Relay models for protection studies

Power system protection relays have changed significantly during the last ten years. Processor based designs are now highly reliable integrated protection, control and monitoring systems that significantly outperform the suite of relays and control equipment from the electromechanical and static era. Technological advances and utility restructuring ensures protection remains an immensely challenging field, especially for young IT literate electrical power engineers. Modelling and simulation can help engineers better understand how a new or proposed relay reacts during a fault or other non-fault disturbances. Such knowledge can help a manufacturer improve the quality of the design and hopefully correct any weaknesses before the relay is applied to an actual network. Similarly, utilities can use a simulator to investigate whether a particular relay is suitable for their network and perhaps if one has maloperated what caused the problem. The paper describes various software relay models (developed using FORTRAN IN PSCAD/EMTBC) and discusses how they can assist a protection study. Numerous types of faults were applied to the simulated networks to verity the robustness and functional accuracy of the model. The results from these tests and the steady state operating characteristics of each relay model are presented.