FAULT IMPEDANCE ESTIMATION ALGORITHM FOR DIGITAL DISTANCE RELAYING

Fault impedance is one of the major parameters that must be estimated accurately in digital distance relaying application. In this paper, a new algorithm is proposed based on symmetrical components theory. The proposed algorithm has computational advantage over previously suggest ed symmetrical components based algorithms. A procedure for applying s hunt fault conditions to the sequence equations to estimate fault impe dance of the protected transmission line is discussed. Alternative Tra nsient Program (ATP) that is available on personal computers was used in evaluating the proposed algorithm. ATP models a power system arid s imulates many fault conditions on a selected transmission line. Fault data obtained were used in calculating fault impedance using the propo sed algorithm. Fault impedance estimates were inserted in relay charac teristics to determine suitability of the proposed algorithm for first zone distance protection. Sample results of these studies which show stable fault distance estimates are presented and discussed in the pap er.