Development of Automatic Fault Point Locating and Sectional lsolating System for Power Distibution Line

This paper describes the development of Automatic Fault Point Locating and Sectional Isolating System. This system locates a single-line-to-ground fault point at each pole by using ground-current-sensors and isolates the faulted section by controlling pole switches with no outage of unfaulted sections. The ground-current-sensor is connected to the line between allied earth terminals of pole devices and grounded conductor. It detects a ground fault current of more than 0.64 amperes that is determined so as to avoid an unexpected operation by stray-current but to detect the fault current certainly and sends out a emergency signal with time delay of 0.1 seconds. Sectional isolation starts when both the emergency signal from the sensor and relay operation signals from substation are received and ends within a feeder circuit breaker's tripping time of 1.5 seconds.