Effects of inorganic fillers on withstanding short‐time breakdown and long‐time electrical aging of epoxy composites

Inorganic fillers were added to epoxy resin for preparing micro and nano filler/epoxy composite, and then the breakdown strengths, depths of erosion caused by partial discharge, and electrical tree experiments of composites were investigated. It was found that the loading of micro fillers usually decreases the short‐time breakdown strength (breakdown under a continuously rising voltage) of the composites. On the contrary, it increases the ability to withstand long‐time electrical aging (erosion or breakdown caused by electrical tree under a discontinuously rising voltage or constant voltage) of the composites. The effect of inorganic fillers in suppressing the electrical tree or erosion channel propagation in the composite is different during the process of withstanding short‐time breakdown and long‐time electrical aging. Defects are introduced during the mixing of fillers and epoxy resin, which play a role to decrease the short‐time breakdown strength and accelerate long‐time electrical aging. It is concluded that micro and nano inorganic fillers can suppress the electrical tree channel propagation and erosion caused by partial discharge, whereas defects play the opposite role in composites. Two opposite effects of inorganic fillers and defects exist simultaneously during the process of electrical aging and breakdown; whereas inorganic fillers play a primary role in long‐time electrical aging, defects play a primary role in short‐time breakdown.     

偶联剂协同低温等离子体的复合材料氧化铝填料表面改性

环氧树脂广泛应用在电机绝缘领域,向树脂中添加微米氧化铝可以减缓绝缘老化的侵蚀,为了进一步提升氧化铝/环氧树脂复合材料电气性能,本文引入偶联剂协同低温等离子体复合改性方法对氧化铝填料进行表面处理。将偶联剂包覆改性后的微米氧化铝置于重复脉冲低温等离子体中分别进行0~9min表面改性处理,其次将氧化铝掺杂进环氧树脂中制备复合材料。观测氧化铝填料外表的形貌、官能团及结构变化,对复合材料局部放电起始电压进行测试分析。结果表明,偶联剂和低温等离子体复合改性能有效提升氧化铝填料表面活性官能团的含量,为氧化铝与树脂基体的紧密键合提供了基础,进而提升了氧化铝/环氧树脂复合材料的电气性能。在复合改性中等离子体处理时间为3min时,氧化铝填料表面含氧基团的含量相对于单一偶联剂改性增长了3.32%,表面偶联剂的接枝率提升了24.5%,复合材料的电气性能提升了7.9%。     

The mechanisms leading to the useful electrical properties of polymer nanodielectrics

Polymer nanocomposites with metal oxide nanoparticle fillers exhibit enhanced electrical breakdown strength and voltage endurance compared to their unfilled or micron filled counterparts. This paper presents the following hypothesis for the mechanisms leading to improved properties. The inclusion of nanoparticles provides myriad scattering obstacles and trap sites in the charge carriers' paths, effectively reducing carrier mobility and thus carrier energy. The result is homocharge buildup at the electrodes, which increases the voltage required for further charge injection due to blocking by the homocharge. The hypothesis is supported by electroluminescence, pulsed electro acoustic analysis, thermally stimulated current measurements, a comparison of AC, DC, and impulse breakdown, as well as absorption current measurements, in silica/crosslinked polyethylene matrix composites with supporting evidence from titania/epoxy composites.     

环氧树脂掺杂微纳米氧化物粒子改性研究综述

随着电网电压等级提高及电气设备小型化发展,人们对环氧树脂绝缘材料的绝缘性能提出了更为苛刻的要求。添加微纳米氧化物粒子是提高环氧树脂电气性能的重要方法之一,该方法具有大量的实例且操作简便;同时,各种电力技术的不断更新换代为提升环氧树脂绝缘性能增加了更多可能性。文中介绍了环氧树脂掺杂微纳米氧化物填料复合材料制备过程,同时对掺入微纳米氧化物粒子对环氧树脂基本物理性质与主要绝缘性质的影响进行了总结。最后归纳了微纳米氧化物颗粒添加对环氧树脂绝缘性能提升的研究难点及其可能的解决方案,期望对填料掺入环氧树脂复合材料电气绝缘性质改善的学术研究与工程运用起到引领和推动作用。     

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.     

