Performance testing of the protection relays ensures that a particular protection scheme will operate reliably and fast enough to disconnect a faulty zone from the rest of the network, thus mitigating the effect of fault on the power system. It is therefore important to validate the settings of power protection equipment and to confirm its performance when subject to different fault conditions. Traditionally, commissioning engineers make use of standalone protection relay test sets for analyzing the performance of relays when subjected to different voltage and current injections. With the advent of digital simulators the model of the power system can be executed in real-time and protection relays can be interfaced as hardware-in-the-loop to evaluate their performance when subjected to different faults in the simulated power system. This gives an added value of analyzing the overall behavior of the power system coupled with the relay performance under faulty conditions. In addition, the utilization of GOOSE messages for status, control and protection purposes puts an extra requirement to completely test the IEC 61850 capabilities of the protection relays.
This article illustrates two different techniques namely standalone testing and real-time hardware-in-the-loop testing used for protection relays performance verification. Both techniques are evaluated for hardwired and IEC 61850-8-1 (GOOSE) signals. The instantaneous overcurrent protection feature of Schweitzer Engineering Laboratories Relay SEL-421 is used for complete standalone and RT-HIL testing. For RT-HIL testing, the test case is modeled in MATLAB/Simulink and executed in real-time using Opal-RT's eMEGAsim real-time simulator. The event reports generated by standalone and RT-HIL testing for both hardwired and GOOSE signals is used to verify the tripping times achieved. Finally the performance of hardwired and GOOSE tripping times are compared and the overall standalone and RT-HIL techniques are evaluated.