继电保护中英文翻译精Word下载.docx
《继电保护中英文翻译精Word下载.docx》由会员分享，可在线阅读，更多相关《继电保护中英文翻译精Word下载.docx（11页珍藏版）》请在冰点文库上搜索。
Thegreatestthreattothesecurityofasupplysystemistheshortcircuit,whichimposesasuddenandsometimesviolentchangeonsystemoperation.Thelargecurrentwhichthenflows,accompaniedbythelocalizedreleaseofaconsiderablequantityofenergy,cancausefireatthefaultlocation,andmechanicaldamagethroughoutthesystem,particularlytomachineandtransformerwindings.Rapidisolationofthefaultbythenearestswitchgearwillminimizethedamageanddisruptioncausedtothesystem.
Apowersystemrepresentsaverylargecapitalinvestment.Tomaximizethereturnonthisoutlay.thesystemmustbeloadedasmuchaspossible.Forthisreasonitisnecessarynotonlytoprovideasupplyofenergywhichisattractivetoprospectiveusersbyoperatingthesystem,butalsotokeepthesysteminfulloperationasfaraspossiblecontinuously,sothatitmaygivethebestservicetotheconsumer,andearnthemostrevenueforthesupplyauthority.Absolutefreedomfromfailureoftheplantandsystemnetworkcannotbeguaran-teed.Theriskofafaultoccurring,howeverslightforeachitem,ismultipliedbythenumberofsuchitemswhicharecloselyassociatedinanextensivesystem,asanyfaultproducesrepercussionsthroughoutthenetwork.Whenthesystemislarge,thechanceofafaultoccurringandthedisturbancethatafaultwouldbringarebothsogreatthatwithout
equipmenttoremovefaultsthesystemwillbecome,inpracticalterms,inoperable.Theobjectofthesystemwillbedefeatedifadequateprovisionforfaultclearanceisnotmade.Noristheinstallationofswitchgearalonesufficient;
discriminativeprotectivegear,designedaccordingtothecharacteristicsandrequirementsofthepowersystem.mustbeprovidedtocontroltheswitchgear.Asystemisnotproperlydesignedandmanagedifitisnotadequatelyprotected.
Protectivegear
Thisisacollectivetermwhichcoversalltheequipmentusedfordetecting,locatingandinitiatingtheremovalofafaultfromthepowersystem.Relaysareextensivelyusedformajorprotectivefunctions,butthetermalsocoversdirect-actinga.c.tripsandfuses.Inadditiontorelaysthetermincludesallaccessoriessuchascurrentandvoltagetransformers,shunts,d.c.anda.c.wiringandanyotherdevicesrelatingtotheprotectiverelays.
Ingeneral,themainswitchgear,althoughfundamentallyprotectiveinitsfunction,isexcludedfromthetermprotectivegear,asarealsocommonservices,suchasthestationbatteryandanyotherequipmentrequiredtosecureopera-tionofthecircuitbreaker.Reliablity
Theperformanceoftheprotectionappliedtolargepowersystemsisfrequentlyassessednumerically.Forthispurposeeachsystemfaultisclassedasanincidentandthosewhichareclearedbythetrippingofthecorrectcircuitbreakersandonlythose,areclassedas'
correct'
.Thepercentageofcorrectclearancescanthenbedetermined.
Thisprincipleofassessmentgivesanaccurateevaluationoftheprotectionofthesystemasawhole,butitissevereinitsjudgementofrelayperformance,inthatmanyrelaysarecalledintooperationforeachsystemfault,andallmustbehavecorrectlyforacorrectclearancetoberecorded.Onthisbasis,aperformanceof94%isobtainablebystandardtechniques.
Completereliabilityisunlikelyevertobeachievedbyfurtherimprovementsinconstruction.Averybigstep,however,canbetakenbyprovidingduplicationofequipmentor'
redundancy'
.Twocompletesetsofequipmentareprovided,andarrangedsothateitherbyitselfcancarryouttherequiredfunction.Iftheriskofanequipmentfailingisx/unit.theresultantrisk,allowingforredundancy,isx2.Wherexissmalltheresultantrisk（x2may
benegligible.
Ithaslongbeenthepracticetoapplyduplicateprotectivesystemstobusbars,bothbeingrequiredtooperatetocompleteatrippingoperation,thatis,a'
two-out-of-two'
arrangement.Inothercases,importantcircuitshavebeenprovidedwithduplicatemainprotectionschemes,eitherbeingabletotripindependently,thatis,a'
one-out-of-two'
arrangement.Theformerarrangementguardsagainstunwantedoperation,thelatteragainstfailuretooperate.
