C₅F₁₀O as a new type of environmental protection gas insulation medium has attracted extensive attention. Its switching impulse breakdown characteristic is an important basis for insulation design in the future. In this paper, the saturated vapor pressure characteristics of C₅F₁₀O/CO₂ mixed gas at different mixing ratios are calculated firstly by combining the Antoine vapor pressure equation and the basic law of vapor liquid equilibrium. Secondly, the needle-plate electrode structure is used to simulate the extremely non-uniform electric field that may occur in the gas insulation equipment. The influence of air pressure, mixing ratio, and voltage polarity on the insulation characteristics of the mixed gas is analyzed. Finally, the synergistic effect of the mixed gas is analyzed.
According to the experimental results, the polarity effect of C₅F₁₀O/CO₂ mixture under the switching impulse voltage is obvious in the extremely non-uniform electric field. When the applied voltage is negative, the switching impulse breakdown voltage of the mixed gas increases linearly with the increase of the air pressure. The breakdown voltage under positive polarity appears "hump" with the change of air pressure because the positive space charge distorts the space electric field. Moreover, the position of the “hump” will change under the modulation effect of space charge on the electric field. The insulation strength of mixed gas increases obviously with the increase of C₅F₁₀O content at a low mixing ratio and shows a saturation trend at the higher mixing ratio. The synergistic effect between the components of the gas mixture is also affected by air pressure and C₅F₁₀O content. Due to the influence of positive space charge, the synergistic effect under the positive polarity switching impulse voltage shows greater fluctuations and is slightly weaker than the synergistic effect under negative polarity. The results show that considering the liquefaction temperature and other factors, the switching impulse breakdown characteristic of C₅F₁₀O/CO₂ mixed gas under an extremely non-uniform electric field can be improved by increasing the air pressure or C₅F₁₀O content. Mixing C₅F₁₀O with CO₂ is expected to achieve effective replacement of SF₆ under proper mixing ratio and air pressure conditions.
 

SF6 alternative gas,C5F10O/CO2 mixed gas,Switching impulse voltage