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Earth Fault Relay Settings for 11kv Distribution Feeders
Why is earth fault relay settings for distribution feeders in solidly grounded systems usually between 10% and 20%?

In the power distribution company where I work, the earth fault relays are usually set to 20% of the nominal feeder current. I have also seen online sources that specify between 10% and 20% for earth fault settings.

I am aware that even in an unbalanced load situation, there is a very negligible ground fault current. So I wonder why go as high as 10%? Why not 2% or even 1%?

This is to avoid nuisance tripping. You don't want your settings so tight that any small transient event will cause an outage.

Thanks for your reply.

>This is to avoid nuisance tripping. You don't want your
>settings so tight that any small transient event will cause
>an outage.

Will transients typically or even sometimes result in earth fault current flowing, when there is no actual earth fault present? I understand that during restoration, CT saturation may result in a phantom earth fault.