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Capacitive current interruption with high voltage air-breakdisconnectorsCitation for published version (APA):Chai, Y. (2012). Capacitive current interruption with high voltage air-break disconnectors. TechnischeUniversiteit Eindhoven. https://doi.org/10.6100/IR728755

DOI:10.6100/IR728755

Document status and date:Published: 01/01/2012

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https://doi.org/10.6100/IR728755https://doi.org/10.6100/IR728755https://research.tue.nl/en/publications/capacitive-current-interruption-with-high-voltage-airbreak-disconnectors(eb4d87bf-4ad6-41ee-8a93-e803c7a3f809).html

CapacitiveCurrentInterruptionwithHighVoltageAir‐breakDisconnectors

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,AgricultureandInnovationinanIOP‐EMVTprogram.AcataloguerecordisavailablefromtheEindhovenUniversityofTechnologyLibrary.ISBN:978‐90‐386‐3097‐7

ToMilošandRuirui

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.dr‐ing.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 low‐cost 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)fastinterruptingbyhigh‐velocityopeningcontacts;(iii) reduction of arc energy by adding resistive elements. Finally, a qualitativedescription isprovidedon thephysicalnatureof thearcandhowtheevaluatedmethodsaffectthearccharacteristics.Allresultsareobtainedbyanalysisofhigh‐resolutionmeasurementofarccurrent(includingallrelevanttransients),voltagesacrossthedisconnectorandhigh‐speedvideoobservation.Itwas found that, depending on the current to be interrupted, the interruptionprocessisgovernedbythedielectricand/orthermalprocesses.In thedielectric regime, the interrupted current is low (roughlybelow1A) andtheswitchingarcischaracterizedbyahighrateofrepetitionofinterruptionsandre‐strikesthatonlyceaseafterasufficientgapspacinghasbeenreached.There‐strikesinteractseverelywiththecircuitryinwhichthedisconnectorisembedded,exciting transients in current and voltagewith frequenciesup to themegahertzrange.Highovervoltagescanbegenerated.Theirmagnitudescanbelimitedbyaproperchoiceofthecapacitanceatsupplysideofthedisconnector.Thearc‐circuitinteraction has been studied and relevant processes have been modelled andverifiedbyexperimentsinfull‐powertest‐circuits.In the thermal regime, the switching arc behaves less vehemently, interruptingandre‐ignitingbasicallyoccurateverypowerfrequencycurrentzero.Becauseofthepresenceofsufficientthermalenergyintheswitchinggapalongthearcpath,the voltage to re‐ignite the arc is limited, and the arc‐circuit interaction is lesspronounced.Thoughnotproducingverysevereovervoltages, thearcdurationislongerandthecurrentmaynotbeinterruptedateverycurrentzerocrossing.Theultimate thermal regime is reachedwhen thearc continues toexist afterpowerfrequencycurrentzerowithoutanyappreciablevoltagetore‐ignite.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 re‐strike. This energy extends the arcing time by lowering thebreakdownvoltage.Ithasbeenobservedthatthearcinitsthermalmodealwaysre‐ignitesinitsformertrajectory.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 arc’s foot point. A substantial gain ininterruptioncapability isdemonstrated,butat thecostofgenerating re‐ignitiontransients at a very rapid succession. Specifically, the experiments showed that7.5Acouldbeinterruptedsuccessfullyat90kVrmsvoltagewithashorterarcingduration(afactorof0.5wasobserved)thanwithoutairflow.Withapplicationofair flow, the frequencyof re‐ignitionsoccurring, 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.Thismethodreducesthenumberofre‐strikes.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 fast‐opening 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 transiënten) alsmede doorobservatiemetsnellevideotechnieken.Afhankelijk van de grootte van de te onderbreken stroom, wordt hetonderbrekingsprocesgekenmerktdoordiëlektrischeen/ofthermischeprocessen.Inhetdiëlektrischeregimeisdeteonderbrekenstroomklein(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 transiënten 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.Debelangrijkstefactorendiehetonderbrekingsprocesbeïnvloedenzijndehoogtevan 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 rest‐ionisatieafkomstigvande(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 geïoniseerde 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.Deexperimententonenaandatbijeenfase‐aardespanningvan90kVstromen 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 (vacuüm‐,SF6onderbrekersenonderbrekinggebaseerdopablatie)zijngeëvalueerduitdeliteratuur.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.HulponderbrekersinvacuümofSF6gasiseffectiefmaarkostbaarenconstructiefingewikkeldvanwegedehoogtevande spanning die serie schakeling van elementen vaak nodigmaakt. Oplossingenmet behulp van ablatie zijn minder kansrijk omdat de stroom hiervoorwaarschijnlijktelaagis.

viiiSamenvatting

Contentsix

Contents

SUMMARY..................................................................................................................................I

SAMENVATTING.....................................................................................................................V

CONTENTS..............................................................................................................................IX

CHAPTER1...............................................................................................................................1

HIGHVOLTAGEAIR‐BREAKDISCONNECTORS.............................................................1

1.1DEFINITIONOFDISCONNECTORS..................................................................................................1 1.2TYPEOFDISCONNECTORS..............................................................................................................1 1.3INTERRUPTINGCURRENTWITHDISCONNECTORS......................................................................3 1.4STANDARDIZATIONSTATUS...........................................................................................................4 1.5OBJECTIVEOFTHESIS.....................................................................................................................5

CHAPTER2...............................................................................................................................9

LITERATUREREVIEW...........................................................................................................9

2.1AWARENESSOFTHECAPACITIVECURRENTINTERRUPTIONWITHDISCONNECTORS...........9 2.2FUNDAMENTALASPECTSOFCAPACITIVECURRENTINTERRUPTION....................................14 2.3TRANSIENTSCAUSEDBYCAPACITIVECURRENTINTERRUPTION..........................................16 2.4APPROACHESTOENHANCETHEINTERRUPTIONCAPABILITY...............................................17 2.5ARCMODELSRELATEDTOCURRENTINTERRUPTIONWITHADISCONNECTOR..................26 2.6CONCLUSION.................................................................................................................................29

CHAPTER3............................................................................................................................35

BASICCIRCUITANALYSIS.................................................................................................35

3.1THEINTERRUPTIONPROCESS.....................................................................................................35 3.2THREE‐COMPONENTSANALYSIS................................................................................................37 3.3SIMULATIONOFRE‐STRIKES.......................................................................................................41 3.4RE‐STRIKETRANSIENTSINDISTRIBUTEDELEMENTLOADCIRCUITS...................................43 3.5CONCLUSION.................................................................................................................................45

CHAPTER4............................................................................................................................47

EXPERIMENTALSETUP.....................................................................................................47

4.1HIGHVOLTAGESOURCE...............................................................................................................47 4.2MEASUREMENTSYSTEM..............................................................................................................51 4.3DISCONNECTORMAINBLADESOPENINGVELOCITY................................................................57 4.4CONCLUSION.................................................................................................................................59

xContents

CHAPTER5............................................................................................................................61

CURRENTINTERRUPTIONMECHANISM.....................................................................61

5.1EXPERIMENTALOBSERVATIONS................................................................................................61 5.2ARCINTERRUPTIONCHARACTERISTICS....................................................................................69 5.3DISCONNECTORCONTACTSSPACING.........................................................................................75 5.4RE‐STRIKEVOLTAGE....................................................................................................................76 5.5ELECTRICALARCCHARACTERISTICS.........................................................................................80 5.6ENERGYINPUTINTOTHEARC....................................................................................................82 5.7TRANSIENTSUPONRE‐STRIKE...................................................................................................85 5.8CONCLUSION.................................................................................................................................88 5.9RECOMMENDATIONFORSTANDARDIZATION...........................................................................90

CHAPTER6............................................................................................................................91

INTERRUPTIONWITHAIRFLOWASSISTANCE.........................................................91

6.1EXPERIMENTALSETUP................................................................................................................91 6.2EFFECTOFAIRFLOWONARCING...............................................................................................92 6.3INTERRUPTIONDATAANALYSIS.................................................................................................97 6.4CONCLUSION...............................................................................................................................103

CHAPTER7..........................................................................................................................107

HIGH‐VELOCITYOPENINGAUXILIARYINTERRUPTER........................................107

7.1OPERATINGPRINCIPLE..............................................................................................................107 7.2EXPERIMENTALSETUP..............................................................................................................108 7.3OVERVIEWOFTHEEXPERIMENTALRESULTS........................................................................109 7.4RE‐STRIKEVOLTAGE..................................................................................................................114 7.5ENERGYINPUTINTOTHEARC..................................................................................................117 7.6CONCLUSIONANDRECOMMENDATION...................................................................................120

