiblearcmodelsrelatedtothecurrenttopic.2.1AwarenessofthecapacitivecurrentinterruptionwithdisconnectorsF. E. Andrews et al. belonged to the earliest authors on the field of currentinterruptionwith airbreakDSs. They carriedoutnumerous laboratory tests ontransformer excitation current, loop current switching at 33kV level and linedropping at 132kV using DSswith horngap on the Public Service Company ofNorthernIllinois,USA,inthe1940s.Theresultswerepublishedinathesis[1]andinasubsequentpaper [2].A typicalhorngapdevice (alsocalledarcinghorn) isshowninFigure2.1.Thehorngapnormallyactsasthelastpointofmetaltometalcontact on the DS when opening. Thus the arc burns between the arcing hornratherthanbetweenthemainbladesoftheDS.Thegoalofthesetestswastofindthe correlation between the voltage across the DS after switching off and theinterruptedcurrentononehand,andthearclength,reachontheotherhand.Thearclengthwasdefinedasthecompletelengthoftheirregularpathfollowedbythearc.Thearcreachwasdefinedasthedistancefromapointmidwaybetweenthebladeendstothemostremotepointofthearcatthetimeofitsmaximumlength(seeFigure2.2). Itwasrecognizedthatthearc lengthscaledproportionaltothearcvoltage.Themainattentionwaspaidto"arcreach",sinceitwasconsideredtobemoresignificantthanthe"arclength"inswitchingoperationsifthephasetophaseandphasetogroundclearancewereconsidered[2].Forthisreasonthearcreachhasbeentakenasameasuretoprovideacriterionforswitchingclearance.

10Chapter2

Figure2.1.ArcinghornmountedonaverticalbreakDS(copiedfrom[50]).

Figure2.2.DefinitionofarcreachandlengthaccordingtoAndrewsetal.[2].TheoverallresultsplottedinFigure2.3,copiedfrom[2],presentthearcreachintermsof "feetperkilovolt"asa functionof initial interruptedcurrent.Fromtheresults,thecriticallimitsdescribedthe"LimitoftheProbableReach"(LPR)ofthearc,werederivedforexcitationcurrentandloopcurrentinterruption:

LPR=5.03UocI,when0Cl.ThemaximumcurrentthroughtheDSintheHF loop is H Hr C LU (neglecting HF damping). Obviously, iH increases withincreasingUrandCHanddecreaseswithincreasingLH.ThusUrandCs/Cl(orCl/Cs)arekeyparameters that affect theHF transientbehaviouron restrikes.TheHFtransientsinthecurrentarecandidatestocauseelectromagneticinterferenceinsecondarysystems,as itwillbereported inChapter5.Giventhehighfrequencyand amplitude derivatives of the current, up to a few kiloamperes permicrosecondsinlatertests,itcancoupleinductivelywithneighbouringcircuitry.Also,itprovidesasignificantpowerinputintotherestrikingarc,albeitduringalimitedtime.3.2.2Mediumfrequency(MF)componentUpon restrike, also a "mediumfrequency" (MF) oscillation starts. The MFcomponent,whichlastsaboutafewmilliseconds,alsocausesatransientvoltageandcurrent.AtthisstagethevoltageacrossthearcisneglectedandtheanalysisstartsafterdecayoftheHFtransient,withvoltageofeachcapacitorequalizedtoUE.LHinFigure3.3isneglectedaswell,becauseitsequivalentimpedanceismuchsmaller than the capacitances impedance at MF. Therefore, Cs and Cl with anidenticalinitialvoltageUEareinparallelandtheequivalentcircuitofFigure3.1atMF applies. Because of the charge redistribution during the HF oscillation, thevoltagesacrossCsandClhavechanged,andwilldischargeviaLsandRsduringthedurationoftheMFoscillation.The instant of restrike is again taken as t = 0. On the time scale of the MFoscillation, us can be treated as a constant (Em sin). Similarly as for the HFanalysis,uCM(thevoltageacrossCsandCl),andiM(thecurrentthroughtheDS)canbedetermined:

