The Laboratory Investigation of a Digital System for the Protection of Transmission Lines

The results and conclusions of a feasibility study of a digital system for the protection of transmission lines are presented. In this laboratory investigation, a computer with its data acquisition system was connected to a transmission line model. The minicomputer program for a two-zone stepped-distance protection scheme utilizes an algorithm based on the system differential equation. Extensive testing with a wide range of fault types, fault locations, fault inception angles, and power flows demonstrated the success of the system. Trip times were on the average equal to or less than 0.5 cycle for the primary protection zone. The program successfully determined fault type and location with the fault locations usually within a mile over the range of the model of a 72 mile transmission line.