高温超导电缆及其低温绝缘研究现状

概述了世界上高温超导电缆的研究历史和现状,介绍了高温超导电缆本体的基本结构及绝缘要求,分析了高温超导电缆主绝缘的结构及存在的问题。针对高温超导电缆中使用的液氮和几种低温固体绝缘材料,分别介绍了其在低温环境下介电性能的相关研究进展。总结发现：液氮的击穿场强受到气泡和电极材料的影响;液氮下绝缘材料的直流击穿场强高于交流击穿场强;聚酰亚胺在液氮下的交直流击穿场强高于聚丙烯层压纸;低温会抑制环氧树脂中电树枝的生长。     

低温温度梯度下环氧玻璃纤维材料表面电荷积聚行为及其对沿面闪络特性的影响

超导能源管道终端由于其特殊的运行环境,终端用绝缘材料在承受高电场的同时,也承受着近百摄氏度的低温温度梯度。为此基于超导电缆终端常用绝缘材料——环氧玻璃纤维材料,研究了低温温度梯度下绝缘材料表面电荷积聚特性及其对沿面闪络特性的影响机制。首先测量了环氧玻璃纤维材料在不同温度以及不同温度梯度下的沿面闪络特性;随后利用仿真软件建立了绝缘材料气-固界面的电荷迁移模型,分析了不同温度以及不同温度梯度对材料表面电荷积聚特性和表面电场分布特性的影响;最后结合试验结果与仿真结果,提出了低温温度梯度对绝缘材料沿面闪络的影响机制。试验结果表明：当温差ΔT=100K时,绝缘材料表面的局部放电起始电压与闪络强度分别为无温度梯度时的74.0%和75.9%。而仿真结果显示,低温温度梯度下绝缘材料表面电荷积聚现象明显,表面最高电场强度可达到不存在温度梯度时的10倍左右。因此,温度梯度下材料表面电荷积聚以及电场的畸变被认为是造成绝缘材料沿面绝缘强度下降的重要原因。该研究有助于理解低温温度梯度下材料表面电荷积聚特性及其对电场分布和闪络电压的影响机制,对低温下绝缘材料的绝缘特性研究以及绝缘优化设计具有重要意义。     

热老化对交联聚乙烯电缆绝缘理化结构的影响

按照XLPE电缆热老化过程中绝缘材料理化结构的变化规律,对不同老化程度的电缆绝缘材料的热裂解活化能、结晶形态、分子结构进行分析。结果表明:不同温度热老化过程中羰基指数均随着老化时间的增加而增大;低温热老化有利于XLPE结晶形态的完善,XLPE活化能有所升高,高温热老化对XLPE结晶形态有显著的破坏作用,XLPE活化能成指数规律下降。电缆绝缘材料在热老化热裂解的同时也发生后交联,低温热老化电缆绝缘材料后交联作用占主导地位,而高温热老化电缆绝缘材料热裂解为主要因素。     

超导直流电缆低温绝缘材料的研究进展

随着柔性直流输电技术的发展,高温超导(HTS)直流电缆研究越来越受到各界重视。与超导交流电缆相比,低温绝缘结构HTS直流电缆损耗更低、传输容量更大,是HTS直流电缆的重要发展方向。本文在查阅国内外大量文献资料的基础上,结合绝缘介质在直流电场下暂态和稳态时的电场分布特点,综合考虑低温绝缘材料力学性能、绝缘特性、成本等因素,综述了HTS直流电缆低温绝缘材料的研究进展、存在的问题和发展趋势。     

高温高气压下XLPE电缆电树枝生长规律及局放特性

交联聚乙烯(XLPE)绝缘材料电热老化产生的气体会在电缆绝缘层产生局部高气压,为了研究不同温度下气压对电缆电树枝发展特性的影响,以XLPE短电缆为样品搭建试验系统,研究了不同温度下气压作用在绝缘层内壁时电缆电树枝的生长规律及其局部放电特性。分析实验结果可知:低温下XLPE处于玻璃态,局放初期材料保持了良好的机械性能,气压的升高对局放引发和生长初期无影响。局放后期,剧增的局部放电使插针区域软化,在气压作用下产生形变,电树枝沿应力集中区迅猛发展;高温下XLPE处于高弹态,自由体积分数增加,气压越高绝缘材料受到的轴向拉力越大,材料电气性能下降越明显,电树枝越易引发。高温高气压下XLPE电缆的绝缘性能下降明显,电缆稳定运行受到严重威胁。     

