低温高强度复合材料绝缘子的研制和性能测试

在EAST全超导核聚变实验装置中,绝缘子担负着超导磁体冷却回路和带电回路之间的绝缘重任,是保证超导磁体稳定运行的关键部件,EAST装置进行放电实验时绝缘子必须承受4.2K低温、高氦气压(5MPa)和高电压环境的多重考验。文中介绍了一种使用环氧树脂和玻璃纤维复合材料制作的高强度绝缘子的研制工艺,并对该绝缘子在室温和低温下的机械性能测试、冷热循环测试、耐氦气压测试和电绝缘性能测试进行了详细的介绍,一系列测试结果表明,该类型绝缘子能满足EAST复杂条件下的绝缘性能要求。     

高强度氦气密复合材料绝缘子的性能研究

用于超导磁体冷却回路和电回路绝缘的绝缘子是EAST超导托卡马克装置中一个关键部件,在装置实际运行过程中它必须经受在一定的弯矩和拉力的动态情况下高电压和高内气压的考验。该文主要利用有限元程序对绝缘子力学性能、热学性能和电性能进行了分析与计算,并根据低温实验对绝缘子性能进行了进一步的研究。     

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用有限元法对ITER装置磁体系统的高性能氦气密复合材料绝缘子的结构设计进行电场分析和力学性能分析。分析结果表明,绝缘子能够承受耐电压56kV、耐气压4MPa、耐拉力2000N、耐弯矩1000Nm、耐扭矩100Nm的技术参数要求;同时热应力分析结果表明,与外力作用的影响相比,热应力是影响绝缘子性能的关键因素;绝缘子在拉力、弯矩和扭矩受力下发生变形的是金属部分,外力对绝缘部分的影响不大。     

一种表面具有纳米孔穴的聚合物绝缘子

绝缘体表面结构和微观形貌对提高器件真空闪络特性有重要影响。首次提出了表面具有均匀分布纳米级空穴聚合物绝缘子的化学制备方法。通过本体聚合制备纳米级二氧化硅颗粒均匀分布的交联聚苯乙烯复合材料,机械加工成聚合物绝缘子后,采用氢氟酸化学腐蚀的方法将绝缘子表面氧化物颗粒去除。采用透射电子显微镜、表面电阻率和短脉冲高压测试平台分别对处理前后绝缘子的表面形貌和绝缘等性能进行了表征,结果表明:处理后的交联聚苯乙烯复合材料绝缘子的表面形成了20~50 nm直径的空穴,空穴的大小和数量分布分别由二氧化硅颗粒的粒径和加入量控制。这种具有特殊表面结构的新型绝缘子的沿面闪络电压较纯交联聚苯乙烯绝缘子提高了15%~20%,并保持了较好的力学及加工性能。研究方法和实验结果对聚合物绝缘子的表面结构设计及高性能绝缘子的研制提供了一种新的途径。     

亚微秒脉冲下高梯度绝缘子的沿面闪络特性

介绍了一种由聚酰亚胺和不锈钢叠加而成的高梯度绝缘子的实验研究工作。该绝缘子样品的直径60 mm,厚度8 mm,在脉冲宽度120 ns(FWHM)的电压脉冲加载下最高获得了接近13 MV/m的绝缘强度。研究了测试方法以及绝缘层厚度与金属层厚度的比例对高梯度绝缘子绝缘强度的影响,并与相同尺寸的普通材料绝缘子的绝缘强度进行了对比。结果表明,高梯度绝缘子的绝缘强度明显高于仅由聚酰亚胺构成的普通绝缘子。     

ITER轴向绝缘子性能测试研究

对ITER高性能氦气密复合材料轴向绝缘子的性能作了全面的试验测试研究分析,并简单的介绍了一下绝缘子的结构和工艺设计。试验测试结果表明:绝缘子能够承受室温到液氮温度50次冷热循环冲击,耐电压等级56kV、耐气压4MPa、耐拉压2000N、耐弯矩100Nm、耐扭矩100Nm的参数要求。绝缘子在电绝缘性能、机械性能、热冲击性能和气密性方面都能满足ITER磁体系统的技术要求。     

