Transient Inrush and Fault Current Signal Extraction Using Discrete Wavelet Transform for Detection and Classification in Shunt Capacitor Banks

An unbalanced current protection relay (60C, 51NC) cannot operate fast enough to avoid catastrophic failure against high system fault currents within capacitor units because a traditional unbalanced current protection relay is not capable of classifying the transient fault current and switching inrush current. This article proposes a new algorithm for the detection and classification of these transient current signals. Simulations are performed using PSCAD/EMTDC programs. The outputs of the current signals are used as inputs for the discrete wavelet transform (DWT) process. The wavelet-based fault and inrush current detection and classification unit receive the captured transient current signals and use DWT to detect and analyze these signals. Actual inrush current signals from an experimental setup and shunt capacitor banks of 115 kV, 22 kV, and 6.6 kV are used to verify the proposed algorithm. The results show that the proposed algorithm provides good performance and accuracy in identifying faults and inrush currents.