Partial discharge and surface flashover characteristics with O2 content in N2/O2 mixed gas under a non-uniform field

The effect of electronegative gas on the insulation characteristics of mixed gases as alternatives to SF6has widely been investigated to identify an appropriate insulation medium and to develop SF6-free high-voltage power equipment (HVPE). However, few studies have provided physical information on the surface discharge mechanism and physics of gas discharge to clarify this effect. This paper presents the surface discharge characteristics of SF6and imitation air (I-Air), i.e. N2/O2mixed gas, under a nonuniform field, and focuses on their characteristics in relation to the oxygen concentration in N2/O2mixed gas. According to experimental results, the insulation characteristics of I-Air, especially the surface flashover voltage, decreases with increasing O2content, when over 20% in the N2/O2mixed gas. These characteristics are explained by the proposed surface discharge mechanisms including photoionization, electron detachment, and photoemission in accordance with changes in the O2concentration in the N2/O2mixed gas. In addition, the surface insulation performance of I-Air corresponding to 0.1 MPa SF6is examined.