Testing line current differential relays using real-time digital simulators

Real-time digital simulators in conjunction with current and voltage amplifiers offer an opportunity for detailed testing of modern microprocessor based relays in conditions as close to realistic as possible. Testing a digital line current differential protection system creates challenging problems as a number of communications-related test scenarios should be examined in combination with power system disturbances. This paper presents a methodology for testing 2- and 3-terminal line current differential systems. Sample test results and a number of recommendations for testing digital relays have been included. The Real-Time Digital Simulator (RTDS) and Communications Data Link Simulator (CDLS) were the testing tools used.