Striking distance and interception probability

The relation between the striking distance and interception probability is experimentally investigated under standard lightning impulse voltages of both polarities. By using the rod-plane gap as a reference case, results are presented relating to the discharge interception probability of an earthed rod inserted in the gap. There is a critical separation distance between the stressed and earthed rods at which breakdown occurs either to the plane or to the earthed rod with the same probability. Besides the impulse voltage polarity, the length of the reference gap and the earthed rod height are considered as parameters influencing on interception probability. Results are discussed on the basis of the breakdown mechanism and electric field calculations. The striking distance is defined with the aid of an expression that takes into account, besides lightning peak current, the interception probability and the effects of lightning polarity and struck object height. The results introduce the design of lightning protection systems on the basis of lightning interception probability. Index Terms--Air gaps, electric breakdown, interception probability, lightning, striking distance.