Working time coordination of over current relay (OCR) and ground fault relay (GFR) in 20 kV feeder distribution

Abstract

Over current relay (OCR) and ground fault relay (GFR) are used to protect phase to phase faults (3 phase and 2 phase) and single phase faults to ground by giving an open signal to the circuit breaker. In the 20 kV feeder these relays are located in the outgoing circuit breaker (outgoing CB) and one or more reclosers. OCR and GFR working time must be coordinated so that it is selective and can function well as a back up relay. This study analyzes the working time of OCR and GFR on outgoing CB, recloser 1 and recloser 2 on a 20 kV radial feeder due to miscoordination of work when a fault occurs in the recloser 2 protection zone which is located downstream of the existing 20 kV radial feeder. The analysis refers to IEC 60255 standard, IEEE 242-2001 standard and SPLN 52-3:1983. The results of the analysis found that the grading time (Δt) of OCR recloser 1 and recloser 2 was < 2 s, not in accordance with SPLN 52-3:1983, the working time coordination between recloser was 0.2-0.4s. Therefore, coordination of working time is carried out so that the grading time of OCR recloser 1 and OCR recloser 2 becomes 0.2 s, while the grading time of OCR outgoing CB and OCR recloser 1 is 0.4 s according to the standard in order to get a new time multiple setting (TMS). With the new grading time, so TMS recloser 1 is 0.112 and TMS OCR outgoing CB is 0.255. With the new TMS, for If3ø, grading time (Δt) OCR recloser 1 and OCR recloser 2 of 0.2 s for fault location 0% protection zone of recloser 2 and 0.443 s for fault location 100% protection zone of recloser 2. Meanwhile grading time (Δt) of OCR outgoing CB and recloser 1 of 0.4 s for fault location 0% protection zone of recloser 2 and 0.980 s for fault location 100% protection zone of recloser 2. For If2ø, grading time (Δt) OCR recloser 1 and OCR recloser 2 of 0.215 s for fault location 0% protection zone of recloser 2 and 0.519 s for fault location 100% protection zone of recloser 2. Meanwhile grading time (Δt) of OCR outgoing CB and recloser 1 of 0.432 s for fault location 0% protection zone of recloser 2 and 1.189 s for fault location 100% protection zone of recloser 2. Thus in accordance with the standards used.