【作者】 曾晗；

【导师】 林福昌；

【作者基本信息】 华中科技大学 ， 高电压与绝缘技术， 2012， 博士

【摘要】 在脉冲功率系统中开关是关键元件之一,其性能优劣直接影响到输出脉冲的技术参数。石墨型两电极气体开关作为大电流闭合开关的一种,具有转移电荷高、通流能力强、使用寿命长、价格低廉、工作性能稳定等优点。本文针对在大电流、高库仑量工作条件下的石墨型两电极气体开关中的石墨电极烧蚀、电接触烧蚀、静态工作特性以及动态触发特性等问题进行研究。首先,分析了气体开关石墨电极本体由于放电电弧而产生的烧蚀。以热力学理论的热传导模型为出发点,结合实验中对烧蚀量的测量验证,得到了石墨在高能脉冲放电情况下烧蚀的理论解释。并基于该理论解释,结合了热力学中的热传导公式,给出了石墨电极本体烧蚀的几点结论,其一,在放电中,石墨电极表面各阴极斑点由初始状态升温至升华温度所耗时间在亚纳秒级甚至10-4ns的范围,对于微秒级或是更长放电持续时间的放电电流,可以认为整个放电时间进行的都是电极去除过程。其二,在石墨电极的材料去除过程的分析中得出石墨电极烧蚀量与库仑转移量之间的关系。根据该关系式计算得到单位库仑转移量下的石墨电极烧蚀质量与实验中的实测值基本吻合。因此,该关系可以在石墨电极的设计中作为石墨电极寿命的依据。其次,研究了石墨电极与电极座之间的电接触烧蚀问题。建立了电接触面温升模型,并运用该温升模型分析计算了各参数变化对温升的影响。在原理上解释了电接触面温升与材料物理属性以及开关机械参数之间的关系,并认为在一定的工作电流作用下,静态电接触温升与接触材料的物理属性,以及工程实现中的加工精度有关。选择高热导率、高比热容、高密度、低电阻率、低弹性模量、低泊松比的材料并提高电极座接触面加工精度有助于降低电接触面的温升,减轻熔焊。然后,分析了气体开关的结构及其静态工作特性。采用了锥形与柱形结合的结构形态以减小在安装电极时所产生的应力；以压接式安装结构作为电极安装方式,并在安装螺栓处辅以绝缘措施以减少金属套筒与金属电极座之间的烧蚀；通过对开关直流击穿电压的分析可以得到开关工作电压介于自击穿电压的40%-60%之间,气体开关工作气压的初始值为130kPa,该气压值是在一个较长的工作时间内使得误动作概率与拒动作概率都位于一个优化的取值。在实验平台上对研制的气体开关进行了实验研究。该气体开关通过了峰值达到570kA的冲击电流测试。在电流峰值316kA,单次电荷转移量可达103.4C的工况下,通过了1500次以上的寿命试验。最后,分析了气体开关的触发特性。对气体开关的开通过程以及开通气体开关所需要的条件进行了仿真,Marx发生器的输出端需要串联安装一个阻值不大于50Ω的电阻,以利于气体开关的击穿。在上述研究的基础上对气体开关触发装置的工作特性作出了分析,Marx发生器的工作点应该选择靠近自击穿曲线。并且无触发信号球隙开关间的铜盘上连接有接地电阻将会使得Marx发生器触发成功概率得到提高,同时其工作气压范围将会被拓宽。更多还原

【Abstract】 Switch is one of the key components in the pulsed power system. The performances of the switch directly influence the output characteristics of the system. As one kind of high current closed switches, the spark gap switch with two graphite electrodes has the advantages such as large charge transfer, high current capability, long lifetime span, stability and low cost. The paper mainly studies the graphite electrode erosion, electrical contact erosion, static characteristics and triggering characteristics in the high current application of spark gap switch with two graphite electrodes.Firstly, the erosion mechanism of graphite electrode under the arc was analyzed. The erosion mechanism of the graphite electrode is investigated based on the theory of thermodynamics and validated by experimental result. An erosion mechanism was developed to explain the erosion of graphite electrode under pulsed discharge condition. Based on the analysis of the erosion mechanism and thermodynamics theory, the erosion of the graphite electrode has the characteristics as follows:(1) for the graphite electrode, the duration of heating process is less than a nanosecond. Thus the duration of heating process can be ignored for a microsecond or longer discharge process. (2) the relationship between the graphite electrode erosion and charge transfer can be considered linear. This relationship can be used to predict the life of graphite electrode.The electrical contact between the graphite electrodes and electrode erosion was studied in this paper. Computing model of contact temperature rise is proposed based on contact surface model and heat-conduction equation. The model can theoretically illustrate the relation between the electrical contact surface temperature rise and material physical properties as well as switch mechanical parameters. The model analyzing conclusion indicated that the static contact temperature rise was influenced by material physical properties and engineering manufacturing accuracy. Appropriate contact area, contact pressure and low surface roughness contributed to reducing temperature rise and preventing static welding. The structure and static operating characteristics of the spark gap switch were then studied in the paper. A structure with combined conical and cylindrical shape is proposed in order to reduce the electrode installation stress. Crimp style installation and insulation structure at the bolt area can avoid the erosion between the metal sleeve and the metal electrode holder. Based on above construction, switch operating voltage is in the range of the 40% to 60% of the self-breakdown voltage. Initial value of working air pressure of the gap is 130kPa in the spark gap, which is an optimal value to reduce the self-fire probability and refuse act rate.A spark gap switch has been developed. The experimental results show that the switch can bear the impulse of the large current with the peak of 570kA. In the lifetime test with the peak current of 316kA of and charge transfer of 103.4C each shot, the switch remained well after 1500 shots.At last, the trigger characteristics of spark gap switch was studied. The switch on process of the spark gap was simulated. The simulation results showed that a 50 ohm resistor should be installed at the output of the Marx generator to facilitate the breakdown of a spark gap. Based on above result, operation characteristics of trigger device were analyzed. The results indicated that the operating point of the Marx generator should be close to its breakdown curve. For the sphere gap without trigger signal, a grounding resistance connecting to the copper coil can improve the breakdown probability, and broaden the working pressure range of the Marx generator.更多还原