FDTD analysis of the current distribution within the grounding system for a wind turbine generation tower struck by lightning

Abstract

Transient current distribution within the grounding system for a wind-turbine-generation tower of height 61 m struck by lightning has been calculated using the finite-difference time-domain (FDTD) method. The grounding grid for the lightning-struck tower considered in this paper is connected electrically via an insulated wire to one neighboring-tower grounding grid located 50 m away from it. High-frequency components of a lightning current tend to flow in ground through the grounding grid of the lightning-struck tower, and they become larger with increasing the ground conductivity. Relatively-lower-frequency components of the lightning current flow in ground through each of the two grounding grids roughly in inverse proportion to the grounding resistance of each grid. For example, when two identical grounding grids for the lightning-struck tower and the neighboring tower are buried in the same ground, about 50% of the lightning current flows in the grounding grid for the neighboring tower via the insulated wire connecting these two grounding grids. When the grounding resistance of the neighboring tower is about 1/4 of that for the lightning-struck tower, about 4/5 of the lightning current flows in the neighboring-tower grounding grid. This agrees well with the trend shown by Nagaoka et al. from their measurement in the grounding system for an actual wind-turbine-generation tower struck by natural lightning. © 2008 The Institute of Electrical Engineers of Japan.