Wavelet energy-based stable and unstable power swing detection scheme for distance relays

Abstract

Distance relays are susceptible to maloperation during postfault power oscillations in the system. Thisunintended operation of relays may lead to power system blackout. It is due to their inability to distinguish a stablefrom an unstable power swing and to take a tripping decision appropriately. This research paper proposes a fastand wavelet energy-based method to detect stable and unstable power swings for distance relays. The proposed methodcomputes the angular velocity of an equivalent machine developed from the measurements available at a bus. The energyin the low frequency band of the equivalent machine angular velocity will assist the tripping decisions of transmission linerelays during power swings. Compared to the conventional method using blinders, the advantage of this method is that itrequires less hardware and less time to know whether the resulting power oscillations after fault clearing are going to bestable or not. The performance of the proposed method has been evaluated on 5-bus system, WSCC 9-bus system, andIEEE 14-bus and 30-bus systems considering different test scenarios. The results show that using this method improvesthe performance of distance relays in detecting stable and unstable power swings.