Construction of a fault location specifying method for the transmission line tower of an isolated neutral system

Overhead power transmission lines are subject to many faults caused by lightning strikes and contact with wildlife. At the time a fault occurs on a transmission line, many maintenance workers of the power utilities need to inspect the overhead power transmission lines for early finding of the fault point and rapid recovery. Most towers with transmission lines below 154kV of the Chubu Electric Power Co., Inc. (CEPCO) have a Ground Fault Finder (G-FinderTM) for efficient location of a transmission line fault. The advantages of GF are its highly accurate fault point finding; it needs no power source; and requires minimal maintenance. For transmission lines with overhead ground wires, the fault current in the opposite phase flows through the overhead ground wire on both sides across the fault tower. In the case of a non-fault tower, the fault current flows in the same phase as the ground wire. The GF identifies the fault point by attaching two current transformers to an overhead ground wire on both sides of the transmission tower and detects the difference in the phase of the current. However, this method cannot be used for power transmission lines without overhead ground wires. Moreover, it is difficult to detect a fault on the transmission lines without the overhead ground wires of isolated neutral systems and neutral grounding systems with delayed resistor insertion, because the fault current is extremely small and has a peculiar waveform. Therefore, it is hard to identify a faulty tower on the transmission line. Against this background, we establish a new detecting method for the Ground Fault Finder to find a fault point on an isolated neutral grounding system and grounding system with delayed resistor insertion. We made a prototype-GF, installed it on the actual transmission line, and conducted field verification to evaluate the operational characteristics. In this paper, we introduce the outline of this new type of GF and its field verification results.