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.

Answer Posted / ashish

as per my knowledge ref protections hav to be assigned
separately on both sides of traffo it protects 90% of
winding.
it is unit protection and its very sensitive.

while talking about diff protection two cts in each phase
on both sides of trafo is there any diff in incoming and
outgoing current will leads to trip so both are equally
required.

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