Study On Electric Characteristics And Selection Of Snowed Composite Insulators

There are more and more high-voltage transmission lines across the region which is covering with the heavy snow with the rapid development of the power grid. Snow will threaten the reliability of a power system. Therefore, it has important engineering value and significance to study the electric characteristics and selection of snowed composite insulators.Through outdoor natural snowfall tests of insulators, triangular and approximate rectangular snow simulation models of composite insulators were put based on characteristics of insulators for snow and rule. Through the quasi-static electric field finite element method, we studied electric field distribution along the surface, after changing area and height of snow on the large sheds, air length and position when the large sheds are completely bridged by snow. Also we analyzed snow parameters’ influence on the electric field along the surface. Then we calculated electric field distribution along the surface, after changing snow height and ice length in the ice and snow coexisting conditions. The results show that, when snow only exists on the large sheds, snow height and thickness have little influence on electric field distribution along the surface. And electric field distribution along the surface has improved when the large sheds are completely bridged by snow. The maximum field intensity of insulators increases with the increase of relative permittivity when snow only exists on the large sheds. Snow parameters changes seriously threaten the electrical insulation properties of the insulators when the large sheds are completely bridged by snow. The longer the length of the ice is, the greater the influence of snow on electric field distribution along the surface is. Besides, the higher snow height is, the more serious distortion degree of electric field on the snow surface is.Based on natural snow law composite insulators, we carried through artificial snow flashover tests, researched the relationship between 50% flashover voltage and conductivity rate of snowmelt, and analyzed the flashover process of snowed composite insulators. The results show that, with snowmelt conductivity rate increased, 50% flashover voltage of snowed composite insulators declined, rendering saturated trend. 50% flashover voltage of thaw period is general below dry snow period’s. Dry clean snow and salt snow(or dirt snow) of snow period influenced little on insulation performance of composite insulators. Salt snow(or dirty snow) of snowmelt period made insulation performance of insulators severely reduce.The effect of the big umbrella diameter and the grading ring for improving the electric field and potential distribution on snowed composite insulators by changing the parameters of the big umbrella diameter, the grading ring, including the ring diameter, the ring gauge, the elevation, was investigated. Finally, the recommended parameter of the big umbrella diameter and the grading ring for the snowed composite insulators was put forward.