A Static Polyphase Distance Relay

The paper describes a Static Polyphase distance relaying scheme responding correctly to all Single line-to-ground faults and all doible-phase faults, with or without ground, by the phase-comparison of line-to-neutral compensated fault point voltages. It has been shown that if any two, out of the three, phase voltages at the fault point derived at the relaying point, are fed to a 90°phase comparator, then such a polyphase distance relay will operate correctly for all types of faults, except in one case of single line-to-ground fault, in one case of double phase-to-ground fault, and also in case of three-phase fault. To cater for all types of faults, a scheme has been proposed by the authors, which utilises four 90°transient free phase comparators based on block average phase-comparison principle. Out of these four comparators one is meant for catering three-phase fault and the remaining ng three respond correctly for all single line-o- ground and all double- phase faults, with or without ground. The outputs from the four units, are fed to a logic ´OR´ gate which initiates tripping. Theoretical performance ormance characteristics of this relaying scheme during different types of faults have been explained by a generalised theory of 2-input phase comparator. Experimental verification on a laboratory model shows that the scheme is feasible and may be adopted in practice.