Why 2 types of earth fault relays in 6.6 kV side of transformers?

Why 2 types of earth fault relays in 6.6 kV side of transformers?
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1 Answer

Answer :

I – Trips 6.6 kV breakers only. It gives primary protection for 6.6 kV bus bars.

I1 – Trips the both HT and LT breakers. It acts as a backup to ref and also acts as backup to bus bar earthfault relay. 


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