Basic Research for an Environmentally Friendly Circuit Breaker by Studying Surface Discharge Characteristics in Vacuum

我们研究了长10- 50mm的聚合物绝缘子和玻璃绝缘子在直流或交流电压激励下的充电和闪络特性。这是一项开发适用于高于100千伏电力系统的高压vcb（真空断路器）的基础研究。高压真空断路器被认为是GCB（气体断路器）的替代方案，以减少具有高全球变暖潜力的SF6。玻璃或陶瓷真空瓶的绝缘设计对于研制高可靠性和紧凑性的真空断路器具有重要意义。我们进行了闪络试验、电荷测量和表面电荷分布计算。绝缘体由PMMA或硼硅酸盐（Pyrex）制成。)，形状为正圆柱体或空心圆柱体。利用静电探针对绝缘体的充电特性进行了研究，该探针嵌入在固定绝缘体的一个平面电极中，可以对充电过程进行更精确的测量。认为绝缘子表面带电先于电桥真空间隙产生闪络。本研究的目的之一是了解试件在交流电压作用下的充电机理。已经阐明，充电具有三个连续状态的特征；起始态、准稳定态和稳定态，这些状态下电荷的极性都是正的，与电压相无关。比较了交流电压激励下和直流电压激励下的充电特性。我们发现稳态的电荷大小与直流电法得到的一致。因此，接地电极上的电场强度随表面粗糙度而减小，并随绝缘强度的增加而减小。计算机模拟表明，表面电荷分布与电压相同步的转变是导致准稳定状态的原因。二是阐明表面粗糙度对充注的影响，为高压真空瓶的设计提供有用的数据。对于长度小于10mm的相对较短的试样，wet先前已经澄清，随着粗糙度的增加和绝缘能力的提高，电荷会减少。本研究的目的是证实这种影响对较长的绝缘子。在右圆柱体的情况下，试样的侧面被抛光到亚微米的平均粗糙度，镜面光洁度，或者粗糙到几微米。在空心圆柱体中，试样的内表面被抛光，而外表面有足够的粗糙度，以防止充电。因此，我们已经确认，粗糙的表面防止充电，从而提高绝缘强度的试样长达50mm的长度。这主要是由于在真空中，电子在充电过程中距离表面的跳变高度小于1 μm，表面的不规则性对这些跳变电子起到了屏障作用，这是导致绝缘子闪络的主要预放电现象之一。少

We have examined charging and flashover characteristics of polymeric and glass insulators with 10-50 mm long under DC or AC voltage excitation in vacuum. This is a basic study for developing high voltage VCBs (Vacuum Circuit Breakers) adapted to electric power systems higher than e.g. 100 kV. The high voltage VCB is considered as an alternative of GCB (Gas Circuit Breaker) in order to reduce SF6 that has a high global warming potential. The insulation design of the vacuum bottle made of glass or ceramics is of importance for developing such VCBs with high reliability and compactness. We conducted flashover tests, charge measurements and calculation of surface charge distributions. The insulator was made of PMMA or borosilicate (Pyrex【○!R】), and was in the shape of a right cylinder or a hollow cylinder. The charging characteristics of insulators were investigated by using an electrostatic probe, which was embedded in one of the plane electrodes that holds the insulator and allowed a tim … More e-resolved measurement of the charging process. It is believed that the charging of insulator surface precedes and leads the bridged vacuum gap to the flashover.One of the purposes of this study is to find out charging mechanism when specimens are subjected to AC voltages. It has been clarified that the charging is characterized by three sequential states; initiation, quasi-stable and stable states, and that the polarity of the charge is positive for these states irrespective of the voltage phase. The charging characteristics with AC voltage are compared to the results with DC voltage excitation. We found that the charge magnitude at the stable state coincides with that obtained by DC. The electric field strength on the grounded electrode, therefore the charge magnitude, decreases with the surface roughness and decreases as the insulation strength is increased. A computer simulation clarified that the transition in surface charge distribution being synchronous to the voltage phase is responsible for causing the quasi-stable state.The second purpose is to clarify the effect of surface roughness on charging and to obtain useful data for designing a high voltage vacuum bottle. For comparatively short specimens with less than 10 mm in length, wet have clarified previously that charging is depressed as the roughness increases and that the insulation ability improves. The purpose of the present study is to confirm this effect for longer insulators. In the case of right cylinder, the side surface of the specimen was polished to have an average roughness of sub microns, mirror finish, or roughened up to several microns. In the hollow cylinder, the inner side surface of the specimen was polished, while the outer side had a roughness which is enough to prevent from charging. As a result, we have confirmed that roughening the surface prevents the charging and thus improves the insulation strength for a specimen up to 50 mm in length. This improvement can be attributed to the fact that the electrons in vacuum during the charging process have less than 1 μm in hopping height measured from the surface, the surface irregularities act as barriers against those hopping electrons, which is one of the main pre-discharge phenomena leading the insulator to flashover. Less