Transient analysis of grounding electrodes in a two-layer soil considering frequency dependence of soil

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.