Phase Dependence of Surface Charge Accumulated on Epoxy Insulator in C4F7N/CO2 under AC voltage

The application of binary gas mixtures consisting of heptafluorobutyronitrile (C
4
F
7
N) and carbon dioxide (CO
2
) in AC GIS is currently attracting much attention. The charge accumulation on epoxy insulators is a crucial problem restricting the safety of gas-insulated equipment, and whether the charging behavior is phase-dependent hasn't been fully understood yet. In this study, the charge distribution characteristics on a down-scaled disc epoxy insulator surface in C
4
F
7
N/CO
2
mixtures under AC voltage were investigated, and the influence of the truncated phase and duration of AC voltage on surface charge accumulation were analyzed. The results showed that the area of the negative charge speckle first increased and then decreased over time. However, the phase angle was found to have a negligible impact on the surface charge distribution characteristics of the insulator.