Answer / ram niveth

REF is a backup protection for transformer incipient
faults.
if differential fails REF comes on line.
if both protections are used , usually REF time setting
will be less than differential setting

Answer / shipra

restricted earth faukt protn is for unprotected zone of
neutral to earth.
Diffetential protn will work only if the falt is with in
zone of CT so that it can get a differential current. If
there is a fault between neutral CT and earth the fault
will be feeded and no diffential current will be there as
it is balaced through primary side, secndary side & nutral.

Answer / erharisheee51

RESTRICTED EARTH FAULT PROTECTION IS GENERALLY PROTECT FROM
THE DEFFERENTIAL CURRENT WITH IN THE GENERATOR CORE , WHERE
AS DIFFERENTIAL PROTECTION IS USED FOR OVERALL DIFFERENTIAL

Answer / pradeep

mainly there is some drawbacks in differential protection.
the protection is mostly surrounding at the certain region.
for example, if the transmission line length is 10km
means,we locate differential protection in between the
transmission line we can't able to protect the outerside of
the transmission line. so that we go for earth fault
protection. earth consist the infinite resistance.

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