I. Introduction
Lightning impulse performance of grounding devices is important for lightning protection of transmission and distribution lines [1]–[3]. Lightning current has the characteristics of high amplitude, steep front and short duration. The inductive effect of grounding conductors and soil ionization often have a significant impact on impulse grounding research [4]–[7]. The potential rise of the grounding down-conductor and the uneven distribution of the ground potential during the lightning will produce a high transient touch/step voltage, which threatens the safety of humans and animals around.