Transient analysis of soil resistivity influence on lightning generated magnetic field

This paper proposes a full-wave analysis to consider the influence of soil resistivity on the magnetic field inside buildings hit directly by a lightning strike. An electromagnetic theory approach based on the method of moments is used. This method allows for a transient analysis and accounts for the effects of soil resistivity. Calculations are performed in the frequency domain for a simplified case where the lightning channel is modeled assuming a constant current along the channel. The model is selected for ease of comparisons with the examples described in the IEC 62305-4 standard. A time domain numerical analysis is carried out to estimate the influence of soil resistivity on the radiated magnetic field. The effect of the soil resistivity on both the resultant and on the time derivative of the magnetic field is investigated for a 2 m mesh grid-like spatial shield of 10x10x10 m located in horizontally layered soil structures. Examples of transient resultant magnetic field induced by a typical positive stroke on a building represented as a grid like shield are presented, emphasizing the impact of soil resistivity. It is shown that the transient electromagnetic field is moderately affected by soil resistivity changes which, therefore, can be, in some cases, neglected in the computation process.