A second generation microprocessor line protection relay

The authors describe a line protection with distance relay and auxiliary functions, having an optimized hardware and software structure, for power transmission and sub-transmission as well as distribution applications. The development of this relay has evolved from an earlier prototype line protection equipment which was based on a single Intel 8086 16-bit microprocessor hardware and programmed in assembler language. The protection algorithms for the new line protection relay have thereby been thoroughly proven through many successful laboratory and field tests. The firmware and menu-driven man-machine interface (MMI) concepts are the same as for a new bus-oriented multi-processor generator protection system. Since the line and generator protection equipment share a common firmware concept, all available protection or measurement functions are compatible with both equipments. Through the use of continuous self-monitoring and self-testing, any hardware failures can be immediately reported, thereby reducing the probability of relay maloperation to virtually zero