An improved transmission-line model of grounding system

This paper presents a time-domain transmission line model of grounding system, which includes the mutual electromagnetic coupling between the parts of the grounding structure and the influence of air-earth interface. The model can be used to simulate the transient behavior of the grounding system under lightning strike. The simulation results are in good agreement with that of the model based on the solution of full Maxwell's equations [1], [2] and also with the measurements reported in [1]. The influence of different parameters, such as the soil relative permittivity epsilon (r), the soil resistivity rho, and the conductivity and diameter of the conductor, on the transient voltage distribution of the grounding system is investigated. It shows that, among the parameters investigated here, the soil resistivity is the most important parameter that affects the transient response of bare buried conductors. The soil permittivity has very little influence on the transient response of the grounding system when the grounding system is buried in the soil with low resistivity, but have moderate influence in the soil with extremely high resistivity. The conductivity of the conductor and skin effect have practically no influence on the peak transient voltage of the grounding system. Increase in conductor diameter tends to decrease the peak transient voltage. The model presented in this paper is simple, but sufficiently accurate and can be used easily in engineering practice. Since the model is in the time domain, it could be easily coupled to the other time-domain models of nonlinear surge-protection components.