Study on Flashover and Creepage Discharge Characteristics of Oil-Paper Insulation with Mixed Synthetic Ester Insulating Liquid

Retrofilling mineral oil transformers with synthetic ester insulating liquid enhances their environmental friendliness and fire safety. However, the influence of residual mineral oil on the electrical insulation performance of the oil-paper insulating structure after retrofilling remains unclear. This paper investigated this influence by establishing oil-paper insulating structure models with varying concentrations (0%, 3%, and 10%) of residual mineral oil in a synthetic ester liquid. Partial discharge inception voltage and flashover voltage were measured to assess the influence of residual mineral oil, and the mechanisms were analyzed.