Sir We have a REF relay connected to 10MVA(Y-Y) Transformer.on
External earth fault REF relay trips along with earth fault
relay.The REF relay has no complant as we tested relay.Why is
it happening?

Answer Posted / k.prakashchandra

Also may be due to 1 .reverse connection of NCT leads ( Unbalanced current of lines and NCT current add to each other ). 2. Low saturation point of NCT as Kv of bushing NCT is usually less than that of line CTs

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