Commissioning and maintenance testing of multifunction digital relays

Protective relay technology over the past twenty-five years has evolved from single-function electromechanical (E-M) 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 E-M and static relay technologies, digital relays also require commissioning and relay setting verification. This paper 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.