CHAPTER8..........................................................................................................................123

INTERRUPTIONWITHINSERTEDRESISTORS.........................................................123

8.1SERIESRESISTOR........................................................................................................................123 8.2PARALLELRESISTOR..................................................................................................................128 8.3DISCUSSION.................................................................................................................................130

CHAPTER9..........................................................................................................................133

PRE‐BREAKDOWNPHENOMENAINDISCONNECTORINTERRUPTION...........133

9.1CLASSICALMODELLINGOFBREAKDOWN................................................................................133 9.2PRE‐BREAKDOWNCURRENTINDISCONNECTORINTERRUPTION.......................................137 9.3DISCUSSION.................................................................................................................................138

Contentsxi

CHAPTER10........................................................................................................................141

CONCLUSIONSANDRECOMMENDATIONSFORFUTURERESEARCH...............141

10.1CONCLUSIONS...........................................................................................................................141 10.2PROPOSEDFUTURERESEARCH..............................................................................................146

PUBLICATIONSRELATEDTOTHISWORK................................................................147

NOMENCLATURE...............................................................................................................149

ACKNOWLEDGEMENT.....................................................................................................153

CURRICULUMVITAE........................................................................................................155

xiiContents

HighVoltageAir‐breakDisconnectors1

Chapter1

HighVoltageAir‐breakDisconnectors1.1DefinitionofdisconnectorsHigh voltage disconnectors are commonly used switching devices in powersubstations. According to the International Electro‐technical Vocabulary IEVnumber 441‐14‐05 [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 C37.100‐1992 [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.TheHVair‐breakDS comes inavariety of types and mounting arrangements. The most common fourconfigurations are: vertical‐break, centre‐break, double‐break, and pantographtype. They can be mounted in various orientations, depending on the spaceofferedbythesubstation[3],[4].The vertical‐breakDS 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)Athree‐phasevertical‐breakDSmountedhorizontally inaclosedposition(CourtesyofHAPAMB.V.);(right)centre‐breakDSinaclosedposition(CourtesyofSiemens).Figure 1.1 (left). It can also be vertically mounted, i.e. the blade is verticallyoriented in closed position. The vertical‐break DS requires minimum phasespacing.Anexampleofacentre‐breakDSisillustratedinFigure1.1(right).ThistypeDSisused mainly in locations with low overhead clearances. However, it requireslarger phase spacing than a vertical‐break DS. The active parts consist of twoblades, disconnecting at the centre. Both insulators rotate in a vertical plane toopenorclosetheDS.Adouble‐breakDSisavariationofacentre‐breaktypeandisshowninFigure1.2(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 significantlyhighercurrentthanthesingle‐breaktypeDSs[3],[4].Thisisbecausethesystemvoltageisdistributedacrosstwogaps.ThepantographDStype,showninFigure1.2(right),isusedworldwide(butonlyoccasionally in North America) for Extra High Voltage application, 345‐800kV.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.


Figure 1.2. (left)Double‐breakDS 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 today’s 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.Thetypicalrangeofthesecurrentsforstationair‐breakequipmentisshowninTable1.1[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,currentsofpermanentlyconnectedgradingimpedancesofcircuit‐breakersandcurrentsofvoltagetransformersanddividers.Forratedvoltagesof420kVandbelow,a currentnot exceeding0.5A isanegligible current for thepurposeof thisdefinition; forratedvoltageabove420kVandcurrentsexceeding0.5A, themanufacturershouldbeconsulted.NOTE3:Foradisconnectorhavingaratedvoltageof52kVandabove,aratedabilityofbustransfercurrentswitchingmaybeassigned.SimilarlyintheIEEEstandard[8],thefollowingnoteismade:NOTE:Itisrequiredtocarrynormalloadcurrentcontinuously,andalsoabnormalorshort‐circuit 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].

EquipmentCapacitivecurrent(A)

72.5kV 145kV 245kV 300kV 420kV 550kVCT ≤0.04 ≤0.04 ≤0.04 0.05 0.08 0.1CVT(4μF) 0.05 0.11 0.18 0.22 0.3 0.4Busbars/m 1.7×10‐4 0.32×10‐3 0.54×10‐3 0.66×10‐3 0.84×10‐3 1.1×10‐3


NOTE:Adisconnectingswitchandahorn‐gapswitchhavenointerruptingrating.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 air‐break equipment from72.5kV to 1200kV. This is the newest IEC technical report, released in 2009,whichdescribes thecapacitivecurrentswitchingduty forhighvoltageair‐breakDSsforratedvoltagesabove52kVandprovidesguidanceonlaboratorytestingtodemonstrate 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 re‐strikes. Thedifference between the two types of interruptions is that for each capacitive currentinterruption,a charge ismore likely tobe retainedby the capacitivedevice.Eachof thesetrappedchargescreatesanadditivebiasvoltagethatincreasestheprobabilityofre‐strikingacross 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 so‐called "negligible current" doesnot exceed0.5A forratedvoltagesof420kVandbelow.Inthepast,thecurrentinterruptingcapabilityof air‐breakDSs therefore has been taken as 0.5A or less. However, at presentwith the fast development of power networks, user’s requirement for smallcapacitive current interruption using air‐break DSs is frequently higher due tocomplexity of the network or financial reasons. The subject of this thesis"InterruptionofcapacitivecurrentbyHVair‐breakdisconnectors"addressesthechallengingtaskofinterruptingrelativelylargecapacitivecurrents(uptofewtensofamperes).CapacitivecurrentinterruptionwithaDSconsistsmicroscopicallyofasuccessionof interactiveeventsbetweenthepowercircuitandtheACarcwitharepetitivesequence of interruptions, re‐ignitions/re‐strikes. The arc re‐establishment 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,re‐strikevoltage,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,currentleveltobeinterruptedandre‐strikevoltagefromtheelectricalside.Fromthephysical side, the influencesof (forced)arc coolingand (forced)elongationareanalyzedexperimentally.

‐ Thebreakdownvoltageandthepre‐breakdownmechanismintheairduring

thenumerousre‐ignitionsandre‐strikes.‐ Approachestoenhancetheinterruptioncapability.

i. Anairflowsystemassistingarcquenchingii. Auxiliaryhigh‐velocitycontactsiii. Insertionofresistorsintothecircuitiv. Otherapproaches(discussiononly)


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] IEVnumber441‐14‐05,[online].

Available:http://std.iec.ch/iev/iev.nsf/display?openform&ievref=441‐14‐05.[2] IEEE StandardDefinitions for Power Switchgear, IEEE Standard C37.100‐1992, Oct.

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

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

[5] IEEE Guide to Current Interruptionwith Horn‐Gap Air Switches, American NationalStandard(ANSI)IEEEStandardC37.36b‐1990,Jul.1990.

[6] IECTechnicalReport IEC/TR62271‐305, "Highvoltage switchgear and controlgear–Part 305: Capacitive current switching capability of air‐insulated disconnectors forratedvoltagesabove52kV",Nov.2009.

[7] IEC Standard on "High voltage switchgear and control gear–Part 102: Alternatingcurrentdisconnectorsandearthingswitches",IEC62271‐102,Dec.2001.

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

[9] AmericanNationalStandardDefinitionsandRequirementsforHighvoltageAirSwitches,Insulators, and Bus Supports, American National Standard (ANSI) IEEE StandardC37.30‐1971,Apr.1971.

