Calculating the Potential Difference Between the Ground Electrodes of a Building Struck Directly by Lightning

We investigated the mechanism by which a lightning strike generates overvoltage at a building's distribution board. We analyzed the overvoltage using VSTL electromagnetic analysis software and constructed a simplified mathematical model for calculating the overvoltage. The results confirmed that the overvoltage generated at the distribution board is not affected by the arrangement of the grounding wires. The overvoltage is instead dominated by the potential difference between the ground electrodes, which is determined by the potential distribution in the surrounding earth. Therefore, the cross-sectional area within the earth through which the lightning current flows out can be modeled using a simple mathematical expression to calculate the potential difference. The overvoltages calculated with the constructed formula coincide with the simulation results within ±10% if the ground electrode is buried within 5 m of the building exterior.