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Ingeneral,themainswitchgear,althoughfundamentallyprotectiveinitsfunction,isexcludedfromthetermprotectivegear,asarealsocommonservices,suchasthestationbatteryandanyotherequipmentrequiredtosecureopera-tionofthecircuitbreaker.
Inordertofulfiltherequirementsofdiscriminativeprotectionwiththeoptimumspeedforthemanydifferentconfigurations,operatingconditionsandconstructionfeaturesofpowersystems,ithasbeennecessarytodevelopmanytypesofrelaywhichrespondtovariousfunctionsofthepowersystemquantities.Forexample,observationsimplyofthemagnitudeofthefaultcurrentsufficesinsomecasesbutmeasurementofpowerorimpedancemaybenecessaryinothers.Relaysfrequentlymeasurecomplexfunctionsofthesystemquantities,whichareonlyreadilyexpressiblebymathematicalorgraphicalmeans. |
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