Using the computer to set transmission line phase distance and ground back-up relays

The size and complexity of modern power transmission systems, plus the recent advances in computer technology, have made the manual calculation of relay settings impractical. Although the settings of many relays can be best handled by programmable calculators or minicomputers, one relay at a time, the time interval coordination required for phase distance and directional ground overcurrent relays dictates that a systems approach be used. The data and calculations inherent in considering a system of reasonable size require that a large core computer be utilized. Several programs have been developed to perform this function. The unique approach taken in developing the program outlined in this paper was to provide the engineer, with a knowledge of the system under study, the power to interact with the computer in making decisions of how to best make compromises to optimize system protection and reliability.