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Why do we require additional REF on star connected windings of transfo

Why do we require additional REF on star connected windings of transfo

Why do we require additional REF on star connected windings of transfo

(OP)
Transformer differential protection will operate for LL and LG faults within transfomer, then y we need a additional REF protection for star connected winding, in addition there is another neutral overcurrent relay,

RE: Why do we require additional REF on star connected windings of transfo

REF is more sensitive for a ground fault low in the winding.  REF protection is included in most modern transformer protection relays at no extra charge.  If you have a neutral CT, there is not cost for the additional protection.
 

RE: Why do we require additional REF on star connected windings of transfo

What Jghrist say.
In additional, if your grounding is resistance or compensated, REF is storngly recommended function.
Best Regards.
Slava

RE: Why do we require additional REF on star connected windings of transfo

Hi,

87T doesn't cover 100% of the star winding, this is why we add REF to cover 100% of the star winding in case of L-G faults.

thanx
SMB

RE: Why do we require additional REF on star connected windings of transfo

(OP)
Thanks to all for their valuable reply

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