Microprocessor Based Digital Relays Application in Tepco

Two types of digital relaying systems using high speed microcomputers have been placed in service in the Tokyo Electric Power Co., Inc. (TEPCO). One is a current differential carrier relaying system for the protection of EHV (275 kV, 500 kV) transmission lines. This system will be used as the standard primary protection system for EHV transmission line. The other is a balance and directional distance relaying system for the protection of 66 kV parallel transmission lines. This system will mainly be applied around metropolitan area. This paper first describes the details of the above mentioned two digital relay systems now in service, then describes their background technology, that is, high speed microcomputer, automatic checking and other-means for higher reliability, and noise withstand capability.