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1、PowerSystemProtectionsThesteady-stateoperationofapowersystemisfrequentlydisturbedbyvariousfaultsonelectricalequipment.Tomaintaintheproperoperationofthepowersystem,aneffective,efficientandreliableprotectionschemeisrequired.Powersystemcomponentsaredesignedtooperateundernormaloperating
2、conditions.However,duetoanyreason,sayafault,thereisanabnormality,itisnecessarythatthereshouldbeadevicewhichsensestheseabnormalconditionsandifso,theelementorcomponentwheresuchanabnormalityhastakenplaceisremoved,i.e.deletedfromtherestofthesystemassoonaspossible.Thisisnecessarybecauset
3、hepowersystemcomponentcanneverbedesignedtowithstandtheworstpossibleconditionsduetothefactthatthiswillmakethewholesystemhighlyuneconomical.Andtherefore,ifsuchanabnormalitytakesplaceinanyelementorcomponentofthepowersystemnetwork,itisdesirablethattheaffectedelement/componentisremovedfr
4、omtherestofthesystemreliablyandquicklyinordertorestorepowerintheremainingsystemunderthenormalconditionassoonaspossible.Theprotectionschemeincludesboththeprotectiverelaysandswitchingcircuits,i.e.circuitbreakers.Theprotectiverelaywhichfunctionsasabrainisaveryimportantcomponent.Theprot
5、ectiverelayisasensingdevice,whichsensesthefault,determinesitslocationandthensendscommandtothepropercircuitbreakerbyclosingitstripcoil.Thecircuitbreakeraftergettingcommandfromtheprotectiverelaydisconnectsonlythefaultedelement.thisiswhytheprotectiverelaymustbereliable,maintainableandf
6、astinoperation.Inearlydays,thereusedtobeelectromechanicalrelayofinductiondisk-type.However,verysoonthediskwasreplacedbyinvertedcup,i.e.hollowcylinderandthenewrelayobtainedwasknownasaninductioncuporinductioncylinderrelay.Thisrelay,whichisstillinuse,possessesseveralimportantfeaturessu
7、chashigherspeed;highertorqueforagivenpowerinputanmoreuniformtorque.However,withtheadventofelectronictubes,electronicrelayshavingdistinctfeaturesweredevelopedduring1940s.Withthediscoveryofsolidstatecomponentsduring1950s,staticrelayswithnumerousadvantagesweredeveloped.Theuseofdigitalc
8、omputersforprotecti
