SF_6/N_2混合气体电击穿特性仿真及实验

通过求解两项近似Boltzmann方程,得到SF_6/N_2的放电参数,并将该参数引入流体模型。结合有限元法和通量校正传输法对SF_6/N_2的流注放电过程进行循环迭代求解,计算其击穿电压。以均匀电场中压强0.1~0.6MPa、间隙5mm为例进行数值模拟,通过气体放电实验对计算结果进行验证。根据计算及实验结果得到不同混合比、压强下SF_6/N_2的协同效应系数,分析采用上述计算方法研究混合气体协同效应的准确性。为更全面地反映混合气体应用条件,进一步开展压强低于0.1MPa的SF_6/N_2击穿特性实验研究。研究表明:随着电子崩不断向前发展,放电间隙的空间电子数密度快速增长,SF_6放电过程中的空间电子数密度增长速度低于SF_6/N_2。0.1MPa下20%SF_6/80%N_2放电5ns时的电子数密度峰值达到4.6×1014m~(-3),而SF_6中该值仅为3.7×1012m~(-3)。当气压为0.1~0.6MPa时,SF_6/N_2击穿电压计算值与实测值的最大误差为9.23%,协同效应系数计算值随压强、混合比的变化趋势与实验结果相符,误差均值为5%。0.02~0.08MPa下SF_6/N2击穿电压、协同效应系数随压强、混合比的变化趋势与0.1~0.6MPa下的基本相同。

Simulations and Experiments of Dielectric Breakdown Characteristics in SF6/N2 Gas Mixtures

SF6/N2 discharge parameters used in fluid model were obtained by two-term Boltzmann equation analysis. Combined finite element method with flux corrected transport method, breakdown voltages of SF6/N2 were calculated by loop iterative solutions of streamer discharge processes. The gas discharge experiments in uniform electric field were simulated to prove the computation accuracy, where the gas gap is 5mm and gas pressure is between 0.1~0.6MPa. Based on the computed and experimental data, synergistic effect coefficients of SF6/N2 in different pressures and mixing ratios were obtained, which were used to analyze the accuracy of above computing method in synergistic effect study. Breakdown properties below 0.1MPa were further studied for a more comprehensive reflection of mixed SF6/N2 application conditions. Results show that electron number density in discharge gap increases rapidly with electron avalanche moving forward, and growth rate of SF6 is slower than that of SF6/N2. Peak electron number density of 20%SF6/80%N2 in 0.1MPa reaches 4.6×1014m?3 at 5ns, while it is only 3.7×1012m?3 in SF6. When the gas pressure is in 0.1~0.6MPa, the maximum error of the calculated and measured breakdown voltages of SF6/N2 is 9.23%. The trends of calculated synergistic effect coefficients with pressures and mixing ratios are consistent with theexperimental results, and the average error is 5%. The trends of breakdown voltages and synergistic effect coefficients with pressures and mixing ratios in 0.02~0.08MPa are similar to those in 0.1~0.6MPa.