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1、PowerSystemProtectionsThesteady-stateoperationofapowersystemisfrequentlydisturbedbyvariousfaultsonelectricalequipment.Tomaintaintheproperoperationofthepowersystem,aneffective,efficientandreliableprotectionschemeisrequired.Powersystemcomponentsaredesignedtooperateundernormaloperatingconditions.Howev
2、er,duetoanyreason,sayafault,thereisanabnormality,itisnecessarythatthereshouldbeadevicewhichsensestheseabnormalconditionsandifso,theelementorcomponentwheresuchanabnormalityhastakenplaceisremoved,i.e.deletedfromtherestofthesystemassoonaspossible.Thisisnecessarybecausethepowersystemcomponentcanneverbe
3、designedtowithstandtheworstpossibleconditionsduetothefactthatthiswillmakethewholesystemhighlyuneconomical.Andtherefore,ifsuchanabnormalitytakesplaceinanyelementorcomponentofthepowersystemnetwork,itisdesirablethattheaffectedelement/componentisremovedfromtherestofthesystemreliablyandquicklyinordertor
4、estorepowerintheremainingsystemunderthenormalconditionassoonaspossible.Theprotectionschemeincludesboththeprotectiverelaysandswitchingcircuits,i.e.circuitbreakers.Theprotectiverelaywhichfunctionsasabrainisaveryimportantcomponent.Theprotectiverelayisasensingdevice,whichsensesthefault,determinesitsloc
5、ationandthensendscommandtothepropercircuitbreakerbyclosingitstripcoil.Thecircuitbreakeraftergettingcommandfromtheprotectiverelaydisconnectsonlythefaultedelement.thisiswhytheprotectiverelaymustbereliable,maintainableandfastinoperation.Inearlydays,thereusedtobeelectromechanicalrelayofinductiondisk-ty
6、pe.However,verysoonthediskwasreplacedbyinvertedcup,i.e.hollowcylinderandthenewrelayobtainedwasknownasaninductioncuporinductioncylinderrelay.Thisrelay,whichisstillinuse,possessesseveralimportantfeaturessuchashigherspeed;highertorqueforagivenpowerinputanmoreuniformtorque.However,withtheadventofelectr
7、onictubes,electronicrelayshavingdistinctfeaturesweredevelopedduring1940s.Withthediscoveryofsolidstatecomponentsduring1950s,staticrelayswithnumerousadvantagesweredeveloped.Theuseofdigitalcomputersforprotecti
