Restricted Earth Fault - REF & SBEF Relay

A Restricted Earth Fault (REF) means an earth fault from a restricted/localized zone of a circuit. The term "REF protection method " means not to sense any earth faults outside th is restricted zone. REF is a type of "unit protection" applied to transformers or generators and is more sensitive than the method known as differential protection. An REF relay works by measuring the actual current flowing to earth from the fra me of the unit. If that current exceeds a certain preset maximum value of milliA mps (mA) then the relay will trip to cut off the power supply to the unit. Differential protection can also be used to protect the windings of a transforme r by comparing the current in the power supply's neutral wire with the current i n the phase wire: if the currents are equal then the differential protection rel ay will not operate; if there is a current imbalance then the differential prote ction relay operates. However, REF protection is also applied to transformers in order to detect ground faults on a given winding much more sensitively than dif ferential protection can do. Read more: http://wiki.answers.com/Q/What_is_restricted_earth_fault_protection_a nd_how_is_it_provided#ixzz1sjyn901n

Re: what is the diff. b/w restricted earth fault relay & standby earthfault rel ay and where they are used? Answer # 1 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. Is This Answer Correct ? 0 Oes

52 Yes 7 No

Re: what is the diff. b/w restricted earth fault relay & standby earthfault re lay and where they are used? Answer # 2 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. Is This Answer Correct ? 5 Ramniveth

51 Yes 3 No

Re: what is the diff. b/w restricted earth fault relay & standby earthfault re lay and where they are used? Answer # 3 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.