Streaming electrification of cryogenic fluid/polymer insulator composite insulation system and evaluation of electrical insulation capability of the system

1.流经PVC管的液氮带电(1)流经聚氯乙烯(PVC)管后，液氮带电。液氮为正电。与已报道的电绝缘油相比，液氮的电荷量要小得多。(2)随着液氮体积的增加，PVC管流动后的液氮电荷量变大。液氮流量越大，装药量越大。(3)对于L形聚氯乙烯管，液氮入口到L管弯头之间的长度越长，流动的液氮电荷量越大。2.固体绝缘材料或过滤器对流经聚氯乙烯管的液氮带电(1)固体绝缘材料的存在增加了流经…的液氮的电荷量更多的在烟斗里。电荷量随着绝缘材料数量的增加而增加，然后趋于平稳。随着绝热材料数量的增加，液氮与绝缘料的接触面积变大，但在绝热材料较多的情况下，液氮的速度减小。(2)在液氮路径上加装过滤器后，液氮的带电量增加。装药量取决于过滤器的材料。使用铜过滤器将液氮充电为负电荷，而使用聚合物过滤器则为正电荷。这一结果与材料带电的顺序是一致的。3.在流动的液氮中销售的绝缘材料的表面电位(1)随着液氮的重复流动，表面电位先升高后逐渐降低。结果表明，测点表面经过多次循环后形成的霜和/或冰对流动带电形成的表面电荷起逃逸作用。(2)绝缘材料表面的电位分布比较复杂。在液氮中浸泡固体绝缘材料的闪络电压较低，表面带电的绝缘材料闪络电压较低。这可能归因于表面电荷引起的局部电场增强。较少

1.Electrification of liquid nitrogen flowing through PVC pipes(1)Electrification was confirmed for liquid nitrogen after flowing through a poly-vinyl-chloride(PVC) pipe. Liquid nitrogen was charged positive. The amount of charge is much smaller compared with that reported for electrical insulating oil.(2)The amount of charge of liquid nitrogen after flowing PVC pipe became larger with increase of volume of liquid nitrogen. Higher flowing rate of liquid nitrogen resulted in increase in the amount of charge. The amount of charge increased and then leveled off with increase of the length of PVC pipe.(3)In the case of L-shaped PVC pipe, the amount of charge of flowing liquid nitrogen was larger when the length was longer between the inlet of liquid nitrogen and the elbow of L-shaped pipe.2.Electrification of liquid nitrogen flowing through PVC pipe with solid insulating materials or filters(1)Existence of solid insulating material increased the amount of charge of liquid nitrogen flowing i … More n the pipe. The amount of charge increased with the number of insulating materials and then leveled off. The area of contact between liquid nitrogen and the insulating material becomes larger with increase in the number of the insulating materials, but velocity of liquid nitrogen reduces under the condition with many insulating materials.(2)When a filter was installed in the path of liquid nitrogen, the amount of charge of liquid nitrogen increased. The amount of charge depended on the material of the filter. Liquid nitrogen was charged negative with a copper filter, while charged positive with polymeric filters. This result agrees with the order of electrification of materials.3.Surface potential of sold insulating material placed in flowing liquid nitrogen(1)Surface potential increased first and then decreased gradually by repetitive flowing of liquid nitrogen. It was suggested that frost and/or ice on the surface of measuring point, which was formed after several cycles, played a role to escape surface charge formed by streaming electrification.(2)Distribution of potential on the surface of insulating material is complicated. It seemed that surface potential at the upward position was higher than that at the downward, suggesting that interaction between the insulating material and flowing liquid nitrogen was stronger at the upward side due to high flowing velocity.4.Flashover voltage of solid insulating material immersed in liquid nitrogenLower flashover voltage was obtained for insulating material with surface charge. It may be attributed to local electric field enhancement caused by surface charge. Less