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In lightning discharge, the grounding systems' transient behavior is influenced by frequency-dependent effects. These effects are related to complex phenomena arising from the fast rise time of the impulse current. In this paper, a new frequency-dependent (FD) model of grounding systems (GSs) is presented that can be deployed in time-domain analysis. The proposed wideband modeling considers the frequency dependence of the soil electrical parameters (conductivity and relative permittivity). This model is sufficiently accurate for single-port and multi-port GSs buried in uniform and non-uniform soil in the frequency range of lightning. The main innovation of the proposed model is that it can be implemented in the time domain without requiring the inversion of the GS impedance matrix. Hence, this method is less complex than conventional approaches. As one of its applications, the effect of FD modeling of GS is investigated on the lightning overvoltages of a wind farm. The simulation results show that the frequency dependence of soil has a huge impact on overvoltage magnitude and the energy absorption of surge arresters (SAs) in wind farms; this effect varies according to the type of the GS and the soil resistivity, so it is of great importance from technical and economical points of view.

In a previously published work, performances of three practical earthing systems consists of 2, 3 and 4 rod-bed electrodes buried at the same site, thus the same soil resistivity were investigated. It was found that the degree of reduction of the earth resistance values is the highest in the poor earthing systems (2 rod electrodes). The non-linearity effect or the reduction of earth resistance values as the currents were increased was also observed in previous study. However, in that study, the effects of the soil resistivity on the performance of earthing systems were not observed. This paper is a continuation of previously published paper where the detailed investigations of the soil ionisation in earthing systems under high impulse conditions for different soil resistivity values are presented. Similar configurations of earthing systems of 2, 3 and 4 rod-bed as in were used in each site, and combined grid-multiple rods where the results have been presented before were used for the purpose of comparison.

This article is the first of five based on a series of lectures which was sponsored by the power and industrial group of the AIEE New York Section during the 1943–44 season. The behavior of currents flowing in the earth, as influenced by the resistivity of the soil, frequency of the current, and size and shape of electrodes, is analyzed here.

STUDIE SDEVOTED TOP REDETERMINATION of ground resistance on the basis of geometric dimensions and ground resistivity generally assume that the resistivity of the soil is uniform. While this assumption is frequently justified in view of the usually meager knowledge of the actual ground resistivity distribution and the mathematical difficulties caused by any nonuniformity of the ground resistivity, it also can be misleading under certain conditions.