FDTD simulation of lightning current along vertical grounding rod appended to a horizontal grounding grid

Vertical grounding rods are usually needed to be appended to a horizontal grounding grid to decrease the grounding resistance. When a lightning current flows through a grounding grid appended by some vertical rods, it´s valuable to reasonably arrange these vertical rods to reach an optimum design. In this paper, lightning discharge current distribution among the vertical grounding rods appended to a horizontal grounding grid are numerically calculated by FDTD (finite-difference time-domain) method. The discharge effectiveness of the vertical grounding rod appended at different position is compared. The shielding effect of a horizontal grounding grid to obstruct the lightning current to flow downward is shown. The conclusions obtained will give a reasonable guidance for the formation and reformation of grounding grid.