Negative DC Breakdown Characteristics of C3F7CN and CO2 Mixture with Different Electrode Materials

Sulphur hexafluoride (SF6) is an insulating medium widely used in the power industry due to its high dielectric strength and arc quenching capability. There is a growing interest in identifying an environmentally friendly alternative to SF6 and a mixture of C3F7CN and CO2 is one potential candidate. This project investigates the effect of different electrode materials on the breakdown performance of the aforementioned gas mixture over 300 breakdowns under negative DC. Three sets of rod-plane electrodes manufactured in stainless steel, aluminum and brass are tested for a fixed gap distance of 3 mm and pressure of 4.8 bar absolute. The results show that stainless steel has the highest breakdown voltage and the lowest change in surface roughness compared to aluminum and brass. The post-testing gas analyses have shown negligible reduction in the C3F7CN content after 300 breakdowns.