8Chapter1

LiteratureReview9

Chapter2

LiteratureReviewFromthehugenumberofpublicationsondevicesappliedinpowersystems,thereappearstoexistonlyalimitedamountofpapersonair‐breakDSs.Especially,onlyafewofthemareactuallyconcernedwiththephenomenarelatedtofairlysmallcapacitive current interruption with DSs in high voltage systems. The reviewpresented in this chapter is based on selected papers (partly) related tointerruptionofsmallcapacitivecurrent.Inparticularthischapterwillinvolvefivetopics:‐ Engineeringguidelinesoncurrentinterruptionwithair‐breakDSs.‐ Fundamental aspects of capacitive current interruptionwith a stand‐alone

DS(i.e.withoutanyauxiliarydevicestoaidinterruption).‐ TransientscausedbyDSswitching.‐ ApproachestoimprovecapacitivecurrentinterruptingcapabilityoftheDS.‐ Possiblearcmodelsrelatedtothecurrenttopic.2.1AwarenessofthecapacitivecurrentinterruptionwithdisconnectorsF. E. Andrews et al. belonged to the earliest authors on the field of currentinterruptionwith air‐breakDSs. They carriedoutnumerous laboratory tests ontransformer excitation current, loop current switching at 33kV level and linedropping at 132kV using DSswith horn‐gap on the Public Service Company ofNorthernIllinois,USA,inthe1940s.Theresultswerepublishedinathesis[1]andinasubsequentpaper [2].A typicalhorngapdevice (alsocalledarcinghorn) isshowninFigure2.1.Thehorngapnormallyactsasthelastpointofmetal‐to‐metalcontact 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"inswitchingoperationsifthephase‐to‐phaseandphase‐to‐groundclearancewereconsidered[2].Forthisreasonthearcreachhasbeentakenasameasuretoprovideacriterionforswitchingclearance.

10Chapter2

Figure2.1.Arcinghornmountedonavertical‐breakDS(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,when0<I

LiteratureReview11

Figure2.3.Arcreachperkilovoltasafunctionoftheinterruptedcurrent,copiedfrom[2].The teston thecapacitivecurrent interruption,performed in [2], showed itwassafe to drop a 27km line (about 7A charging current) at 132kV for a 5mhorizontalphasespacingowingtoa favourableobliquewind. Inaddition, itwaspointed out the arc reach from the capacitive current interruption was clearlylargerthanthatfromtheexcitationandloopcurrentinterruptionobservedinthelaboratorytests.Consequently, forthevoltageusedforthecalculationofthearcreach from interrupting capacitive current probably value twice of the actualvoltagewastaken.Nofurtherinformationonthisissuewasprovided.TwoAIEEcommitteereports,whicharecited frequently,areof interest [8], [9].The initial goal of the study reported in [8]was to investigate the transformermagnetizingcurrentand itseffectonrelayingandDSoperation. Inaddition, theinterruption of (capacitive) overhead line charging current by a horn‐gap wassurveyed in1949bydistributionofaquestionnaire to250utilities,ofwhich59responded. The main results are presented in Figure 2.4. About 70% of theresponsesindicated100%successwithalimitedcurrentrange(e.g.22Aat66kV,13Aat118kV).Amore recent survey on line and cable charging current interruptionwithDSswas made in 1962 amongst 71 utilities to collect the operating practice andexperienceofutilities[9],theresultsofwhichareshowninFigure2.5and2.6.In Figure 2.5 the utility responses were divided into three categories, stating100%successful,90‐99%successful,andlessthan90%successfuloperationsinlinechargingcurrentinterruption.Forcablecharginginterruption(Figure2.6)alloperationsreportedweresuccessful,butthetotalnumberofoperationswasverysmall(only12operationswerereported).

12Chapter2

Figure2.4. Interruptionofoverhead line charging currentbyahorn‐gapDS (copied from[8]).Note:•:signifies100%successfuloperation;o:signifies90%‐99%successfuloperation;×:signifies75%‐80%successfuloperation.

Figure2.5.Companyexperiencesreportedontheuseofair‐breakDSforinterruptionoflinecharging current.Note: •:grounded‐100% successful, :grounded‐90%‐99% successful,X:companiesusingquick‐breakorothersimilardevices.(Quick‐break,or"whip"isanauxiliarydevicetoaidarcquenching,seeChapter7).”grounded”meansgroundedwyesystem(copiedfrom[9]).TheAIEEreportsweretheearliestthoroughsurveys,whichwerecarriedoutsofartothebestknowledgeoftheauthorofthisthesis.Itwasfoundthatmostoftheutilitiesandcompaniesdidusetheair‐breakDSstointerruptcapacitivecurrentatsystem voltage lower than 138kV in the 1950s. It was reported that mostcompanies did not have any guide for general use except previous experiences.Someofthemusedmanufacturer’sdata,andothersused(2.1)asaguide.

LiteratureReview13

Figure 2.6. Company experiences reported on the use of air‐breakDSs for interruption ofcablechargingcurrent.Note:•:grounded‐100%successful;o:ungrounded‐100%successful(copiedfrom[9]).Asfromthemid1980smostimportantcontributionsarefromPeelo[6],[10]‐[13].Inhisearlierpapers[10]and[11],thecurrentinterruptingcapabilityofDSswasanalyzedbyconsideringthegivenphasespacing,arcreach(basedontheequationfromF.EAndrewsetal.[2]).

LPR=2.75×5.03×Uoc×I(2.2)HereLPRisthearcreachinmm,Uocisthevoltageinkilovolt(rms)acrossswitchafter interruption, and I is the interrupted current in ampere (rms). Comparedwith(2.1),afactorof2.75wasintroduced.Thisvaluecamefromthetestresultsreported in [2] and [4]. Based on (2.2), safemaximum capacitive current levelsthatcanbeinterruptedwerecalculatedandcomparedwithactualcurrentstobeinterrupted. A criterion for the application of DSs from a current interruptingpointofviewwasalsoprovidedinTable2.1.BasedmainlyontheresultsfromAndrews[2]andPeelo[10],theIEEEguideforDStointerruptcapacitivecurrentratingswaspublishedin1990[7].Inthisguide,Table2.1:Maximumcapacitivecurrentlevelsforsafeinterruptingbyair‐breakDSs.Note:dФ is thedifferencebetween theminimummetal‐to‐metalphase‐to‐phase clearance,dr isthemaximumallowablearcreach,Icismaximumcurrenttobeinterruptedsafely(copiedfrom[11]).

Maximumsystemvoltage(kV)

dФ(m) dr(m) Ic(A)

15.0 0.31 0.22 1.8427.5 0.38 0.22 1.0272.5 0.79 0.37 0.65145.0 1.35 0.52 0.45253.0 2.26 0.81 0.40550.0 4.30 2.20 0.50

14Chapter2

recommendationsforsystemvoltageupto362kVaregivenrelatedto:minimumphasespacingtogroundedobjects(orhorn‐gapswitch‐phasespacing),calculatedarc reach and maximum operation voltage, safe capacitive currents to beinterruptedwith vertical‐breakDS equippedwith arcing horns andmounted inhorizontaluprightposition.Inaddition,in2001IECalsopublishedastandard[14],whereitdefinesthattheDSissupposedtobeabletodisconnecta"negligible"current(i.e.lessthan0.5A)at system voltage below 420kV. Based on the work of Peelo and Smeets, IEC62271‐305(2009)Highvoltageswitchgearandcontrolgear–Part305:Capacitivecurrent switching capability of air‐insulatedDSs for rated voltages above 52kVwas released.Two alternatives circuits for test are recommended for capacitivecurrentinterruptionwithaDSinthelaboratory.Summarizingthissubsection,alreadytensofyearsagoitwasrecognizedthroughfield experience, surveys of utilities and power companies that a DS is able tointerrupt the capacitive current.Principally, basedon theworkofAndrewsandPeelo,theIEEEguideincludesthemaximumcapacitivecurrenttobeinterruptedsafelybyverticalDSs(seeTable2.1).TheIECstandard,however,alsostatesthecurrent limitation, being 0.5A for below 420kV, but without supportinginformation. A test circuit for DS on the capacitive current interruption isproposed.2.2FundamentalaspectsofcapacitivecurrentinterruptionMost literature sources referred in the previous subsection deal with currentinterruption from the point of view of the interrupted current level throughexperiments and surveys. The literature cited in this subsection describes theinvolvement of the circuit, e.g. by investigating the factors affecting theinterruptioncapability[15]‐[20].The laboratory experiments of Knobloch on interrupting capacitive currentsdescribed in [15] were carried out using a pantograph DS with rated voltage245kV. Itwasconcluded thatboth thesourceand loadsidecapacitancesplayarole during the operations. During the interruption, in the voltage and currentwave shapes, transients of two distinct frequencies were observed, i.e. a lowfrequency (specific data was not provided) and a high‐frequency (750kHzapproximately). In [15] all DS tests succeeded in switching off 1A capacitivecurrentreliably.ApaperbyBoehne[16]wasprobablythefirsttobespecificallyrelatedtosmallcapacitive current interruption using a DS to study transients in EHV systems.This paper analyses the field performance of EHVDS operations at 400kV and505kV in the Pennsylvania Electric Company, through computer simulation. Itpresents modelling study of various phenomena associated with interrupting

