外文翻译交流电气化铁路牵引系统.docx

外文翻译交流电气化铁路牵引系统.docx

《外文翻译交流电气化铁路牵引系统.docx》由会员分享，可在线阅读，更多相关《外文翻译交流电气化铁路牵引系统.docx（11页珍藏版）》请在冰豆网上搜索。

外文翻译交流电气化铁路牵引系统

Abstract

Increasingattentionhasbeenshowninrecentyearsinthea.c.electrificationofrailwaytractionsystemsandanumberofestablishedsystemsnowexistthroughouttheworld.Wherethetractionsystemissupplieddirectlyfromahigh-voltagenational-gridnetwork,acommoncomponentofsuchschemesisastepdowntransformerconnectionbetweenthetwosystems.Theelectrical,mechanicalandthermaldesignofthesetransformersissubjecttoanumberofspecialconsiderationsnotnormallyencounteredinthedesignofdistribution-typetransformersofsimilarratingandvoltageclass.Thepaperreviewstheoperatingconditionspeculiartorailwaytractionsuchasovervoltages,shortcircuits,cyclicandpeakloadingsanddiscusseshowtheseconditionsinfluencethedesignandconstructionofsingle-phasetransformerssupplyingpowerfortractionpurposes.ThepaperdescribestheengineeringpracticeandoperatingexperienceobtainedwiththeBritish25kVa.c.railway-tractionsysteminparticular,butmuchofthesystemandtransformer-designphilosophyandoperationalexperiencereferredtoappliestoa.c.tractionsystemselsewhereintheworld.

KeyWords:

Powertransformers,Railways,Traction

1Introduction

InMarch1956theBritishTransportCommissionannouncedtheirintentiontoadopta25kVsingle-phase50Hza.c.systemasthestandardforfutureelectrificationofBritishRailwaysinallRegionsexcepttheSouthern,whereextensionoftheexistingthird-railsystem,whichhadbeenoperatingsatisfactorilyforsomeyears,wasconsideredtobethemostsatisfactorycoursetofollow.

Thecommissionhadearlierauthorizedastudytobemadeofthecomparativecostsofelectrificationat1500Vd.c.andat25000Vsingle-phase50Hza.c.Thisshowedbotheconomicandtechnicaladvantagesinfavorofthea.c.system,andthedecisionwastakentoadoptit.AnotherdecisivefactorwasthesuccessfuloperationalexperiencegainedbytheFrenchRailwayAuthoritiesfromanexperimentalline,installedafewyearsearlierinNorthEasternFrance,operatingatthesamevoltageandfrequency.

Itwasconsequentlydecidedtoadopta50Hza.csystemtointroduceitontheScottish,EasternandLondonMidlandRegions.25kVwaschosenasthegeneralstandardformain-lineservicesand6-25kVasasubsidiarystandardforuseinthoseareas,mainlysuburban,whereitwasnotpracticabletomodifyexistingstructures,suchastunnelsandoverheadbridges,whichatthattimeimposedrestrictionsontheelectricalclearancestoliveconductors.

Asaresultofoperationalexperience,625kVsystemsarenowbeingconvertedto25kV,anditisvisualizedthateventuallythiswillbetheoperatingvoltageforallregions.

Thispaperreviewstheoperatingconditionspeculiartorailwaytraction,resultingfromovervoltages,shortcircuits,cyclicandpeakloading,anddiscusseshowtheseconditionsinfluencetheelectrical,mechanicalandthermaldesignandconstructionofthesingle-phasetransformerssupplyingpowerfortractionfromtheNationalGridsystemtoBritishRailat25kV50Hza.c.AlthoughthepaperdescribesBritishpracticeinparticular,muchofthesystemandtransformerdesignphilosophyandoperationalexperiencereferredtoisapplicabletosystemselsewhereintheworld.

2Systemdata

2.1Supplytotherailway-trackfeederstations

Bulksuppliesaretakenfromthe132kVand275kVgridsystemsviasingle-phasetraction-supplytransformersandfedtothefeederstationsat25kV.Thefeederstationsarelocatedadjacenttotherailtracksat40or50kmintervals,andwhereverpossibleincloseproximitytogridsubstationstoavoidthedisadvantageoflongfeeders.OnthefirstRegionstobeelectrified,suppliesweretakeninduplicate,butonrecentextensionstotheNorthWesternandEasternRegionsasingletransformerhasbeenprovidedateveryalternatesupplypoint,andthepossibilityofinstallingonlyonetransformerinfutureateachsubstationisnowbeingconsidered.

Atypicaltwo-transformerinstallationisillustratedinFig.1.The25kVtractionsupplyistakentothefeeder-stationbusbarseitherbyconcentric2-coreoil-filledundergroundcablesorbysingle-circuitwood-poleoverheadlines.Onefeeder-stationbusbarsuppliescurrenttotheoverhead-contactsystemandaseparatelymountedbusbarisconnectedbysheathedcabletothetrackrunningrail,which,byvirtueoftheoverheadlinesupportingstructurebondedtoit,iswellearthed.