高梯度绝缘子的实验研究与性能分析

为解决脉冲功率系统中绝缘部件的真空沿面闪络问题,开发了基于二次电子崩理论的层叠式高梯度绝缘材料。利用全金属超高真空分析系统,对高梯度绝缘子的真空出气特性进行检测;利用四极质谱仪,对高梯度绝缘子真空出气的气体成分进行分析。利用阻抗分析仪测试不同结构绝缘材料的高频介电性能。基于纳秒脉冲真空实验平台,对高梯度绝缘子的真空沿面闪络性能进行测试。研究结果表明:高梯度绝缘子具有良好的高频介电性能,其拐点频率高达200 MHz;锻炼后高梯度绝缘子的闪络场强可达190 kV/cm,其闪络性能和高梯度绝缘结构中绝缘层的材料及绝缘层与金属层的比例直接相关。     

EAST超导托卡马克装置主机支撑结构极低温条件下应力应变分析

报道了国家"九五"重大科学工程EAST超导托卡马克核聚变实验装置中心液氦冷却冷质部件的钢/高分子复合材料支撑装置在模拟冷却收缩条件下的应力应变分析结果。单个支撑结构由高分子复合材料桶状结构固定在垂直薄板板簧结构上部组成。实验表明该支撑装置在顶部水平负荷作用下发生S型扭曲,而不是简单的悬臂梁式形变。支撑部件整体在试验范围内,在常温、低温条件下均对外加顶部水平推力呈线弹性形变。但在低温下,环氧树脂部件与不锈钢板簧结合部的应变,随外力呈非线性弹性形变,这与室温下的线性变化成鲜明对照。低温下整个部件刚性增加,与常温比较,同等水平位移需要的外力增加,但是环氧树脂部件上的应力反而较常温下显著减小;不锈钢板簧底部上部与环氧部件结合部应力则显著增加。     

环氧树脂基真空绝缘材料的制备和性能测试

 介绍了一种用于脉冲功率装置真空绝缘子的环氧树脂基复合材料的研制机理、制备过程和典型性能。初步测试结果表明，添加一定量的水合氧化铝颗粒可以使环氧树脂材料的表面电阻率由5×10¹⁶ Ω降低为6×10¹¹ Ω，这一特性有利于释放由于沿面闪络等原因沉积在真空绝缘子表面的电荷，从而使材料在脉冲电压下的沿面闪络电压有所提高，实验得到在上升沿400 ns的脉冲电压作用下， 沿面闪络电压可从17 kV 提高到 28 kV。     

EAST外杜瓦协同仿真技术的研究

为验证EAST(Experimental and Advanced Superconducting Tokamak)外杜瓦工程设计的可靠性,借助三维设计软件CATIA和有限元分析软件ANSYS,基于协同仿真技术对其进行了研究,结果与EAST运行过程中外杜瓦的实验数据较好的吻合,进行的研究为同类装置外杜瓦的研发提供了有益的参考。     

弧形核磁共振传感器设计及其在复合绝缘子老化状态检测中的应用

硅橡胶复合绝缘子具有憎水性、强度高和重量轻等优势,被广泛应用于电力系统,然而,目前尚没有准确有效的方法来检测硅橡胶复合绝缘子的老化状态.许多学者对复合绝缘子伞裙的老化状态开展了相关研究,但目前尚未有对复合绝缘子芯棒护套老化状态的研究报道.针对这一问题,该文设计了一种能够测量弧形表面样品的核磁共振(NMR)传感器,并应用于芯棒护套老化状态的检测.首先,对产生主磁场(B_0)的磁体结构进行了设计及优化,使得主磁场的分布具有和芯棒护套一样的曲率.其次,设计并优化了一种可弯曲的螺线线圈作为射频线圈.最后,用该传感器测量了3种在220 k V输电线路上挂网运行了不同年限的复合绝缘子的芯棒护套.采用CPMG脉冲序列激励样品,并得到横向弛豫衰减曲线,然后对横向弛豫衰减曲线做拉普拉斯逆变换获得横向弛豫时间(T_2)谱.T_2谱显示,随着运行年限的增长,复合绝缘子芯棒护套的T_2会减小.因此,从T_2谱中提取的T_(2,long mean)可以作为一个衡量复合绝缘子芯棒护套老化状态的参数.     