玻璃纤维-碳纳米管共掺杂环氧树脂复合材料绝缘性能的研究

为研究玻璃纤维、碳纳米管共掺杂环氧树脂复合材料的绝缘性能,制备了纤维不同掺杂量和排布方式时的玻璃纤维-碳纳米管环氧树脂复合材料,并分别测试了其介电常数、介质损耗因数及交流短时击穿电压,研究了掺杂工艺参数对复合材料绝缘性能的影响。研究发现,玻璃纤维掺杂量在15~20wt%、纤维束间距在1.0~1.2mm时,复合材料介电常数和介质损耗因数均达到最小值,分别为3.63和0.0303;而其交流短时击穿电压在40wt%掺杂量、1.5mm纤维束间距时,达到最大值39.6k V。与单向排布方式相比,正方形网格排布的复合材料击穿电压更高。研究表明,玻璃纤维的引入改善了碳纳米管-环氧树脂复合材料的绝缘性能,玻璃纤维、碳纳米管与环氧树脂之间的界面效应在复合树脂绝缘性能的改善中发挥主要作用。     

Experimental enhancement for dielectric strength of polyethylene insulation materials using cost-fewer nanoparticles

The use of nanocomposite polymers as electrical insulating materials has been growing rapidly in recent decades. The base polyethylene properties have been developed by adding small amounts of different fillers to the polyethylene material. It is economically to get polymer development by using cost-fewer nanoparticles; therefore, polyethylene dielectric properties are trapped by presence cost-fewer nanofillers like clay and fumed silica which are importance in development manufacture of power cables products. Dielectric strength is a vital pointer for quality of insulation materials of electrical power applications; hence, experimental measurements have been investigated on ac high voltage breakdown of new cost-fewer polyethylene nanocomposites materials. All experimental results of the new polyethylene nanocomposites have been compared with conventional polyethylene insulation materials; therefore, it has been specified the influence types and their concentrations of cost-fewer nanofillers on dielectric strength of polyethylene nanocomposite insulation materials.     

Modification of electrical properties and performance of EVA and PP insulation through nanostructure by organophilic silicates

Nanostructured materials are attracting increased interest and applications. Exciting perspectives may be offered by electrical insulation. Polymeric nanofilled materials may find new and/or upgraded applications in the electrical and electronic industry, replacing conventional insulation to provide improved performances in electrical apparatus, as regards, e.g., reliability, environmental compatibility and power rating. This paper shows that electrical properties of nanocomposite insulating materials for DC applications, specifically space charge, conductivity and breakdown voltage, can improve significantly with respect to the basis, unfilled materials. Reference is made to two polymeric materials, i.e. poly(ethylene-covinylacetate) (EVA) and polypropylene (PP), that are widely used as electrical insulation, e.g. for cables and capacitors. The nanofiller consists of an organophilic layered silicate, specifically an extra-pure synthetic fluorohectorite modified by means of interlayer exchange of sodium cations for protonated octadecylamine NH/sub 3//sup +/ (ODA), in a weight concentration of maximum 6%. In both materials the space charge accumulation rate as a function of applied electric field is significantly reduced, while the electrical conductivity is raised. The breakdown voltage can increase for the nanofilled materials.     

环氧云母绝缘定子线棒多因子老化过程中交流参量变化规律的研究

交流电流参量常用来评定绝缘的老化程度。在环氧云母绝缘线棒多因子老化过程中,交流电流参量随老化呈现的变化规律,而且第二电流激增电压有较强的相关性;可以作为特征能量来评定环氧去母约缘的老化程度。所以,通过交流电流试验可以有效地评定环氧云母绝缘的劣化程度。     

Nonlinear dc and ac conductivity in electrically insulating composites

The non-linear electrical behavior of zinc oxide, used to practical advantage in surge arresters on distribution power systems, has been replicated in epoxy resin, which has been filled with an appropriate volume fraction of this intrinsically semi-conducting material. Comparison has been made with epoxy resin containing a similar volume fraction of aluminum oxide in order to establish that the non-linearity observed in zinc oxide filled resin is a function of the zinc oxide itself and not simply an artifact resulting from the presence of any filler and the interfacial phenomena thereby arising. Previous work in this field, in both thermo-setting and thermo-plastic insulation has concentrated on dc voltage application. This work, in addition to extending the range of host materials to include epoxy resin using dc, has also explored the ac behavior. The results demonstrate that the inclusion of zinc oxide in epoxy resin is capable of producing non-linear conductivity when the filler volume fraction exceeds the percolation threshold ( /spl sim/ 15%).     

