Modelling relays for use in power system protection studies

Computer models of relays can play a major role in evaluating the performance of protection systems during system faults and other disturbances. The purpose for which utility engineers and manufacturers can use relay models is outlined in this paper. The various components of relays that should be included in the models are then identified. The reasons for modelling each component are reviewed. The issue of modelling transducers is discussed as well. Procedures for modelling signal conditioning filters and analog to digital converters are outlined. Techniques for computing phasors are briefly discussed. Procedures for developing phasor and transient models and their possible applications for protection studies are described. Before these issues are addressed, the types of models and the circumstances in which they could be used are reviewed