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why we use REF and Differential Protection in one
transformers?my doubt is both protections are operated in
internal fault only.why we want to use 2 protections?please
clarify.
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Answer Posted / nikhil thakkar
REF and Differential both pritection are for internal zone and SEF for external zone. Actual all protections are voltage/current/power based and they are back to each other. DIFFERENTIAL AND REF both protection is for internal fault i.e trafo winding . differential sense unbalance between both end of trafo. /Gen. . REF sense unbalance caused between NCT and phase CTdue to earth fault abd actual backup for REF is SEF.
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