REF and BEF Protection
REF and BEF Protection
(OP)
Is there any difference between restricted earth fault (REF) protection and balanced earth fault (BEF) protection?
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RE: REF and BEF Protection
Regards
Marmite
RE: REF and BEF Protection
I recommend to you will start from link:
FAQ238-1287: What are good references for a Power Engineer?
in additional some small tips:
Theory and considerations
When the sum (residual) connection of the phase CT's is used instead of core balanced CT (known as ring or toroidal CT) the small dissimilarities of the CT's and especially partial saturation will cause not-true apparent current in the secondary circuit. This might cause false relay operations.
Normally the apparent earth-fault current seen by the relay because of the CT errors is relative small. In case of a phase-fault, the phase current can easily be 5..20 times the nominal load current. Assuming, for example, that because of the CT errors 1% of the phase fault current will be seen by the earth-fault relay this becomes 5..20 x 1% = 5..20% of the rated secondary current.
Partial saturation of CT's is also very possible with high fault currents and also with lower currents because of DC component (motor start-ups, transformer inrush situations and cold load pick-ups). Saturation will increase the error of CT's rapidly causing even higher apparent E/F-current in the secondary circuit. There is therefore a potential danger that the earth-fault relay can activate at phase-faults etc. when actually no earth current is flowing in primary circuit.
(When the protection has stability in such way that earth-fault protection will not trip (faster) in case of phase-faults is known as phase-fault stability.)
Recommendations
The recommended minimum setting is 10% of the rated load current. Settings especially below 5% has been found problematic.
Serial resistance (stabilising resistor) might also be required for the measuring circuit in order to limit effects of the partial CT saturation.
REF it' stype of differntial protection, as saied Marmite and Ralph.
I will found linl abot REF and will send to you.
Best Regards.
Slava
RE: REF and BEF Protection
thread238-3460: Restricted Earth Fault Relays