40Chapter3

0

2

sin e sin( )11 e sin( )(1 )

M

M

tMrCM m M M

s l M

trM M

s Ms l

Uu E t

C CU

i tLC C

(3.4)

where 2 2 20 01 , , , arctan2 ( )

S MM M M M M M

S S s l M

RL L C C

.TheoscillationfrequencyMmainlydependsonthesumofbothcapacitancesandthe inductance Ls. In general the frequency of this oscillation is in the order ofseveralkilohertz.Similarlyasforthehighfrequencytransient,thevoltagesduringtheMFoscillation across both capacitanceswith initial voltagesUE are dampeddue to the equivalent resistance in the loop and finally reach the value us. Themaximumvoltageacrossthecapacitancesis sin 1

rm

s l

UEC C

.Itincreaseswithincreasing Ur, ratio Cl/Cs and Em Similar to the HF oscillation, the maximumtheoretical voltage is 3Em. The maximal current during the MF oscillation is:max(iM) 21 (1 )

r

s l s M

UC C L ,whichdependsonUr,Cs/ClandLsaswell,andscales

withUr.3.2.3ThreecomponentssynthesisAfterHFandMFcomponentshavedampedout,onlythePFcomponentremains.Sincethetimeconstantsinvolvedarehighlydistinct,theHFcomponentvanishesonthetimescalefortheMFoscillationandtheMFoscillationhasdisappearedonthe timescale forPF.The initialvoltage,atwhichtheMFoscillationstarts, is thefinalsteadystatevoltageafterHFoscillationdecayandtheinitialvoltageforthePFoscillationisthefinalsteadystatevoltageoftheMFoscillation.Inordertoquantifythecompletetransientbehaviour,thethreecomponentsarecombined. The voltage ucl across the load side capacitance and the current idflowingthroughtheDSonrestrikecanbewrittenas:

0 0

2

e sin( ) e sin( ) sin( )1 11 e sin( ) e sin( ) cos( )(1 )

H M

H M

t tH Mr rcl H H M M m P

l s H s l M

t tr rd H M l P m P

H H s l s M

U Uu t t E tC C C C

U Ui t t C E tL C C L

(3.5)

BasicCircuitAnalysis41

Figure3.4. Simulatedwaveshapesofucs,ucl,udduringonepower frequencycycleuponrestrike.Equation(3.5)containsthethreefrequencycomponentsinthevoltageacrosstheloadsidecapacitanceandinthecurrentthroughtheDSarc.Thevoltageacrossthesourcesidecapacitancecanbecalculatedinasimilarmanner.Itturnsoutthatthetransientvoltagesandcurrentsdependontheairgapbreakdownvoltage,voltagesupply level, the ratioofCs/Cl andso forth In the following sections thedistinctfrequency contributions to overvoltages and currents will be discussed on thebasisoftheanalysisaboveandcomparedwithexperimentaldata.3.3SimulationofrestrikesFor illustrating the restrike phenomena in voltage and current waveforms asimulation is performed using MATLAB Simulink (SimPowerSystems). Theparameters taken are: Em=702kV, Ls=10mH, Cs=10nF, Cl=100nF, theresistanceforarcatrestrikeistakenas20andLH=15H.Initially,theDSisinclosed position. The DS gap starts to recover at t=5ms, and restrikes att=10ms. The simulated wave shapes for the current id, voltages ucl, ucsand udtogether with their zoomed in of the HF and MF components, are plotted inFigures 3.43.6. In Figure 3.4, the threecomponents are indicatedwith arrows.According to Section3.2, the charges of the source and load side capacitanceCsandClexchangeduringthehighfrequencyperioduntiltheequalizationvoltageUEis reached, shown in Figure 3.5. The mediumfrequency component, after thehighfrequencyoscillationhasdisappeared, isdepictedinFigure3.6.Inasimilarway, the wave shapes of the current id and its high and mediumfrequencycomponentsareshowninFigures3.73.9.It can be observed that the high andmediumfrequency components last about10sand23msrespectivelyinthissimulation.Duringtheoscillation,thereisatransient currentwith a peak value up to 2kA upon restrike at t=10ms. TheobservedovervoltageacrossthesourcesidecapacitanceCsis1.5p.u.

