为了在弧后电击穿评估时得到热态SF6及其替代或混合气体的准确临界击穿场强,通过求解两项近似Boltzmann方程,得到了SF6气体在0.4 MPa和0.8 MPa下、300～3 000 K范围内的折合临界击穿场强(E/N)cr.结果表明:SF6气体的(E/N)cr随温度升高而跌落,其减小速度与SF6的分解速度有关；在1 500～2 500 K范围内,SF6气体在0.8 MPa下的(E/N)cr明显高于0.4 MPa下的(E/N)cr,而在其他温度下,二者的(E/N)cr非常接近.同时,计算了SF6-CF4、SF6-CO2、SF6-O2、SF6-CH4、SF6-C2H6和SF6-CHF3在300 K下的(E/N)cr,发现当x(SF6)超过10％以后,6种混合气体的(E/N)cr随x(SF6)近似线性变化,且6种纯气体中CF4和O2的(E/N)cr最大,而与SF6混合后,SF6-CF4和SF6-O2的(E/N)cr相当,仍高于其他混合气体.此外,还引入了SF6与混合气体击穿场强的比值r,在一定范围内只要混合比例与压强适当,混合气体可得到与SF6相当的击穿场强.%The reduced critical electric breakdown field (E/N)cr of SF6 and its substitute or mixtures gets very crucial for electrical breakdown evalution. The (E/N)cr of SF6 is investigated under 0. 4 MPa and 0. 8 MPa respectively, and over the temperature range of 300 to 3 000 K, by solving the two-term Boltzmann equation. The results show that the (E/N)cr of SF6 decreases with increasing temperature, and the decreasing rate depends on the SF6 decomposition rate; at temperature within 1 500 and 2 500 K, the (E/N)cr of SF6 under 0. 8 MPa is evidently higher than that under 0. 4 MPa, however almost equal between 0. 8 MPa and 0. 4 MPa at other temperature. The calculations for (E/N)cr of SF6-CF4、SF6-CO2、SF6-O2、SF6-CH4、SF6-C2H6 and SF6-CHF3 under 300 K indicate, when χ(SF6) in mixture is over 10%, the (E/N)cr of all these mixtures changes approximately linearly with χ(SF6); among these gases, the (E/N)cr of CF4 and O2 approaches to the highest; the (E/N)cr of SF6-CF4 and SF6-O2 closely appears, and both higher than that of the others. And r, the ratio of the critical breakdown field of SF6 to that of a gas mixture, is introduced to conclude that under proper pressure and mixing ratio, the critical breakdown field of a gas mixture becomes equivalent to SF6.
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