Microprocessor based inverse-time multiple overcurrent relays

Inverse-time overcurrent relays are used to protect transmission lines and other power system equipment. The use of microprocessors to implement single and multiple overcurrent relays has been reported in the literature. In this paper it is shown that several independent overcurrent relays and other tasks can be implemented using a single microcontroller: the Intel 8051. An interrupt-driven array based program is designed to monitor and control up to 128 overcurrent relays from a single monitor/control board. The system consists of a personal computer and several monitor and control interface boards, each built around the 8051 microcontroller. The proposed system surpasses the previously published systems in its efficiency, response time, and its ability to implement hundreds of different overcurrent relays of various types in addition to performing other tasks.