Study on X-Ray Imaging of Soil Discharge and Calculation Method of the Ionization Parameters

Soil discharge occurs when it is subjected to high impulse current, and it is closely associated with the impulse performance of grounding systems. In this paper, a new method is put forward to visualize the inner impulse discharge region of simulate soil (fine sand) directly, using X-ray imaging technology. According to the three views of the discharge region, the boundary surface of the discharge region can be obtained based on image filtering and edge extraction by 3-D reconstruction. On this basis, the ionization parameters (i.e., the residual resistivity of soil discharge region ρ_res and the critical breakdown electric-field strength E_c) are calculated by a finite-element method. The results show that discharge region volume enlarges with water content increasing, and ρ_res is approximately equal to 0.001%-0.003% of the original soil resistivity ρ₀. E_c increases from 100 to 150 kV/m, as soil water content decreases from 5% to 2%.

I. Introduction

Characteristics of soil discharge region are vital for studies of the soil discharge mechanism and parameter calculation, while the residual resistivity and the critical breakdown electric-field strength of the discharge region are key parameters for studying the soil discharge process under high impulse current. The degree of the resistance reduction depends on the magnitude of [1] and . Hence, and are the critical parameters in any transient numerical models of grounding devices considering soil discharge, and the choice of these two parameters has an important influence on the accuracy of impulse characteristic calculation results [2] –[8].