Multifunction digital relay commissioning and maintenance testing

This paper discusses with the protective relay technology over the past 25 years has evolved from single-function electromechanical (EM) relays, to static (electronic) relays, and, finally, to digital multifunction relays. A significant number of these multifunction digital relays are being installed on medium-voltage electric power systems within industrial and commercial facilities. As was required in earlier EM and static relay technologies, digital relays also require commissioning and relay-setting verification. This article discusses the unique challenges the user faces in testing and commissioning digital multifunction relays. It also explores the impact on maintenance testing of self-diagnostics, the digital relay´s internal capability to check itself for failures.