At lightning discharge, the grounding systems' transient behavior is influenced by time-dependent nonlinear behavior and frequency-dependent effects. These effects are related to complex phenomena arising from the soil ionization surrounding the conductors at high current and to the fast risetime of the impulse current, respectively. Most of the performed investigations were either focused on soil ionization effects or frequency-dependent effects. This paper proposes a model that incorporates both aspects including the mutual coupling and air-soil interface effects, giving a more realistic representation of the grounding systems behavior. Based on the transmission line approach, the model can compute the grounding systems transient response buried in uniform and nonuniform soil. The model is applied to horizontal, vertical electrodes, and grounding grid subjected to impulse currents of variable magnitudes and shapes. The model results are validated against published measurement results obtained with low-current and high-current impulses. The time-domain transient potential and transient impedances show good agreement with experimental results. Other impulse impedance parameters used for the grounding systems analysis are reproduced quite accurately. As an application, the impulse impedance of a horizontal electrode and a grounding grid buried in two-layer soil is discussed when the upper layer depth and the resistivity of soil layers are varied.

This investigation is devoted to study, in time domain, the transient behaviour of vertical and horizontal grounding conductors submitted to impulse current using state space representation‐based transmission line method. This study has been carried out with and without incorporating soil ionisation and mutual coupling between conductor elements for soils of low and high resistivities. The results are focused on the time‐domain solution of the electrode's transient potential rise and its impulse performance parameters. The results show the importance of including the mutual coupling between segments of the same electrode and soil ionisation. The results are compared with both published theoretical approaches and experimental measurements, and show acceptable agreement. This method has been applied to compute the transient potential of horizontal electrodes buried in vertically stratified soil, a situation which can occur where long horizontal counterpoise is buried in a highly contrasting soil along its length.

This paper discusses the impulse analysis of horizontal ground electrode buried in uniform and two-layer soils, describing applications of a recently developed model based on transmission line approach for the analysis of high frequency and transient behavior of grounding systems. Simulations were carried out to compute the ground electrode’ potential and the impulse impedance. A practical method to estimate the effective length of horizontal ground electrodes is presented. The results have been successfully compared with those computed using formulas reported in the literature and only developed for uniform soils. The proposed method is intended for estimation of the effective length of horizontal electrodes buried in soils having a two-layer stratification, which has not yet been considered so far. Based on this method, parametric analysis carried out has shown that the parameters influencing the effective length are mainly the soil resistivity and the rise time of the injected current for uniform soils or associated with the upper layer depth and the refection factor for two-layer soils. Using a genetic algorithm, mathematical expressions for the effective length of horizontal ground electrodes are proposed in terms of these parameters.

This investigation is devoted to analyse the impedance behaviour of long horizontal grounding electrodes as function of frequency for several soil resistivity values. The real and imaginary parts of grounding impedance have been analysed in order to characterize its nature at several points along the electrode. We show that the impedance increase reflects its inductive behaviour. This impedance increases with the grounding electrode length. For high soil resistivities, resonant peaks appear. They are attenuated with the electrode length increase.