A high-speed algorithm to discriminate between power swing and faults in distance relays based on a fast wavelet

Distance relay should be blocked during a power swing, but it should operate reliably when any fault occurs even during a power swing. Therefore, this paper introduces a high-speed algorithm based on wavelet transform (WT) to discriminate between a power swing and symmetrical/asymmetrical faults. The algorithm uses a fast mother wavelet, with a 3-coefficient high-pass filter, to decompose the voltage and current signals into their corresponding frequency levels. In this regard, two distinct levels are chosen. The first level of the voltage signal and the eighth level of the current signal are chosen to detect a fault and a power swing, respectively. Depending on the percentage change in the spectral energy of these discriminative signals, the distance relay can discriminate between a power swing and any fault that may occur during a power swing. To evaluate the performance of the introduced algorithm, several faults, including high resistance faults, and power swings cases are simulated on a typical extra high voltage transmission system using MATLAB environment. The simulation results show that the introduced algorithm has a high speed and an efficient performance, even if the signals are noised; where a power swing is detected in a suitable time and faults are detected in a cycle or less.