Check relaying for feeder sensitive earth fault protection

[dfdt]

SEF protection on 11 or 22kV distribution feeder is set very sensitive to detect high resistance fault yielding mere 10 amp primary current.Such scheme is checked by relay fed from the CT on neutral of transformer.This is done to improve security of the scheme as SEF needs real current to be sourced from the feeding transformer.
My question is do you use SEF check feature or you just rely on SEF of the feeder relay alone?

 

[Mohamed Farghaly]

I rely on SEF relay for each feeder to trip feeder CB with time delay "for ex 0.2 sec", SEF relay for incomer CB to trip incomer CB with time delay "for ex 0.35 sec" & relay fed from the CT on neutral of transformer to trip upstream CB with time delay "for ex 0.5 sec".

 

[dfdt]

Thanks Mohamed
Are you referring to normal earth fault normally set at 80 0r 100Amp or sensitive earth fault set at 10A primary?

 

[Mohamed Farghaly]

I refer to sensitive earth fault set at 10A primary for feeders and incomer CB using Core Balance CT