Fault-performance analyses of transmission-line differential protection systems related to their polar-characteristic requirements

A comprehensive study of the relaying quantities available for the differential protection of transmission lines considers the performance of both the summation transformer and the phase-sequence current-segregating network. From this study, it is possible to determine the performance of a protection scheme utilising typical summation devices for differential protection. The optimum selection of protection characteristics is discussed and a comparison made with the polar characteristics of protection equipments currently in use. Some limitations in present protection methods are pointed out. The analytical work uses a mathematical model of the power system, and the fault analyses are carried out using a large high-speed digital computer. The application of the computer to the solution of these problems is described.