中英文資料外文翻譯FaultsonPowerSystemsEachyearnewdesignofpowerequipmentbringaboutincreasedreliability of operation. Nevertheless, equipment failures andinterferencebyoutsidesourcesoccasionallyresultinfaultsonelectricpowersystems.Ontheoccurrenceofafault,currentanvoltageconditions become abnormal, the delivery of power from thegenerating station to the loads may be unsatisfactory over aconsiderablearea,andifthefaultedequipmentisnot disconnectedfromtheremainderofthesystem,damagemayresulttootherpiecesofoperatingequipment.Afaultyistheunintentionalorintentionalconnectingtogetheroftwoormoreconductorswhichordinarilyoperatewithadifferenceofpotentialbetweenthem.Theconnectionbetweentheconductorsmaybebyphysicalmetalliccontactoritmaybethroughanarc.Atthefault,thevoltagebetweenthetwopartsisreducedtozerointhecaseof metal-to-metalcontacts, or to averylowvalue in case connectionisthroughanarc.Currentsofabnormallyhighmagnitudeflowthroughthenetworktothepointoffault.Theseshort-circuitcurrentswillusuallybemuchgreaterthanthedesignedthermalabilityoftheconditioninthelinesormachinesfeedingthefault.Theresultantriseintemperaturemaycausedamagebytheannealingofconductorsandbythecharringofinsulation.Intheperiodduringwhichthefaultispermittedtoexist,thevoltageonthesysteminthenearvicinityofthefaultwillbesolowthatutilizationequipmentwillbeinoperative.Itisapparentthatthelateconditionsthatexistduringafault,andprovideequipmentproperlyadjustedtoopentheswitchesnecessarytodisconnectthefaultedequipmentfromtheremandingofthesystem.Ordinarilyitisdesirablethatnootherswitchesonthesystemareopened,assuchbehaviorwouldresultinunnecessarymodificationthesystemcircuits.Adistinctionmustbemadebetweenandanoverload.Anoverloadimpliesonlythatloadsgreaterthanthedesignedvalueshavebeenimposedonsystem.Undersuchacircumstancethevoltageattheoverloadpointmaybelow,butnotzero.Thisundervoltageconditionmayextendforsomedistancebeyondtheoverloadpointintotheremainderofthesystem.Thecurrentintheoverloadequipmentarehighandmayexceedthethermaldesignlimits.Nevertheless,suchcurrentsaresubstantiallylowerthaninthecaseofafault.Servicefrequentlymaybemaintained,butatbelow-standardvoltage.Overloadsarerathercommonoccurrencesinhomes.Forexample,ahousewifemightplugfivewaffleironsintothekitchencircuitduringaneighborhoodpart.Suchanoverload,ifpermittedtocontinue,wouldcauseheatingofthewiresfromthepowercenterandeventuallystartafire.Topreventsuchtrouble,residentialcircuitsareprotectedbyfusesorcircuitbreakerswhichopenquicklywhencurrentsabovespecifiedvaluespersist.Distributiontransformers aresometimesoverloadsascustomersinstallmoreandmoreappliances.Thecontinuousmonitoringofdistributioncircuitsisnecessarytobecertainthattransformerssizesareincreasedasloadgrows.Faultsofmanytypesandcausesmayappearonelectricpowersystems.Manyofusinourhomeshaveseenfrayedlampcordswhichpermittedthetwoconductorsofthecordtocomeincontactwitheachother.Whenthisoccurs,thereisaresultingflash,andifbreakerorfuseequipmentfunctionsproperly,thecircuitisopened.Overheadlines,forthemostpart,areconstructedofbareconductors.Therearesometimesaccidentallybroughttogetherbyactionofwind,sleets,trees,cranes,airplanes,ordamagetosupportingstructures.Overvoltagesduetolightingorswitchingnaycauseflashoverofsupportingorfromconductortoconductor.Contaminationoninsulatorssometimesresultsinflashoverevenduringnormalvoltageconditions.Theconductorsofundergroundcablesareseparatedfromeachandfromgroundbysolidinsulation,whichnaybeoil-impregnatedpaperor a plastic such polyethylene. These materials undergo deteriorationwithage,particularlyifoverloadsonthecableshaveresultedintheiroperationatelevatedtemperature.Anysmallvoidpresentinthebodyoftheinsulatingmaterialwillresultsinionizationofthegascontainedtherein,theproductsofwhichreactunfavorablywiththeinsulation.Deteriorationoftheinsulationmayresultfailureofthematerialtoretainitsinsulatingproperties,andshortcircuitswilldevelopbetweenthecableconductors.Thepossibilityofcablefailureisincreasediflighteningorswitchingproducestransientvoltageofabnormallyhighvaluesbetweentheconductors.Transformerfailuresmaybetheresultofinsulationdeteriorationcombinedwithovervoltageduetolightningorswitchingtransients.Shortcircuitduetoinsulationfailurebetweenadjacentturnsofthesamewindingmayresultfromsuddenlyappliedovervoltage.Majorinsulationmayfail,permittingarcstobeestablishedbetweenprimaryandsecondarywindingsorbetweenwindingandgroundedmetalpartssuchasthecoreortank.Generatorsmayfailduetobreakdownoftheinsulationbetweenadjacentturnsinthesameslot,resultinginashortcircuitinasingleturnofthegenerator.Insulationbreakdownmayalsooccurbetweenoneofthewindingandthegroundedsteelstructureinwhichthecoilsareembedded.Breakdownbetweendifferentwindingslyinginthesameslotresultsinshort-circuitingextensivesectionofmachine.Balancedthree-phasefaults,likebalancedthree-phaseloads,maybehandledonalineto-neutralbasisoronanequivalentsingle-phasebasis.Problemsmaybesolvedeitherintermsofvolts,amperes,andohms.Thehanding offaultsonsingle-phase linesisofidenticaltothemethodofhandingthree-phasefaultsonanequivalentsingle-phasebasis.Faultsmaybeclassifiedaspermanentortemporary.Permanentfaults are those in which insulation failure or structure failureproducesdamagethatmakesoperationoftheequipmentimpossibleandrequiresrepairstobemade.Temporaryfaultsarethosewhichmayberemovedbydeenergizingtheequipmentforashortperiodoftime,shortcircuitsonoverheadlinesfrequentlyareofthisnature.Highwinds may cause two or more conductions to swing togethermomentarily.Duringtheshortperiodofcontact.Anarcisformedwhichmaycontinueaslongaslineremainsenergized.However,ifautomaticequipmentcanbebroughtintooperationtoserviceassoonastheareisextinguished.Arcsacrossinsulatorsduetoovervoltagesfromlighting orswitching transients usually can becleared byautomatic circuit-breaker operation before significant structuredamageoccurs.Becauseofthischaracteristicoffaults onlines,manycompaniesoperatefollowingaprocedureknownashigh-speedreclosing.Ontheoccurrenceof