A New Measure of Operating Speed and Consistency of Digital Protection Instruments Based on IEC 60255

Assessing and installing digital protection relays with higher operating performances are essential to improve the continuity of service in power networks. This article proposes a new test procedure for comparative evaluation of the dynamic performance of digital relays particularly with respect to their response speed and consistency. In the proposed test procedure, relay operating times are measured for various fault scenarios established based on the IEC 60255 standard. The measurement data are processed to calculate the averages, weighted variances, and distribution functions of the relay operating times. Given the statistics, four new indices are developed to calculate total performance scores for relative comparison of the relays. Simulation studies are conducted on the proposed and conventional test procedures when applied to several types of protection relays. Experimental studies are also carried out using real relays in a hardware-in-the-loop simulation setup. The study results verify that the proposed test procedure and numerical indices lead to comparative total scores, large decidability index values, and small equipment variation values, thus ensuring effectiveness and robustness in assessing relative performances of relays.