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

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