Surface Discharge Mechanism with a Change of Gas Pressure in N2/O2 Mixed Gas for Insulation Design of SF6-Free High-Voltage Power Equipment

This paper presents the surface discharge characteristics with changes in gas pressure under a sphere-plane electrode with a Teflon dielectric in N
₂
/O
₂
mixed gas (80:20) and focuses on interpreting the surface discharge mechanism at both high pressure (0.3-0.6 MPa) and low pressure (0.1-0.2 MPa). The partial discharge and surface flashover voltages are measured under AC high voltage between 0.1 and 0.6 MPa of the N
₂
/O
₂
mixture gas. It is clearly observed that two surface discharge paths are revealed with the pressure change in the N
₂
/O
₂
mixed gas. In the high pressure case, the surface discharge path develops from the cathode-triple junction to a Teflon surface, and in the low pressure case, the path passes through the bulk gas at the sphere-electrode surface away from the triple junction and then advances to the Teflon surface. Surface discharge models for these two patterns are proposed based on surface discharge mechanisms including electron avalanche, photoionization, photoemission, electron attachment, electron detachment, and dielectric charging.