Investigating the Effect of Metal Particles and Air Gap Defects on the Surface Charge Distribution of Epoxy Resin Using a Modified Capacitive Probe

Metal particle and air gap defects on the surface of insulators can induce localized electric field distortions and exacerbate charge accumulation, subsequently triggering surface flashover. In this study, we first enhanced traditional capacitive probes to improve stability and effectively suppress charge leakage. The modified probes achieved a charge leakage time constant exceeding 5600 s, with a leakage amount of only 4.9% over a single data acquisition period (210 s). Based on this improvement, we developed a system for measuring surface charges on insulators, investigating the characteristics and influencing factors of surface charge accumulation under metal micro-particles and air gap defects. The results demonstrate that metal micro-particles adhering to the insulator surface accumulate charges of opposite polarity at different locations under applied voltage. These charges tend to diffuse over time and with increased voltage. The presence of air gap defect accelerates charge accumulation in its vicinity, with charge polarity and location being closely related. When the air gap is near the high-voltage electrode, the insulator surface predominantly accumulates positive charges. Conversely, when the air gap is near the ground electrode, negative charges accumulate at both the high-voltage and ground electrodes, with positive charge accumulating in the central region. Both the amplitude and duration of the applied voltage affect the charge accumulation on the air gap surface. Interestingly, with prolonged voltage application, the surface positive charge density in the air gap decreases. Different defect models exhibit charge inversion phenomena occur as the voltage amplitude increases.