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

本文研究了10-50 mm长的聚合物绝缘子和玻璃绝缘子在真空中直流或交流电压激励下的充电和闪络特性。这是开发适用于高于例如100 kV的电力系统的高压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）的替代品，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是研制高可靠性、紧凑型真空瓶的关键。我们进行了闪络试验，电荷测量和计算表面电荷分布。绝缘体由PMMA或硼硅酸盐（Pyrex[○！R]），并且呈直圆柱体或中空圆柱体的形状。用静电探针研究了绝缘子的带电特性，探针埋入固定绝缘子的一个平面电极中，并允许一个时间间隔。 ...更多信息 充电过程的电子分辨测量。认为绝缘子表面的带电先于桥接真空间隙并导致闪络，本研究的目的之一是找出试样在交流电压作用下的带电机理。已经澄清的是，充电的特征在于由三个连续的状态;启动，准稳定和稳定状态，并且电荷的极性对于这些状态是正的，而不管电压相位。与交流电压的充电特性与直流电压激励的结果进行了比较。我们发现，在稳定状态下的电荷量与直流获得的一致。接地电极上的电场强度，因此电荷大小，随着表面粗糙度而减小，并且随着绝缘强度的增加而减小。通过计算机模拟，阐明了表面电荷分布与电压相位同步的转变是产生准稳态的原因.第二个目的是阐明表面粗糙度对充电的影响，为高压真空瓶的设计提供有用的数据.对于长度小于10 mm的相对较短的试样，湿澄清之前，充电是压抑的粗糙度增加，绝缘能力提高。本研究的目的是确认这种效果较长的绝缘体。在直圆柱体的情况下，样品的侧表面被抛光以具有亚微米的平均粗糙度、镜面光洁度或粗糙度高达几微米。在中空圆柱体中，试样的内侧表面被抛光，而外侧具有足以防止充电的粗糙度。因此，我们已经证实，粗糙化的表面防止充电，从而提高了绝缘强度的试样长达50毫米。这是由于真空中电子在充电过程中从表面测量的跳跃高度小于1 μm，表面的不规则性对这些跳跃的电子起了阻挡作用，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