Influence of conductor surface roughness on insulation performance of C4F7N/CO2 mixed gas

C
4
F
7
N/CO
2
is one of the most promising alternatives to SF
6
in high-voltage electrical equipment such as gas insulated switchgear (GIS) because of its excellent electrical performance and low environmental impact. However, the insulation characteristics of C
4
F
7
N/CO
2
is still unclear regarding the effect of conductor surface roughness. To obtain a figure of merit of C
4
F
7
N/CO
2
gas mixtures and to evaluate its sensitivity to local inhomogeneous electric field, the breakdown voltage of electronegative gas considering surface roughness is developed using the streamer discharge theory. A gas discharge experimental platform for C
4
F
7
N/CO
2
mixed gas is set up and the discharge test is carried out under gas pressures from 0.15∼0.5 MPa having a maximum protrusion height of 15 μm. The results demonstrate that when the volume fraction of C
4
F
7
N is 10%, the figure of merit of C
4
F
7
N/CO
2
mixture is slightly higher than that of SF
6
gas. Therefore, at the same pressure, the standard of conductor surface roughness for C
4
F
7
N/CO
2
equipment can refer to the original SF
6
gas equipment.