LiteratureReview15

small capacitive currents in airwith aDS. Particular attentionwas given to thecurrentandvoltagetransientmagnitudesasafunctionofbusMVArating,switchresistance (a resistor in serieswith theDS)and thecapacitive load.Specifically,the simulations covered nineMVA‐values (500‐2500MVA), seven values of theinterrupted current (0.25A, 0.5A, 1A, 2A, 3A, 4A, 5A), and four separateresistor values (250Ω, 500Ω, 1000Ω, 2000Ω). The results included the linecurrent,busvoltageand itsrateofchange, linevoltage,and thearcvoltage.Themain conclusionswere: the overvoltagewas higher for disconnecting a smallerbusbar(intermsofMVA)thanalargerbusbar;therateofswitchingovervoltagerisecouldreachvalues in theorderof300kV/µs; twonatural frequencieswerepresentinthevoltageandcurrentduringtheinterruption;thearcvoltageandtheswitching resistance can readily assist to reduce the overvoltage below 2.0p.u.(theratioofthetransientvoltageandamplitudeofthephase‐to‐groundvoltage).Aprojectwasinitiatedin1984atGeorgiaPowerCompany[17]todeterminetheinfluence of parallel lines and line/conductor configuration on the chargingcurrentof115kVlines,whichwereswitchedoffwithanair‐breakDS.Atotaloffive types of centre‐break and pole‐mounted DSs, to de‐energize a section of115kV lineswere investigatedby computer simulationaswell asby field tests.Several line/conductor configurations and parallel line arrangements wereincluded.Theresultsindicatedthatparallellineshadanegligibleeffectonvaluesof the charging current. However, the conductor configurations affected thechargingcurrentsignificantly.In Peelo’s Ph.D dissertation [6] and subsequent papers [12], [13] capacitivecurrent interruption was studied through a series of experiments. The mainresultscanbesummarizedasfollows:‐ The interrupted current and the ratio of source and load side capacitance

playakeyrole.‐ Theovervoltagewashighestand thearcingdurationwas longestwhenthe

ratioofsourceandloadsidecapacitancewassmallest.‐ Twotypesofappearanceoftheswitchingarc(socalled"erratic"and"stiff"

mode) were recognized during the interruption with different ratios ofsourceandloadsidecapacitances.

As a conclusion, according to the consulted literature, transient phenomena,togetherwithhigh‐frequencyoscillations,onre‐ignitionsorre‐strikesduringtheinterruptionwere found.Thecapacitancesatbothsidesof theDSplaya crucialrole. The level of the current to be interrupted influences the interruptioncapabilityaswell.However,thedetailsarestillnotclear.Forinstance,howdothecapacitancevaluesaffectthearcingtime,thetransientovervoltageandtransientcurrent?Howdothehigh‐frequencyphenomenaariseandhowtoquantifythem?Inthisthesis,theseissueswillbedealtwithindetail.

16Chapter2

2.3TransientscausedbycapacitivecurrentinterruptionResearch during the last two decades has confirmed that interruption ofcapacitive currents by DSs can be a major source of interference in secondarycircuits of HV substations [21], [22]. DS operation generates high‐frequencytransients,whichmayendangersensitivesecondarycomponentsof thenetworkthroughelectromagneticcoupling.DuetotheslowmotionoftheDSmainbladesduringoperation,anarcoflongduration(uptoseveralseconds)arises.Thearcischaracterized by numerous interruptions and re‐strikes and is associated withhigh‐frequency phenomena. These voltage and current transients have beenreportedtointerferewithorevendamagesecondarysystems[23]‐[28].Reportedexamplesare:(i)PG&ECompanyintheUSAexperiencedproblemswithswitchingoff the DSs leading to an equipment damage [23]; (ii) transients in substationshavebeenidentifiedtointerferewiththecontrolsignalwiringandpowersupplyunitsforprotectionrelaysburneddownduringDSoperationinEurope[24]‐[26];(iii)afaultyrelayperformanceoccurredbecauseoftheDSoperationina500kVswitching operation in China [27]; (iv) computer simulations and fieldmeasurement confirmed the possibility that normal operation of air DSs couldresultinadamagedcurrenttransformerinArgentina[28].Theliteraturerelatedtotransientphenomenamainlyfocusesonsystemvoltagesabove220kV.Amajorpartof thepublicationseitherdescribes field tests inHVsubstations directly, orwas related to investigation of expected surge levels bycomputersimulationafterhavingobservedfaultsinsecondarysystems[29]‐[32],[40].Duetovariousfactorssuchasswitchyardconfigurationandbuslength,therangeof overvoltage levels caused from operations by air‐break DS is broad. Forexample,seriesoftestweredoneat362kV,787kVand1200kVsubstations,withanovervoltagelevelofmaximum1.9p.u.duringswitchingoffoperationsofEHVbusesinRussia[30].Anearlierfieldtestdoneina500kVsubstationinShanghai,Chinarevealedanovervoltagelevelof1.81p.u.whendisconnectinganunloadedbuswithan interruptedcurrentof0.75A [31].Amaximumovervoltage levelof1.4p.u. was observed in two 220kV substations in Bosnia [21], [32], [33]. Alaboratorytestshowedthattheovervoltageisabout2.3p.u.whileinterruptingacapacitivecurrentupto2.3Aat170kVphasevoltage[13].Overvoltagereached2.6p.u. at the termination of the bus, and 3.1p.u. value at a secondary servicecircuitinthestationappeared,duringde‐energizinga396mlongbuswithaDSat345kVintheUSA[40].Thedominanthigh‐frequencytransientwasalsooneofthefactorsofconcerninprevious references. Frequency values reported were in the order of a fewhundredkilohertz.Forinstance,itreached720kHzat138kVwhilede‐energizingthetransmissionline[34];itwasfoundthatdominantfrequencywasintherange

LiteratureReview17

ofabout400‐500kHzat200kVand500kVsubstationfieldtestsreportedin[21],[31],[35].Inconclusion,mostof theworkrelated to transientphenomenaassociatedwithcapacitive current interruption using air‐break DS focused on the overvoltagelevel in a specific substation and also focused onmethods to protect secondarysystems. However, the origin of the transients from disconnecting capacitivecurrents has hardly been studied yet. The influential factors on overvoltage arealsonotconsideredsystematicallyandindetail.Inaddition,thetransientcurrentwas hardly investigated at all. Regarding the dominant frequencies, none of theliteraturegavedetailedanalysisof the fastmechanisms involved.Therefore, thefundamental phenomena resulting in high‐frequency behaviour during theswitchingprocesswillbestudiedinthisthesis.2.4ApproachestoenhancetheinterruptioncapabilitySeveralapproachestoenhancetheabilitytointerruptthecapacitivecurrentwithair‐breakDSsareaddressedintherelatedliterature.Uptonow,mainattentionispaidtohigh‐velocitycontactopeningdevices,inserteddampingresistorsandgas‐blastdevices.2.4.1FastcontactseparationAhigh‐velocitycontactopeningdevice(alsocalledwhiptypequick‐break)canbeattachedtotheDS.Itassistsinextinguishingthearcbyachievingalargeairgapwithinashorttime.AnexampleofsuchdeviceisshowninFigure2.7.In 1989, a series of laboratory testswas conducted based on 10 differentwhiptype quick‐break devices mainly attached at vertical‐break DSs by the U.S.DepartmentofEnergy[36].Thegoalwastodeterminethemaximuminterruptingcapacitive current capability of 115kVDSswith this type of device. The resultsshowed successful interruptions up to 11A at 115kV, managed by the devicehavingthehighesttipspeed.Itwasfoundthattheinterruptedcurrentmagnitudeplayedamoreprominentrole thantheRVacross theDSmainblades.However,therewerenofurtherdetailsreportedonthedesignofthedeviceitself.Inastudyreportedin[17]atotaloffivetypesofDS/quick‐breakdevices,togetherwithacentre‐breakandpole‐mountedDStode‐energizeasectionof115kVline,were tested. The results showed that one of the quick‐break DS designs couldsuccessfully drop a 29km line at 115kV (corresponding to 6.5A). It was alsostated that high tip speed and minimum bounce of quick‐break devicessignificantly enhance the charging current interruption capability, withoutmentioninganysupportingdetails.

