基于斜面法试验研究SiO_2质量分数对RTV硅橡胶涂料性能的影响

针对室温硫化(roomtemperature vulcanization,RTV)硅橡胶涂料应用中存在的黏附力不强、涂层易划破的问题,提出通过添加二氧化硅来提高硅橡胶的机械强度,改善材料的耐电痕化和耐电蚀损性。为此,结合热导率的概念,通过斜面法试验讨论了二氧化硅对RTV硅橡胶性能的影响,试验中采用西安交通大学电力电子专用设备研究所研制的高精度交流漏电起痕试验装置配合自行研发的多路泄漏电流实时监测采集装置,对制备的3种RTV硅橡胶涂料试片(只添加二氧化硅,且二氧化硅质量分数为20%、30%、50%)按照GB/T6553—2003《评定在严酷环境条件下使用的电气绝缘材料耐电痕化和蚀损的试验方法》进行试验。结论为:二氧化硅质量分数越高的硅橡胶热导率越大,热量越容易传导,耐电痕化和耐电弧烧蚀性越强;二氧化硅含量高、热导率大的硅橡胶试片到达过流保护动作的临界状态时,其烧蚀区域面积和烧蚀深度都较低二氧化硅含量的试片大;二氧化硅填料的增加使硅橡胶电蚀损后憎水性恢复过程减慢。     

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.     

Silicone rubber dielectrics modified by inorganic fillers for outdoor high voltage insulation applications

The paper discusses the mechanisms by which inorganic fillers in silicone rubber dielectrics enhance the properties of thermal conductivity, relative permittivity, and electrical conductivity making them useful in outdoor high voltage insulation applications. The addition of alumina trihydrate or silica fillers to silicone elastomers, forming binary composites with enhanced thermal conductivity, is discussed in relation to filler type, particle size, shape, and concentration, and its use as a housing material for non-ceramic insulators to minimize material erosion at dry band arcing sites by lowering hot spot temperature. Also discussed is the enhanced relative permittivity of silicone dielectrics that is obtained through the addition of barium titanate powder which can be further increased with the addition of aluminium powder forming a tertiary composite, resulting in a significant grading of the surface electric field when applied as a housing material to high voltage bushings. Controlled electrical conductivity of silicone dielectrics is discussed through the use of antimony-doped tin oxide filler binary composites and when applied as a housing material to outdoor bushings, the pollution performance is greatly enhanced.     

Erosion resistance and mechanical properties of silicone nanocomposite insulation

The results of erosion resistance, tensile strength, elongation at break, hardness, and thermal stability measurements are presented for silicone nanocomposites prepared using various nano and micro silica and alumina fillers in a two-part silicone rubber (SiR) matrix. The fillers are used to improve the erosion resistance of SiR, which is necessary for outdoor insulation housing applications. Good dispersion of the fillers is achieved using Triton/sup TM/, a common surfactant. An optimal surfactant concentration imparts good erosion resistance to the nanocomposites in laser heating tests without adverse effects, but excess surfactant has a negative impact on the mechanical properties of the silicone. Thermal gravimetric analysis demonstrated that nano fumed silica imparts better heat resistance to silicone than natural nano silica or nano alumina fillers. Fourier transform infrared spectroscopy analysis of the nanofillers indicated a significantly higher concentration of silanol groups in the nano fumed silica filler than in micro silica. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites and their mechanical properties is discussed.     

Erosion resistance of nano-filled silicone rubber

The paper presents the experimental results obtained on the erosion resistance of silicone rubber (SIR) filled with 12 nm size fumed silica (nano filler) to those filled with 5 /spl mu/m size silica filler (micro filler). The ASTM 2303 inclined plane tracking and erosion test was used in the comparison as well as an infrared laser as the source of heat to erode the SIR samples. The erosion resistance of the SIR materials increased with increasing percentage of the fillers, and it was observed that 10% by weight of nano-filled SIR gives a performance that is similar to that obtained with 50% by weight of micro-filled SIR. The low frequency components of leakage current and the eroded mass are used to evaluate the relative erosion resistance of the composites and the third harmonic component of the leakage current shows good correlation to the measured eroded mass. The paper discusses the possible reasons for the improvement in the erosion resistance of nano-filled silicone composites.     