Theduplicatesuppliestothebusbarsareseparatedbyasectionswitchwhichisnormallyopen,andeachcircuitsuppliesanupanddownsectionofthetrack.Whenoutagesarenecessary,formaintenanceoremergencyoperation,thesectionswitchatthesupplypointisclosed.Theremainingtransformermustbecapableoffeedingthewholelengthofthesectionofthetracknormallyfedbytwotransformers.Thedesignedratingofthetransformermustthereforebeadequatetocaterforthemaximumdemandunderthisemergencycondition.Thisdemandmayoccuratanytimeoftheyear,ineithersummerorwinterconditions,thereforethethermalratingofthetransformersmustbeadequatetoensurewindingandoiltemperaturesdonotexceedtheguaranteedmaximumundertheprevailingambienttemperature.

3.Systemoperationalfactors

3.1Loadcurrent

Theload-currentdemandonatraction-supplypointinstallationisofahighlyfluctuatingpatternandisnosinusoidalinwaveform.Thecurrentfluctuationsarerandomintimeandmagnitudeanddependuponthedensityoftrafficwithinthesectionoftractioncircuitsuppliedbythetransformersanduponthemodeofoperatingthelocomotives.Thenosinusoidalcurrent,Fig.2,isofapproximatelysquarewaveformandoccursbyreasonoftheharmonicsgeneratedbytherectifierequipmentonthelocomotives.

Thesignificanceofthistypeofload-currentdutyuponthedesignaspectsofthetransformerisofparticularrelevancewhenconsideringtheratingofthetransformer,theeffectuponregulationandthemechanicalforcesactingonthewindings.

Fig.3representsatypicalload-current-demandcurveobtainedonasupply-pointtransformer.Themaximumvariationofcurrentcanbebetweenzeroandtwoandahalftimesthefull-loadratedvalue.Thecombinedheatingeffectonthetransformerwindingsofacurrentvaryinginthismanner,andhavingthetypicalnosinusoidalwaveformreferredto,isgreater

Fig.1 Typical25kV2-transformerpower-supplyinstallation

Supplyauthoritysupplyrailwayauthoritysupply:

（a）132/33kV3-phasearea-boardtransformers（b）132/25kVsingle-phaserailway-supplytransformers（c）Supply-authoritycircuitbreakers（d）Railway-authoritycircuitbreakers（e）Concentriccablesoroverheadlines（f）Pilotcablesforprotection,telecommunicationandsupervisoryduties.

thanthatwhichwouldbeproducedbyasteadycurrenthavingavalueequaltomeanvalueofthefluctuatingcurrent,althoughbothwouldindicateequalMWreadingsonthehalf-hourintegratedmaximum-demandmeters.

Correlationoftypicalsupply-current-demandcurves,obtainedduringmeasurementsunderbothnormalandemergencysupply-pointoperation,indicatesthatifatransformeristocaterfortheworstexpectedloadconditionwithoutexceedingtemperature-riselimits,theequivalentratinghastobesome1-2to1-3timestheexpectedcircumstances.Thevaryingmagnitudeoftheloadcurrentalsohasaneffectupontheintegratedhalfhourlymaximumdemandfortheparticularoperatingmechanicalstrengthsofthetransformerwindings.Inservice,thewindingsaresubjectedtopulsatingforcessimilar,inmanyrespects,tothoseexperiencedby

Fig.2 Onecycleoftypical25kVand50Hztractionvoltageandcurrent

rectifierandarc-furnace-supplytransformers.Theseforcescanhavedeleteriouseffectsontheperformanceofthewindingsandassociatedinsulationinservice,unlessmeasuresaretakeninthedesignandconstructionofthetransformertoensurethattheycanbewithstood.

Fig.3 Typicaltractionload-current-demandcurve

3.2Harmonicsandunbalancedcurrenteffects

Duringthedevelopmentoftherailwaysingle-phasetractionsystem,oneofthemaincharacteristics,towhichparticularattentionwasgiven,wasthequestionofsingle-phaseunbalancedloadsandharmonicsimposedonthe3-phasesupplysystem.Theharmoniceffectsariseasaresultoftherectificationequipmentinstalledonthelocomotives.1'2'3Fromthemanyinvestigationswhichhavebeenmadeonthesystem,ithasbeenshownthegrid-supplysystemislargeenoughtoabsorbtheseeffectswithoutsignificantinterferencetootherconsumersorgeneratingplant.Itwillberemembered,however,thattheearlydevelopmentofthesystemwasinurbanandindustrialareaswherethefaultlevelswereveryhigh.Inruralareas,suchasthewestcoastextensionbetweenManchesterandGlasgow,andwherelowerfaultlevelsprevail,conditionsaremarginalandprovisionforthelateradditionofharmonicfiltershasbeenmadeshouldtheseberequired.

4.1TransformerdesignGeneralspecification

Thetraction-supplytransformersareofcore-typeconstructionandaredesigned,manufacturedandtestedinaccordancewithBEBSpecificationT2andCEGBSpecificationRT（1971）,BS171andothernationalspecificationswhichmayberelevant.Anyspecialrequirementsarespecifiedinpertinentcontractdocuments.

4.5Considerationsaffectingthechoiceoftransformerconstruction

Thepaperhasoutlinedthedifferentmethodsofconstructionwhichhavebeengenerallyadoptedtomeettherequirementsdeterminedbyfactorsarisingfromconsiderationofthesystemortest.Itisbelievedthesedesignsareofequalmeritinprovidingthebestoveralleconomicandtechnicaladvantagesandthis