Research on spherical graphite cast iron electrode based gas switch
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摘要: 高功率容量的气体开关是国内外大型脉冲功率装置的首选，但因气体放电随机性导致的自击穿电压抖动一直以来是脉冲功率装置的瓶颈问题。电极是影响气体开关稳定性和寿命的关键，开关设计总要面临低抖动和长寿命之间的取舍，提出一种兼顾低抖动、长寿命特性的球墨铸铁气体开关。基于对球墨铸铁材料的特性分析，提出球墨均布于电极有利于提高气体开关击穿稳定性的机制，且球状石墨均布于整个电极体内，相比表面结构，具有长寿命的原生优势。设计开展了单级开关稳定性测试实验，结果表明球墨铸铁电极可将传统电极结构3%～4%的重频自击穿抖动有效降低至2.5%。最终利用低抖动球墨电极，设计了5级1 MV等自击穿概率型全密封气体开关，开关抖动进一步降低至2%以下。在测试电压范围960～980 kV，放电电流约9 kA，无维护条件下开展了开关30万脉冲寿命考核，自击穿抖动维持在2%以下，最优达1.7%。开关导通前沿小于5 ns，传输效率大于90%。此结果展现了球墨铸铁作为气体开关电极的应用潜力。Abstract: Gas switches with high power capacity are the first choice for large-scale pulsed power devices at home and abroad, but the self-breakdown voltage jitter due to the randomness of gas discharge has always been the bottleneck problem for pulsed power devices. The electrode is the key to affect the stability and life of the gas switch, and the previous designs had to face the trade-off between low jitter and long life. This paper proposes a spherical graphite cast iron gas switch that takes into account the characteristics of low jitter and long life. Based on the characterization of the spherical graphite cast iron material, it is proposed that the uniform distribution of spherical graphite in the electrode is conducive to the mechanism of improving the breakdown stability of the gas switch, and the spherical graphite is uniformly distributed in the whole electrode, which has the native advantage of long life compared with the surface structure. A single-stage switching stability test experiment was designed and carried out, and the results show that the ductile graphite electrode can effectively reduce the heavy frequency self-breakdown jitter of 3%−4% in the traditional electrode structure to 2.5%. Ultimately, a 5-stage 1 MV equal self-breakdown probability type fully sealed gas switch was designed using low jitter ductile electrodes, and the switching jitter was further reduced to less than 2%. Under the test voltage range of 960-980 kV, discharge current of about 9 kA, and maintenance-free conditions, the switch was tested for 300 000 pulses, and the self-breakdown jitter was maintained at less than 2%, with an optimum of 1.7%. The switch conduction front is less than 5 ns, and the transmission efficiency is more than 90%. The results demonstrate the potential application of spherical graphite cast iron cathodes as gas switches.
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Key words:
- gas switch /
- low jitter /
- long life /
- spherical graphite cast iron
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图 1 电极材料扫描电镜图
Figure 1. SEM image of QT500-spherical graphite cast iron and 316L stainless steel
图 2 阴极真空场致电子发射图像
Figure 2. Field emission electron image of QT500-spherical graphite cast iron and 316L stainless steel
图 4 单间隙击穿电压累积概率分布(SF6, 0.9 MPa)
Figure 4. Cumulative distribution function of gas discharge for typical gas gap (SF6, 0.9 MPa)
图 5 典型放电间隙击穿抖动对比(SF6, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 MPa)
Figure 5. Comparison of breakdown jitter along typical gas gaps (SF6, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 MPa)
图 8 多级等自击穿概率球墨铸铁开关场强分布（V=−1 MV）
Figure 8. Electric field distribution of spherical graphite cast iron equal breakdown probability gas switch (V=−1 MV)
图 9 多级球墨铸铁开关的静电场模拟
Figure 9. Electrostatic simulation for multi-stage spherical graphite cast iron gas switch
图 10 Tesla型驱动源气体主开关工作典型波形
Figure 10. Typical waveform of gas switch for Tesla pulse generator
图 11 球墨铸铁开关30万脉冲寿命考核的电性能演变趋势
Figure 11. Evolution of breakdown voltage and jitter for spherical graphite cast iron gas switch under 300 000 pulses test
表 1 QT500球墨铸铁材料与316L不锈钢材料性质对比
Table 1. Comparison of material properties between spherical graphite cast iron and stainless steel
material mass fraction/% tensile
strength/MPayield
strength/MPathermal conductivity/
(W∙m−1∙K−1)melting
point/℃hardness/HB metallographic
structureQT500 C: 3.55～3.85;
Si: 2.34～2.86
Mn,S,P,Mg: 0.02～0.04
RE: 0.03～0.05≥500 ≥320 35.7 1200 ～1300 170～230 austenitic stainless steel 316L C: ≤0.03; Si: ≤1.00;
Mn: ≤2.00; S: ≤0.03;
P: ≤0.045; Mo: 2.00～3.00≥480 ≥177 16.3 1375 ～1450 ≤187 ferrite+pearlite 
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表 2 四个实验组的开关结构
Table 2. Basic structure of 4 experimental groups
experiment group electrode structure electric field enhancement f cathode material anode material group 1 annular spherical 1.1 316L 316L group 2 blade-plane 3.6 316L 316L group 3 annular spherical 1.1 QT500 QT500 group 4 annular spherical 1.1 QT500 316L
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