Transmission Line Dynamic Circuit Model for Effective Length of Ground Electrode Under Lightning Transients

The effective length of the ground electrode is one of the primary research interests of lightning grounding system design. In this article, using a practical numerical analysis, a new expression for estimating the effective length of the simple ground electrode is proposed. A new dynamic circuit model based on the transmission line is developed to derive the expression. The model considers the soil ionization, frequency-dependent soil parameters, mutual reactance, and skin effect. Several rigorous impulse test simulations are performed on different electrode lengths, soil properties, and lightning currents to estimate the effective length of ground electrode numerically. A new expression is arrived at using the curve-fitting and optimization technique from the relationships of the effective length with soil resistivity, impulse rise time, and current. The proposed dynamic model and the expression to obtain the effective length are validated by published results.

I. Introduction

The ground electrode length (EL) is critical in the dissipation of lightning current in the soil under transient conditions. The electrode shorter in length has more impedance, which decreases the effective dissipation of current, leading to an increased ground potential rise (GPR). The electrode excess in length does not contribute to any useful dissipation of current and reduction in GPR. The electrode with optimum length will provide the satisfactory performance of the grounding system under transient conditions. This length is determined by the electrode dimension, soil properties, and impulse characteristics. The effect of the electrode's useful length under transient conditions is studied in many articles [1]–[5]. This useful length of the ground electrode is termed the effective length of ground electrode (ELGE) and is defined differently by the researchers [1]–[5].