电缆开裂原因分析

岭澳核电站主控室照明用电缆（核级K3类），运行不到3年，伸入灯管段的电缆芯线绝缘发生变色脆化开裂现象，而其它低压动力电缆未发现有该异常现象。为了验证现场所用类似电缆的整体可靠性，项目组对4种不同电缆的样品进行了性能测试，并对该电缆芯线绝缘的开裂机理进行了分析。分析认为：在光、热、氧、应力的共同作用下，该照明电缆芯线绝缘发生了变色及脆性开裂，绝缘材料的耐光性较差。建议的纠正行动是：一方面，目前应改变主控室照明电缆在灯光侧的接线方式，芯线不能直接裸露在灯光下；另一方面，在电缆有可能受到灯光照射或类似环境时，电缆护套及绝缘材料设计应有耐光性的要求。     

直流电缆试验标准体系分析及±535 kV电缆系统试验中关键问题

直流电缆系统开发过程中材料选型、制造工艺、验证直流电缆系统可靠性的方法等成为国内外关注的焦点问题。在过去10里,高压直流电缆系统的试验方法体系得到全面的发展,已建立的规范或标准包括CIGRE TB 496、GB/T 31489.1和IEC 62895等,均对直流电缆系统在开发过程中的试验鉴定方法做出了明确要求。依据国产化±535kV直流电缆研发试验经验,综述上述3个标准要求制定的背景,着重梳理对比GB/T 31489.1和IEC 62895在条款规定中的差异性,总结研发过程中绝缘材料电性能评价方法和直流电缆系统在低温环境下电性能型式试验经验,提出在标准化工作中的建议,可作为试验方案制定的参考。     

复合绝缘材料的液氮温度击穿特性

为解决大容量的输电,以及短距离例如水电站的出线等问题,采用工作在液氮温度的有阻电缆是解决问题的方法之一。由于工作在低温下的绝缘材料要承受电缆各部位不同材料的收缩率造成的机械应力以及高电场的双重作用,工作条件苛刻,所以考虑采用复合材料满足低温绝缘的要求。     

超导电缆绝缘及其材料性能

在26篇文献的基础上综述了超导电缆本体及终端结构和绝缘特点。分析了不同绝缘结构的特点及主要绝缘材料常温和低温条件下的电气及机械性能。固体绝缘在低温下具有更优异的电气性能,但机械性能下降。EPR绝缘在液氮低温下的机械性能优于同条件下PE及XLPE的性能。液氮浸渍复合绝缘结构较易产生局部放电,纤维基绝缘材料的耐局部放电性能比薄膜材料差。提高液氮浸渍复合绝缘中液氮的压力可提高绝缘层局部放电的起始放电电压。     

电缆热老化寿命的预测

利用热分析技术,对电缆绝缘材料的热老化寿命进行研究,得到电缆绝缘材料的热老化寿命的计算公式。在不同载流量下,对电缆绝缘材料热老化寿命进行了比较,给出了电缆热老化寿命与载流量的函数关系,为电流致热型线缆火灾的预防提供了基础数据。     

IGBT器件封装用有机硅凝胶宽频介电特性与温度影响

有机硅凝胶材料作为IGBT器件封装用绝缘材料,在器件的运行工况下,器件承受着重复性导通关断电压,对应频谱宽,且器件损耗将引起温度升高。为了能够准确分析器件内部电场特性,运用频域介电谱技术对有机硅凝胶在宽频、宽温度范围内的介电特性进行研究,利用叉指电极,实现对有机硅凝胶在不同温度下的宽频介电谱测试。采用Cole-Cole介电模型对实验数据进行拟合,并分析温度对Cole-Cole模型特征参量的影响规律。研究结果表明：频率和温度对有机硅凝胶的介电特性均有较大影响,在低频高温下,有机硅凝胶材料相对复介电常数的实部、虚部都显著增加。在所提取的Cole-Cole介电模型的特征参量中,直流电导率σ₀及特征参量Δε₁与温度之间的关系都满足Arrhenius方程,热活化能分别为0.233 eV与0.691 eV;弛豫时间τ₁和τ₂随温度的变化规律有所不同,但在高温时都明显增加。对半导体器件封装用有机硅凝胶材料介电特性的认知可以为器件内部电场分析和绝缘设计提供基础数据支撑。     

