Power swing detection, blocking and unblocking logic in distance relay

Power swing is a phenomenon that may occur due to sudden cut off heavy loads, trippings of lines due to faults in system, charging of lines etc. Due to Power swing if not properly detected and blocked there may be harm to electrical equipments also may cause the maloperations of distance relays. Hence to avoid such unwarranted trippings of distance relays, power swing must be detected correctly and fastly. However, if fault occurs during unstable power swing, distance relays must extend trippings with satisfying unblocking delay criteria. This paper provides, the different practical settings for traditional impedance-based PSB schemes. If relay settings are correctly chosen for load impedance and fault impedance, power swing detection, distance relay operation and out of step protection provides a stable protection system. Application of these setting guidelines are demonstrated using a power system real time F6TesT digital simulator, study performed on MiCOM P442 relay and disturbance analyzer SIGRA software.