Fault identification in AC and DC systems using stft analysis of high frequency components

Abstract

Transient response has significant importance for the fault analysis of both the established high voltage AC transmission and upcoming high voltage DC (HVDC) power systems. Due to negligible impact of line inductance, faults in DC power system would result in fast rising currents as compared to its AC counterpart. Thus, the transient current signatures are essentially different in both systems. Hence, a robust and universal fault identification method is of great interest, so that the same relays can be used for both the AC and DC systems. In this paper, Short-Time Fourier Transform (STFT) has been applied for fault identification in the AC and DC power systems. The main idea is to investigate the superposition of the high- frequency components during the transient period. Transient signals both from AC and DC systems are analyzed. The AC fault record was obtained from the power transmission network in South Africa, through the DFR, sampled at 2.5 kHz. For DC grid, the point-to-point system has been simulated and experimentally validated. For the multi-terminal networks, the CIGRE B4 based multi-terminal DC system has been analyzed in PSCAD/EMTDC. Successful application of the STFT-based method substantiates its potential as universal fault identification method for both the AC and DC systems.