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Why restricted earth fault protection is needed? Why can’t
differential
Protection is sufficient?
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Answer Posted / anaz.a
restricted earth fault protection is a protection scheme given in assistance to the differential protection.it is given to protect an earth fault which occurs very close to the neutral point in star connected windings of the transformer.this kind of fault a very low fault current only and this current may not be sufficient to activate the differential protection relays.
The sensitivity of the differential relays cannot be increased beyond a limit since this may lead to unnecessary tripping(the transformer may trip even for an earth fault occurring on the outgoing feeder Side)
Hence a special scheme of protection called REF(Restricted earth fault)is provided in order to protect a restricted area of the winding from internal earth fault.
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