Pilot-wire differential-protection characteristics for multiended circuits

The steady-state characteristics of differential-protection systems for multiended circuits are discussed and alternative characteristics, which appear to give improved performance, are proposed. Circuits for the implementation of these characteristics, incorporating pilot-circuit compensation and amplitude comparators, are presented. A design basis for compensation circuits is given by expressing the comparator performance in terms of its admittance-measurement characteristics and associating these with the input-admittance characteristics of the pilot circuit. By this means it is possible to investigate the various comparator arrangements, and to determine the most suitable arrangement for the protection of a multiended circuit. By a transformation of axis, the admittance-plane characteristics can be presented in terms of the ratio of the comparison quantity at one end to the summated quantity at the remaining ends, making it possible to investigate power-system fault conditions on the same diagram to determine available discriminating margins.