Visualization of the inner discharge of soil under impulse current and calculation of the ionization parameters

Soil discharge occurs when it is subjected to a high impulse current, and it is closely associated with the impulse performance of grounding systems. To date, there have been few studies on the observation of the inner discharge process of soil. In this letter, a typical soil, fine sand containing water, was selected as a sample. A new method is put forward to visualize the inner impulse discharge area directly using X-ray image technology. On this basis, the ionization parameters (i.e., the residual resistivity of the discharge area ρ_res and the critical breakdown electric-field intensity E_c) are calculated by a finite-element method (FEM) according to the experimental parameters and 3-D reconstructive diagram of the discharge area. The results show that ρ_res is approximately equal to 0.001%-0.003% of the samples' original resistivity ρ0, and E_c ranges from 100 kV/m to 150 kV/m.