Striking distance factors and practical lightning rod installations: a quantitative study

Abstract

This paper presents the results of a sensitivity analysis of upward leader initiation from lightning rods in response to an approaching lightning downward leader, with particular focus on rods installed on practical structures. The analysis takes into account the effect of the charge distribution on the downward leader, the criterion used to determine leader initiation, structure geometry, rod height and rod tip radius. The analysis shows that the: (i) “constant plus head” charge distribution results in smaller striking distances, particularly for larger charges or peak currents; (ii) choice of leader initiation criterion can result in significant differences in striking distance—the “critical radius” concept results in larger striking distances; (iii) structure geometry, particularly height but also the structure width and shape, are significant factors in the determination of striking distance, as is the position of the rod on the structure; and (iv) lightning rod geometry (tip radius) is an important parameter, particularly for larger rod heights. Therefore, it is suggested that any model for lightning interception must take into account both geometric and lightning parameters. The paper also makes some comparisons with the predictions of the simple Electrogeometric Model often used to determine the protection zone of lightning rods.