C4F7N混合气体电弧等离子体热力学性质研究

Research on Thermodynamic Properties of Arc Plasma of C4F7N Gas Mixture

摘要:

C4F7N/CO2混合气体作为目前极具潜力的SF6替代气体之一，在开断大容量短路电流中存在固体碳析出的问题。研究表明，向混合气体中加入O2能够抑制固体碳的生成，也能有效增大灭弧室压力并提高气体的熄弧性能。为深入探究O2对混合气体电弧能量耗散影响，在假设局部热力学平衡条件下，基于吉布斯自由能计算了不同O2含量的C4F7N/CO2混合气体电弧等离子体粒子组分，并用标准的统计热物理的计算方法得到了不同混合比例气体的热力学性质，对比分析了不同O2含量及压强对混合气体电弧等离子体热力学性质的影响。结果表明：O2在低温区抑制了CO的生成，导致不同O2含量的混合气体在热力学性质上有一定的差异；C4F7N混合气体的轴向热对流能力大于SF6，且在低温(大于8 kK)区与O2浓度成正相关;温度小于5 kK时，C4F7N混合气体的径向热对流能力弱于SF6，且在低温(大于8 kK)区与O2浓度成正相关。

Abstract:

C4F7N/CO2gas mixture is one of SF6 alternative gases, but it still exists solid carbon precipitation problems in interrupting large capacity short circuit current. The researches show that the addition of O2 can effectively inhibit the generation of solid carbon, and at the same time can effectively increase the pressure of arc-extinguishing chamber to improve the arc extinguishing performance of gas. In order to further study the effect of O2 on energy dissipation of arc of gas mixture, the particle size compostion of arc plasma of C4F7N/CO2gas mixture with different content of O2 is calculated based on Gibbs free energy minimization principle under the assumption of local thermodynamic equilibrium conditions, the thermodynamic properties of the gases with different mixing ratios are obtained by standard statistical thermophysics calculation methods, and the effects of different contents and pressures of O2 on thermodynamic properties of arc plasma of gas mixture are analyzed comparatively. The results show that O2 inhibits the generation of CO in low-temperature region, which leads to some differences in thermodynamic properties of gas mixture with different contents of O2. The axial thermal convection capacity of C4F7N gas mixture is larger than that of SF6, and is positively correlated with the concentration of O2 in lowtemperature (＞8 kK) region. The radial thermal convection capacity of C4F7N gas mixture is weaker than that of SF6at temperatures less than 5 kK and is positively correlated with the concentration of O2 in lowtemperature (greater than 8 kK) region.