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

1.(1)液氮通过聚氯乙烯（PVC）管道后，确认液氮带电。液氮带正电。与电绝缘油相比，其电荷量要小得多。(2)随着液氮体积的增大，液态氮流经PVC管后的充装量增大。液氮流速越高，电荷量越大。随着PVC管材长度的增加，电荷量先增大后趋于平稳。(3)对于l型PVC管，液氮入口与l型管弯头之间的距离越长，流动液氮的电荷量越大。(1)固体绝缘材料的存在增加了在管道中流动的液氮的电荷量。电荷量随绝缘材料数量的增加而增加，然后趋于平稳。随着绝缘材料数量的增加，液氮与绝缘材料的接触面积增大，但在绝缘材料数量较多的情况下，液氮的流速减小。(2)在液氮路径上加装过滤器后，液氮的电荷量增加。电荷的多少取决于过滤器的材质。液氮用铜过滤器带负电，而用聚合物过滤器带正电。这一结果与材料的电气化顺序一致。(1)由于液氮的反复流动，表面电位先升高后逐渐降低。结果表明，经过多次循环后，测点表面形成的霜或冰起到了逃逸流通电形成的表面电荷的作用。(2)绝缘材料表面电位分布复杂。向上位置的表面电位似乎比向下位置的表面电位要高，这表明由于流动速度大，绝缘材料与流动的液氮在向上方向的相互作用更强。固体绝缘材料浸泡在液氮中的闪络电压带表面电荷的绝缘材料获得了较低的闪络电压。这可能归因于表面电荷引起的局部电场增强。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