Impedance-Differential Protection: A New Approach to Transmission-Line Pilot Protection

Differential protection is able to provide the most selective protection compared with other protective schemes. In this paper, a new differential scheme is proposed for pilot protection of transmission lines. The concept of differential impedance ( Zdiff) is introduced using the synchronous voltages and currents of both terminals of the line. The proposed scheme is capable of fast discriminating between the internal and external faults, even in the worst operating conditions. The dependence on the line capacitive charging current and the source strength are common problems in conventional pilot protection methods which have been removed in the proposed scheme. Moreover, compared with the conventional differential protection, the proposed scheme can exactly determine the fault location. Both computer and experimental simulation studies have been performed to evaluate the proposed scheme. The obtained results approve the high efficiency of the proposed scheme as powerful pilot protection.