Comprehensive simulation of snow crystal deposition and electric field characteristics of composite sheath improved porcelain cantilever insulator in a wind and snow environment

The installed porcelain insulators on existing railway lines in China are prone to“snow flash”in winter.In order to prevent the occurrence of“snow flash”and improve the reliability of the insulators,a composite-porcelain insulator is designed.A multi-physics coupling simulation model is built based on numerical simulation methods of the electromagnetic field theory and computational fluid dynamics.Taking average electric field intensity on the surface of the insulator as the characteristic parameter of the electric field distortion degree and the snow crystal collision coefficient and distribution coefficient as the characteristic parameter of snow crystal deposition,the characteristics of snow crystal deposition under different wind speeds and wind direction angles and the electric field characteristics under two snow cover types are analyzed.The simulation results show that the average electric field intensity of composite-porcelain insulators is 10.4%and 13.8%,respectively,lower than that of porcelain insulators in vertical and horizontal wind snow covers,which can effectively reduce the degree of electric field distortion.The collision coefficient of snow crystals on the surface of the composite-porcelain insulator sheds is 16.0%higher than that of the porcelain insulator,and the collision coefficient of the trunk and the fittings are lower 20.2%and 11.9%than that of the porcelain insulator.There is almost no change in the distribution coefficient of the insulator sheds.

Performance Evaluation of 800 kV Porcelain Multicone Type Insulators Under Heavy Rain

An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insulators.Ageing process can cause degradation of the cement used in this type of insulator and this fact can affect its dielectric performance under heavy rain.This paper presents results of an investigation based on power frequency high voltage tests performed on 800 kV porcelain multicone type insulators,removed from service after having operated for more than 20 years,as well a non-used one that had been stored on site for long time.The insulators were tested in different arrangements:each section at a time and the two sections assembled in series,as actually used insulator columns.The tests were carried out under artificial rain ranging from 1 mm/min to 5 mm/min.The results have confirmed a reduction of up to 30% in the insulator power frequency flashover voltage under 5 mm/min rain conditions and gave important information to the utility about radial cracks that were observed in many insulators and about the discharge mechanisms along the insulators under rain.

ON MICROSTRUCTURE AND STRENGTH OF ALUMINIUM-TOUGHENED PORCELAIN INSULATOR

In this paper the relatienship between mi-crostructwtie and strength of alnminiiim-totighed porcelain insu-lator has been investigated .the microstructural characteristic of the porcelain insulator has been put forward. The results shoiu that the main factors that lead to the strength decreasement of aluminium toughened porcelain insulator are pore, fracture,' coarse alumina grain, aluminium agglomerate and bearing fer-ric matter. The technological factors have also been analysed and appropriate measures have been taken.

Study on Glass Fiber Dispersion Technology in SiO_2 Aerogel-glass Fiber Composite Insulation Materials

In order to improve the mechanical properties of SiO_2 aerogel-glass fiber composites, effects of different solvents(cyclohexane, n-hexane, ethanol, acetone) and different dispersing modes(planetary ball milling, ultrasonic dispersion and mechanical stirring) and dispersing duration(10-40 min) on the dispersion of chopped alkali-free glass fiber bundles were studied to determine the best dispersion process. On this basis, the materials were batched according to the mass fraction of SiO_2 aerogel powder to chopped alkali free glass fiber bundles of 90:10, and a certain amount of zinc oxide light-screening agent and phenolic resin binder were added. SiO_2 aerogel glass fiber composite specimens were prepared by direct adding chopped alkali free glass fiber bundles and pre-dispersed chopped alkali free glass fiber bundles, respectively. The cold crushing strength and the thermal conductivity at different surface temperatures(300, 400, 500 and 600 ℃, respectively)of the specimens were measured. The results show that:(1) the optimum dispersion process of chopped alkali-free glass fiber bundles is using ethanol as solvent and mechanical stirring for 30 min;(2) pre-dispersion of chopped alkali-free glass fiber bundles has little effect on the thermal conductivity of SiO_2 aerogel-glass fiber composites but can improve the cold crushing strength.

