| Compared with the traditional ceramic or glass insulators, the composite insulators of high temperature vulcanized (HTV) silicone rubber have been widely used in ultra-high voltage power transmission because of their merits, for instance, strong pollution flashover resistance, low weight and high mechanical strength and so on. However HTV silicone rubber is very easy to aging under the influence of factors such as discharge, acid rain, ultraviolet radiation, ozone etc in the outdoors, which affects the working life and safety of HTV insulator. HTV composite insulator is the main insulation equipment in the system of ultra-high voltage power transmission. Research on the running characteristic of composite insulators, studying on microscopic properties and the aging characteristic of HTV silicone rubber under ultraviolet irradiation, all are very important and become more urgent.The two series of ultraviolet irradiation accelerated ageing experiments have been carried out in this dissertation. First, the accelerated aging of HTV silicone rubber was carried by the irradiation of short pulse248nm ultraviolet laser. Second, combing with European standards, the ultraviolet radiation aging experimental box that simulated the main aging of HTV silicone rubber under outdoor solar ultraviolet was designed and set up, accelerated aging tests were carried out by365nm ultraviolet irradiation. The surface static contact angles of samples were measured before and after irradiation, for the angles were used to evaluate hydrophobicity. The surface morphologies of samples were observed by scanning electron microscope (SEM). The changes of the relative contents of functional groups were analyzed by Fourier transform infrared spectrometer (FTIR) on the samples. The changes of chemical element valence, relative content and component were analyzed by results of X-ray photoelectron spectrometer (XPS). The tensile propertis of samples were measured by universal material testing machine. The behaviors of microscopic structure and property of HTV silicone rubber have been obtained by analyzing the all measurement results of samples before and after aging test.The experimental results demonstrate that the static contact angle of the new HTV silicone rubber is around118°,which means its excellent hydrophobicity. The smoothness of new samples is high, the contrast is even, no particles and holes. Additionally, the tensile property of HTV silicone rubber is excellent, but the toughness of some sample would be low. The surface hydrophobicity of sample has risen weakly under248nm ultraviolet irradiation. However, hydrophobicity has reduced dramatically after365nm ultraviolet irradiation. When the sample is irradiated by248nm or365nm ultraviolet, the smoothness steps down, a large number of particles and holes appear, the particles are the mixture of SiO2and Al2O3, the fills exposure further, chemical reactions such as fracturing, oxidation, crosslinking have happen on the sample. The ageing of samples is more likely to happen under248nm ultraviolet laser irradiation compared with the365nm ultraviolet.248nm ultraviolet can damage or cut off almostly all combination keys such as Si-O, Si-C, C-C, C-H on the sample, the new free radicals form, new radicals crosslink further, O and Si free radical crosslink to form SiOx(x=3-4), all which lead that the nonpolar of macromol-ecular chain is weakened or destroyed. However the small molecules which are in sample or are formed by free radicals migrate and proliferate to the surface, the unity of CH2O enhances, allthese prompt the restoration of hydrophobicity, so the change of hydrophobicity is very weak under248nm ultraviolet irradiation.365nm ultraviolet light mainly brokes Si-C bonds which are on both sides Si-O main chains with symmetrical arrangement, methyl groups are oxidized on the side chains, which lead that the shield of strongly polar of Si-O bonds have been abated, the polar of macromolecular chains enhances, so hydrophobicity of samples decline after ultraviolet irradiation. In addition, increasing groups (-COOH) and declining smoothness of sample also can drop hydrophobicity. In a word, there main are light oxidation reaction on HTV silicone rubber under two categories of ultraviolet irradiation.Ozone can accelerate the ageing of HTV silicone rubber under a condition. The duration of248nm short ultraviolet laser pulse is short, so the concentration of ozone is very low. Ozone is produced during365nm ultraviolet irradiation, its concentration ranges from0to2ppm, which belows the critical value (2ppm) where HTV silicone rubber is ageing by Ozone, so the Ozone aging effect of HTV silicone rubber are very weak under two categories of ultraviolet irradiation.The thesis studies the change of microcosmic physical property of HTV silicone rubber under ultraviolet irradiation, respectively explains the change of hydrophobicity under the short-wave or long-wave ultraviolet irradiation, deeply discusses the ageing mechanism and regularity of HTV silicone rubber. There are important significance and engineering value in the net application and ultra-high voltage power transmission line construction and maintenance for HTV silicone rubber composite insulator. |
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