Torque and its application in the designs of microprocessor distance relays

The paper discusses phase comparators, magnitude comparators, and their applications in the design of a high-speed microprocessor distance relay. Regarding ground distance units and phase-to-phase distance units, torque created by phase comparators and magnitude comparators is described in terms of fault impedance and source impedance ratios. Both long- and short-data window approaches for computing torque are described. Post-filters which process torque are utilized to ensure speed and security of the high-speed distance relay. Finally, typical test results of the high-speed distance relay tested on a model power system and digital fault record data from the relay are presented