Thesetwofeaturescanbeobtainedtogetherbyadoptinga'
two-out-of-three'
arrangementinwhichthreebasicsystemsareusedandareinterconnectedsothattheoperationofanytwowillcompletethetrippingfunction.Suchschemeshavealreadybeenusedtoalimitedextentandapplicationoftheprinciplewillundoubtedlyincrease.Probabilitytheorysuggeststhatifapowernetworkwereprotectedthroughoutonthisbasis,aprotectionperformanceof99.98%shouldbeattainable.Thisperformancefigurerequiresthattheseparateprotectionsystemsbecompletelyindependent;
anycommonfactors,suchascommoncurrenttransformersortrippingbatteries,willreducetheoverallperformance.SELECTIVITY
Protectionisarrangedinzones,whichshouldcoverthepowersystemcompletely,leavingnopartunprotected.Whenafaultoccurstheprotectionisrequiredtoselectandtriponlytheneareatcircuitbreakers.Thispropertyofselectivetrippingisalsocalled'
discrimination'
andisachievedbytwogeneralmethods:
aTimegradedsystems
Protectivesystemsinsuccessivezonesarearrangedtooperateintimeswhicharegradedthroughthesequenceofequipmentssothatupontheoccurrenceofafault,althoughanumberofprotectiveequipmentsrespond,onlythoserelevanttothefaultyzonecompletethetrippingfunctiopn.Theothersmakeincompleteoperationsandthenreset.
bUnitsystems
Itispossibletodesignprotectivesystemswhichrespondonlytofaultconditionslyingwithinaclearlydefinedzone.This'
unitprotection'
or'
restrictedprotection'
canbeappliedthroughoutapowersystemand,sinceitdoesnotinvolvetimegrading,canberelativelyfastinoperation.
Unitprotectionisusuallyachievedbymeansofacomparisonofquantitiesatthe
boundariesofthezone.Certainprotectivesystemsderivetheir'
restricted'
propertyfromtheconfigurationofthepowersystemandmayalsobeclassedasunitprotection.Whichevermethodisused,itmustbekeptinmindthatselectivityisnotmerelyamatterofrelaydesign.Italsodependsonthecorrectco-ordinationofcurrenttransformersandrelayswithasuitablechoiceofrelaysettings,takingintoaccountthepossiblerangeofsuchvariablesasfaultcurrents.maximumloadcurrent,systemimpedancesandotherrelatedfactors,whereappropriate.
STABILITY
Thisterm,appliedtoprotectionasdistinctfrompowernetworks,referstotheabilityofthesystemtoremaininerttoallloadconditionsandfaultsexternaltotherelevantzone.Itisessentiallyatermwhichisapplicabletounitsystems;
theterm'
istheequivalentexpressionapplicabletonon-unitsystems.
SPEED
Thefunctionofautomaticprotectionistoisolatefaultsfromthepowersysteminaverymuchshortertimethancouldbeachievedmanually,evenwithagreatdealofpersonalsupervision.Theobjectistosafeguardcontinuityofsupplybyremovingeachdisturbancebeforeitleadstowidespreadlossofsynchronism,whichwouldnecessitatetheshuttingdownofplant.
Loadingthesystemproducesphasedisplacementsbetweenthevoltagesatdifferentpointsandthereforeincreasestheprobabilitythatsynchronismwillbelostwhenthesystemisdisturbedbyafault.Theshorterthetimeafaultisallowedtoremaininthesystem,thegreatercanbetheloadingofthesystem.Figure1.5showstypicalrelationsbetweensystemloadingandfaultclearancetimesforvarioustypesoffault.Itwillbenotedthatphasefaultshaveamoremarkedeffectonthestabilityofthesystemthandoesasimpleearthfaultandthereforerequirefasterclearance.
SENSITIVITY
Sensitivityisatermfrequentlyusedwhenreferringtotheminimumoperatingcurrentofacompleteprotectivesystem.Aprotectivesystemissaidtobesensitiveiftheprimaryoperatingcurrentislow.
Whenthetermisappliedtoanindividualrelay,itdoesnotretertoacurrentorvoltagesettingbuttothevolt-ampereconsumptionattheminimumoperatingcurrent.
Agiventypeofrelayelementcanusuallybewoundforawiderangeofsettingcurrents;
thecoilwillhaveanimpedancewhichisinverselyproportionaltothesquareofthesettingcurrentvalue,sothatthevolt-ampereproductatanysettingisconstant.Thisisthetruemeasureoftheinputrequirementsoftherelay,andsoalsoofthesensitivity.Relaypowerfactorhassomesignificanceinthematteroftransientperformance.Ford.c.relaystheVAinputalsorepresentspowerconsumption,andtheburdenisthereforefrequentlyquotedinwatts.
PRIMARYANDBACK-UPPROTECTION
Thereliabilityofapowersystemhasbeendiscussedinearliersections.Many
升级会员 