Effects of Bubble Distribution on the Electric Discharge in the DC Insulator

Silicone rubber insulators have been widely used in high-voltage direct current (HVDC) systems. However, insulation failures have frequently occurred in insulators where optical fibers are embedded internally and filled with a sealing paste, in which bubbles are often detected. In this paper, the effects of bubbles within the filling paste on electric field distribution and discharge characteristics have been experimentally investigated. The results show that the presence of bubbles significantly enhances the electric field strength, although the field intensity decreases as the bubble size increases. Additionally, under the same field orientation, the electric field strength within individual bubbles slightly varies as the number of bubbles increases. Furthermore, the discharge threshold has been found to decrease sharply with the formation of bubbles. Reductions in bubble size and number, under the same field direction, also contribute to a lower discharge threshold. These findings suggest that smaller bubbles exert a more pronounced impact on the electrical performance of the filling paste.