Distance protection of asymmetrical overhead lines

Distance protection is based on the measurement of the impedance of power system short-circuit loops and the comparison with given settings. Conversion of the measured short-circuit impedances using kilometric impedance values allows distances to be evaluated. In any case, an ideally symmetrical line structure is assumed. In practice, however, such an ideal symmetry cannot be reached for overhead power lines, even if transposed. Complete transposition of an overhead line, for instance, is effective only in case of a short-circuit at the end of the line. Today, overhead lines often are not transposed to reduce costs. This paper shows how asymmetries of single- and double-circuit power lines can be taken into account when fault distances are determined using various compensation methods. The asymmetry is directly included in the process of modeling of the distance protection