Frequency Dependence of Soil Parameters: Experimental Results, Predicting Formula and Influence on the Lightning Response of Grounding Electrodes

An experimental methodology was applied to determine the frequency dependence of the soil resistivity and permittivity under field conditions. A large number of soils of low-frequency resistivity ranging from 50 to 9100 .m were tested and showed strong variation of both parameters in the Hz frequency interval. Simplified expressions were proposed to predict this frequency dependence. The response of grounding electrodes subjected to lightning currents was simulated using an electromagnetic model under the assumption of variation of soil parameters given by such expressions and obtained from measurements. The results were very similar, though quite different from those obtained under the assumption of constant values for soil resistivity and permittivity.

I. Introduction

The response of grounding electrodes subject to lightning currents is a complex matter. Despite the current availability of advanced computational models based on different approaches to simulate this response, such as those described in [1]–[4], the accuracy of the results they provide depends largely on the assumptions of soil parameters. In particular, the frequency dependence of soil resistivity and permittivity can strongly affect such a response.