Effect of Rusck's Approximation on the Indirect Lightning Performance Assessment of Aerial Power Lines

This article investigates the effect of a simplified procedure, referred here as Rusck's approximation, which consists in obtaining the electrical potential at a given height by multiplying the vertical electric field computed at ground surface by the height considered, instead of integrating the vertical electric field from the ground surface up to the given height. This procedure is currently considered by several authors but, so far, has not been investigated in detail. The article shows that this approximation leads to significant deviations at close range from the strike but provides accurate results if the distance from the strike is higher than three times the height of the point considered. The article also shows that the distance between the line and the flash must be higher than three times the line height to obtain lightning induced voltage peak-values sufficiently high to produce line flashovers, as otherwise the flash will strike the line directly. As Rusck's approximation provides accurate results under such condition, it can be used for the assessment of indirect lightning performance of aerial power lines without any significant loss of accuracy.