18Chapter2

Figure 2.7. A centre‐break DSwith a high‐velocity auxiliary device (indicatedwithin theellipse,fromthetestinthisthesis).Reference[37]alsoconfirmedthatahigh‐velocitydevicewasabletosuccessfullyinterruptacapacitivecurrentof8Aat138kV. In [38]both laboratoryand fieldtestswerecarriedoutintheAlleghenyPowerSystem.Theresultshowedthatthehigh‐velocityopeningdevicesucceededinterrupting17.6Aat80kV.The cited literature revealed that a fast‐opening device usually is employed at138kVorbelow,anditwasmainlyinstalledwiththevertical‐breakDStype.Itcanbe concluded that a high‐velocity opening device extends significantly thecapabilityofinterruptingcapacitivecurrentofaDS.Theinterruptionmechanismwith this high‐velocity interrupter on a centre‐break DS will be furtherinvestigatedinChapter7ofthisthesis.2.4.2ResistivetransientssuppressionA resistor inserted into the circuit can reduce the transients imposed on thesystem [5], [39]‐[44]. In [39], itwas reported that the resistance in series or inparalleltothearccanlimittheamplitudeandthedurationofthetransients.Inordertoevaluatetheswitchingsurgelevelbydisconnectingcapacitivecurrentsandmagnetizingcurrents,reference[5]describedaseriesoftestsonanAmericanEHVexperimentalline.Theswitchingsurgewasstudiedwhiledisconnectingwasachievedwithaconventionalswitchwithandwithoutsurgevoltagesuppressingresistors. Charging currents of 2.4A at 400kV and 3.0A at 505kV wereinterrupted.Comparedtothesituationwithoutresistor,thesurgeleveldecreasedbyabout15%,whichmeanstheinsertedresistorwasbeneficialfordisconnectingacapacitivecurrent.In Figure 2.8 three remedial approaches to reduce the surge level in a 345kVsubstation, according to [40], are shown. These methods are: (i) a resistor in

LiteratureReview19

serieswiththeDSduringopening;(ii)aporcelain‐enclosedresistorplacedatthesame vertical position as the stationary contact of the vertical‐break DS, whichwas inserted automatically step by step during the operation; (iii) a parallelcombinationoflinetraps(adevicethatblocksthehigh‐frequencycarrier(24kHzto500kHz)andletspower‐frequency(50Hz‐60Hz)passthrough)andaresistorconnectedinserieswiththeDS.Itappearedthatmethod(iii)didnotproveveryeffective in limiting overvoltages, but methods (i) and (ii) were effective. Theovervoltage at the station service (secondary) circuit dropped to 1.7p.u. and toonethird,respectively,comparedwith3.1p.u.fromtheinterruptionwithoutanyremedial devices. The resistor, which was bypassed whenever the DS was inclosedposition,alsoappearedtobethemosteffectivewaytoreduceovervoltages.Asimilarmethodtograduallyinsertaresistancewasagainemployedin[41]‐[43].A computer simulation of a three‐phase 550kV system using distributedparameters was carried out to investigate the re‐strike transients upondisconnecting unloaded transmission line. The simulations indicated that thesurge‐suppressing resistors were effective in limiting the surge current andsignificantly contributed to damping of the re‐strike transients [41], [42].Reference [43] reports a series of field tests, in which a 0.5MΩ resistor wasinstalled in parallel to themain blades of theDS including a small arcing horn,conductedat a220kVpower station (Figure2.9).The results at switchingoff abusbarshowedthatthearcingdurationwasreducedfrom2.5swithoutresistorto thevaluebetween1.1sand1.5swithparallel resistors. Itwasalso reportedthatthehigh‐frequencycomponentofthevoltagewaveshapesmeasurednearbywas damped. The overvoltage in the antenna of the secondary system in thevicinityreducedfrom3.1p.u.withoutresistortoonly1.6p.u.withresistor.Fromthese results it can be concluded that the damping resistor has a strongsuppressing effect on the transient overvoltages caused by interrupting smallcapacitivecurrent.Further,in[44]theeffectofthearcresistanceontransientssuppressionduetoDSswitchingwasstudiedanditwasconfirmedthatarcresistancereducedtransientovervoltages.Insummary,mostoftheworkonemployingresistivedevicesfocusesonthesurgeor overvoltage level. However, still the conclusion can be drawn that a resistorenhancesthecapacitivecurrentinterruptioncapabilityoftheDSs.Forinstance,a396m long bus of 345kV was successfully interrupted according to [40].Reference [43] showed that arcing time was reduced greatly by a resistor inparallel to themainbladesof theDS. Inaddition, itwasmentionedthatwithaninsertedresistorcurrentsupto4Aat230kV,3Aat345kVand1.5Aat500kVwereinterrupted.However,nospecificdetailswereprovided[45].

20Chapter2

Figure2.8.Sketchof345kVDSwithvariousremedialdevicesmountedinplace(copiedfrom[40]).

Figure2.9.InstalledDSwithdampingresistorina220kVsubstation(copiedfrom[43]).Inthisthesis,aresistorinseriesorinparalleltoacentre‐breakDSwillbestudiedthrough simulation and laboratory experiments. The pros and cons will bediscussed.2.4.3ArccoolingA gas‐blast device, as a method to improve the DS capability, is not usedfrequently. Such gas–blast interrupting attachment was mounted on a vertical‐breakDSasindicatedinFigure2.10.Eachpoleunitwasequippedwithaporcelain

LiteratureReview21

Figure2.10.Gas‐blastinterruptertestatTiddtestsite(copiedfrom[47]).tubemountedbetweenthebladeinsulatorstacks,andeachporcelaintubehadaconvergent‐divergentnozzle,aiming todeliver thehigh‐speed jetofgas into thearc.Thismethodwas foundtobeamosteffectivemeans to interruptcapacitivecurrentsaccording to [5], [37], [46]‐[48]. Itwas stated that gas‐blasthas strongeffectinreducingthearcreachandarclengthbyvisualobservation,butwithoutquantitativedatasupport[5];Testsshowedthatavertical‐breakDSwithgas‐blastdevicecoulddrop20AataU.S.138kVstation[37];a135kmlinewasdroppedsuccessfullyat230kV(estimatedcurrent25A)withthesupportofthegas‐blastas reported by a test program on a vertical‐break DS at the U.S. Bureau ofReclamation[46];a330kVvertical‐breakDSwithgas‐blastdevicewasdesignedasshown inFigure2.10 [47].Specifically theporcelain tubewasconnected toagastank,whichwasmountedundereachsingle‐poleswitchunit.Thetest intheAmerican Gas and Electric 500kV Tidd test site showed that it was capable tointerruptcapacitivecurrentupto8.5Aat220kVsuccessfully.Further,anitrogenpufferwasusedinanefforttofacilitatetheDSintheinterruptionofmagnetizingcurrent[48].The work related to gas‐blast is relatively old. Exclusively, an extra tube wasappliedunderthevertical‐breakDS.Sinceitwasprovedthismethodtobemosteffective,inthisthesis,thisapproachwillbecontinuedtostudy,butmainlyfocusonthearcextinguishingmechanismandinterruptionperformances.2.4.4VacuumandSF6interrupterDue to the extraordinary arc interruption performances, vacuum and SF6interrupters(seeFigure2.11)arealsoimplementedinconjunctionwithanairgapDSinsomedesigns[45].However,inthesecases,thecostsinvolvedarehighandtheconstruction iscomplex,because the interruptersmustbeable towithstandthe full RV.Most commonly, only vertical‐breakDSs are providedwith such anauxiliary interrupter. In principle, during the opening operation of the DS

22Chapter2

Figure2.11.(Left)multiplevacuuminterruptersand(right)asinglegapSF6interrupterperphase(copiedfrom[45]).the current is transferred into a loop with the SF6 or vacuum interrupter thatperformstheswitching.TheSF6orvacuuminterruptersareoutofcircuitduringtheclosedpositionoftheDS.Theworkingprincipleofthissortofapproacheswillbe described below in detail using vacuum medium as an example. The SF6interrupterdoesinasimilarmanner.Arcs in vacuum are easier to interrupt than in air, because the vacuum has anelectricalstrengthoftypically30kV/mmincaseofwellpolishedcontactsurfaces.Thishighelectricfieldwithstandstrengthandveryfastrecoveryensurethatoncethearcisextinguished,usuallyatthefirstcurrentzero,nore‐ignitionoccursanddielectric recovery is achieved within a few microseconds [51]. The idea ofcombining the DS with vacuum interrupters is to commutate the current paththrough the vacuum interrupters first and then open the contacts within thevacuum. In general, multiple series vacuum interrupters are needed for highvoltage since a single vacuum interrupter can only function atmedium voltagelevel[52].TheworkingprincipleofaninsertedsinglevacuumbottlewithverticalDSisplottedinFigure2.12.Itworksaccordingtothefollowingsteps:‐ Step 1: the DS is in closed position. The vacuum interrupter is out of the

circuit. The current flows between jaw (metal part connected with mainbladesattherightside)andbladecontacts.Thevacuumcontactsareclosed.

