A PILOT BASED POWER SWING BLOCKING UNIT FOR DISTANCE RELAYS

Abstract

Power swing may lead to malfunction of distance relays in tripping transmission line incorrectly which endangers the stability of power systems. Therefore, distance relays include power swing blocking (PSB) unit to discriminate power swing from other faults, preventing relay operation during power swing. In this paper, a simple but applicable PSB scheme is proposed for distance relay based on the direction of power flows in the distance relays at two ends of transmission line. The PSB function is simply based on the fact that, the power flows direction in far end and near end bus relays of line are similar in case of faults, but opposite during power swing. The effectiveness proposed method is studied on a 9-bus test system for short circuit faults as well as power swing events in DigSILENT PowerFactory 15.0. The results show that, even with high ration of X/R and also not considering faults resistance, the calculated power flow of distance relays at two ends of line, are still considerable during short circuit, concluding the applicability of the proposed PSB scheme in power systems with high value of X/R ratio.