Discover relay design and application problems using pseudo-transient tests

The authors describe how pseudo-transient tests using commercially available instruments have revealed several relay design problems and application limitations. The test method is briefly described, and the results of several series of tests are discussed as examples of its application. The method is not suitable for fully assessing the performance of relays. Its limitations are discussed. In series compensated transmission lines, or in EHV cable circuits (with high shunt capacitance), where power system signals have a large proportion of nonfundamental frequency components, pseudo-transient tests may be of limited use. Even in such cases, depending on the design of the relay input filters, pseudo-transient tests may provide useful benchmark test results for future routine maintenance tests