Aging in silicone rubber used for outdoor insulation

A hypothesis for aging produced by dry band arcing in silicone rubber material used for outdoor insulation is presented and experimentally proven. Aging is indicated by permanent changes. The analytical techniques used to study the permanent changes are Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and surface roughness measurement. The authors highlight the fact that there are permanent changes occurring in the material that lead to progressive degradation in the long run, even though there can be a complete recovery of surface hydrophobicity in a short time     

Surface recovery of silicone rubber used for HV outdoor insulation

Results of a study performed to obtain a better understanding of the material characteristics responsible for hydrophobicity recovery leading to a high wet surface resistance in silicone rubbers used for outdoor HV insulation, are reported. The samples were obtained from new and artificially aged HV insulators using HTV silicone rubbers (3 different formulations) as weathershed and RTV silicone rubbers (2 different formulations) as a protective coating. The main experimental facilities employed consist of a salt fog chamber for artificially aging the insulators, and a scanning electron microscope (SEM) for material studies. New results of practical significance that have emerged from this study are: (1) hydrophobicity recovery, predominantly due to diffusion of low molecular weight (LMW) silicone polymer chains, occurs with only a fraction (<20%) of the total LMW polymer content initially available in an unaged material surface, (2) LMW chain regeneration and hence surface hydrophobicity recovery occurs even after the initial supply of LMW polymer is depleted, and (3) hydrophobicity recovery is significantly affected by ambient temperature. The results show the same pattern for different formulations of HTV and RTV rubber materials studied. The X-ray Mapping feature in the SEM provides a visual indication of the diffusion process which is a noteworthy contribution     

The role of inorganic fillers in silicone rubber for outdoor insulation alumina tri-hydrate or silica

A systematic study to understand how alumina tri-hydrate (ATH) and silica fillers improve the erosion resistance of silicone rubber during dry band arcing showed that the thermal conductivity of the resulting composite material is the main criterion governing material erosion. The thermal conductivity of the composite material is dependent on the thermal conductivity, concentration, particle size, and bonding of the filler particles to the silicone matrix. In this context, either filler can be shown to perform better than the other, depending on the formulation, in the ASTM inclined plane tracking and erosion test. Therefore, the industry perception that ATH filler imports better erosion resistance than silica in silicone rubber can be misleading. The release of water of hydration from ATH appears to have a secondary effect that may be more relevant in silicone compositions having a low concentration of a filler.     

Thermal conductivity of filled silicone rubber and its relationship to erosion resistance in the inclined plane test

Silicone rubber samples having various concentrations and mean particle sizes of either alumina tri-hydrate or silica filters, prepared by room temperature and heat cured under pressure (hot pressed), are tested for erosion resistance in the ASTM D2303 inclined plane tracking and erosion test. Their corresponding thermal conductivities are determined using a transient temperature technique in which an infrared laser is employed as the heat source and a thermal imaging camera as a temperature detection device. Scanning electron microscope observations show greater filler bonding to the silicone matrix in the hot pressed samples than in the room temperature vulcanized samples leading higher thermal conductivity and increased resistance to erosion, for both ATH and silica filled samples. The correlation study shows a strong relationship between the erosion resistance and the thermal conductivity of the tested samples, highlighting the importance of an outdoor insulating material to have high thermal conductivity in order to withstand dry band arcing. The results can be used to provide guidance on filler selection for silicone rubber compounding for outdoor insulation applications.     

ADSS光缆外护套抗干带飞弧能力的新试验方法

首先简要地回顾了ADSS光缆外护套受干带飞弧侵蚀的机理，介绍了国外近年来研究试用的外护套抗干带飞弧试验的新方法和应用这种新方法所取得的实验结果。根据这些结果和其他考虑，提出了尚待进一步探讨的若干问题。     

Electrical and environmental aging of silicone rubber used inoutdoor insulation

This is a laboratory study on the aging of SIR and hydrophobicity recovery. UV radiation, corona discharges, acid rain and dry-band arcing are employed as sources of the aging. Chemical and morphological analysis is used to detect the surface chemical and structural changes derived from these stresses. The nature of highly mobile low molecular weight (LMW) chains achieving a quick recovery of the hydrophobicity is carefully examined. Their generation and extinction caused by these stresses are investigated. From this study, it is shown that oxidation that induces crosslinking, branching, interchanging and a formation of silanol groups are the most dominant chemical reactions during the aging of SIR. Furthermore, silanol groups that are byproducts of oxidation restrict the diffusion of mobile LMW chains, which decreases the recovery speed of hydrophobicity and accelerates the aging. A typical aging scenario of SIR from the installation to the end of their life is drawn     

A novel technique to evaluate the erosion resistance of silicone rubber composites for high voltage outdoor insulation using infrared laser erosion

The standard methods available to test tracking and erosion resistance of filled silicone rubber do not allow to delineate the fundamentals of the thermal degradation, although the heat from the dry band arcing is the main degradation factor. In this work a thermal imaging camera is used to investigate the performance of filled silicone rubber in an inclined plane test, and a scheme is established to relate the temperature and the electrical discharge energy. Further, an infrared laser technique, based on constant energy approach, is developed to study the material performance under laser heating. The technique consists of applying a certain amount of infrared laser energy during a set time period, in order to produce erosion in the silicone rubber samples. Through correlation studies the applicability of the proposed laser technique to rank silicone rubber samples with various fillers has been validated. The laser tests show identical ranking of samples when compared to samples ranked using inclined plane tests, yet offering significant advantages of being faster, simpler, and reproducible.     

