FDTD calculation of lightning-induced voltages on an overhead two-wire distribution line

Abstract

We have calculated lightning-induced voltages on a 680-m long overhead two-wire line using the finite-difference time-domain (FDTD) method for solving Maxwell's equations. The FDTD method employed here uses a three-dimensional nonuniform grid, which is fine (cell side length is 0.875 m) in the vicinity of overhead wires and coarse (maximum cell side length is 7 m) in the rest of the space. The overhead wires having radii of several millimetres are simulated by placing a wire having an equivalent radius of about 0.2 m (≈ 0.23 × 0.875 m) in the center of an artificial rectangular prism having a cross-sectional area of (2 × 0.875 m) × (2 × 0.875 m) and the modified electrical constants: low permittivity and high permeability. The induced-voltage waveform, calculated for the condition that the return-stroke wavefront speed is 130 m/μs, the ground conductivity is 3.5 mS/m, and the grounding resistance ranges from 30 to 75 Ω, agrees well with the corresponding waveform measured by Barker et al. in a rocket-triggered lightning experiment.