What is the difference between sensitive earth fault and
restricted earth fault in power transformers?
Answer Posted / raghavendran
A Restricted Earth Fault (R.E.F.) has nothing to do with the
magnitude of the current. It is in fact a normal earth fault
that is restricted to a 'zone'. That is, the R.E.F.
protection is only looking for earth faults occuring in a
given zone. Any earth fault outside the zone (restricted
area) is ignored by the R.E.F. protection. It is typically
used on power transformers, with the protected zone
typically being between the star-point current transformer
and the phase transformers of the star-wound winding.
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