A Digital System for Directional - Comparison Relaying

The results and conclusions of a study of a directional-comparison protection system for a transmission line are given. The laboratory investigation of this system with two minicomputers communicating with each other via power line carrier is described. The system includes a directional-comparison blocking relaying scheme with first zone high- speed tripping. Also included is an out-of- step blocking scheme for power swing conditions. After the successful laboratory test program, the system has been installed in the field on a 500 kV, 116 km (72 mile) transmission line. Some preliminary discussion of the field installation is given.