Transient grounding behavior considering frequency-dependent soil parameters: Field versus transmission line theories

This paper presents a study on the transient behavior of grounding conductors. Two important physical quantities are analyzed: the harmonic impedance and the ground potential rise (GPR). For the determination of such quantities, two theories widely used in the literature are used: one based on field computation and the other based on transmission line theory. The first requires high computational time, while for the second this time is greatly reduced. Two geometric configurations (one horizontal electrode and four counterpoises) are considered. Soil parameters are modelled as constant and frequency-dependent. The results show that transmission line theory should be used with care, since for soils with high resistivities and frequency-dependent parameters the results may differ from those generated by the field theory.

I. Introduction

Lightning is considered one of the main responsible of unplanned shutdowns of electrical systems [1], [2]. About 5% to 10% of lightning failures result in permanent damage to power system equipment [1], [2]. Various equipment and components are designed to reduce the severe damage caused by lightning. Among them are the following: ground wires, arresters, grounding and surge protectors.