Monitoring results of the effectiveness of surge arrester spacings on distribution line protection

Surge arresters were evaluated as a means of improving reliability by reduction in 13 kV distribution line flashovers; five feeders were extensively monitored for three years. Lightning-caused faults were detected with the US National Lightning Detection Network, magnetic-field and optical sensors attached to fault recorders, and lightning-activated camera systems. Three circuits had arresters added on all phases with spacings of 40 m (every pole), 200 m, and 400 m respectively. Two other control circuits had no additional arresters. There was no discernible difference in the lightning performance of the circuits outfitted with the different arrester spacings when line length and lightning flash exposure are considered. Evidence indicated that most of the faults were caused by direct strokes rather than induced voltage flashovers. The monitored circuits are in areas with relatively heavy tree coverage which should reduce the number of direct strokes but cause higher induced voltages. In a surprising result, the circuit with arresters installed on every pole had several lightning-caused faults.