Microwave absorption and thermal properties of coral-like SiC aerogel composites prepared by water glass as a silicon source

As a heat-resistant wave-absorbing material,silicon carbide(SiC)aerogel has become a research hotspot at present.However,the most common silicon sources are organosilanes,which are costly and toxic.In this work,SiC aerogels were successfully prepared by using water glass as the silicon source.Specifically,the microstructure and chemical composition of SiC aerogels were controlled by adjusting the Si to C molar ratio during the sol–gel process,and the effect on SiC aerogel microwave absorption properties was investigated.The SiC aerogels prepared with Si:C molar ratio of 1:1 have an effective electromagnetic wave absorption capacity,with a minimum reflection loss value of-46.30 dB at 12.88 GHz and an effective frequency bandwidth of 4.02 GHz.They also have good physical properties,such as the density of0.0444 g/cm^(3),the thermal conductivity of 0.0621 W/(m·K),and the specific surface area of 1099 m^(2)/g.These lightweight composites with microwave-absorbing properties and low thermal conductivity can be used as thermal protection materials for space shuttles and reusable carriers.

Simulation of Electric Field Distribution along Insulator Surface in Polluted Environments

In recent years,more than 50%of the cities in the inland area of our country have suffered from moderate pollution.It can affect the distribution of electric field along the surface of insulator and the pollution characteristics of its surface area,even endanger the safe operation of transmission lines.This paper takes the XSP-160 porcelain three umbrella insulator under the action of 0–±30 kV DC voltage as the research object,and establishes the physical model of the insulator;uses COMSOL software to simulate the electric field of the insulator.The comparison with the results of the wind tunnel test of North China Electric Power University verifies the rationality of the simulation method.In view of the medium pollution environment which often occurs in the inland area,the force of the polluted particles deposited on the insulator under 110 kV DC voltage was analyzed.The distribution characteristics of the electric field along the surface in the clean and three kinds of pollution environment(light,medium and heavy)were simulated and compared.The results showed that:1)In the moderate pollution environment,the influence of fluid drag force on the movement of polluted particles is greater at the initial stage(0.28–0.33 s);at the late stage(after 0.33 s),the influence of the electric field force begins to increase,and gradually plays a major role in the process of fouling.2)In the three different polluted environments,the potential along the surface of each umbrella skirt of the insulator increases non-linearly with the increasing of the pollution concentration,and there are apparent potential inflection points near b and l.3)The pollution particle concentration has the most obvious influence on the electric field along the low-voltage umbrella skirt,whose potential distortion rate can be up to 220 times in the heavy polluted environment.

Preparation and Properties of TiO2-Coated Hollow Glass Microspheres as Thermal Insulation Materials for Energy-Saving Buildings

A hollow glass microsphere(HGM)/TiO2 composite hollow sphere was successfully prepared via a simple precipitation method.The TiO2 coating layers grew on the surface of the HGMs that range from 20 to 50μm in diameter as nanoparticles with the formation of the SiO Ti bonds.The growth mechanism accounting for the formation of the TiO2 nanolayers was proposed.The morphology,composition,thermal insulation properties,and visible-near infrared(VIS-NIR)refl ectance of the HGMs/TiO2 composite hollow spheres were characterized.The VIS-NIR reflectance of the HGMs/TiO2 composite hollow spheres increased by more than 30%compared to raw HGMs.The thermal conductivity of the particles is 0.058 W/(m K).The result indicates that the VIS-NIR reflectance of the composite hollow spheres is strongly influenced by the coating of TiO2.The composite hollow spheres were used as the main functional filler to prepare the organic-inorganic composite coatings.The glass substrates coated by the organic-inorganic coatings had lower thermal conductivity and higher near infrared reflectivity.Therefore,the HGMs/TiO2 composite hollow spheres can reflect most of the solar energy and effectively keep out the heat as a thermal insulation coating for energy-saving constructions.

Anisotropic Structure of Glass Wool Determined by Air Permeability and Thermal Conductivity Measurements

We want to conclude on the interest of the “crimping” process used to produce the glass wool and to make a comparison for anisotropic factor obtained from structural property (air permeability) as well as thermal property (thermal conductivity and diffusivity). The main structural (densities, porosity, specific surface, air permeability) and the thermal (conductivity, diffusivity, heat capacity) characteristics of this glass wool are presented. Thermal results are determined by using several methods (Hot disc (HD), Heat Flow Meter (HFM) and Guarded Hot Plate).

