Study on Surface Flashover Mechanism of Epoxy Impregnated Paper Insulation in Dry-Type Bushings under Thermal Gradient

This study investigates the surface flashover characteristics of epoxy resin-impregnated paper used in dry-type bushings under combined electrothermal stress. The effects of electrode spacing and temperature on insulation performance were examined experimentally. AC surface flashover tests were performed on samples with gaps of 2 mm, 3 mm, and 4 mm at three controlled temperatures: 25 °C, 90 °C, and 120 °C. The breakdown voltage data were analyzed using the Weibull distribution. Results indicate that at a fixed temperature, flashover voltage increases nonlinearly with gap distance, which is attributed to persistent electric field nonuniformity introduced by the finger-type electrode geometry. At larger spacings (3 mm and 4 mm), elevated temperature significantly reduces the flashover strength due to enhanced surface conductivity and increased electron kinetic energy, both of which facilitate discharge initiation and propagation. In contrast, at the 2 mm gap, the electric field dominates the flashover process, and temperature exerts negligible influence within the tested range. This work elucidates the spacing- and temperature-dependent flashover mechanisms in epoxy-impregnated paper under electrothermal conditions, providing insights for condition assessment and reliability improvement of dry-type bushing insulation.