Lightning performance of distribution lines due to positive and negative indirect lightning flashes

The paper deals with the performance of overhead distribution lines against indirect lightning. The lightning performance, i.e. the annual occurrence of lightning events potentially able to cause insulation flashovers, can be assessed by means of statistical procedures capable to account for the probabilistic distribution of the most influent parameters, among which those that describe the waveform of the return stroke current. Usually, only downward negative first strokes are taken into account when calculating the lightning performance of overhead lines. The aim of this paper is to extend a procedure previously proposed by the authors in order to include also positive downward events and to discuss how their incidence would affect the line lightning performance.