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

C<inf>4</inf>F<inf>7</inf>N/CO<inf>2</inf> is one of the most promising alternatives to SF<inf>6</inf> 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<inf>4</inf>F<inf>7</inf>N/CO<inf>2</inf> is still unclear regarding the effect of conductor surface roughness. To obtain a figure of merit of C<inf>4</inf>F<inf>7</inf>N/CO<inf>2</inf> 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<inf>4</inf>F<inf>7</inf>N/CO<inf>2</inf> 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<inf>4</inf>F<inf>7</inf>N is 10%, the figure of merit of C<inf>4</inf>F<inf>7</inf>N/CO<inf>2</inf> mixture is slightly higher than that of SF<inf>6</inf> gas. Therefore, at the same pressure, the standard of conductor surface roughness for C<inf>4</inf>F<inf>7</inf>N/CO<inf>2</inf> equipment can refer to the original SF<inf>6</inf> gas equipment.

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