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What is difference between earth leakage relay and
restricted earth fault relay ?
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Answer Posted / prasun bhaumik
REF sense the residual or differential current in between
two sets of CTs installed at two sides of protected unit
i.e Tr or Gen. It is a high imedance differential
protection it will only operate when
1) There is a earth fault inside the object which will
produce sufficient differential current.
2) In case fault occures out side the zone any of the CT
may satuarate then it will mal operate.
But earth leakage relay is conncetd with a CT which is
commonly ring type and surronded the earthing path of the
instrument or cable with armour it operates on Over current
principle not differential principle so there is no
requirement of stabilizing resistance as in the case of REF
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