Solid-gas interfaces stressed with HV impulses: Surface flashover behaviour and control in the 100s kV regime

该项目将需要表征用不同固体间隔材料桥接的电极系统在空气环境中的闪络行为。施加的脉冲电压将具有高达300千伏的峰值幅度，时间为数百纳秒的一半。将描述三种不同间隔材料（HDPE， Delrin和Ultem）的圆柱形样品在不同相对湿度水平（<10%，~50%和>90% RH）的空气中，在0.5至1.5 bar绝对压力范围内的闪络行为。将研究如何修改所选材料样品的表面光洁度，以控制潮湿环境中的闪络行为。将测试具有相同电极间隙距离但没有固体间隔的开放间隙，以提供基线击穿数据进行比较。所使用的电极轮廓将产生一个准均匀的场分布，并且在不同测试条件下的极性效应将被量化。然后将在强制气流中进行测试，以确定对击穿特性的影响。污染物将被引入绝缘系统，定位在固体隔离器的表面，并集中在三联结，并确定任何协同效应。将使用两种不同的测试程序：升压程序，以确定在不同测试条件下引发闪络的峰值冲击电压；以及过电压测试，其中各种绝缘系统的击穿时间将被表征以进行比较。将对使用升压程序产生的击穿电压结果进行威布尔统计分析，以在不同压力和相对湿度水平下，根据材料和表面光洁度分离绝缘系统的性能。这将揭示诸如不同绝缘系统对施加电压增加的敏感性等信息，以及施加电压的阈值水平，低于该阈值预计不会发生绝缘系统的击穿。过电压试验中产生的击穿时间数据将进行von Laue统计分析，从而可以估计在各种测试条件下平均统计时间和形成时间对总体击穿时间的相对贡献。在整个项目中产生的实验数据，以及对放电开始和发展机制的相关讨论，将对脉冲电源系统的高压绝缘设计人员感兴趣，这些系统需要在潮湿条件下可靠运行，并且可能存在表面污染物。根据不同的环境条件，对固体垫片的材料选择和表面光洁度提出建议。

The project will entail characterisation of the flashover behaviour of electrode systems bridged with different solid spacer materials, in air environments. The impulsive voltages applied will have peak magnitudes of up to 300 kV, with a time to half-value of the order of hundreds of nanoseconds. The flashover behaviour of cylindrical samples of three different spacer materials (HDPE, Delrin and Ultem), in air with different levels of relative humidity (<10%, ~50% and >90% RH), and in the pressure range 0.5 to 1.5 bar absolute, will be characterised. Methods to modify the surface finish of samples of the chosen materials, with a view to controlling flashover behaviour in humid environments, will be investigated. Open gaps, of the same inter-electrode gap distance but without a solid spacer, will be tested to provide baseline breakdown data for comparison. The electrode profiles used will give rise to a quasi-uniform field distribution, and the polarity effect under the different sets of test conditions will be quantified.Tests will then be performed in forced airflows, in order to determine the effect on the breakdown characteristics. Contaminants will be introduced into the insulation systems, positioned on the surface of the solid spacers and focussing on triple junctions, and any synergistic effects will be determined. Two different test procedures will be used: a step-up procedure, to determine the peak impulse voltages that initiate flashover under the different sets of test conditions; and overvoltage tests, where the time-to-breakdown of the various insulation systems will be characterised for comparison.Weibull statistical analysis will be performed on the breakdown voltage results generated using the step-up procedure, to separate the performance of the insulation systems by material and surface finish, at different pressures and levels of relative humidity. This will reveal information such as the sensitivity of the different insulation systems to an increase in applied voltage, and threshold levels of applied voltage, below which breakdown of the insulation system is not expected to occur. The time-to-breakdown data generated in overvoltage tests will be subjected to von Laue statistical analysis, allowing estimation of the relative contributions of the mean statistical time and the formative time to the overall time to breakdown under the various sets of test conditions.The experimental data generated throughout the project, and the associated discussion of the mechanisms of discharge initiation and development, will be of interest to designers of high-voltage insulation for pulsed power systems, required to operate reliably in humid conditions, and potentially in the presence of surface contaminants. Recommendations will be made on material selection and the surface finish of solid spacers, tailored for different environmental conditions as appropriate.