Five years experience with a new method of field testing cross and quadrature polarized mho distance relays. I. Results and observations

Since 1981, the Saskatchewan Power Corporation (SaskPower) has used a method based on the expanding polar characteristic to field-test cross and quadrature-polarized mho distance relays. Experience gained from the use of this method to test distance relays from different manufacturers over a five year period is presented. The test method has been used successfully to predict and improve distance relay discrimination and to solve unexplained problems of relay operations that were unresolvable using the previous test method. Discussions on the problems that arise from using this new method are included. It is shown that unless the test procedures are properly designed, based on an understanding of the relay architecture, the distance relay can give erroneous results without malfunctioning. The test method described deals with circular relay characteristics, the type most commonly used by SaskPower