The Use of Communication Facilities in Transmission Line Relaying

This paper outlines the fundamentals of a method of obtaining overall protection of transmission lines by a comparison of the relative direction of fault current flow at the line ends by means of a communication system. The results obtained are equivalent to differential protection. The carrier-current pilot or d-c pilot wire schemes which have been introduced during the past few years are applications of this method. The optional use of a communication system to link the trip circuits at the ends of a transmission line provided with any conventional form of relay protection is described. This insures the simultaneous tripping of both line ends for all fault positions. The various types of communication systems adaptable for relay purposes are described and discussed in regard to coordination with the telephonic communication, telemetering or supervisory control systems employed as adjuncts of the power system.