Frequency Dependence of Soil Parameters: Effect on the Lightning Response of Grounding Electrodes

Quantities related to the response of grounding electrodes subject to lightning currents are simulated under the assumption of constant and frequency-dependent soil resistivity and permittivity for 100-4000 Ω·m soils, using an accurate electromagnetic model. It was found that the frequency dependence of soil parameters is responsible for decreasing the grounding potential rise of electrodes and, thus, their impulse impedance and their impulse coefficient. This effect is more pronounced with increasing soil resistivity and for typical currents of subsequent strokes. The reduction of these quantities is negligible for soils of 300 Ω·m and below. It is considerable for soils above 500 Ω·m and is very significant above 1000 Ω·m. Reductions of around 23%, 30%, 40%, and 52% are found, respectively, for soils of 600, 1000, 2000, and 4000 Ω·m and typical subsequent stroke currents. Lower values, around 8%, 11%, 18%, and 28%, are found for first stroke currents.