Characterization of Ionization Phenomena in Soils Under Fast Impulses

TLDR

Protective devices such as spark gaps and surge arresters rely on earthing systems with low impedance, yet while power‑frequency behavior is well studied, the transient response of these systems remains poorly understood. This study aims to clarify the transient ionization behavior of earthing systems under fast impulses. Laboratory experiments using soil samples and a novel pre‑ and post‑ionization resistance model, combined with a new measurement technique and equivalent circuit, were employed to quantify ionization thresholds and characterize soil ionization phenomena.

Abstract

Protective devices such as spark gaps and surge arresters are used to divert surges to earth. It is, therefore, necessary that earthing systems are designed with a low-magnitude earth impedance value so that the overvoltage protection devices can divert high fault currents effectively to earth for all types of fault. Power frequency characterization of earthing systems is extensively researched and fairly well understood. However, the behavior of such systems under transient conditions is still not fully clarified. This paper addresses some of these shortfalls. Laboratory experiments were set up to study the characteristics of the ionization phenomenon in various soil conditions. The soil ionization characteristics were investigated using a proposed new concept of pre- and post-ionization resistances. A measurement technique was developed to establish more accurate estimates of ionization electric field threshold, and an equivalent circuit representation is proposed.