‐ Step 2: the DS contacts separate but the circuit ismaintained through themovingarchornandthefixedarchorn.Asthebladescontinueopening,themoving arc horn engages the vacuum interrupter’s actuating arm. Thevacuumcontactsremainstillinaclosedposition.

‐ Step 3: as the blade movement continues, the fixed and moving hornsseparate. The current is transferred to a path through the closed vacuumcontacts.Afteranadequateclearancedistance isestablished, the current isinterrupted insideof thevacuuminterrupterwithnoexternalarcingasthecontactsopen.

LiteratureReview23

Figure2.12.InterruptionforDSwithinsertedvacuumbottle(s),(obtainedfrom[52]).‐ Step4: theDSmovesto the fullyopenpositionreleasingtheactuatorarm,

whichisspringloadedtoreturntoitsoriginalpositionandclosethevacuumcontacts.

Thisapproach isactually closer toa load‐breakswitch than toaDS switch.Themainadvantageisthatitcaninterrupthighercurrentsthananair‐breakDSalone.The level of the current to be interrupted is determined by the number of thevacuummodulesconnectedinseries.Forinstanceitiscapabletointerruptupto70Acapacitivecurrentforuptoratedsystemvoltage230kV[45].Thedrawbacksofavacuuminterrupterare:‐ There is no visual indication of the dielectric integrity prior to operation,

creatingapotentialsafetyhazardtopersonnelwhenoperatingtheDS.‐ EachvacuumbottleinaDSwithamulti‐bottlestackcanhandleonlytheMV

voltage level (up to 30 kV). Grading capacitors are required to divide thevoltage evenly across the multiple gaps for successful performance. Avacuuminterrupterstackcanonlybeinstalledonavertical‐breakorasingle‐sidebreakDSsduetoitscomplexconstruction.

Sincemostoftheliteratureisrelatedtothevertical‐breakDSasatestobject,thepotential interrupting capabilityof thevertical‐breakDSwith theaidof variousapproachesandtheircorrespondingcostsaresummarized inTable2.2.Vacuuminterrupterscanbeusedtointerrupthighercurrent.Issuestobeconsideredarethecostsandtheneedforgradingcapacitors.SF6mayinterruptthehighestlevelcurrentcomparedwiththeotherapproaches,butwithhighestcost.

24Chapter2

Table2.2.Potentialinterruptionratingsofvertical‐breakDSswithdifferentauxiliarydevices.Note:thecostsaretakenfrom[45],assumingthecostofthearcinghornis"1".

Typeofauxiliarydevices

Interruptingcapability(Arms) Cost

Arcinghorn Interruptsverysmallcurrent,referto[7] 1High‐velocitydevices

Higherthanwitharcinghorn(e.g.upto8Aat138kV[37])

1.2

Gas‐blast Higherthanwithhigh‐velocitybreakdevices NoliteratureMultiplevacuuminterrupters 70Aatupto230kV 2.8

SF6interrupters Upto300Aatupto230kV 3.6

Resistors4 A—230 kV3A—345kV1.5A—500kV

Noinformation

2.4.5.AblationassistedapproachesTheuseofarccoolingthroughablation,i.e.evaporatedmaterialsfromcompoundslike polyvinyl chloride, polymethylmethacrylate, etc. is a method commonlyappliedinloadbreakdevices[53],[54].Theworkingprincipleisconfinementofthehotarcinanarrowtubecausingahighpressureandfastflowinggas,whichfacilitates rapid arc extinction. Based on thismethod, a special arcing horn hasbeen developed [55]. This device was designed originally to prevent lightningdamage on overhead line, capable of interrupting ground fault currents. It wasconfirmed experimentally that it can interrupt ground fault current up to 1kAwithinhalfcycleat77kVsystemvoltage.Figure2.13showsthearrangementandworkingprinciple.Thereisanarrowtube,madeofpolyvinylchloride,mountedatthe tip of the arcing horn electrode in order to interrupt the current. Theinterruption portion, located in the ground side horn, is a tube with anintermediateelectrode.Thiselectrodeisasmallcolumn,whichpiercesataspotinthe tubewall.When excessive voltage is applied between the horns at line andground side, a breakdown occurs between their tips through the intermediateelectrode. Then, the arc arises between the horns. The gas during arcing in theinterruptiontubehasgainedahigh‐velocityandahigh‐pressure.Thedevicewasnotableto interruptashort‐circuitcurrentabove10kA.Nofurther informationabout the interruption performance below 445A was reported. Pressure andvelocityofthegasinsidethetube,andtheablationofthetubematerialatcurrentlevelsaround10Amightbetoolowforeffectiveoperation.

LiteratureReview25

Figure2.13. WorkingprincipleofablationassistedarcinghornwithPVCtube(copiedfrom[55]).Arcinterruptionthroughablationisverysuccessfullyappliedinmediumvoltageloadbreakswitches.Oneapplicationisdiscussedhere[56].Figure2.14showsthestructure and working mechanism. Upon disconnecting, the main contacts "1"openfirstandthecurrent isbrieflytakenoverbytheparallelconnectedlaggingpins "2". During this breaking motion, the opening springs "3" acting on thelaggingpinare tensioned.Onreachingastop, the laggingpin leaves theholdingcontact "4".Thearcoccurringbetweenthearcing tipof theholdingcontactandthetungstentipofthelaggingpinisextinguishedinthearcingchamber"5".Thearcing chamber itself is closed. This device contains four sections and has apressurechamber"6"andanexpansionchamber"7".Twoextinctionplates "8",arranged in thepressure chamber, are forced into thepathof thearcby lateralspringpressure.Atlowcurrentsthearcisextinguishedduetothecoolingeffectofthewalls. In the higher current range arc extinction is achieved by the ablatedgases produced in the pressure chamber flowing out of this chamber into theexpansion chamber. Owing to this complementary combination of severalextinctionprinciplesawidecurrentinterruptionrangeiseffectivelycovered.Thisdevice is capable to interrupt cable charging currentsup to20A at lowvoltagelevel 38.5 kV. For higher current and higher voltage levels, no informationwasprovided.Basedonusingablationassistedarcextinctionascommonlyused in loadbreakswitches was considered. Present designs require high current (for sufficientablation)orarelimitedtorelativelylowvoltagelevel.Theirapplicabilityonhighvoltageair‐breakDSsmaybequestionablebecausethelonglengthofthearcandthe lowerenergydensity. Inaddition,confining theDSarc inasmall spacemayhaveadverseeffectsbecausecoolingfromambientairisobstructed.Thismaybeconsideredforfurtherinvestigation.

26Chapter2

Figure2.14. Workingprinciple foran indoor loadbreakswitchwithtwochambers(copiedfrom[56]).2.5ArcmodelsrelatedtocurrentinterruptionwithadisconnectorAnelectricarcisadischarge,characterizedbyahighcurrentflow(ascomparedtoothergasdischarges,likeglowdischarge),resultinginacurrentflowingthroughausually non‐conductive medium such as air. Understanding the phenomenaassociated with the electric arc requires combined knowledge of electro‐magnetism,thermodynamicsandplasmaphysics.The electric arc related to current interruption with a DS is a so called freeburningACarcwith relatively lowcurrent (up toa few tensof amperes) in theatmosphere. It behaves differently from the well‐studied and well‐documentedfault arc in circuit breakers because of its much higher length (metres vs.centimetres), its much lower current (amperes vs. kilo‐amperes) and itsunconfined ("free‐burning") nature. Compared with the short arc, where theinfluenceofanodeandcathoderoots issignificant [57], thearc lengthofDSarcmay reach up to a few metres depending on the system voltage and current.Comparedtotheconfinedarc,thefreeburningarcbehavesmorerandomlyandisinfluenced by external conditions as wind, humidity, and surroundingelectromagnetic fields. An overview of the free burning arc literature waspresentedin[6].Arcmodellingmaybeaneffectivecomputationaltoolwhenfieldexperimentsaredifficult to manage. Selected models from literature are therefore discussed inrelationwiththeirapplicabilityforthearcfromalowcurrentinterruptionorfreeburningarcintheair.Duetotherandomnatureofthefreeburningarc,itispracticallynotpossibletoduplicatethegenuinearccharacteristicsbyacomputermodel.Sometimesthearcisrepresentedbyaresistororasavoltagesourcewithperiodicrectangularwaveform, changing its sign at each arc current zero crossing; sometimes a more

