Analysis of grounding grids influence on lightning generated magnetic field

This paper proposes a realistic approach to consider the influence of grounding grids on the magnetic field inside buildings due to lightning strikes. An electromagnetic theory approach based on the method of moments is used. This method allows for a transient grounding grid analysis in both the frequency and time domains, and accounts for the effects of the soil. Calculations are performed for a simplified case where the lightning channel is modeled assuming a constant current along the channel. This approach takes radiated fields into account but neglects propagation effects. The model is selected for ease of comparisons with the examples described in the IEC 62305-4 standard. A numerical analysis is carried out to estimate the reduction of lightning-induced magnetic fields inside grid-like spatial shields typically used in reinforced concrete buildings. The influence of grounding grids and soil resistivity on the radiated magnetic field is studied. The performance of various possible grounding grids for the building is compared. Emphasis is given to the effect of the soil resistivity on the results. Major advantages and disadvantages of both analytical and numerical methods are pointed out as well.