| Summary: | This study presents the surface discharge characteristics of insulating gases, including sulfur hexafluoride (SF<sub>6</sub>), dry air, and N<sub>2</sub>, under a non-uniform field. Surface discharge experiments were conducted, with the gas pressure ranging from 0.1 to 0.6 MPa, on samples of epoxy dielectrics under an AC voltage. The experimental results showed that the surface insulation performance significantly improved in insulating gases possessing electronegative gases, such as SF<sub>6</sub> and dry air. Surface flashover voltages of SF<sub>6</sub> were saturated with an increasing pressure, compared to dry air and N<sub>2</sub>. The surface discharge mechanism is proposed to explain the improvement and saturation of dielectric characteristics of the electronegative gas in complex dielectric insulations, as well as its influence on the surface flashover voltage. As an application, an insulation design method is discussed with regards to replacing SF<sub>6</sub> gas in high-voltage power equipment based on the knowledge of the physics behind gas discharge.
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