LiteratureReview27

complicatedmodelwithpiecewisecharacteristicsisadoptedtopresentthearcatvariablelength,resultinginavariablearcvoltage.However,thesearcmodelsdonot take into account the actual interaction of the arc and the electromagnetictransients in the circuit [58], [59]. No model exists, taking into account thediscontinuouscharacterof thearc,which isobserved in thepresentstudy tobethemainfeatureofthelow‐currentDSarc.Therefore,onlymodels,moredistantlyrelatedtothearcinDScurrentinterruptionwillbeintroducedhere.Anarcmodelsimulatingthebehaviourofarcsdrivenbymagnetic force inagas[57], [60]‐[62],was proposed first in [62]. The arc is assumed to be a chain ofsmall rigid cylindrical current elements. Each element experiences the Lorentzforce from themagnetic field and a fluid drag force from the surrounding gas.Each element moves with the velocity determined by these forces. The arcbehaviour is determined by the position and the motion of each element.Consequently,thebehaviourandtheshapeoftheentirearcmaybeconstructed.Experimentsin[62]withcurrentof1kAat50HzinSF6showedgoodagreementbetweenmodelandtheobservedarcinpractice.Inoverheadline,generally,anarcinghornisusedtoprotecttheinsulatorsagainstdamage from arcs after switching, or by lightning induced breakdown to earth.The arcing horn is installed in parallelwith the insulator. The arc between thearcinghornsbehavesasafreeburningarcintheair.Basedonthemodel[60],itcanbeestimatedhowfarthearcisfromthecolumnoftheinsulator.Asituationforacurrentof160Awasstudiedin[61],resultinginagoodmatchbetweenthesimulationandexperiments.Suchanarcmodelcanpotentiallybeusedtodescribearc movement related to DS current interruption, and to evaluate the risk ofendangeringthesurroundingequipment.However,thecurrentrelatedtotheDSinterrupting has much lower values and their arc movement is much moreinfluencedbyconvectionprocessesthanbyelectro‐magneticinteraction.Comparedwith all other types of arcmentionedbefore, the secondary fault arcfrom EHV power overhead line resemblesmost closely the arc from capacitivecurrent interruption with a DS because of a comparable length and similarenvironmental(unconfined)conditions.Asecondaryfaultarcfollowstheprimaryfaultcurrentinsinglephasetrippingandreclosingschemesduetocapacitiveandinductivecouplingwiththesoundphases[63].Thevalueofthesecondarycurrentmayreachuptoafewhundredamperesandisdeterminedbythestructureoftheoverheadline,suchaslinearrangement,length,earthing,etc.TheCassiearcmodel[64],frequentlycited,assumesthatthearcchannelhastheshape of a cylinder and is filled with highly ionized gas with a constanttemperature,butwithavariablediameter.Cassiedevelopedhisarcmodelbasedontheassumptionthatahighcurrentarcisgovernedmainlybyconvectionlosses.OneofthemostcommonusedCassiearcequationformulationsis:

28Chapter2

2

20

d[ln( )] 1 ( 1)daug

t u (2.3)

whereu0 is the static arc voltage,ua is themomentary arc voltage, is the arctimeconstant,gistheinstantaneousarcconductance.Throughstudyofexperimentalu‐icharacteristicsofarcs,havingpeakarccurrentvalues from 68A to 21kA, it was found that the Cassiemodelmay be used tomodel the behaviour of the secondary arc [59]. Knowing 0,au u , from specificexperiments, the arc conductanceg can be determined to represent the arc forcomputersimulation[66],[67].Based on the Cassie model, Kizilcay defined the arc behaviour according [53],[68]‐[70]as:

0 0

d 1 ( )d ( )

a

a a

g G gt

iG

u r i l

(2.4)

whereiaistheinstantaneousarccurrent,latheinstantaneousarclength, 0u isthearc voltage per unit length, 0r is the arc resistance per unit length, G is thestationaryarcconductance.Parameters , 0u , 0r dependonarclength,andcanbeobtained over a certain time interval due to the required high accuracy ofmeasured arc current and voltage from specificmeasurements, as described indetailin[59].Thismodelnotonlyconsiderstheheatofthearc,butalsotakesintoaccountthesecondaryarcelongation.Theexperimentswithacurrentuptoafewhundred amperes matched the simulated results well. It may be feasible todescribethearcwithlowercurrent(fromcapacitivecurrentswitchingaswell).Terzijatookconsiderableefforttomodellongarcsinfreeair[71]–[75].Thearcinhis experimentswas initiatedbetween twoelectrodeswith adistanceof 60cm,thecurrentranged from100Ato20kAatasystemphasevoltageof20kV.Theequationused is a generalizationof (2.3): d ( , , , )d

aa a a

g f g u i tt

.Byobserving thearcvoltagewaveform,presentedroughlyasarectangularshapeinphasewiththearccurrent,thearcwasmodelledthroughthefollowingnonlinearequation:

0( ) ( ) sgn( )( )a a b b abIu t U U R i t ii t

(2.5)

LiteratureReview29

where ( ), ( )a au t i t arearcvoltageandarccurrent,

0 0

0

( ) <( ) ( ) ( ) a

ba a

I i t Ii t

i t i t I

(2.6), , a bU U R areparametersdefining theshapeof thearcvoltage, is toaccount

forGaussiannoisewith.Ua=Eala,theaverageofEawastakenbetween1.2kV/mand 1.5kV/m for the chosen experimental current range. The term 0( )b b

IUi t

models the arc re‐ignition voltage, and ( )bR i t is an additional term, which isdeterminedby the arc current ia,R , is part of the arc resistance, at the chosencurrentrange,intheorderoftenthsofohm.Theauthoraddedtheeffectofthearcelongationin[75]bymultiplying(2.5)withasuitableelongationfunctionL(t)in[73].Thearccurrentfromtheexperimentswasintherangetakenoffaultcurrent.For instance, the model was applied to a secondary arc in overhead line [74].However, the method may also be considered to describe the arc related tocapacitivecurrentoperationwithaDS.Exceptforthearcmodelbasedonmagneticforces,theothermodelsintroducedinthissectionareexclusivelybasedontheCassiearcmodel.Mostmodelparametersmustbeobtainedfromspecificfieldexperiments.Asaconclusion,althoughthereis no detailed arc model connected to current interruption with a DS, the arcmodels mentioned above may be considered as a first step. Because of therandom,inhomogeneousandtimedependentnatureoftheconductingmedium,ithasnotbeenattemptedtodesignanarcmodelinthepresentstudy.2.6ConclusionCapacitivecurrentinterruptionusinganair‐breakDShasnotattractedtoomuchattention, and the existing literature provides only a limited insight into themechanism.However,certain literaturesourcesdoexist,whicharemoreor lessrelated to this subject. Each from different points of view and with differentapplication purposes, such as surges imposed on secondary systems,disconnectionofmagnetizingcurrents,loopcurrentsandsoforth.It is recognized thatDS requirements should include the capability to interruptsmall capacitive current. Based on field tests and computer simulations atdifferent system voltage levels, it was found that interrupting even of smallcapacitive currents can cause large transients, which potentially can damagenearbyequipment.Also,arcswithunacceptabledurationand/orreachcanarise.

