The Role of Defect Aspect Ratio in the Partial Discharge Phenomenology under DC Voltage and Temperature Gradient

This research is focused on the influence of defect aspect ratio on partial discharge (PD) activity within solid dielectrics subjected to direct current (DC) stress and thermal gradients. Employing finite element method (FEM) simulations by Comsol Multiphysics software, the PD inception conditions under both transient and steady-state voltage conditions was evaluated. The focus centered on investigating the effect of charge injection at the dielectric-cavity interface and the subsequent migration of these charges through the gas medium within the defect. This migration was studied through a laminar flow model considering ionized air movement within the defect, driven by the electric field. Treating the charge motion within the cavity akin to an electric current, an equivalent gas conductivity characteristic of the cavity was derived. The findings show that the shape of the defect profoundly influences the variability of equivalent gas conductivity within the defect during both voltage ramp-up and stable phases.