【作者】 郭锐；

【导师】 潘垣； 何俊佳；

【作者基本信息】 华中科技大学 ， 脉冲功率与等离子体， 2010， 博士

【摘要】 开关是脉冲功率技术中的关键元件之一,开关的特性直接决定了脉冲功率系统的性能。气体放电开关作为大电流闭合开关的一种,在脉冲功率系统中得到了广泛的应用。此类开关一般在高电压、大电流条件下工作,在开关导通过程中会产生高温电弧,电弧与电极之间的相互作用直接影响到开关的特性和使用寿命。本文针对开关在大电流、高库仑量工作条件下电极烧蚀小、长寿命的要求,设计研究了一种轴向磁场控制的旋转电弧开关,并对其中的电弧运动特性进行研究。首先介绍了该轴向磁场控制的旋转电弧开关的原理及结构设计,此开关通过使电弧运动,增大电极与电弧的接触面积,减小电弧输入到电极表面的热流密度,从而达到减小电极烧蚀,延长开关使用寿命的目的。开关的结构设计具有以下几个特点：开关电极采用同轴圆柱结构,电极形状经过优化,使得间隙中的电场分布均匀,保证电弧的起弧点分散在电极表面；电流流经内电极时从上下两路分流,保证这两个电流对电弧的作用力平衡：在开关上下分别设置一组线圈,当开关通过电流时,该线圈产生类似磁镜位形的磁场结构,在开关间隙处磁场的轴向分量占主要部分,电弧在该轴向磁场的作用下围绕电极作旋转运动,而径向分量使得电弧向电极中部即磁场最弱处运动。利用时序放电实验平台进行了开关的大电流实验,目前开关通流能力达到峰值电流250kA,单次转移电荷量745C,开关电极烧蚀轻微。为研究开关中电弧的旋转运动,采用B-dot探针法进行测量。分析了在三种测试方式下探针的信号波形,通过比较,选择了其中两种测试方式进行测速实验。对影响探针信号的各因素如电弧方向、电弧直径和电流密度分布等进行了分析,结果表明,电弧方向对探针信号波形的影响最大,分析了由此对判断电弧位置及计算电弧速度带来的测量准确性的问题,证明采用B-dot探针来研究电弧运动速度是可行的。在时序放电实验平台上进行了电弧测速实验,电流波形采用近似梯形波。根据测速实验结果,在单次放电过程中,在不同条件下,存在电弧运动速度的变化滞后于电流的变化及电弧运动存在低速-高速-低速的转变过程这两个现象；对不同电流、不同线圈匝数下多次测速实验的结果数据进行拟合得到了适用于此开关的电弧运动速度公式,即电弧运动速度可以由间隙中的轴向磁感应强度唯一确定,且为指数关系；当线圈匝数为2匝时,电弧在起始阶段出现停滞现象。借鉴链式模型对开关中的电弧运动过程进行了建模和仿真。该模型将电弧视为若干小电流元链接而成,每个电流元都看作圆柱体,其位置、方向和长度等遵循一定的原则进行设置和计算,所有电流元的运动就构成了整个电弧的运动。考虑弧根特性,引入电极表面阻力系数和弧根跳跃规则,对一般的链式模型进行了改进。通过该模型分析了电弧运动速度特性及电弧在运动过程中的形态变化,主要研究了电极表面阻力对电弧运动速度及形态的影响,当电极表面阻力大小不同时,电弧的运动速度和形态分别由内电极弧根和弧柱决定。结合实测速度结果,在一定条件下推测了电弧直径的大小,并得到了电弧直径与轴向磁感应强度之间关系的拟合结果。更多还原

【Abstract】 Switch is one of the most important parts of the pulsed power technology. It determines the output performance of the pulsed power systems. Gas discharge switch is a popular application in pulsed power system among closing switches. It usually works at high voltage and high current. The interaction between the arc and electrode material is complicate and it determines the performance and lifetime of the switch. A rotating arc gap switch controlled by axial magnetic field is designed and built in this paper to meet the requirements of high voltage, high current, large transfers, slight electrode erosion and long lifetime. The arc motion characteristics are studied.The rotating arc gap switch makes the arc move between the electrodes; therefore, the area contacting with the arc is much larger than that in the static arc condition. It makes the arcing time on unit area much shorter and then less heat is conducted into. Therefore, the electrode erosion is slighter and switch lifetime is longer. The electrodes are coaxial cylinder configuration and its shape is optimized to make the electric field uniformly distributed in the gap. This makes the arc starts random in the gap when triggered. The current flow in inner electrode are symmetrical and opposite in direction. So their force on the arc is balanced and will not lead the arc moving in axial direction. The coils which connected to the inner electrode are placed both at the top and bottom of the switch. The resultant magnetic field is in axial direction and forms a mirror-like configuration. It makes the arc stabilized rotate in the middle of the switch where the magnetic field is weakest. The switch operation characteristics are studied by experiments. Its specifications of current and coulomb per shot can reach 250kA and about 745 Coulomb respectively.The B-dot probes are installed to measure the arc velocity. The probe voltage signal is calculated in three different measurement ways and two of them are adopted in experiments. The factors that influence the probe signal are analyzed, such as the direction of the arc, the arc column diameter and the arc current distribution. The accuracy in arc velocity calculation is discussed. The results show that the method is believable.A power supply system consist several independent modules discharging in sequence provides a trapezoidal pulse of current on the switch. The arc velocity variation is lagging behind the current variation and there is abnormally high-speed motion during the arc acceleration in one shot in some experimental conditions. The arc velocity in different amplitude of current and magnetic flux density are studied. The expression that describes the relationship between arc velocity and axial magnetic flux density is found. When the coil number is 2, the arc is stationary in the ignition place for a few microseconds, it results severely damage to the electrode.A chain model is employed to describe the arc motion in this rotating arc gap switch. The arc is assumed to be a chain of small cylindrical current elements like a string of beads, and they are linked by a certain rules. Each element moves individually which determines the behavior of the whole arc. The chain model is improvement by considering the arc root motion and surface drag force. The arc velocity and shape variation during the movement are studied based on this model. The results showed that the surface drag force is an important factor that influences the arc velocity and shape. The arc column diameter is calculated and the relationship between it and axial magnetic flux density is obtained.更多还原