Differential protection of muIti-ended circuits

Representative power system networks incorporating multi-terminal feeders are analysed under typical pre-fault load conditions, to establish suitability for differential protection on the basis of a circular relay characteristic of marginal operation expressed on a complex plane in terms of the ratio of local current to the sum of remote currents in the steady state. Differential protection is shown to be feasible, with discrimination improved at lower levels of protective circuit energisation by expanding the radius of the area of stability on the complex plane inversely as the magnitude of the equivalent remote relaying quantity. The desired effect is demonstrated practically in an analogue realisation using ideal signalling, by the modification of a two-input mean amplitude comparator relay through the provision of additional restraint with 1 cycle operating time achievable.