High Impedance Single Line to Ground Fault Detection and Wavelet-alienation Based Faulty Phase Identification

This paper presents a wavelet based technique for fault detection and faulty phase identification in transmission lines. The current signals from both ends of the transmission line have been utilized to identify the faulty phase. This technique gives accurate result for high impedance faults which is a challenging task and relays cannot perform effectively under high impedance faults. The discrimination between internal and external fault has been obtained from the difference of phase angles of positive sequence current signals after and before the inception of fault. The first level of approximation coefficients of current signals from a sliding window of quarter cycle length have been utilized to calculate the alienation coefficients. An appropriate threshold value of fault index has been considered which can clearly identify the faulty phase for single line to ground fault. The proposed technique provides accurate results within a quarter cycle from the inception of fault.