SF_6替代气体与空气混合的绝缘性能研究

Study on the Insulation Properties of the Mixture of SF_6 Substitute Gas and Air

CF_3I和c-C_4F_8作为目前研究最多的SF_6替代气体,需要与缓冲气体混合以降低液化温度。为了评估使用空气作为SF_6替代气体缓冲气体的可能性,通过求解两项近似的Boltzmann方程,计算了CF_3I/空气、c-C_4F_8/空气混合气体的电子崩参数。首先,分别计算了CF_3I/空气、c-C_4F_8/空气混合气体的约化电离系数、约化附着系数、约化有效电离系数、约化临界场强,以及表征对不均匀电场敏感程度的c值(约化有效电离系数关于约化电场的关系曲线中零点附近的斜率值)。然后,将计算值与约化临界场强和c值分别与CF_3I/CO_2、CF_3I/N_2和c-C_4F_8/CO_2、c-C_4F_8/N_2混合气体进行对比,从绝缘强度、对不均匀电场的敏感程度两个方面评估空气作为缓冲气体的优劣。结果表明,70%/30%的CF_3I/空气、c-C_4F_8/空气混合气体绝缘性能与SF_6相当;在空气、CO_2、N_23种缓冲气体中,与CF_3I混合,空气是最佳选项;与c-C_4F_8混合,空气和N_2难分高下,二者均优于CO_2。

As the most studied SF6 substitute gas,CF3I and c-C4F8 need to be mixed with buffer gases to reduce liq-uefaction temperature. For the purpose to assess the possibility for air to be buffer gas in SF6 substitute gas,electronswarm parameters of CF3I/air and c-C4F8/air are calculated through two-term approximated Boltzmann equation.First,the reduced ionization coefficient,reduced attachment coefficient,reduced effective ionization coefficient,limiting reduced electric strength and c value（the slope around zero point of reduced effective ionization coefficientas a function of reduced electric field strength）which reflects the sensitivity to non-uniform electric field of CF3I/airand c-C4F8/air are calculated. Then,the limiting reduced electric strengths and c values are compared to the mixturewith the same electronegative gases but different buffer gases（CO2 and N2）. Assessment is made from two aspects：in-sulation strength and sensitivity to non-uniform electric field. The consequence is that CF3I/air or c-C4F8/air with themix ratio 30%/70% possesses similar insulation property to SF6. According to the result,among air,CO2 and N2,air isthe best choice to mix with CF3I,and air and N2 possess similar properties to mix with c-C4F8,both better than CO2.