0 5 10 15 20200

100

0

100

200

time (ms)

Vol

tage

(kV)

ucl ucs ud

MF

PF

HF

42Chapter3

0 5 10 15 204

2

0

2

time (ms)

Curre

nt (k

A)

10 10.01 10.02 10.03 10.04 10.05 10.062

1

0

1

time (ms)

Curre

nt (k

A)

Figure 3.5. Simulated wave shapes of ucs, ucl, ud at highfrequency (zoomed in fromapproximately9.96msto10.06msinFigure3.4).

Figure 3.6. Simulated wave shapes of ucs, ucl, ud at mediumfrequency (zoomed in fromapproximately9.5msto12.5msinFigure3.4).Figure3.7.Simulatedwaveshapesofidoveronepowerfrequencycycleuponrestrike.

Figure3.8. Simulatedwave shapesof idathighfrequency (zoomed in fromapproximately10.00msto10.06msinFigure3.7).

0 5 10 15 20 25100

0

100

time (s)

Vol

tage

(kV)

ucl ucs ud

UE

9.5 10 10.5 11 11.5 12 12.5

100

0

100

time (ms)

Vol

tage

(kV)

ucl

ucs

ud

BasicCircuitAnalysis43

Figure3.9.Simulatedwaveshapesofidatmediumfrequency(zoomedinfromapproximately9.5msto12.0msinFigure3.7).3.4RestriketransientsindistributedelementloadcircuitsInthecircuitofFigure3.1onlylumpedcomponentsareconsidered.Asmentionedin Chapter 1, the capacitive current to be interrupted arises from substationcomponents,suchascurrenttransformer,capacitivevoltagetransformer,butalsofromdistributedelements,suchasbusbars,overheadline,andpowercables.If thephysicaldimensionsof theconsideredcomponentsaremuchshorter thanthewavelengthcorrespondingwith thecurrentandvoltageoscillations, lumpedparameters can be used to model the power system. Otherwise, a distributedparameter approach has to be adopted. The transmission line specific (per unitlength)parametersL,C andR (G isomittedsince theair isconsideredaperfectinsulator) are uniformly distributed over the length of the line. For the steadystateoperation(powerfrequency,50Hzor60Hz),thetransmissionlinescanberepresentedby lumpedparameters.But for transientbehaviour the lines itmaybenecessarytoberepresentedbydistributedparameters.During the capacitive current interruption by a DS, transient phenomena occurwithhighfrequencycontent,duetotherepeatedbreaksandrestrikes.Therefore,a distributed parameter simulation for transmission lines is considered in thissection.Thesimulatedresultsofalumpedparameterandadistributedparameterapproachofatransmissionlinearecompared.ThevalueofthelumpedelementparametersinFigure3.10aretakentoproducethesamepowerfrequencyresultsasthoseinFigure3.1.Theunloadedoverheadline is simulatedwithdistributedparameters.A line lengthof50km is taken tomatch the interrupted current Id (PF current of 9A) of the lumped circuit (linecapacitanceandinductanceare8.48nF/kmand1.33mH/km,matchingalumpedload side capacitance ofCl = 424nF). The simulated results are shown in theFigures 3.113.13,where thewave shapes of the interrupted current id and thevoltageacrosstheDSud,arepresentedrespectively:id1,ud1aresimulatedresultsfromsimulationwithdistributedelements, and id2,ud2 are simulated results areobtainedfromsimulationwithlumpedelements.

