Computer aided/evaluation and application of distance relays

Distance relays were developed and introduced more than fifty years ago and yet, despite the many years of excellent work conducted in this field by manufacturers, universities and users of protective relays, there is still a great diversity of distance relay characteristics available and a general lack of agreement on what characteristics are best suited for protecting transmission lines under different power system conditions. This situation is partly the result of the difficulties associated with the analysis of distance relay characteristics when complex power system conditions such as fault resistance, pre-fault load, multi-terminal lines, mutual coupling in parallel circuit lines, etc. are taken into account. Under these circumstances, there is a clear need for a tool to help protection engineers evaluate relays under varying conditions. The computer programme described by the author was developed for this purpose