What are the possible causes of REF operation on a power transformer

What are the possible causes of REF operation on a power
transformer

Question Posted / a.i.umar

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What are the possible causes of REF operation on a power transformer..

Answer / k.prakashchandra

All cts(Phases and neutral) are connected in parallel.If
there are unbalanced currents in phases, the resultant
current in REFR is zero as the difference is also measured
by NCT .If there is an earth fault inside the transformer
or between cts and bushings ,the fault current is sensed by
NCT only. Hence current balnce is lost in REFR resulting in
trip command by the relay

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What are the possible causes of REF operation on a power transformer..

Answer / k.prakashchandra

Please note that REFR will not act under earth faults in
phases beyond the CTs. As its coverage is limited
(restricted) to Tr only ,it is called ristricted earth
fault relay.

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3 Yes

0 No

What are the possible causes of REF operation on a power transformer..

Answer / k.prakashchandra

An earth fault between CTs of primary and secondary sides,
as the fault current will not pass through secondary side CT

Is This Answer Correct ?

2 Yes

2 No

What are the possible causes of REF operation on a power transformer..

Answer / jaimin modi

actually i dont know the answer but i wanted to know what
is the REF operation of power x'mer...plz explain in detail