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

[loganath4880]

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,

 

[jghrist]

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.

 

[slavag]

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

 

[SMB1]

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

 

[loganath4880]

Thanks to all for their valuable reply