Comparison of equivalent circuit models for the simulation of soil ionization

• High impulse currents cause soil ionization that reduces the grounding resistance.
• Measured impulse responses both with one and two current peaks are simulated.
• Three equivalent circuit models implemented with the ATP-Draw program are compared.
• The model by Nor et al is selected as the most general and adjustable approach.

The main characteristic of the transient behaviour of a grounding system is the decrease of the grounding impedance, due to soil ionization phenomena that take place, when the density of the injected current exceeds a critical value. In this paper three circuit models proposed by researchers have been implemented using the ATP/EMTP programme in order to simulate the transient response of a grounding system taking soil ionization into account. The simulation results are compared to measurements received by imposing impulse voltages on soil samples. The accuracy of each model is evaluated according to the level of proximity to the oscillograms and conclusions are drawn about the effectiveness of each modelling approach.