磁吹直流空气断路器弧根跃迁及对开断特性的影响研究

Research on Arc Root Transition of Magnetic DC Air Circuit Breaker and Its Influence on Breaking Characteristics

直流空气断路器的弧根跃迁与其开断特性有着密切的关系。该文搭建实验平台,采用高速摄像机拍摄电弧演变过程,得到清晰的弧根跃迁图像,观测弧根跃迁过程中的“双弧根”现象。基于磁流体动力学理论,建立二维磁吹直流空气电弧模型。模型中赋入鞘层条件,通过耦合外电路模块模拟实验工况,对开断过程中电弧温度场、气流场及弧根跃迁现象进行分析。在此基础上,完成磁场、烧蚀金属蒸气浓度变化对弧根跃迁及开断特性影响的仿真研究。结果表明:磁场强弱会改变弧柱高温区的运动轨迹,影响前后侧的气流场分布,改变局部区域电导率,产生弧根的停滞与跃迁现象,显著影响断路器的开断性能。外施50m T磁场会发生弧根跃迁现象,弧根跃迁可以减少烧蚀,加速开断,其本质成因是通过“双弧根”完成的。“双弧根”现象是由于引弧板表面电导率增大,在其表面形成新的导电斑点形成的。烧蚀产生的金属蒸气不总是阻碍熄弧,当灭弧室中铜蒸气浓度达到50%~60%时,出现弧根跃迁,减少燃弧时间,有利于开断。

The arc root transition of DC air circuit breaker is closely related to its breaking characteristics. In this paper,the experimental platform is built. The arc evolution process is photographed with a high-speed camera, the clear arc root transition image is obtained, and the "double arc root" phenomenon in the arc root transition process is observed.Based on the theory of magneto hydro dynamics(MHD), a two-dimensional magnetic blowout DC air arc model is established. The sheath conditions are added into the model. By coupling the external circuit module to simulate the experimental conditions, the arc temperature field, air flow field, and arc root transition are analyzed. On this basis, the effects of magnetic field and ablated metal vapor concentration on arc root transition and breaking characteristics are simulated. The results show that the magnetic field will change the trajectory of the arc column in the high temperature zone,affect the distribution of the air flow field at the front and rear sides, change the local regional conductivity, produce the stagnation and transition of the arc root, and significantly affect the breaking performance of the circuit breaker. Applying 50mt magnetic field will cause arc root transition, which can reduce ablation and accelerate breaking. Its essential cause is completed through “double arc roots”. The “double arc root”phenomenon is due to the increase of the surface conductivity of the arc striking plate and the formation of new conductive spots on its surface. The metal vapor produced by ablation does not always hinder arc extinguishing. When the concentration of copper vapor in the arc extinguishing chamber reaches 50%~60%, the arc root transition occurs, which reduces the arcing time and is conducive to breaking.