Electrical performance of RTV silicone rubber coatings

The role played by two major constituents in a room temperature vulcanized (RTV) silicone rubber coating, namely, the inorganic alumina trihydrate (ATH) filler and the silicone polymer, on the coating's electrical performance was examined. The principal variable in the RTV silicone rubber coatings evaluated was the different weight fraction of the silicone polymer and ATH inorganic filler normally used for improving the tracking and erosion resistance. Other formulation details were essentially the same in the cured rubber. The coatings were spray coated on glazed porcelain rods and subjected to accelerated aging in a salt fog chamber. The changes produced by accelerated aging on the contamination withstand capability, leakage current suppression and erosion resistance were determined and correlated with the ratio of polymer to inorganic filler in the coating. It is shown that critical aspects of electrical performance necessary for satisfactory service operation such as contamination withstand capability before flashover and leakage current suppression are superior for the coating with a relatively high ratio of polymer to inorganic filler in comparison to the coatings with a relatively low ratio of polymer to inorganic filler. While all the coatings showed a high erosion resistance under mild discharge activity, the erosion resistance was found to be superior for the formulations with high inorganic filler under conditions of intensive surface discharge activity     

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.     

Tracking and erosion of HTV silicone rubber and suppressionmechanism of ATH

Tracking and erosion of high temperature vulcanizing (HTV)-silicone rubber (SIR) and the suppression mechanism of alumina trihydrate (ATH) filler were investigated in the present study. The tracking and erosion resistance of HTV-SIR filled with 0 to 60%wt ATH was evaluated by employing an IEC 587 inclined plane (IP) tracking and erosion test, during which leakage current pulses on HTV-SIR were counted. Surface temperature distributions and the occurrences of thermal spots >400°C also were observed by means of an infrared thermovision study. We employed thermogravimetry (TG)-differential thermal analysis (DTA)-mass spectrometer (MS) to observe the thermal degradation of unfilled and filled HTV-SIR in both air and argon. The test results indicate that 40%wt is a critical ATH level and whether tracking and erosion is allowed in the IP tracking and erosion test. Highly filling ATH (>40%wt) reduces the number of low unit silicone oligomer precursors which promote dry-band arcing as well as the presence of residual carbon which leads to carbonization. Chemical modifications of water vapor liberated from heated ATH to methyl groups, which occurs at the thermal decomposition temperature of silicone rubber, were found to result in the above process. The protection mechanisms of ATH for the tracking and erosion of HTV-SIR are formulated herein     

Contamination performances of silicone rubber insulator subjectedto acid rain

Acid rain causes one of the more severe environmental contaminants, and there is an increasing interest in the degradation of outdoor polymer insulating materials in severe pollution conditions such as acid rain. The performance of high temperature vulcanizing (HTV) silicon rubber insulators in accelerated aging of artificial acid rain is investigated by the salt fog method. Experimental results and theoretical analysis show that acid rain exerts a large erosion effect on the silicone rubber insulator. The inorganic filler alumina trihydrate (ATH) in the silicone rubber easily dissolves in acid rain, and the increasing discharge heat from dry band arcing due to acid rain can further cause the loss of ATH. The hydrophobic groups of hydrocarbon branch (ie. methyl in silicone rubber), are also degraded in acid rain. Therefore, the surface of aged insulators becomes rough, they become less hydrophobic, and the surface discharge current increases. However, in a subsequent dry environment, the low molecular weight (LMW) polymer silicone liquid or oil in the bulk of the insulator diffuses and migrates to the surface to provide a hydrophobic layer so that the degraded surface of silicone rubber insulator is compensated, and the contamination performance is restored to some extent. Such recovery of contamination indicates why silicone rubber insulators can be used for long times under severe environmental stress     

UV-A辐射对外绝缘用液态硅橡胶和高温硫化硅橡胶的影响及其机理

在强紫外环境下,外绝缘用硅橡胶材料(高温硫化(HTV)硅橡胶和液态硅橡胶(LSR))的老化将会威胁输电线路的安全运行。为研究UV-A紫外辐射对二者的影响,该文对UV-A辐射老化后的HTV硅橡胶和LSR进行X射线光电子能谱(XPS)和傅里叶红外光谱(FTIR)等微观结构,以及耐热特性、机电特性和交联密度等宏观性能的测试。研究发现,1000h UV-A老化后,HTV硅橡胶表面碳元素含量减少13.4%,氧元素含量增加10.0%,甲基含量、热稳定性和力学强度下降。但是,LSR表面碳元素含量增加5.8%,氧元素含量下降7.6%,Si(—O)4结构减少,甲基含量增加65.7%,热稳定性增加。分析结果表明,UV-A老化中二者的差异主要是由交联结构、ATH含量,以及含氢硅油造成。最后,基于提出的LSR在UV-A老化过程中发生的提氢反应,建议通过减少含氢硅油的含量和增加生胶的分子量提高LSR的耐UV-A老化性能。该文可为理解外绝缘用硅橡胶材料的紫外老化特性提供支撑,也可用于指导高海拔地区的外绝缘材料选型。     

