Chalking Characteristics Of Composite Insulators And It’s Influence On Physical And Chemical Properties

Silicone rubber composite insulators are widely used in power grid construction due to their excellent ability of anti-pollution flashover.However,composite insulators are more likely to deteriorate than porcelain and glass insulators due to weak bonds and forces between organic material elements.Various phenomena of aging may occur on composite insulators with the increase of operating time,and the chalking studied in this paper is one of them.Chalking means that the surface of composite insulator is powdered due to the degradation of the silicone rubber sheds.At present,there are few reports on the research on the composition of chalking products and the effects of chalking on the performance of insulators.Based on overseas and domestic researches on aging,a series of research were conducted on three chalking composite insulators samples that have been aged for more than ten years.These samples were collected from three regions with distinctly different climate and environment,including China-Henan Power Grid Line,China-Fujian Power Grid Line,and Xuefeng Mountain Natural Observation Station of Chongqing University.The main work of the thesis consists of two parts.Firstly,the physical and chemical characteristics of the chalked layer of each sample are analyzed,the purpose is to obtain the composition of the chalking products and analyze the chalking formation mechanism.Besides,performances of chalking samples sheds were studied,aiming to obtain the effects of chalking and removing chalking layer on the performance indicators of insulator.The following conclusions were reached:(1)The chalking product of each composite insulator sample contains two parts:the organic silicon which is oxidative degradation product of the original raw material polydimethylsiloxane(PDMS),and the partially dehydrated and deteriorated flame retardant filler aluminum hydroxide(ATH).However,not only the thickness of the chalking layer,that is,the degree of chalking,but also the particle size distribution of the chalking product and the composition ratio between the two components are different.This has certain relations with the insulator production formula and process and the aging stress.(2)Combined with the different operating environment of each insulator sample in this study,the influence of different aging factors on chalking are analyzed,and the essence of chalking is that the composite insulator is severely oxidized and degraded under the effect of various aging factors.The organic component silicone rubber are decomposed to fragments,and the bonding between inorganic flame retardant filler and polymer become weak.They will be detached from the main body skeleton and lost partly,then build up at the surface.So the connection between multifactor functioning of operating environment and the occurrence of chalking phenomenon are inseparable.(3)The surface of chalking composite insulators is uneven,and a large number of holes are exposed due to removing chalking layer.The influence of chalking on the surface hydrophobicity is not obvious.Removing chalking products may lead to surface hydrophobicity decreasing,because the scanty LMW chain inside the material colliding with unresponsive supply.And the pollution covering the outermost part of the chalking layer also has a greater effect on the surface hydrophobicity.The rough surface of chalking composite insulator is related to chalking product,and the roughness is more affected by the chalking layer than the pollution.(4)During the chalking process of composite insulator,a large number of fractures occurred in the main and side chains of silicone rubber.The changes in the elements and functional groups caused by the material oxidative decomposition are significant.After removing chalking layer,the surface can be restored to a state closer to the interior of the sample,but it will still be significantly different from that when it is completely new.Chalking composite insulators have deteriorated electrical corrosion resistance,and their dielectric properties will deteriorate slightly after removing process.