On-line fault location system for 66 kV underground cables with fast O/E and fast A/D technique

A fault location system, which continuously monitors a 66 kV underground transmission line and instantaneously locates the distance to the point of fault at a ground fault, is being developed. A prototype system for straight lines was developed as the first step. The surge current which flows, at a ground fault, from the point of fault to each end of the line is detected by a fast optical current transformer based on the Faraday effect. The detected surge current is converted to digital data through a fast O/E converter and a fast A/D converter, and the distance to the point of fault is determined from the time difference of arrival of surge currents to both ends. A location test was carried out on single phase coaxial cable of 1000 m long. The average location error of the system is below 10 m