RTV/纳米层状硅酸盐复合绝缘的抗电痕性

为提高RTV的抗电痕性,用纳米技术对其改性,合成RTV纳米复合材料并试验研究了它的耐漏电起痕及电蚀损能力,分析层状纳米材料的抗电痕机理的结果表明,层状纳米材料可大大提高RTV的抗电痕性。     

真空沿面闪络过程放电光谱分析

选取高压真空绝缘体系中常用的环氧树脂为研究对象,通过添加不同粒径的纳米无机填料,分析不同填料对沿面闪络过程的影响。利用闪络过程光谱实时测量系统分别研究红外光、可见光及紫外光范围内的闪络发光光谱的时域波形,从发光光谱的角度分析闪络过程的发生和发展机理。结果表明:闪络光谱强度并不随闪络电压的升高而增强,纳米无机氧化物的添加会引入更多的深陷阱能级,且会增加高能光子的发射。     

低介电常数绝缘纸的制备及其击穿性能

为提高油浸式变压器绕阻中纸-油-纸复合绝缘系统的击穿电压,实验室制备了能降低绝缘纸介电常数的微纳米级SiO2空心微球以及含不同质量分数SiO2(wSiO2)空心微球的实验用绝缘纸手抄片。测量浸油后的含不同质量分数SiO2空心微球绝缘纸的介电常数,wSiO2=5%空心微球的绝缘纸介电常数最低,比未加SiO2空心微球的绝缘纸介电常数低34%。用双层电介质场强公式分析绝缘纸介电常数以及复合绝缘系统中油隙厚度对油、纸中场强分配的影响。设计纸-油-纸复合绝缘系统模型,用COMSOL仿真软件对模型进行计算,得出模型中纸、油中电场为均匀电场,双层电介质场强公式可用于纸-油-纸模型的理论分析。最后,用含不同质量分数SiO2空心微球的绝缘纸组成纸-油-纸复合绝缘系统进行电击穿实验,介电常数越低的绝缘纸组成的纸-油-纸复合绝缘系统击穿电压越高,介电常数最低的wSiO2=5%空心微球的绝缘纸组成的纸-油-纸复合绝缘系统比未加SiO2空心微球的绝缘纸组成的纸-油-纸复合绝缘系统的击穿电压高15.5%。     

Increase of breakdown voltage due to composite insulation in SF6 gas

The breakdown characteristics using a hemispherical tip rod (10 ～ 60 mm) molded with epoxy resin-to-plate gap in SF₆ gas up to 0.20 MPa was studied. The result shows that breakdown characteristics are classified into three regions (A, B and C region) depending on gap length. In the A-region breakdown voltage is lowered compared with bare hemispherical tip rod-to-plate gap. In the B-region breakdown voltage is raised sharply with gap length and in the C-region it saturates. The maximum increase ratio of breakdown voltage in the B and C region are 1.95 times (ac) and 1.68 times (impulse) compared with a bare hemispherical tip rod-to-plate gap characteristic. The ratios depend on the diameter of the spherical tip rod and the thickness of epoxy resin. It is concluded that the increase of breakdown voltage is attributed to the synergism effect of the decrease of maximum electric field strength by epoxy resin and the suppression of field emission. The use of composite insulation reduces the gap length drastically in the gas-insulated switchgear, for instance, C-GIS (Cubicle-type Gas-Insulated Switchgear).     

Water absorption in a glass-mica-epoxy composite - [I: Influence on Electrical Properties]

Water absorption in an epoxy composite used for insulation of stator bars in large generators is investigated in order to study both diffusion kinetics and effects on dielectric properties. Water absorption can be described by the superposition of two Fickian mechanisms, the first occurring within epoxy and the other at interfaces between epoxy and fillers. A large decrease of breakdown strength versus water uptake is observed. It points to the large deleterious effect of water on insulation reliability. Dielectric spectroscopy is performed under various conditions of water impregnation, electric field and temperature. A very large increase of permittivity and losses is recorded in the presence of water, especially at low frequency. At power frequency, dielectric properties do not show a non-linearity when the field is increased up to service values. At very low frequency, a decrease of losses when the field is increased is observed. It is due to the Garton effect. Most of results show that the wet material behaves as a low frequency dispersion system (LFD).     

