The Influence of the Horizontally Stratified Conducting Ground on the Lightning-Induced Voltages

In this paper, we analyze the influence of the horizontally stratified conducting ground on the lightning-induced over-voltage on the overhead line by using the 2-D Finite-Difference Time-Domain method and the Agrawal coupling model. In order to clearly understand the propagation characteristics of the induced voltage waves along the line, we split the induced overvoltage into the scattered induced wave (U-s) and the incident induced wave (U-i), and the latter is further decomposed into two subcomponents. When the conductivity of the first layer (sigma(1) = 0.001 S/m, epsilon(r) (1) = 10) is less than that of the second layer (sigma 2 = 0.1 S/m, epsilon(r) (2) = 10), the lightning-induced overvoltage increases obviously with the increase of the depth of the first layer due to the increase of the total effective impedance, and we should consider the influence of the stratified ground if the depth of the first layer is more than 2m. However, the lightning-induced overvoltage decreases sharply with the increase of first layer depth with much higher conductivity (sigma(1) = 0.1 S/m, epsilon(r 1) = 10; sigma(2) = 0.001 S/m, epsilon(r2) = 10). Also, we find that when the lower different conductivities between the two layers (i.e., 0.01 and 0.001 S/m) are assumed, the characteristics of the induced voltages are similar to that from the higher difference.