Transient Analysis of Grounding Systems under Lightning Strikes Considering Soil Ionization

High currents leaked to earth, leads to an electric field, which can be capable of breaking down the dielectric strength of the soil. When this happens, the ionization phenomena takes place, which reduce the grounding system impedance and modify its performance. In this paper, a computational model for transient performance of grounding systems is presented. The model is capable of simulating soil ionization and is based in a transmission line approach. The grounding system transient analysis is carried out in the frequency domain. The computer model developed was used to study the performance of vertical rods and grounding grids of different sizes. In every case, different electric field magnitudes and soil resistivity were used, currents of different frequency components and magnitude values where used as well. The obtained results presented here, were compared and validated with other computer model results and measurements published in the literature.

I. Introduction

A Lightning may generate currents up to 200 kA and frequencies from 100 kHz to 10 MHz. At these frequencies, the elements of a grounding system present characteristics mainly inductive.