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

点击翻译按钮获取中文摘要

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