聚丙烯/玻璃纤维复合泡沫的制备及隔声隔热性能

以二缩三丙二醇二丙烯酸酯(TPGDA)和苯乙烯(St)为单体,过氧化二异丙苯(DCP)为引发剂,玻璃纤维(GF)为填料,通过熔融共混法和模压发泡法制备了聚丙烯(PP)/GF复合泡沫,利用PP分子上熔融接枝形成的TPGDA-St共聚物长链支化结构作为相容剂,促进GF在PP基体中的分散,通过GF与TPGDA-St共聚物长链支化结构的协同作用,有效改善PP熔体和复合泡沫的性能。研究了支化结构相容剂和填料用量对PP熔体强度、热稳定性、结晶性能以及复合泡沫微观形貌、隔热性能、声学性能、力学性能的影响。结果表明,TPGDA-St共聚物长链支化结构相容剂能够有效促进GF在PP基体中的分散,强化界面相互作用,形成较为完善的填料网络,显著提升了PP的熔体强度、发泡性能和结晶性能。当GF用量为10份时,PP/GF复合泡沫的泡孔均匀、形状规则、压缩性能良好,具备优异的隔声性能和隔热性能,平均声音传输损耗达到59.7 dB,相较于纯PP泡沫提高了84.8%,导热系数低至0.055 W/(m·K),相较于纯PP泡沫降低了65.6%。

35kV输电线路玻璃绝缘子串中残锤的危害分析

针对35 kV输电线路玻璃绝缘子零值自爆后的残锤,分析残锤的外绝缘、内绝缘特性,并结合两个实例分析在大风大雨作用下35 kV输电线路玻璃绝缘子串中残锤的危害,还针对残锤的危害提出了反措。结果表明:雨水可通过残锤的外绝缘渗浸内绝缘;运行中若未能及时发现和更换残锤,大风大雨将有可能引发存在残锤的35 kV输电线路玻璃绝缘子串发生单相接地闪络故障。其中,在残锤的内绝缘没有被雨水渗浸前,其内绝缘水平高于外绝缘水平,闪络电弧从残锤的外绝缘直接拉弧导通,将有可能导致单相接地闪络故障延时跳闸的35 kV输电线路发生烧断导线故障;在残锤的内绝缘被雨水渗浸后,其内绝缘水平低于外绝缘水平,闪络电弧从被雨水渗浸的残锤内绝缘导通,将有可能发生35 kV输电线路掉串故障。

(Ag,Cu)/TiO_(2)汽车玻璃隔热膜的制备与表征

利用磁控溅射技术制备由金属(Ag,Cu)膜、介质层TiO_(2)膜组成的双层汽车玻璃隔热膜样品。利用单因素分析法考察了溅射时间、溅射功率和Ar溅射流量三个因素对(Ag,Cu)/TiO_(2)汽车玻璃隔热膜透光隔热性能的影响。实验结果表明,在在本底真空度3×10^(-3) Pa,溅射气压2.1 Pa条件下,靶基距均为70 mm时,金属(Ag,Cu)膜溅射时间18 s,溅射功率80 W,Ar溅射流量20 sccm;介质层TiO_(2)膜溅射时间50 min,溅射功率115 W,溅射流量25 sccm时,(Ag,Cu)/TiO_(2)汽车玻璃隔热膜的透光隔热性能最佳。

薄型中空玻璃与发展路径和方向

减薄中空玻璃材料及中空玻璃整体厚度均属于薄型中空玻璃的范畴。薄型中空玻璃可实现节材、节能和节碳多重效益。本文简析了薄型中空玻璃主要种类、制作、成本状况和发展趋势。中置薄玻璃中空玻璃具有产业化基础和成本优势,转型发展具有广阔前景。中置膜材料中空玻璃和真空玻璃复合中空玻璃薄型化程度高,具有良好的适应性发展趋势。气凝胶中空玻璃作为未来发展方向,在采光为目的的围护结构中有应用优势。

影像变形的中空玻璃厚度测量与分析

选取某玻璃幕墙项目同一区域内已有影像变形的不同分格尺寸的中空玻璃,测量了中空玻璃空气层厚度和中空玻璃外片平面外凹陷,并对中空玻璃外片凹陷变形进行等效荷载作用校核分析,为影像变形的中空玻璃整改和安全使用提供了数据支持。

一起35 kV线路两基相邻直线杆玻璃绝缘子串的多点故障分析

针对一起35 kV线路两基相邻直线杆玻璃绝缘子串的残锤、雨闪、电弧风偏及断线等的多点故障,笔者分析了故障原因,并提出改进措施。结果表明:该线路19号杆仅有2片绝缘子、1个残锤的A相2片串发生持续间歇雨闪,扣除残锤后绝缘子的每串最少片数少于规范要求值、单相雨闪故障延时跳闸等是引发该起故障的主要原因;35 kV线路采用4片玻璃绝缘子串或改用复合绝缘子,加强绝缘子串的可恢复绝缘、抗污及灭弧性能,可防止发生此类故障。

