3-D FDTD Simulation of the Lightning-Induced Waves on Overhead Lines Considering the Vertically Stratified Ground

In this paper, we have employed the 3-D finite-difference time-domain technique to analyze the influence of the vertically stratified conducting ground (mixed path) on the lightning-induced voltages of the overhead line at 60 and 200 m from the lightning strike point by using decomposing method. In order to analyze the effect range caused by mixed path, we assumed that the mixed path has much different conductivities with 100:1 ratio. When the conductivity near the strike point (0.1 S/m) is larger than that near the overhead line section (0.001 S/m), the induced voltage clearly increases with the increase of the closest distance from the center of the line to the interface between the two media (dl). However, for strike point with a less conducting earth (0.001 S/m) than the overhead line section (0.1 S/m), when dl is less than 30 m, the influence of the stratification should be considered; when dl is larger than 30 m, it can just be regarded as a homogeneous soil with the conductivity of 0.1 S/m equal to that near the overhead line. For the smaller ratio of conductivities of the mixed path, its effect on the induced voltages decreases.