Modelling an impedance relay using a real time digital simulator

In this paper a real time digital simulator (RTDS) is used to develop and verify protective relay algorithms by modeling the actual protective relay as well as the power system in one simulation. The real time operation of the simulator provides a time and personnel efficient environment for the work. This allows the models to be subjected to exhaustive test case scenarios before final implementation of the protective relay algorithm in the development platform. Since the developmental and final hardware implementations of the relay will be tested with the real time simulator, the use of the RTDS during early design stages also allows one simulation tool to be used throughout the process. Regression testing can be automated using the script features of RSCAD. The scripted cases can be run during non-work hours to minimize personnel requirements and maximize the simulator usage. This paper describes the technique used to model an impedance relay using the RTDS software and hardware. The relay model included a mho characteristic polarized with positive sequence memory voltage Andrichuk and Alexander (1), Roberts and Schweitzer (2). Phase selector logic, loss of potential logic and direction control logic, all of which are essential in a commercial relay (2), were not implemented here to limit the modeling complexity to the basic requirements.