掺银硫系玻璃光电探测器响应波长特性研究

由于硫系玻璃具有良好的光学性质,在非线性光学等方面研究广泛,但基于硫系玻璃光电探测器的相关研究却很少。本文利用真空共热蒸发技术制备了不同掺银比例的硫系玻璃薄膜作为半导体膜层结构,并设计构建了金属-绝缘体-半导体结构的自供电光电探测器,探究了该光电探测器的响应光谱范围。结果表明,该探测器对可见光到近红外区域的光均有响应。针对掺银硫系玻璃光电探测器在635 nm波长激光下,研究了探测器响应电压与激发功率之间的关系。当激光功率小于10 mW时,探测器响应电压与激发功率线性相关;当激光功率大于10 mW时,探测器响应电压逐渐饱和。探测器的上升和衰减时间分别为3.932 s和1.522 s。本研究为硫系玻璃材料在自供电光电探测器领域的应用提供了证明。

多种布设方式下交流220 kV线路瓷绝缘子劣化判别的仿真与实测研究

为提高线路瓷质绝缘子劣化带电检测的准确性,本文研究了布设方式和劣化程度对高压交流绝缘子串电压分布特征的影响。首先,建立交流220 kV瓷绝缘子串在不同布设方式下单电压分布的有限元仿真计算模型,并仿真分析绝缘子串电压分布的特征。然后,结合实际测量得到的山东省交流220 kV输电线路绝缘子串电压分布,验证仿真计算结果与实测结果的一致性。结果表明:输电电路杆塔塔型、绝缘子串片数及布置方式、劣化绝缘子位置及劣化程度等因素对绝缘子串电压分布特征及劣化判别有较大影响,其中不同塔型最大分布电压差可达到35%。不同布置方式最大分布电压差可达到18%,通过分布电压下降比例可判断不同位置绝缘子劣化情况。

纳米填料改性环氧树脂建筑保温材料的制备及性能研究

环氧树脂基混凝土作为一种绿色环保的建筑材料,在道路修补和保温建筑中应用广泛。以环氧树脂E44为原料,二甲苯为稀释剂,纳米玻璃纤维为填料,制备了复合环氧树脂基混凝土,研究了不同纳米玻璃纤维长度对混凝土微观形貌、力学性能和保温性能的影响。结果表明,纳米玻璃纤维的掺杂发挥了“晶种”作用,促进了水化反应的进行,提高了环氧树脂基混凝土的密实度。纳米玻璃纤维长度的适当增加提高了混凝土与纤维的结合强度,当纳米玻璃纤维长度为8 mm时,混凝土的形貌最佳。随着纳米玻璃纤维长度的增加,混凝土的抗压强度和抗折强度先增大后降低。养护28 d,当纳米玻璃纤维长度为8 mm时,混凝土的抗压强度和抗折强度均达到最大值,分别为21.93和4.59 MPa。纳米玻璃纤维的掺杂改善了混凝土的孔结构,降低了导热系数,提高了保温性能,当纳米玻璃纤维长度为8 mm时,混凝土导热系数最低为0.147 W/(m·K),保温性能最佳。

有机硅/改性空心玻璃微珠复合材料的制备与性能研究

以缩合型有机硅为有机树脂基体,以改性空心玻璃微珠为无机填料,基于物理复合法制备出不同空心玻璃微珠含量的有机硅/改性空心玻璃微珠复合隔热材料。系统性研究其隔热机理、隔热性能、力学性能和热稳定性能,实现对复合隔热材料孔隙率和隔热性能的精准调控。研究结果表明,所制得的复合隔热材料的压缩强度最大值达到13.28 MPa,是纯有机硅材料的1.49倍,热导率最低为0.113 W/(m·K),比纯有机硅材料减小了37.91%。

空心玻璃微珠在涂料中的应用与研究进展

简述了空心玻璃微珠的表面改性方法以及在涂料中的应用情况,分类总结了其在隔热涂料、防火涂料、吸波涂料和防腐涂料中的最新研究进展,并对未来空心玻璃微珠在涂料中的应用方向拓展进行了展望。