Basic Studies on Insulation Design of Dielectric Spacers in Vacuum

绝缘子的带电被认为是导致绝缘子桥接真空间隙闪络的关键现象。本研究的目的是获得一个工程方面的设计考虑到充电现象的间隔的形状。为了这个目的，我们已经开发了两种模拟技术来分析的间隔物表面上的电荷分布，也澄清的表面电荷的时间行为的测量技术。模拟技术之一是基于二次发射电子雪崩（SEEA）模型分析充电平衡状态下的电荷分布。这种技术已被应用到一个圆柱形的间隔，基本形状，由丙烯酸树脂（PMMA），聚四氟乙烯（PTFE）或氧化铝陶瓷（92%A12O3），我们已经证实，模拟和测量的分布很好地同意彼此。另一种模拟技术分析了充电发展阶段的电荷分布。这两种技术已被证明是一个强大的工具，研究充电现象，不仅为一个简单的圆柱形绝缘体，而且实际上用于高压装置在真空条件下的间隔。为了研究充电过程，我们采用了一种静电的方法，它使用一个小的隔离部分的阴极作为探针。这种探针技术使我们能够在斜坡或步进直流电压激励下实时观察表面充电。研究了表面粗糙度对真空中绝缘子带电的影响。结果表明，表面粗糙度决定性地影响充电特性，这是更明显的高度抛光的绝缘体。

The charging of an dielectric insulator is considered to be a critical phenomenon leading bridged vacuum gaps by dielectric spacers to flashover. The goal of this study is to obtain an engineering aspects for designing the shape of spacer taking the charging phenomena into account. For this purpose we have developed two simulation techniques to analyze the charge distribution on the spacer surface and also a measuring technique for clarifying the temporal behavior of the surface charge. One of the simulation technique analyzes the charge distribution in an equilibrium state of charging based on the secondary emission electron avalanche (SEEA) model. This technique has been applied to a cylindrical spacer, fundamental shape, made of acryl resin (PMMA), teflon (PTFE) or alumina ceramics (92% A12O3), and we have confirmed that the simulated and measured distributions well agree with each other. The other simulation technique analyzes the charge distribution during developing phase of the charging. Both techniques have been proved to be a powerful tool to study charging phenomena not only for a simple cylindrical insulator but also for spacers actually utilized in high voltage devices under vacuum condition. To investigate the charging process, we have employed an electrostatic method which uses a small isolated part of the cathode as a probe. This probe technique enables us a real-time observation of surface charging under a ramped or stepwise DC voltage excitation. Influence of surface roughness on the charging of an insulator in vacuum has been investigated. The results exhibit that the surface roughness decisively affects charging characteristics, which is more pronounced for more highly polished insulators.