Differential pilot-wire protection systems using phase comparators

The paper provides a comprehensive account of the underlying theoretical basis of pilot-wire differential protection systems, in which, though the relaying signals are subjected neither to amplitude nor phase constraints in transmission through the pilot circuit, the final detection, and corresponding delineation of the protection characteristic, is achieved using phase comparators. It is shown that a wide range of characteristics is in this way realisable, and examples are given in which the stability zone of a complete 2-ended scheme is derived from compounding discontinuous linear or circular-arc sections. From this range, a composite characteristic is proposed that appears to give substantial discriminating margins, when used with conventional phase-current-summation circuits.