REF Protection

1)Check the value of stabilising resistance.

2) Check the relay pick up

during a throughfault(outside of REF zone) just outside the zone maximum currunt will flow through 1 line CT and 1 NCT(current in 2 CT will be in opposite polarity i.e 180 deg apart). this current will circulate and generally will not enter in REF relay path. but, due to lead resistance there will be voltage across the REF path . This voltage may drive a current in REF path and operate REF relay if we do not install a external resistance in series with the REF relay. This is stabilising resistance, and if it is of low value then current will flow in the REF path during through fault.

Please record all your problems in one post and raise query. It will be easy to understand to suggest appropriate solution .

Please indicate whether REF relay trips or directional relay trips or both trips.

Check Neutral CT location. Is it located before earthing of neutral or after earthing.

Are Neutral CT and phase CT characters and ratios matching.

My experience in most of the cases referred to me is CT ratio and location of CT are issues.

besides checking ratio it should be confirmed that in all 4 nos CTs we use PS class secondary core. usage of metering core in any ct may create prob

Looking at his/her other posts, it must be mid-terms in the Middle East