Usage of Wavelet Transform in the Protection of Series-Compensated Transmission Lines

Abstract

This paper presents a new method for the boundary protection of series-compensated transmission lines, as well as fault classification. The boundary protection is based on detecting distinct frequency bands contained in the transient fault current wave. Discrete wavelet transform, using db4 as a mother wavelet, is used to capture two bands of frequencies in the transient current signal. The spectral energies of these two bands are obtained and used to determine if the fault is internal or external to the protected zone. Fault classification is done using the discrete wavelet transform. Using Haar as the mother wavelet, the coefficients of a frequency band in the range of 1 kHz-3 kHz are obtained for the three phase and ground currents. The average value of the coefficients of each current wave is then computed and used to classify the faulted phases. The basic principle of the protection scheme is described and its response to the series-compensated transmission lines is studied for a wide range of compensation levels, fault conditions, fault types, and fault locations. The stability of the algorithm under various load switching cases is also tested. Fault simulations are performed using power system computer-aided design/electromagnetic transient and direct current program and the results are then interfaced to MATLAB, where the algorithm is implemented. It is found that the proposed method gives reliable results in the boundary protection and fault classification of series-compensated lines.