Frequency and Current-Dependent Grounding Resistance Model for Lightning Surge Analysis

The frequency dependence as well as the current dependence of grounding resistance affects lightning overvoltages in electric power system. This paper proposes an equivalent circuit to simulate the frequency dependence of soil resistivity and permittivity. Constants of the equivalent circuit are determined based on empirical formulas for the frequency dependence of the soil parameters proposed by Alipio and Visacro. The equivalent circuit is represented in time domain. Therefore, the equivalent circuit is applicable to the calculation of the current dependence of the grounding resistance. An influence of the frequency dependence of the soil resistivity and permittivity on the current dependence of the grounding resistance is discussed by the use of the equivalent circuit. This paper proposes a modified CIGRE model to calculate the current dependence of the grounding resistance. The equivalent circuit is very convenient and useful for engineers to carry out lightning surge analysis.