Electromagnetic Computation Methods for Lightning Surge Protection Studies

1Introduction

1.1 Historical Overview of Lightning Electromagnetic-Field and Surge Computations

Lightning return-stroke electromagnetic fields have been calculated using analytical expressions, derived for a vertical lightning channel (e.g., Uman et al. 1975). Effects of finite ground conductivity on lightning electromagnetic fields have also been studied using analytical expressions (e.g., Rachidi et al. 1996). These analytical expressions are still being used. Lightning-induced voltages on an overhead power distribution line or telecommunication line have been calculated using an engineering model of the lightning return stroke (e.g., Uman et al. 1975) and a field-to-wire coupling model (e.g., Rachidi 1993). Horizontal electric fields above a finitely conducting ground, which are needed for calculating lightning-induced voltages, have been evaluated using approximate expressions such as the Cooray–Rubinstein formula (Rubinstein 1996). Note that the Cooray–Rubinstein formula is given in the frequency domain, although its time-domain counterparts also exist. Lightning surges due to a direct lightning strike to an overhead power transmission or distribution line have been analyzed using distributed-circuit simulation methods such as the electromagnetic transients program (EMTP) (Dommel 1969). EMTP and other similar programs are still widely used in lightning surge simulations.

Around 1990, electromagnetic computation methods were first applied to lightning electromagnetic and ...