Measurement of the Division of Lightning Return Stroke Current among the Multiple Arresters and Grounds of a Power Distribution Line

A triggered-lightning experiment was conducted during the summer of 2000 at the International Center for Lightning Research and Testing (ICLRT) in north-central Florida for the purpose of studying the lightning current division in an 829 rn long, 18-pole, three-phase plus neutral, unenergized, overhead distribution line equipped with six arrester stations. Eight lightning flashes containing a total of 34 recorded return strokes, as well as low amplitude, long duration steady currents, were artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique, and the flash currents were directed to phase C (the outermost conductor of the three-phase cross-arm-configured line). Six of the eight triggered lightning flashes caused damage to one of the two closest phase C arresters. In the case when no arrester was damaged or was not yet damaged by current in the flash, it is inferred that about 40% of the return stroke peak current and about 25% or more of the return stroke charge transferred in the first millisecond passed to the neutral conductor through each of the two closest arresters on either side of the strike point. The bulk of the peak current then flowed from the neutral conductor to ground through the groundings of the two closest arresters. The charge transferred in the first millisecond from the neutral to the eight system groundings, six at arrester stations and one at each of the two line-end poles, appears to be distributed inversely to the low-frequency, low-current grounding resistances.