纳米碳化硅/硅橡胶复合物非线性电导特性研究

将纳米碳化硅填加到硅橡胶中,可以获得具有非线性电导特性的纳米碳化硅/硅橡胶复合物. 本文研究了质量分数分别为5 wt%,15 wt%,30 wt%,45 wt%的纳米碳化硅/硅橡胶复合物的非线性电导特性,建立了电导率与场强的函数关系,分析了复合物的非线性电导机理,并测试了复合物的介电谱特性和击穿特性. 为了探讨非线性碳化硅/硅橡胶复合物应用于电缆终端和复合绝缘子以均匀其电场分布的可能性,应用COMSOL Multiphysics软件,对电缆终端和复合绝缘子中的电场分布进行了仿真分析. 仿真结果表明,将纳米碳化硅/硅橡胶复合物应用于电缆终端应力锥的绝缘部分,以及应用于复合绝缘子的端部,可以有效地降低其最大场强. 关键词： 纳米碳化硅/硅橡胶复合物 非线性电导特性 电场仿真     

Material Studies in a High Energy Spark Gap

The chemical interactions and physical processes occurring in a high energy spark gap with different combinations of gases, electrodes, and insulators were studied. The electrodes studied were graphite and a tungsten-copper composite; the insulators were Lexan and Blue Nylon; and the gases were N2 and SF6. The gas composition was monitored with a mass spectrometer. Spectroscopic techniques were used to observe the arc channel. The electrode surfaces were studied with several surface analysis techniques, including scanning electron microscopy, electron spectroscopy for chemical analysis, Auger electron spectroscopy, and X-ray fluorescence. The breakdown voltage distribution was examined for different material combinations. The plasma chemistry processes involving the gas, electrode, and insulator materials were found to affect the voltage self-breakdown distribution. The detailed surface analysis gave information about the nature of the chemical processes. The presence of Blue Nylon seemed to have a more adverse effect than Lexan and graphite seemed to have a narrower voltage distribution than the tungsten-copper composite.     

Spin-orbital entanglement and violation of the Goodenough-Kanamori rules

We point out that large composite spin-orbital fluctuations in Mott insulators with t(2g) orbital degeneracy are a manifestation of quantum entanglement of spin and orbital variables. This results in a dynamical nature of the spin superexchange interactions, which fluctuate over positive and negative values, and leads to an apparent violation of the Goodenough-Kanamori rules.     

The insulating state of matter: a geometrical theory

In 1964 Kohn published the milestone paper “Theory of the insulating state”, according to which insulators and metals differ in their ground state. Even before the system is excited by any probe, a different organization of the electrons is present in the ground state and this is the key feature discriminating between insulators and metals. However, the theory of the insulating state remained somewhat incomplete until the late 1990s; this review addresses the recent developments. The many-body ground wavefunction of any insulator is characterized by means of geometrical concepts (Berry phase, connection, curvature, Chern number, quantum metric). Among them, it is the quantum metric which sharply characterizes the insulating state of matter. The theory deals on a common ground with several kinds of insulators: band insulators, Mott insulators, Anderson insulators, quantum Hall insulators, Chern and topological insulators.     