发电机定子主绝缘老化特征的研究

对环氧云母绝缘电机线棒进行了老化试验,在不同的老化阶段,测试了线棒的介质损耗角正切、电容、电流包流点等非破坏性参数和破坏性参数－剩余击空电压。通过非破坏性参数的变化情况和非破坏性参数与破坏性参数的相关性,揭示了环氧云母绝缘体系电机主绝缘的老化特征。     

内部炭化对复合绝缘子绝缘性能的影响研究

随着复合绝缘子在高压线路中的广泛使用,其绝缘击穿事故也越来越多,其中内部炭化是引起绝缘击穿的重要原因之一。为了了解内部炭化对复合绝缘子绝缘性能的影响,建立了以复合绝缘子为研究对象的静电场有限元模型。基于电场数值分析理论,采用有限元分析法实现了对复合绝缘子电位与电场分布的精确计算,计算结果表明在两端金具与棒芯接触处场强最大。同时,对炭化后复合绝缘子的电压分布的分析计算表明,绝缘子的炭化区域基本丧失绝缘性能,并将加速未炭化部分的老化;高压端前数片绝缘子的电压比正常值高出27．09％,有绝缘击穿的可能;炭化区域绝缘子电压出现畸变,局部放电的可能性大大增加。     

纳米AlN改性对干式变压器环氧树脂绝缘性能的影响

聚合物纳米复合材料因其优良的电气绝缘性能在电介质绝缘领域得到了广泛应用。为了获得性能优良的环氧树脂绝缘材料,将采用硅烷偶联剂进行表面处理后的纳米Al N颗粒加入环氧树脂绝缘材料中,采用溶液共混法制备了Al N质量分数分别为0%、0.5%、1%、3%、5%、7%的Al N/环氧树脂复合材料,研究了不同Al N质量分数对Al N/环氧树脂复合材料绝缘性能的影响。结果表明,树脂基体和Al N填料之间实现了有效的结合,提高了环氧树脂的热稳定性;Al N的加入一定程度上减小了复合材料的体积电阻率,并且增大了复合材料的介质损耗因数,但对复合材料电气绝缘性能的影响较小;当纳米Al N颗粒质量分数为3%时,Al N/环氧树脂复合材料的交流击穿电场强度最大。因此,添加适量纳米Al N颗粒能够提高干式变压器环氧树脂的电气绝缘性能。     

纳米绝缘油交流击穿特性分析

绝缘油填充于各型变压器、电力电容器等充油电力设备中,起绝缘、导热、灭弧等作用,在电力系统中有着广泛地应用。随着输电电压等级的不断提高,对绝缘油提出了更高的要求,因此提高绝缘油性能,对中国特高压发展具有重要意义。由于纳米粒子的尺寸效应,传统的小桥击穿理论可能将不再适用,为改善绝缘油的性能提供了新的途径。笔者研究了纳米绝缘油的制备方法,并对不同质量分数纳米粒子的绝缘油进行了交流击穿电压实验。研究结果表明,适当质量分数的纳米粒子能有效地改善绝缘油的交流击穿特性。应用纳米粒子球形介质极化模型,计算了粒子表面产生的势阱,并指出了纳米粒子改善绝缘油击穿特性和添加纳米粒子过多导致绝缘油的击穿性能降低的原因。     

Insulation properties and degradation mechanism of insulating spacers in gas insulated switchgear (GIS) for repeated/long voltage application

Gas insulated switchgear (GIS) has been increasingly being used in recent years and high reliability and rational insulation design are required. This research provided V-N characteristics (the dielectric breakdown voltage versus number of repetitions characteristics) regarding the internal insulation and creeping insulation of the epoxy spacer, which are the main insulation elements of GIS, in order to help set LIWV (lightning impulse withstand voltage) and SIWV (switching impulse withstand voltage). The insulation strength decreased the most when the lighting impulse voltage was applied to internal insulation of the spacer, however, taking the absolute values into consideration, it turned out that the impact of frequent surges is slight. In the experiment in which alternating current voltage is applied for a long period of time, it was found that there is no decline in the insulation properties even after the voltage is applied for the equivalent of 30 years when the electric field intensity is 12 kVrms/mm or less although the combination with the multiple lightning impulse application may bring about damages to the spacer insulation. The degradation mechanism caused by generation of micro-pits was also understood through simultaneous microscopic observation of the surface and of the interface between the electrode and epoxy