Simulation of the Influences of the Pressure Ratio and Cu Vapour on SF_6 Arc Characteristics

The inlet and outlet pressure of the SF6 high voltage circuit-breaker nozzle are of importance in determining the thermal interruption capability of a breaker. Besides, electrode evaporation is inevitable during the arcing process, which may affect the SF6 arc behaviour significantly. In this study a numerical investigation on the arc characteristics of a supersonic nozzle is carried out, by considering the influence of the pressure ratio between the inlet and outlet, and the Cu vapour. It is demonstrated that a lower inlet pressure may result in a higher arc temperature, a lower arc voltage and a smaller mach number, and Cu vapour from electrode evaporation may cool the arc significantly.

Analysis of Arc Characteristics and Flow Field in Arc Chamber of High-Voltage SF_6 Auto-Expansion Circuit Breaker

A new magnetic hydro-dynamics model for nozzle arc emphasizing the interaction of arc with PTFE （polytetrafluorethylene） vapour is established based on the conservation equations. The interruption of auto-expansion circuit breaker is simulated numerically by finite element method and the influence of PTFE vapour on the arc is analysed with this model. The results reveal that the flow field inside the arc chamber is determined by the arc current, the arcing time, the nozzle arc and the clogging of its thermal boundary. The establishment of quenching pressure relies on both SF6 gas and PTFE vapour that absorbed arc energy in the nozzle. The PTFE vapour leads to an increase in the pressure of nozzle arc obviously, and a decrease in the temperature of arc. But it enhances the temperature of arc at zero current and slows down the decreasing rate of arc temperature as the current decreases.

直排型DF/HF化学激光器双喷管模型启动特性

建立了一套直排型DF／HF化学激光器气流通道双喷管小型实验装置，通过选择不同副气流总压（模拟燃烧室气流）进行实验，研究了副气流总压对双喷管实验装置启动特性的影响。实验结果表明：随着副气流总压的增大，装置的启动压力降低，盲腔条件下的启动压力明显高于有副气流时的启动压力。因此，先通入燃烧室气流，再开通引射气流，对直排型连续波DF／HF化学激光器的启动是有利的。采用1维处理方法，建立了从引射气流喷管入口、副气流喷管入口到扩压器出口的理论模型，得到了与实验一致的规律。由于1维理论中采用了一些近似处理，实际启动压力比理论数据高20％～31％。

直流条件下空气与SF_6喷口电弧换热机理分析

空气作为来源丰富的自然气体其绝缘和电流开断性能得到了很多研究。近几年来作为Fluoroketone的稀释气体在中压开关中进行了SF_6替代试验。大量结果表明基于空气的气吹断路器故障电流开断能力远远小于SF_6断路器,但长期以来一直未能回答为什么空气电弧的时间常数远大于SF_6电弧的时间常数、其开断性能远远弱于后者的问题。文中基于可靠的实验数据对二维轴对称微分湍流电弧模型中的湍流参数首先进行了标定,并在此基础上详细分析了空气电弧的能量交换机理。通过对比研究发现小电流空气喷口电弧径向和轴向散热相当,而在SF_6电弧中径向散热占绝对主导地位。两者散热机理的差异与径向温度分布(弧柱半径大小)有直接关系,而径向温度分布由物性参数ρCp通过湍流换热控制。因此,文中的研究结果为找出瞬态电弧中(开断过程)气体的不同开断能力的原因指明了方向。