表面喷砂对有机玻璃沿面闪络性能影响

绝缘子表面粗糙处理是提升其沿面闪络性能的重要途径,表面粗糙化处理方式不当,极易带来表面结构不均匀,难以获得稳定耐压性能的绝缘材料。为提升绝缘子表面粗糙处理的均匀性,本文利用表面喷砂技术对圆柱形有机玻璃(PMMA)绝缘子进行了粗糙化处理研究,以球形二氧化硅(SiO2)颗粒为工作介质,研究了不同喷砂粒径、氢氟酸后处理等因素对绝缘材料表面形貌和组分的影响,并利用短脉冲高压测试平台对喷砂处理前后有机玻璃绝缘子样品进行了真空沿面闪络性能测试。研究结果表明,喷砂处理在有机玻璃表面形成了较为均匀的凹坑,HF酸能够有效去除表面残留的SiO2颗粒,具有表面喷砂粗糙结构的绝缘子沿面闪络电压得到了稳定提升,相较于未处理的绝缘子闪络电压提升了约80%。     

Study of dielectric properties of composite insulators for use in medium voltage overhead lines

The dielectric properties of composite insulator materials based on silicone are studied as a function of ageing factors (temperature, UV). Our study includes composite insulators used in the Tunisian Electricity and Gas Company STEG networks (medium voltage overhead lines). Macroscopic characterization using conventional normalized test was performed at the Center of Measurement Tests of El Omrane (Tunis). In the other hand, samples taken from treated insulator are investigated by dielectric spectroscopy technique. The measurement was carried out according to the same ageing factors. So the correlation between the results of standardized tests and those obtained by laboratory characterization is possible. The results of our measurements show the existence of significant dielectric losses in the case of samples that have been aged under temperature and UV radiation. We attribute these losses to the rate of added filler during material elaboration. The dielectric losses increase respectively with time and ageing factors. This increase is remarkable at the vicinity of industrial frequencies.     

Effect of dipole ordering on the electrical properties of the interface between two organic insulators

The “polar catastrophe” hypothesis on the mechanism of the formation of a two-dimensional conducting channel at the interface between two insulators is investigated experimentally. In particular, the influence of the concentration of dipolar groups at one of the surfaces on the electrical conductivity along the interface between two organic polymer insulators is studied. Poly(diphenylene phthalide) with phthalide side groups, possessing a relatively large dipole moment, is used as the polymer. The concentration of dipoles at the surface is varied by adding a low-molecular compound to the material. It is found that the concentration of dipolar groups has a considerable effect on the electrical conductivity along the polymer/polymer interface. A decrease in the conductivity of the interface at high concentrations of the low-molecular additive is explained on the basis of atomic-force microscopy data by the features of the supramolecular structure of the composite and the increasing imperfection of the interface.     

Topological crystalline insulators

The recent discovery of topological insulators has revived interest in the band topology of insulators. In this Letter, we extend the topological classification of band structures to include certain crystal point group symmetry. We find a class of three-dimensional "topological crystalline insulators" which have metallic surface states with quadratic band degeneracy on high symmetry crystal surfaces. These topological crystalline insulators are the counterpart of topological insulators in materials without spin-orbit coupling. Their band structures are characterized by new topological invariants. We hope this work will enlarge the family of topological phases in band insulators and stimulate the search for them in real materials.     

The recognition and localization of insulators adopting SURF and IFS based on correlation coefficient

The recognition and localization of insulators is a crucial process of insulators’ failure detection. Aiming to identify insulators in test aerial image under the complicated background with no template and segmentation, a novel method of the recognition and localization of insulators based on SURF (Speeded Up Robust Features) and IFS (Intuitionistic Fuzzy Set) based on correlation coefficient is proposed as following: SURF is used to extract a set of feature points of the test aerial image. Then use IFS based on correlation coefficient to partition points into k classes. Find all the connected regions for each class, and calculate minimum circumscribed rectangle and shape characteristic value for each region to identify insulators, and localize them by rectangular boxes. Thus we can detect all the insulators from test aerial image correctly. Experimental results show that the proposed approach can obtain high precision in the recognition and localization of insulators.