Adaptive CWT-based transmission line differential protection scheme considering cross-country faults and CT saturation

In this study a new adaptive continuous wavelet transform (CWT)-based current differential protection scheme is proposed to cope with problems of conventional current differential protection in transmission lines. Current transformer (CT) saturation is a major problem for protection engineers in current differential protection systems. The mentioned problem is highlighted when an external fault occurs and causes mal-operation of differential protection. In this study, three phase currents at both ends of transmission line have been sampled and used as input signals to the proposed method using appropriate communication link. In addition, CWT with the aid of Mexican hat as a mother wavelet has been employed to extract high-frequency information of signals and detect fault occurrence and CT saturation in each phase. As a result, the proposed technique is able to prevent unwanted trip due to CT saturation during external faults. Nevertheless, simulation results confirm sensitivity and security of the proposed protection technique in facing with second internal fault of cross-country faults after a short delay.