Tracking and erosion of HTV silicone rubbers of different thickness

Tracking and erosion behaviors of high temperature vulcanized (HTV)-silicone rubber (SIR) of 0.5 to 6.0 mm thicknesses were investigated in order to obtain the optimum thickness for enhancing tracking and erosion resistance under various leakage current levels. Under low leakage current, thinner samples showed a higher tracking and erosion resistance, while under medium and high leakage current, thicker samples showed better resistance to these behaviors. The optimum thickness to prolong the time to tracking and erosion failure appeared in the range of 1.0 to 3.0 mm thickness. The content of an initial low molecular weight (LMW) silicone fluid was shown to be closely related to the development of leakage current and high temperature thermal spots. The results indicate that the sample thickness is crucial to the ability of HTV-SIR to withstand a large number of high temperature thermal spots under condition of high level leakage current     

高压绝缘防污闪涂层的研究进展

室温硫化(RTV)硅橡胶以其独特的憎水性和憎水迁移性而被用作新型高压绝缘防污闪材料,但仍存在附着力差,强度弱,阻燃性差等缺陷。为提高RTV硅胶的防污闪作用,进一步开展相关的研究工作,综述了污闪产生的机制,RTV硅胶的组成及特点、研究与应用。在概述了国内外RTV硅胶研究近况和RTV硅胶的小分子憎水迁移机理后阐明了纳米技术有效提高RTV硅胶的机械性能和耐老化性能,阻燃剂(如氢氧化铝)改善RTV硅胶的耐漏电起痕性、阻燃性能等的效果。最后指出,进一步提高RTV硅胶的机械性能、电气性能、抗老化性能是今后研究工作的热点。     

添加半导电硅橡胶涂层对运行绝缘子防覆冰性能的改善

近年来,由于冰冻灾害的发生,电力系统的安全运行受到了巨大的威胁,对绝缘子表面进行改性是目前较为合理的解决方案。室温硫化硅橡胶(room temperature vulcanization,RTV)具有优异的憎水性,但是对阻止绝缘子或者减缓表面覆冰的增长并没有太明显的效果。在室温硫化硅橡胶中添加一定含量的导电填料,制备半导电硅橡胶材料,涂覆于绝缘子表面后,运行过程中绝缘子表面产生热效应,可以减缓乃至防止覆冰的增长。为此,对以炭黑为填料的半导电硅橡胶的导电机理进行了分析,建立了具有半导电硅橡胶涂层的绝缘子电阻模型,通过计算得到合适的体积电阻率。同时,在人工气候室中进行了电热性能测试,分析了涂层泄漏电流与表面温度的关系。理论分析和试验结果表明,由于洁净绝缘子和RTV涂层绝缘子具有较高的表面电阻,在运行中表面温度基本无变化;通过在绝缘子表面涂覆电阻率为104Ω.m的半导电硅橡胶后,运行中绝缘子表面有明显的温升。特别是在低温条件下,添加了一定含量炭黑的半导电硅橡胶涂层能够明显提升运行中的绝缘子表面温度,利于在低温条件下防止绝缘子表面覆冰的增长。     

Influence of single and multiple environmental stresses on trackingand erosion of RTV silicone rubber

Single and multiple effects of UV, corona, thermal, water absorption and acid rain stresses on the tracking and erosion characteristics of room temperature vulcanized silicone rubber (RTV) are investigated. It is shown that corona stress and water absorption stress decrease the tracking and erosion resistance of RTV, while thermal stress and UV stress improve it. Synthetic acid rain, 500× stronger than actual rain in Japan, cannot induce the change in the tracking and erosion characteristics. RTV subjected to simultaneous multiple stresses also is evaluated. Significant variations in the tracking and erosion resistance appear. Chemical and morphological analysis for assessing the aging level is carried out by scanning electron microscope (SEM)-energy dispersive X-ray (EDX), attenuated total reflection (ATR)-Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). In this study, DSC plays an important role to detect boiling and combustion temperatures of byproducts affecting tracking and erosion. Noteworthy results are obtained in that the decrease in the resistance to tracking and erosion is related to the formation of byproducts that burn at low temperature (170 to 275°C)     

