Basically Restricted Earth Fault is a protection use to protect the transformer or generator. Different compare to the IDMT Earth Fault as it is used to protect the system...
Restricted Earth Fault is a type of Unit protection applied to transformers or Generators and is more sensitive than the differential protection.
Used to protect the windings of the transformer by comparing the current in the nuetral/earth with that of the phasor sum of the outgoing current in the lines. If equal then no operation of REF relay. If imbalance then REF relay operates
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