Adaptive distance protection of double-circuit lines for faults involving earth

In this paper an adaptive measurement of fault-loop impedance for distance protection of a double-circuit line is presented. Adaptation is applied for single- and double-phase faults involving earth. On the base of analysis of a generalized fault-loop model and constrains for considered faults the compact formula for a fault-loop impedance was obtained. Compensation for an error resulting from a fault resistance was assured. Sample results of evaluation of the developed measurement algorithm are included. (Adaptive distance protection of double-circuit lines for faults involving earth).