Role of the size of particles of alumina trihydrate filler on thelife of RTV silicone rubber coating

The paper reports on a study of the influence of the size of the particles of alumina trihydrate (ATH-Al₂O₃.3H₂O) filler on the life of room temperature vulcanised (RTV) silicone rubber coating in a salt-fog chamber. The particle sizes examined include 1.0, 4.5, 13, 17 and 75 μm. The optimum size to give the lowest leakage current and the longest time to failure of the coating is determined. The particle size affects the roughness of the coating. This is determined by a high resolution surface roughness tester and a scanning electron microscope (SEM) examination. The roughness is enhanced after prolonged testing in salt-fog. The leakage current affects the amount of silicone fluid on the surface. The amount of silicone fluid present on the surface after exposure to dry-band arcing in salt-fog is a function of the particle size. Measurements of surface roughness, the amount of silicone fluid on the surface and the leakage current combined with theoretical analysis of the heat of conduction lead to identification of the mechanisms by which the size of the ATH particle imparts resistance to tracking and erosion     

Degradation Dynamics of Polymeric Housing Materials Used for HV Line and Station Apparatus

A combination of laser irradiation and thermogravimetric analysis has been utilized to understand the degradation dynamics of polymeric materials used for housings of outdoor high voltage (HV) line and apparatus insulators, namely, silicone rubber, ethylene propylene diene monomer rubber and cycloaliphatic epoxy. The induced temperature rise was calculated using laser photo-thermal models and the results were found to be in good agreement with experimental findings. It has been shown that there are significant differences in the degradation dynamics of silicone rubber when compared with ethylene propylene diene monomer and epoxy. It has also been shown that the laser irradiation technique can be used as an efficient method to rank polymers materials for arc tracking and erosion resistance, especially for present day materials that will easily pass the screening tests prescribed in the ASTM and IEC standards.     

室温硫化硅橡胶涂料的改性研究

室温硫化硅橡胶涂料是一种新型防污、憎水、长效涂料,目前已在我国许多地区投入使用。但从目前推广的室温硫化硅橡胶涂料性能来看,涂料与资件的粘附力不够强,影响了涂料的使用效果,而且耐电弧能力也较差。章研究了改进温室硫化硅橡胶涂料机械性能和耐电弧能力的方法,尤其是其防污闪的主要特性－憎水迁移特性没有明显减弱。中还研究了室温硫化硅橡胶涂料的憎水迁移特性。     

Accelerated weatherability of shed materials for compositeinsulators

Shed materials for hollow composite insulators (low temperature vulcanized silicone rubber, high temperature vulcanized silicone rubber, ethylene vinyl acetate and ethylene propylene diene monomer) were examined through accelerated weathering tests and their weathering resistances were evaluated from changes of surface and bulk properties. For silicone rubber, changes in the content of low molecular weight silicone (silicone oil) related to maintaining water repellency were investigated. The results showed that silicone rubbers had excellent weathering resistance and kept high water repellency during long term weathering tests. Using an equivalent model, an investigation was also carried out on how non-soluble contaminations deposited on the surfaces of sheds in outdoor service could cut off UV rays     

热导率测量系统的开发及应用

根据一维稳态的导热原理自主研发了一套聚合物材料热导率（λ）的测量系统,适用范围λ=0～2W/（m.K）。该系统由机械子系统和控制子系统组成。机械子系统包含本体、加载模块、加热模块、冷却模块4部分,控制子系统包含温度传感器、热流传感器、PC和基于LabVIEW的图形化软件,实现了温度与热流量信号的采集、温度的控制及热导率等的显示输出。使用该系统实测了5种聚合物材料的热导率,实验测量值高于文献参考值＋2%～＋10%,其主要原因是样品上表面与加热盘下表面之间的存在热阻,略微降低了样品热端温度的测量值。     

LDPE/MVQ并用胶的组份对其热老化性能的影响

在室温下实现甲基乙烯基硅橡胶(MVQ)和沉淀法白炭黑(SiO2)的共混,制备出MVQ混炼胶。在150~180℃下实现MVQ混炼胶和低密度聚乙烯(LDPE)的熔融共混,制备出LDPE/MVQ并用胶。研究结果表明,随着SiO2含量的增加,LDPE/MVQ并用胶的耐空气热老化性能下降;羟基硅油对材料的热老化性能影响不明显,但甲基乙烯基硅油可显著改善材料的热老化性能;随着LDPE与MVQ混炼胶的质量比的增加,材料的耐热老化性能下降。