**Acknowledgment**

22 Computational and Numerical Simulationse

**Figure 13.** The distribution of the MFI *Bx* on the ground surface (f=16.7 kHz)

**Figure 14.** The distribution of the MFI *Bx* on the ground surface (f=250 kHz)

and some numerical results have been discussed in this paper.

accelerate the calculation, the QSCIM and a closed form of Green's function were introduced. With the inverse FFT, the model can calculate the distribution of lightning currents in any configuration of the grounding system. This can be used for studying the performance of transient lightning responses to grounding systems. Last, the model has been validated through some numerically simulated and experimental results from open published paper, This work was funded by the Science and Technology Projects of State Grid Corporation of China under Contract Number: GY172011000JD and the National Natural Science Foundation of China under Grant 51177153.