9.5 10 10.5 11 11.5 12

0.20.1

00.10.2

time (ms)

Curre

nt (k

A)

44Chapter3

20 21 22 23 24 2564

2

02

4

time (ms)

Vol

tage

(kV)

ud2

ud1

Figure3.10. Simulated circuit for capacitive current interruptionwitha transmission linerepresentedbydistributedparameters.

Figure3.11.(Left)waveshapesofthecurrentid1,id2throughtheDSwithdistributedlinesandlumpedcapacitancerespectivelyand(right)expansionofid1between22.4msand23.2ms.

Figure 3.12. Wave shapes of the voltage ud1, ud2 across theDSwith distributed lines andlumpedcapacitancerespectively.

The wave shapes of current and voltage show that the travelling waves arereflected within 0.33ms. There are transient phenomena on each reflectionmoment(seeFigure3.11,3.12).Nevertheless,thereishardlyanyhighfrequencycomponent at restrikes in the voltage and current waveforms with thedistributedparameters,which consequently reduces the total amountof energy

15 20 25 30

200

0

200

400

time (ms)

Curre

nt (A

)

id2 id1

22.4 22.6 22.8 23 23.2

100

0

100

time (ms)

Curre

nt (A

)

BasicCircuitAnalysis45

inputintothecircuituponrestrike.Thisisbecausethehighsurgeimpedanceofthe line (in thisexample390) limits theHFrestrikecurrentcompared to themuch lower surge impedanceof the lumped capacitor.Therefore, to interrupt acircuit with lumped parameters is a more severe task as compared to aconfigurationwithdistributedparameters.Intheanalysisinthischapter,andalsointheexperimentalarrangementdescribedinthefollowingchapters,circuitswithlumpedelementsareapplied.Thispointshouldbepaidattentionto,becauseofitsimpactontesting,wherenormally(lumped)capacitorbanksareused.3.5ConclusionThemainobservationswithrespecttocalculationsandsimulationsoncapacitivecurrentinterruptionwithhighvoltageairbreakDSsare:CapacitivecurrentinterruptionbyaDSconsistsofrepeatedbreaksandrestrikesasaconsequenceoftheinteractionbetweenarcandcircuit.The transient upon restrike consist of threecomponents: high, medium andpowerfrequencycomponent.Duringthehighfrequencycomponent,thetransientperiod is in the order of a few tens of microseconds. The mediumfrequencycomponent is in the order of a few milliseconds. The overvoltage across thecapacitancesatbothsidesoftheDScanbeupto3p.u.theoretically.Thepeakofthetransientcurrentmaybeuptoafewkiloampereswithinafewmicroseconds.Theratioofsourceandloadsidecapacitance,therestrikevoltageandthecurrentto be interrupted are the key factors that influence the transient voltage andcurrentmagnitudesuponrestrike.Thecircuitwithlumpedelements,whichisadoptedinthisthesis,isaworstcaseapproach. Capacitive current interruption of transmission lines where adistributedparameterapproachappliesislesssevere.References[1] IECTechnicalReport IEC/TR62271305, "Highvoltage switchgear and controlgear

Part 305: Capacitive current switching capability of airinsulated DSs for ratedvoltagesabove52kV",Nov.2009.

[2] L.vanderSluis,"TransientsinPowerSystems",Chichester:JohnWiley&Sons,2001.[3] D.F.Peelo,"CurrentinterruptionusinghighvoltageairbreakDSs",Ph.D.dissertation,

Dept.ElectricalEngineering,EindhovenUniv.ofTechnology,Eindhoven,2004.

