REF relay

What is REF relay?

A) It is restricted earth fault relay. When the fault occurs very near to the neutral
point of the transformer, the voltage available to drive the earth circuit is very small,which may not be sufficient to activate the relay, unless the relay is set for a very low current.
Hence the zone of protection in the winding of the transformer is restricted to cover only around 85%. Hence the relay is called REF relay.