New approach to ultra-high-speed phase selection in single-pole autoreclosure schemes

Single-pole-autoreclosure(SPAR) application demands reliable phase selection. The need to minimise the likelihood of single-phase faults spreading to other phases and a generally increasing requirement for reduced circuit dead-times, increasingly demands that phase-selection be accomplished in a time compatible with ultra-high-speed (UHS) fault clearance. The paper outlines the principles of operation and design of a new UHS digital phase-selector which, by viuture of employing specially filtered versions of the superimposed voltages and currents, is immune to problems of indiscrimination caused by load current. The paper concludes with a consideration of the performance of the new phase-selector in typical 500 kV transmission applications employing SPAR.