All-electronic carrier relaying reduces fault-clearing time [includes discussion]

An all-electronic directional-comparison carrier relay system having a maximum over-all operating time of 1 cycle has been successfully tested both in the laboratory and by staged tests in the field. In order to obtain operating experience, this equipment was placed in temporary service by the Appalachian Electric Power Company to protect a 43-mile 132-kv transmission line between Roanoke and Lynchburg, VA, USA. Permanent installation is planned on the 330-kv system of the American Gas and Electric Company to protect the line between Muskingum and East Lima. This equipment is the result of several years' intensive study and tests to determine the best system of line relaying capable of operating under all conditions in 1 cycle. The expansion in system capacity and the trend to higher line loadings makes it desirable to provide protective relaying equipment which will materially reduce the fringe times of 3 to 4 cycles sometimes - encountered with carrier relaying presently available. Planning studies for higher voltage systems, such as the American Gas and Electric Company 330-kv system, indicated that this development should be completed in time to have such equipment available for these systems. While electronic relays have been used in limited applications in the past, the decision to develop an electronic system for line protection was made only after sufficient study and experience provided assurance that the degree of reliability required for such applications could be obtained. In this paper and three companion papers will be presented system considerations leading to the requirement for maximum relay times of 1 cycle, the reasons for the choice of electronic methods to obtain this performance, detailed description of the equipment, the circuitry, and the results of laboratory and field tests.