Fault Detection During Asymmetrical Power Swing in Distance Relays Based on Wavelet Transform

Power swings occur related to some contingencies. But in some conditions, the relay sends a trip command incorrectly, while in most cases, the power system reaches a new equilibrium after a power swing. Statistically, the probability of the occurrence of a single-phase fault is higher than other faults, and also the intensity of other faults is higher than single-phase faults, so it is easier to identify them. Therefore, the focus of this article is on single-phase fault detection during a power swing. On the other hand, the analysis of asymmetric power swing is challenging compared to the symmetrical power swing, so in this article, the focus is on single-phase fault detection during asymmetric power swing. The suggested approach utilizes the wavelet transform (WT) on the amplitude of the zero-sequence current signal. Then, by calculating the energy of frequency components extracted from the WT and determining a threshold value, the single-phase fault is identified under asymmetric power swing conditions in the network. According to the obtained results and sensitive analysis, single-phase faults are detected by specifying 20 J as the threshold energy for the changes in the extracted frequency components of zero-sequence current. Simulation and analysis results confirm the capability of the proposed method for a standard case study network.