46Chapter3

ExperimentalSetup47

Chapter4

ExperimentalSetupExperimentsinthisthesisareperformedatseverallocationsemployingdifferenttypesofvoltagesources.ThebasiccircuitdiagramforalltestsiteswaspresentedinFigure3.1.Figure4.1depictsthegeneralsetupincludingthemeasuringsystemschematically.The voltage supply is represented by an ideal voltage source us with seriesresistanceRs representing losses and inductanceLs. Their valuesdependon thesource type being used (see Section 4.1). Capacitances Cs and Cl stand for thesourceandloadsidecapacitorbankswithaDSinbetween.Thecapacitancevaluescanbevariedforthetestseries.Thevoltagesucs,uclarethevoltagesacrossCsandCl,respectively.ThesevoltagesaremeasuredbythecapacitivevoltagedividersD1andD2incombinationwiththehighvoltageprobesD3andD4(Section4.2.1).Thedifferentialsignal isusedtodetermine thevoltageacross theDS(Section4.2.2).Thecurrent throughtheDS is indicatedby id.Current transformersCT1andCT2measure the current through Cl (Section 4.2.3). Two current transformers areapplied to cover the dynamic range of different frequency componentssimultaneously (below 1A to several kiloamperes and from 50Hz to severalmegahertz),denotedasipfandihf,respectively.Voltagesandcurrentsarerecordedbyadataacquisitionsystemincludingfourdigitizers,CH14,eachhavingasingleinputchannel(Section4.2.4). Inadditionto theelectricalsignals,arc imagesarerecordedbymeansofahighspeedcamera,whichisinstalledonthesameheightas the DS blades (Section 4.2.5). The opening characteristics of the DS isdeterminedinSection4.3.4.1HighvoltagesourceTwodifferent typesofhighvoltagesourceareemployed.Dependingon the testsites,apowertransformeroraresonancehighvoltagesourceisused.A shortcircuit generator plus a transformer are available in large scalelaboratories,suchasKEMAHighPowerLaboratoriesinArnhemandPrague.TheequivalenttestcircuitisshowninFigure4.2.AsourceinductanceLsisusedwithavalue up to a few hundreds of millihenry. Air gaps are used to protect thecapacitors bank, but are not shown in Figure 4.2. These setups supply up to173kVrms phasetoground voltage, and up to 27A current during theexperiments. The specific test configurations employed for different series ofexperimentswillbepresentedinChapters5,6and7.

48Chapter4

Figure4.1.Experimentalcircuitincludingelectricalandopticaltransducers.

Figure 4.2. Test circuitwith source in KEMA HPL. G: shortcircuit generator;M:masterbreaker; Ls, Rs: reactor and resistor at source side; S: make switch; TR: shortcircuittransformer.In the high voltage laboratory at the Eindhoven University of Technology aresonantsystem(Hipotronics)isavailableashighvoltagesupply.ItstopviewandequivalentschemeareshownFigure4.3(leftandright,respectively).TheresonantsystemincludesanadjustablehighvoltagereactorLs,acapacitorCand an exciter transformer. The variable auto transformer T1 controls thetransformerT2,whichsuppliespower to the resonant circuit, and it isolates thetestspecimenfromtheline.Twotuneablereactors,whichcanbeconnectedeitherin series or in parallel, make up the source inductance. Each of them has aninductancewithavalueintherangeof400H10kH,andresistance(measuredatDC) of about 1k. Each reactor is designed for a voltage of 300kVrms. TheAC

ExperimentalSetup49

Figure4.3. (left)Laboratory source forcapacitivecurrent interruptionwithaDSatTU/e;(right)simplifiedschematicsofHipotronicshighvoltagesource.sourcepoweringtheresonantcircuit,indicatedwithuoutinFigure4.3(right)isatmaximum 22kVrms. The capacitanceCs is chosen either 2nF or 4nF by seriesconnectionsoffourortwo8nF,150kVcapacitors.Differentcombinationsoftenavailable 16nF high voltage capacitors can be made to adjust the (load)capacitanceCltothedesiredcurrent.Eachofthesecapacitorshasaratedvoltageof150kVrmsandtan