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

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

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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