电力外绝缘用硅橡胶清洗修复剂制备及性能研究

硅橡胶广泛应用于电力行业的复合绝缘子和防污闪涂料,然而长时间工况运行后,容易发生老化粉化、污秽沉积,降低了表面憎水性。电网中目前有上亿支硅橡胶绝缘子服役多年,研究能够清除表面污秽,修复硅橡胶老化层的新型清洗剂迫在眉睫。本文探究不同非离子表面活性剂含量和修复剂含量对清洗效率和憎水性的影响。实验表明非离子表面活性剂含量在3%时,洗净率最高达到95%。而修复剂含量为11%时,憎水性最好,其憎水迁移性最佳可以达到HC1级。通过扫描电镜分析,发现清洗后硅橡胶表面微孔和裂缝消失,表面平整,表明该清洗剂具有去除老化层和污秽,修复老化绝缘子的效果。这为继续研发硅橡胶清洗修复剂,延长绝缘子服役期限提供一定的理论和实践基础。     

Review of aging and recovery of silicone rubber insulation foroutdoor use

This paper surveys the properties which give silicone rubber its distinctive and highly desirable performance characteristics for use as outdoor insulation. The methods of assessing these properties are discussed and this is followed by a detailed survey of what is known of aging and recovery mechanisms. Corona is identified as the principle electrical aging agent and evidence is presented for irreversible loss of polymer as a result of aging. However, the surface recovery mechanisms are robust and, provided there is an adequate resting period, the hydrophobic properties recover. This supports the view, from service experience, that there is no substantial evidence to show that normal aging, unless it results in the exposure of the glass fiber core, detracts from the performance of insulators     

Test methods and results for recent outdoor insulation in Japan

This paper describes new test methods and some typical test results for a recently developed external insulation in Japan. The paper starts with the introduction of the results of the tests that were conducted specially on the external insulation for 1100 kV/10 GW ac transmission line and ±500 kV/2.8 GW dc overhead line section, recently constructed in Japan using heavy duty insulators and giant bushings. Various special tests were made on the external insulation in order to investigate the performance at such high service voltages since those had never been used before, and secondly because of the high reliability required and the importance of the lines. Introduces test methods and some related results on long term performance for the new type of insulators, such as semiconducting glaze and polymer insulators. Also included in the paper are the development of some special test methods and results on line arresters for transmission and distribution lines, which have been accepted widely in Japan     

线路绝缘测试用接地线和操作杆和测试流程研究

线路绝缘电阻测试是线路常规开展的作业,安全、高效的开展线路绝缘电阻测试工作对提高作业效率和供电可靠性具有重要意义。本文分析了现有常规线路绝缘电阻测试风险,结合现场作业的技术特点,研制了一种线路绝缘测试试验用接地线、试验用操作杆,并对测试流程进行了优化,不增加投入情况下提高了线路绝缘电阻测试安全性和工作效率。     

硅脂环境下硅橡胶的吸收特性及其关键电气性能研究

电缆附件在长期运行过程中,其界面硅脂与绝缘硅橡胶直接接触使其逐渐被硅橡胶吸收,导致硅橡胶性能下降,甚至引发电缆附件界面问题。文中以附件绝缘硅橡胶吸收硅脂的增重试验为基础,研究不同温度下硅脂/硅油在硅橡胶中的扩散规律并获得相应的扩散参数;研究硅脂对硅橡胶体积电阻率、相对介电常数、介质损耗角正切值和工频击穿场强等电气性能的影响规律。结果表明,不同温度下硅脂/硅油在硅橡胶中的扩散规律服从Langmuir扩散模型;硅橡胶对硅脂/硅油的吸收能力随温度升高而增强,且硅橡胶内硅油分子的脱附过程更强;随着硅橡胶对硅脂吸收量的增加,硅橡胶的体积电阻率逐渐降低,相对介电常数和介质损耗角正切值逐渐增加,但其工频击穿场强呈先增大后减小的趋势。     

丙烯酸酯及氟硅橡胶在变压器中的应用

通过对胶垫、胶条密封不严造成的渗漏原因分析,介绍了丙烯酸酯及氟硅橡胶的特点及在变压器中的应用.     

青铜峡水电站#3主变绝缘干燥的分析和处理

对青铜峡水电站110kV主变故障处理后试验结果异常进行分析,并根据分析结果对设备进行绝缘干燥处理。     

Effect of specimen configuration on deterioration of silicone rubber for polymer insulators in salt fog ageing test

The paper investigates the effects of specimen configuration on the deterioration of silicone rubber insulators in a salt fog ageing test. A cyclic salt fog ageing test was conducted on three types of high-temperature vulcanized silicone rubber (HTV SiR) specimens: two types of insulators having sheds, and plain rods without sheds. The test was based fundamentally on the CIGRE WG 15-04 specifications. After 50 test cycles, the three types of specimens showed different degrees of surface deterioration. Erosion on the straight shed insulator was more severe than that on the alternate shed insulator even though the two had the same leakage distance. No erosion was observed on the rod-type specimens, which had shorter leakage distances than the insulator-type specimens.     

A technique for testing the applicability of insulation systems in the construction of traction machines

Tests of the applicability of new insulation systems for traction motors are considered. Selections of operating loads applied during accelerated comparative testing and the testing technique are described.     

高压电机少胶VPI绝缘的现状及发展方向

在11篇文献的基础上综述了国内外高压电机少胶VPI绝缘的发展状况，分别比较了国外几家公司的少胶VPI绝缘结构的性能，分析了国内VPI绝缘存在的问题以及解决这些问题的方法，指出了我国VPI绝缘的发展方向。