30Chapter2

Amongmany factors, which influence the capability of interruption in practice,such as clearance distance, atmospheric condition (wind, humidity), conductorconfigurationsandsoon,afewfactorswererecognizedandinvestigated.Theroleofbuslength(sourceandloadsidecapacitance),parallellines,lineconfigurationswerepointedout.Inaddition,high‐frequencytransientswererecognizedonlytoapracticalextent,butneitherfundamentallynorsystematicallyinvestigated.Inthisliteraturesurvey,itwasfoundthattherearenointerruptionratingsforDSsexceptthosegivenbyIEEE[7].TheIECstandard[14]alsofailstoclarifythistopic.On the other hand, the present power systems are rapidly increasing in size,requiringperformancesbutalsoenhancingcost‐effectiveness.Incertainlocations,low‐cost DSs having an enhanced current interruption capability could in somesituationsofde‐energizationofunloadingtheshort line/cable/busbartoreplacethecircuitbreakers.It is indispensable to understand the phenomena of capacitive current throughfreeburningarcsinairprofoundlyandtofindapproachestoimprovetheabilityoftheswitchingdevice:thedisconnector.Thisconsiderationisthemotivationoftheworkinthisthesis.References[1] P. A. Abetti, "Arc interruption with disconnecting switches", Master thesis, Illinois

InstituteofTechnology,Jan.1948.[2] F.E.Andrews,L.R.Janes,M.A.Anderson,"Interruptingabilityofhorn‐gapswitches",

AIEETrans.,vol.69,pp.1016‐1027,Apr.1950.[3] M. W. Anderson, "Power autotransformer current interruption with an air‐break

disconnect switch", IEEETrans. onPowerApparatus and Systems, vol.74, pp. 1157‐1163,Jan.1955

[4] CEAProject069‐T‐102report,"Theinterruptingcapabilityofhighvoltagedisconnectswitches",CanadianElectricalAssociation,Jul.1982.

[5] A.FotiandJ.M.Lakas,"EHVswitchtestsandswitchingsurges,"IEEETrans.onPowerApparatusandSystems,vol.83,pp.266‐271,Mar.1964.

[6] D. F. Peelo, "Current interruption using high voltage air‐break disconnectors", Ph.D.dissertation,Dept.ElectricalEngineering,EindhovenUniv.ofTechnology,Eindhoven,2004.

[7] IEEEGuidetoCurrentInterruptionwithHorn‐GapAirSwitches,IEEEStandardC37.36b‐1990,Jul.1990.

[8] AIEECommitteeReport,"Reportontransformermagnetizingcurrentanditseffectonrelayingandairswitchoperation",AIEETrans.,vol.70,pp.1733–1740,Jul.1951.

[9] IEEE Committee Report, "Results of survey on interrupting ability of air‐breakswitches", IEEETrans.onPowerApparatusandSystems, vol.PAS‐85, pp. 1008‐1019,Sept.1966.

[10] D. F. Peelo, "Current interrupting capability of air‐break disconnect switches", IEEETrans.onPowerDelivery,vol.1,pp.212‐216,Jan.1986.

LiteratureReview31

[11] D. F. Peelo, "Current interrupting capability of air‐break disconnect switches", IEEEPowerEngineeringReview,vol.PER‐6,pp.53‐54,Jan.1986.

[12] D.F.Peelo,R.P.P.Smeets,L.vanDerSluis,S.Kuivenhoven, J.G.Krone, J.H.SawadaandB.R. Sunga, "Current interruptionwithhighvoltageair‐breakdisconnectors", inProc.CigreConf.,papernr.A3‐301,2004.

[13] D.F.Peelo,R.P.PSmeets,J.G.Krone,"Capacitivecurrentinterruptioninatmosphericair",inProc.CigreA3/B3Colloquiun,2005.

[14] IEC Standard for High voltage Switchgear and Control Gear –Part 102: AlternatingCurrentDisconnectorsandEarthingSwitches,IEC62271‐102,Dec.2001.

[15] H.Knobloch,"Switchingofcapacitivecurrentsbyoutdoordisconnectors",inProc.FifthInternationalSymposiumonHighVoltageEngineeringConf.,Aug.1967.

[16] E.W.Boehne,"EHVsurgesuppressiononinterruptinglightcurrentswithairswitchesI‐ capacitive currents", IEEE Trans. on Power Apparatus and Systems, vol.PAS‐84,pp.906‐923,Oct.1965

[17] S. G. Patel, W. F. Holcombe, D. E. Parr, "Application of air‐break switches for de‐energizing transmission lines", IEEE Trans. on Power Apparatus and Systems, vol.4,pp.368‐374,Jan.1989.

[18] A. Schutte, H. Rodrigo, "Transient phenomena due to disconnect switching in highvoltage substation", in Proc. 11th InternationalHigh Voltage Engineering SymposiumConf.,London,Aug.1999

[19] I. B. Johnson, A. J. Schultz, N. R. Schultz, R. B. Shores, "Some fundamentals oncapacitanceswitching", IEEETrans.onPowerApparatusandSystems, vol.74,pp.727–736,Aug.1955.

[20] W.M.Leeds,R. C. van Sickle, "The interruptionof charging current athighvoltage",AIEETrans.,vol.66,pp.373–382,Jan.1947.

[21] S. Carsimamovic, Z. Bajramovic, M. Ljevak, M. Veledar, "Very fast electromagnetictransients in air insulated substations and gas insulated substations due todisconnector switching", in Proc. International Symposium on ElectromagneticCompatibility,vol.2,pp.382‐387,Aug.2005.

[22] C. M. Wiggins, D. E. Thomas, F. S. Nickel, S. E. Wright, "Transient electromagneticinterference insubstations", IEEETrans.onPowerDelivery,vol.9,pp.1869‐1883,Oct.1994.

[23] R. J. Gavazza, C. M. Wiggins, "Reduction of interference on substation low voltagewiring",IEEETrans.PowerDelivery,vol.11,pp.1317‐1329,Jul.1996.

[24] M. A. van, Houten, E. J. M. van, Heesch, A. P. J. van, Deursen, "General methods forprotection of electronics against interference, tested in high voltage substations", inProc8thInternationalSymposiumonElectromagneticCompatibilityConf.,pp.429‐434.Zürich,Mar.1989.

[25] A.Rodewald, "Interferencegeneratedbyswitchingoperationsand its simulation", inProc.IEEEInternationalSymposiumonEMCConf.,pp.133‐138,1984.

[26] S.Carsimamovic,R.Gacanovic,Z.Bajramovic,"Switchingovervoltagesinair‐insulatedsubstation(AIS)duetodisconnectorandcircuitbreakerswitching",papernr.C4‐301,CigreConf.,Paris,2006.

[27] W. Mao, "Analysis for malfunction of CBF relay insulating switch operation",AutomationofElectricPowerSystems,vol.26,pp.74‐76,Apr.2002.

[28] A. Funes, A. Ledesema, "Field measurements and modelling of high‐frequencytransientduringdisconnectswitchoperationsinEHVsubstations,assessmentoftheireffectsonCurrentTransformers",papernr.A3‐207,CigreConf.,Paris,2010.

[29] G. Carrsco, "Electromagnetic interference in substation Jose up to 400/115 kV", inProc.IEEETransmission&DistributionConferenceandExposition,pp.1–6,Aug.2006.

32Chapter2

[30] V. S. Rashkes, L. D. Ziles, "Very high‐frequency overvoltages at open air EHVsubstations during disconnect switch operations", IEEE Trans. on Power Delivery,vol.11,pp.1618‐1623,Jul.1996.

[31] Z. Liu, "The test of switching no‐load bus with 500 kV disconnector",HighVoltageEngineering,vol.4,pp.58‐61,1990.

[32] S. Carsimamovic, Z. Bajramovic, M. Ljevak, M. Veledar, N. Halilhodzic, "Currentswitching with high voltage air disconnector", in Proc. International Conference onPowerSystemsTransients,papernr.IPST05–229,Jun.2005.

[33] S. Carsimamovic, Z. Bajramovic, M. Veledar, O. Hadzic, A. Carsimamovic, "Computersimulationoftransientsduetodisconnectorswitchinginair‐insulatedsubstations",inProc.InternationalConferenceonComputerasaTool,pp.2051‐2053,Sept.2007.

[34] S.G.Lodwig,C.C.Scheutz,"CouplingtocontrolcablesinHVsubstations",inProc.IEEEInternational Symposium on Electromagnetic Compatibility, vol.1, pp. 249‐253, Aug.2001.

[35] Z. Lu, C. Wang, "The switching transient electric field measurements in a 500 kVsubstation",inProc.the3rdInternationalSymposiumonElectromagneticCompatibility,pp.194–197,May2002.

[36] R. J. Denis, "Tests to determine the interrupting capabilities of 115 kV quick‐breakdevices",Divisionof laboratoriesreport fromU.S.DepartmentofEnergy,Tech.Rep.BonnevillePowerAdministration,Mar.1989.

[37

capacitive current interruption with high voltage ... - pure · capacitive current interruption...

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