Partial Discharge and Surface Flashover Characteristics with O₂ Content in N₂/O₂ Mixed Gas under a Non-Uniform Field

Abstract

The effect of electronegative gas on the insulation characteristics of mixed gases as alternatives to SF₆ has 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 SF₆ and imitation air (I-Air), i.e. N₂/O₂ mixed gas, under a non-uniform field, and focuses on their characteristics in relation to the oxygen concentration in N₂/O₂ mixed gas. According to experimental results, the insulation characteristics of I-Air, especially the surface flashover voltage, decreases with increasing O₂ content, when over 20% in the N₂/O₂ mixed gas. These characteristics are explained by the proposed surface discharge mechanisms including photoionization, electron detachment, and photoemission in accordance with changes in the O₂ concentration in the N₂/O₂ mixed gas. In addition, the surface insulation performance of I-Air corresponding to 0.1 MPa SF₆ is examined.