what is resticted earth fault protection ? how did it
protect & work in power transformer
Answer Posted / sumit
REFP is mainly used for high speed tripping on star connected earthed secondary winding of power transformer
The relay does not operate for fault beyond the protected zone i.e neutral of the transformer.
Fault occurring near neutral is having small current becoz of small voltage which results in low fault current. To attend this fault the relay must be too sensitive to operate .To operate, the relay is set for the earth fault current of the order 15%of the rated winding current which protects restricted portion of the winding.
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