Development and test of a 120 kV direct current ci

*[e-mail]*J.-P.DUPRAZ,D.-L.PENACHEL.VIOLLEAUAlstomGridRTE-RéseaudeTransportd’ElectricitéFranceFranceSUMMARYWhenconsideringmultipleoffshorewindfarmsfarfromthecoast,aHVDCnetworkconnectingthesefarmstothelandensures,comparedtoDCradialconnections,agoodflexibilityandmultiplepathstoevacuatetheenergytoshore.ForthisreasonwithintheTWENTIESprojectfoundedbytheEuropeanFP7programme,onedemonstrationprojectwasproposedbyRTEinordertoremovethemainbarriersforDCgrids.TheabilityoftheDCgridtoovercomeaDCfaultisoneofthemajorchallenges:whenafaultoccursintheDCgrid,itisnotpossibletoforcetheDCcurrentandvoltagetozeroandtore-startthegridafterthefaultdisconnection.ThelossofenergyfromtheDCGridwoulddestabilizetheoverallnetworkandinfringeGridcodes.Moreover,mostexistingVSCconverterswhichtodateareconfiguredashalfbridgearenotcapableofblockingtheDCfaultcurrent.Thereforethefeasibilityofsuchagridisdirectlydependantonasuitableprotectiondevice:theHighVoltageDirectCurrentCircuitBreaker(DCCB).AlstomGridjoinedthisdemonstrationprojectandbuiltaDCCB.ThispaperdescribesthemainstepsofthesimulationsmadebyRTEandAlstomGridtoevaluatethefaultclearingdutiesofaDCCB.Fromthesecalculationsfaultcurrentswereidentifiedbasedonthemagnitudeandthetimetopeakafterfaultinception.TheratedvaluestargetedfortheDCCBdemonstratorandchosenbyRTEandAlstomGridarethefollowing:•Ratedvoltage:120kV•Rateddirectcurrent:1500A•Currentinclosedstate3000Afor1minute•Ratedshort-circuitcurrent:7500A•Dielectricwithstandinopenstate650kVThenthispaperpresentsthedifferenttypesofDCCBwiththeiradvantagesanddrawbacks,thesolutionadoptedbyAlstomGridandthemainchallengesindevelopingsuchabreaker.Eventually,thetestproceduresdevelopedtoverifytheperformancesoftheDCCBdemonstratorandthetestresultsarediscussed.KEYWORDSHigh-Voltage–DirectCurrent–CircuitBreaker–Research&Development–TwentiesProject–Tests21,rued’Artois,F-75008PARISB4-301CIGRE2014[1].ThesethreeparametersaretheDCnetworktopology,thefaulttype,thefaultlocation.Thefirsttopologyisapointtopointconnection.Inasecondstageathirdsystemwasaddedwithlinkstothetwoothersystems.Figure1showsthelatterconfiguration.Thesefirsttwotopologieswereimplementedinordertocheckthecharacteristicsofthesimulatedmodel.Converterswereallconfiguredas2-levelconverterswithpulsewidthmodulationforsimplicity,smoothingreactorsof40mHwereusedandcablescreensaregroundedateachends.Moredetailsareinreference[1].Figure1:Threeterminalsystem.Thetopologywasaugmentedtoafiveterminalnetwork(seeFigure2)whichismorerepresentativeofaMultiTerminalDirectCurrent(MTDC)gridtopology.Terminals2and4areonshoreconvertersconnectedtotheACnetworkonthelefthandside;terminals1,3and5areconvertersconnectedtooffshorewindfarms.Figure2:SinglelinediagramofafiveterminalMTDCgrid.BlacksquaresstandforACorDCCBs,linelengthsasindicated.Faultlocationsindicatedbyredarrowsareveryclosetothelinebreakers.100kmL24=75kmL14=50km25km200km3Inthefollowing,onlyresultsofline-to-linefaultswillbepresentedbecausetheyyieldthemoreseverefaultcurrents.CalculationswereperformedforfaultslocatedatthreedifferentpointsasindicatedinFigure2.Figure3showstheresultsofthecalculationswhereashort-circuithasbeenintroducedatthelocation‘fault2’.Sensitivityanalysiswasalsoperformed,forinstancethroughvaryingthelinelengthofcablesbetweenstation4andtheneighboringstations1and2.Figure3:Faultcurrentsforafaultlocatedat‘fault2’inFigure2,currentinlinebreakerofstation4connectedbycabletostation1.Resultsareindicatedfordifferentpairsofcablelengths(L24//L14).Oneachcalculationtheamplitudeandtimetopeakofthefaultcurrentinbothbreakersconnectedtothedefectivecablewasreadwhichallowscalculatinganaveragerateofriseofthecurrent.ThemostseverecaseforeachfaultlocationisshowninTable1.Theorderofmagnitudeofthisrateofrisevariesgreatly.Targetingthemostonerousperformancewouldhaveriskednothavingtestresultsofaviablesolutionattheendofthisthree-yearproject.Hence,giventhestateoftheartendof2010,itappeareddesirabletotargetaDCCBperformanceintherangeoffewkA/msto10kA/ms.Table1:CompilationofmostseverefaultcurrentsatthethreedifferentlocationsshowninFigure2.LocationFaultcurrent(amplitudeandpeaktimeafterfaultinception)RateofriseofthefaultcurrentFault35kAafter15ms0.33kA/msFault145kAafter10ms4.5kA/msFault280kAafter4ms20kA/ms2ComparingAC&DCinterruptionForbetterunderstandingthechallengesinherenttotheDCCBdemonstratordevelopmentthissectionpresentssomefundamentalsofinterruptionandintroducesthenecessarytechnicalterms.Thepresenceofmagneticenergyinaloopandcurrentflowareintimatelylinked.Forasuccessfulcurrentinterruptionitismandatorytoremovethemagneticenergyfromth