INFLUENCE OF FREQUENCY-DEPENDENT SOIL ELECTRICAL PARAMETERS ON THE GROUNDING RESPONSE TO LIGHTNING

This paper presents a preliminary analysis of the influence of the frequency-dependent soil electric parameters conductivity and permittivity on the grounding response to lightning currents. The soil electric parameters are calculated at each frequency by means of different formulations based on experimental developments. The results show that the inclusion of frequency-dependent soil parameters leads to a reduction of the grounding impulse impedance. This reduction is more significant in case of subsequent strokes than in case of first stroke currents. Also, the order of such reduction varies depending on the formulation applied to calculate the variation of the soil parameters. Impulse coefficients below the unity are obtained when the frequency dependence of the soil parameters are included, even disregarding the soil ionization effects. These results contradict some presented in the traditional literature.