Answer / ramniveth

i agrre with this answer with little correction
Standby Earth Fault relay is also connected to star side

the difference between SEF and REF is REF operates in
InZone only
SEF operates in In and Out Zones. If there is an earth
fault in outgoing feeders and the feeder protection is not
operated then SEF operates .
Tripping time for SEF will be more than REF and Earth fault
protection in O/G feeders.

Answer / oes

Restricted earth fault (REF) relay is a unit protection
intended for one winding of a transformer (neutral winding)
the input of which is from a neutral bushing CT and in some
applications, balanced by the output of three line CTs in
the Y-winding directly connected to neutral. This provides
accurate sensing of zero-sequence leakage currents for a
fault within its zone of protection, i.e., on the windings.
Whereas, standby EF relay is a back-up overcurrent ground
protection usually connected on the HV side and its main
purpose is to provide local back-up protection in case for
a failure of main protections of the LV feeder/line prots.,
bus prots., and the transf. main protections.

Answer / shirish prajapati

The REF and SBEF are two separate protection functions. The
REF will protect the transformer winding and the cables to
the breaker. SBEF is standby earth fault protection. It is
backup protection in case of uncleared faults out on the
network, or earth faults outside the REF zone. It may also
protect the neutral earthing resistor if there is one, and
may act as a cheap busbar protection system by tripping the
LV bus section first and the transformer LV C/B second. Do
you really want to compromise important backup protection
for the cost of a neutral CT? You have the option to get
another CT fitted in the bushing, or if there is a neutral
cable terminated on the bushing you could install a slipover
CT on the cable, or in the NER cable box. Lots of
possibilities, and not very expensive.

Answer / hari

REF is a kind of protection that is connected to the Star Wnding CT which has a neutral connection.It covers only the protection of restricted regions like windings,breakers & cables.

Wherein SBEF relays are connected to the Star Windings and it detects the Zero sequence current in the neutral CT's.

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