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 SF
₆
has widely been investigated to identify an appropriate insulation medium and to develop SF
₆
-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 SF
₆
and imitation air (I-Air), i.e. N
₂
/O
₂
mixed gas, under a nonuniform field, and focuses on their characteristics in relation to the oxygen concentration in N
₂
/O
₂
mixed gas. According to experimental results, the insulation characteristics of I-Air, especially the surface flashover voltage, decreases with increasing O
₂
content, when over 20% in the N
₂
/O
₂
mixed gas. These characteristics are explained by the proposed surface discharge mechanisms including photoionization, electron detachment, and photoemission in accordance with changes in the O
₂
concentration in the N
₂
/O
₂
mixed gas. In addition, the surface insulation performance of I-Air corresponding to 0.1 MPa SF
₆
is examined.