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

该项目将需要对用不同固体间隔物材料连接的电极系统在空气环境中的闪络行为进行表征。施加的脉冲电压将具有高达300千伏的峰值，时间到半值的数量级为数百纳秒。将描述三种不同绝缘材料(HDPE、Delrin和Ultem)的圆柱形样品在不同相对湿度水平(&lt；10%、~50%和&gt；90%RH)的空气中以及在0.5至1.5bar绝对值范围内的闪络行为。为了控制潮湿环境中的闪络行为，将研究对所选材料样品的表面光洁度进行改进的方法。将测试具有相同电极间间隙距离但没有固体间隔物的开放间隙，以提供基准击穿数据以供比较。使用的电极轮廓将产生准均匀的场分布，并将量化不同测试条件下的极性效应。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，定位在固体间隔物的表面，并集中在三重结上，任何协同效应都将被确定。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脉冲电压；以及过电压测试，其中将表征各种绝缘系统的击穿时间以进行比较。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，以区分不同压力和相对湿度水平下绝缘系统的材料和表面光洁度的性能。这将揭示不同绝缘系统对外加电压增加的敏感性，以及外加电压的阈值水平等信息，低于该阈值水平，绝缘系统预计不会发生击穿。过电压试验中产生的击穿时间数据将经过von Laue统计分析，从而估计平均统计时间和形成时间在各种测试条件下对总击穿时间的相对贡献。整个项目产生的实验数据以及对放电引发和发展机制的相关讨论，将对要求在潮湿条件下以及潜在存在表面污染物的情况下可靠运行的脉冲功率系统的高压绝缘的设计者感兴趣。将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.