A wavelet based protection scheme for EHV asymmetrical teed circuits

Transmission line protection schemes of EHV teed circuits in power systems face typical problems due to intermediate infeed or outfeed from the third terminal and superimposed reflections from T-point and fault point. Asymmetrical nature of the circuit further compounds the problem. In this paper, a novel high speed protection scheme using Wavelet Transform for teed circuits is presented. The proposed method, a unit scheme, utilizes synchronized voltages and currents of three phases from all the three ends of the teed circuit. The scheme makes use of transient high frequency components of the wide band fault voltage and current signals for fault detection & classification and fundamental frequency phasors for locating the fault. While the Wavelet Transform is used to extract the features for detection and classification, the Discrete Fourier Transform based approach is applied to estimate phasors for fault location purpose. The scheme is tested on simulated asymmetrical teed circuit model for various fault locations, types of faults, inception angles and fault resistances. Results indicate that the scheme is fast and accurate.