Finite Antenna and Single Cell FDTD methods applied to near LEMP calculations

Abstract

Two methods for modeling the electromagnetic fields near a lightning channel are considered. These methods can be used in evaluating the effect of a lightning electromagnetic pulse (LEMP) on a distribution line. The first method for evaluating LEMP fields in the time domain uses a Heidler function approximation for the channel base current in the classic Finite Antenna method. This approximation has an analytical integral solution which simplifies the field calculations. The second method is a combination of standard FDTD theory and the mathematics of the Finite Antenna method. The proposed Single Cell or Hybrid FDTD method is derived for spherical co-ordinates and tested against the Finite Antenna method. The results show that under simple modeling criteria both methods are valid for LEMP calculations near a lightning channel. The Single Cell FDTD method only evaluates a single FDTD cell, rather than an entire plane of cells described by the standard FDTD method. This greatly reduces the computational intensity, and makes the Single Cell FDTD method a valuable tool.