Differential equation based impedance measurement for series-compensated lines

Differential equation based digital algorithms for measurement of a fault loop impedance are studied in relation to their application for protective relaying of single and parallel series-compensated lines. Adaptation of the impedance measurement algorithms to the specific nature of transients in the relaying signals for the series-compensated lines is presented. Correct measure of the distance to a fault is provided by incorporating the representation of the series-capacitor equipped with metal-oxide varistor into the fault loop models. The algorithms were investigated for a variety of fault conditions using ATP-EMTP.