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

我们研究了10-50 mm长的聚合物绝缘子和玻璃绝缘子在真空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100千伏以上电力系统的高压真空断路器的基础研究。高压断路器被认为是气体断路器(GCB)的替代品，以减少具有较高全球变暖潜力的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的计算。绝缘子由PMMA或硼硅酸盐(PYREX[0！R])制成，形状为右圆柱体或中空圆柱体。使用静电探头研究了绝缘子的充电特性，该探头嵌入在固定绝缘子的一个平面电极中，并允许TIM…对充电过程进行更多电子解决方案的测量。认为绝缘子表面的充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样品在交流电压下的充电机理。已经阐明，充电具有三种顺序状态的特征：初始状态、准稳定状态和稳定状态，并且对于这些状态，无论电压相如何，充电的极性都是正的。将交流电压下的充电特性与直流电压下的充电特性进行了比较。我们发现稳态时的电荷量与直流电荷量是一致的。接地电极上的电场强度，即电荷量，随着表面粗糙度的增加而减小，随着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，并为高压真空瓶的设计提供有用的数据。对于长度小于10 mm的相对较短的试件，WEAM先前已澄清，充电随粗糙度的增加而降低，绝缘能力提高。本研究的目的是证实对较长绝缘子的这种影响。在右圆柱体的情况下，样品的侧面被抛光到具有亚微米的平均粗糙度，镜面抛光，或粗糙到几微米。在中空圆柱体中，试件的内侧表面被抛光，而外侧有足够的粗糙度来防止充电。因此，我们已经证实，粗糙的表面可以防止充电，从而提高长度达50 mm的样品的绝缘强度。这可能是由于充电过程中真空中的电子从表面测得的跳跃高度小于1μm，表面的不规则性起到了阻挡跳跃电子的作用，这是导致绝缘子闪络的主要预放电现象之一。较少

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