Switching Impulse Flashover Performance of Nonuniform Pollution Insulators in Natural Environment

Under natural conditions, insulators show a nonuniform pollution state, which has a great influence on the switching impulse flashover voltage of insulators. Meanwhile, the insulation level of transmission lines is selected according to the switching impulse flashover voltage of nonuniform pollution insulators. For this purpose, in this article, the wet pollution method is used to simulate nonuniform pollution conditions. Then, the switching impulse flashover tests and the switching impulse flashover tests with preloading ac voltage are conducted on two types of insulators, XP-70 and LXY-70, in natural environment. The flashover voltage of insulators is obtained, flashover performances are analyzed, and the flashover processes of insulators are photographed. Moreover, the equations of flashover voltage gradient
${E}_{{50}}$
under nonuniform pollution conditions are established. The results indicate that there is a conspicuous polarity effect and a polarity reversal phenomenon under different conditions. Besides, as the increase of the ratio of bottom surface pollution to top surface pollution, the flashover voltage changes in the opposite case of preloading and non-preloading ac voltage. Finally, the switching impulse flashover voltage of ordinary porcelain and glass suspension insulators under nonuniform pollution conditions can be calculated based on the established equations of
${E}_{{50}}$
. The results can provide theoretical support for the reasonable selection of the insulation level of transmission lines, which in turn can greatly reduce the cost of the transmission lines.