Innovations in use of microprocessor relays and controls for improved reliability on the distribution system

With increasingly stringent requirements for reliability of service and with availability of more advanced microprocessor-based protective relays, some novel protection schemes have been developed and implemented to provide uninterrupted service or high-speed service restoration. This paper discusses the operation of three power distribution systems requiring different levels of service reliability. In one case, a brief outage with service restoration within 60 seconds was adequate. This requirement was met with an open looped radial distribution system configuration having fault sensors, switch controls, and a central control processor. The second system takes advantage of high-speed relaying and central control for system restoration to limit the extent of the outage to the source-side of the fault of an open loop system configuration. In the third case, a "no-outage" system was required. This system was implemented using a closed-loop feeder configuration with fault interrupters controlled by high-speed relays employing pilot relay systems.