Interception Probability and Proximity Effects: Implications in Shielding Design Against Lightning

The effects of a neighboring object on the interception probability distribution of an air terminal are investigated through scale model experiments. The discharge interception probability of an earthed rod is influenced by the presence of a neighboring shorter one when both inserted in a rod-plane gap. This depends on the polarity of the impulse voltage, the height of the earthed rods and their displacement with respect to the energized rod. The experimental results are interpreted in terms of the breakdown mechanism and electric field calculations; their possible extension to shielding design is discussed. Proximity effects may result in a reduction in the striking distance and interception radius of an air terminal, especially at the lower interception probabilities. A new approach for shielding design is introduced, which considers, besides lightning parameters and height of the prospective struck objects, interception probability and proximity effects.