IGBT器件封装用有机硅凝胶宽频介电特性与温度影响

有机硅凝胶材料作为IGBT器件封装用绝缘材料,在器件的运行工况下,器件承受着重复性导通关断电压,对应频谱宽,且器件损耗将引起温度升高。为了能够准确分析器件内部电场特性,运用频域介电谱技术对有机硅凝胶在宽频、宽温度范围内的介电特性进行研究,利用叉指电极,实现对有机硅凝胶在不同温度下的宽频介电谱测试。采用Cole-Cole介电模型对实验数据进行拟合,并分析温度对Cole-Cole模型特征参量的影响规律。研究结果表明：频率和温度对有机硅凝胶的介电特性均有较大影响,在低频高温下,有机硅凝胶材料相对复介电常数的实部、虚部都显著增加。在所提取的Cole-Cole介电模型的特征参量中,直流电导率σ₀及特征参量Δε₁与温度之间的关系都满足Arrhenius方程,热活化能分别为0.233 eV与0.691 eV;弛豫时间τ₁和τ₂随温度的变化规律有所不同,但在高温时都明显增加。对半导体器件封装用有机硅凝胶材料介电特性的认知可以为器件内部电场分析和绝缘设计提供基础数据支撑。     

Chemical synthesis,structural characterization and electrical studies of nanoceria for CMOS applications

Cerium oxide nanoparticles were synthesized using cerium nitrate hexa hydrate and ammonium carbonate as precursors. Structural characterizations were done using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystallite size and lattice strain on the peak broadening of CeO₂ nanoparticles were studied using Williamson-Hall (W-H) analysis. The dielectric properties of nanocrystalline CeO₂ samples with different calcination temperatures, and frequencies have been studied over a temperature range from 303 to 423 K. It is found that the dielectric constant and dielectric loss for all temperatures have high values at low frequencies, which decreases rapidly as frequency is increased and attains a constant value at higher frequencies. The room temperature dielectric constant ε′ obtained for the as prepared CeO₂ nanoparticle sample is 61, which constitutes the highest value ever reported at low frequency. A.C. conductivity, which was derived from dielectric constant and loss tangent data, has a low value at smaller frequencies that increases as the frequency is increased. The dielectric constant and a.c. conductivity values are shifted upwards as the temperature is raised. However, these values are decreased as the annealing temperature is increased. The desired structural properties and high dielectric constant of nanophase CeO₂ make it as a promising material for the high dielectric constant dielectric gate in complementary metal oxide semiconducting (CMOS) devices.     

35 kV干式空心并联电抗器匝间绝缘材料特性分析

深入开展35 kV干式空心并联电抗器匝间绝缘材料特性分析研究,对35 kV干式空心电抗器制造材料选择、工艺改进和运维方式具有重要意义。为此,文中研究了不同热老化程度和吸湿对电抗器匝间绝缘材料聚酯薄膜介电特性的影响。通过研究发现:不同老化温度(110、130℃)下,干燥的聚酯薄膜相对介电常数、介质损耗正切值和电导率在老化后期(120 d)都呈现增大的趋势。在较高老化温度下,样品介质损耗正切值增加更加明显。不同老化温度下,吸湿对相对介电常数的影响结果不同。在不同老化程度下,吸湿后的样品其低频下介质损耗正切值仍然呈现增加的趋势,但在高频下其值有所减小。     

High-field dielectric properties of polypropylene films in high-temperature region

Nonpolar polymers are used widely as electrical insulation materials, and their operating conditions sometimes become high-electric field and high temperature. Under these conditions, the conduction loss is assumed to affect the dielectric properties and to make the ac dissipation factor (tan δ) increase. Therefore the high-field dielectric properties of polymeric materials in the high-temperature region become very important. This paper describes the high-field dielectric properties of polypropylene films measured at 50 and 400 Hz above room temperature with the new electrodes developed by authors. At low temperature, the high-field tan δ is independent of the frequency of the applied field. However, at high-temperature, the high-field tan δ becomes almost inversely proportional to the frequency, namely, the conductivity is independent of the frequency. The theoretical analysis shows that the high-field dielectric loss is governed by two processes: one is the loss which appears only under ac field; and the other is conduction loss which appears also under dc field. The latter loss becomes prominent under high-electric field at high temperature.     

Dielectric loss anomalies of 0.68PMN–0.32PT single crystal and ceramics at cryogenic temperature

The temperature dependence of dielectric constant and loss were investigated for poled and unpoled [001]-oriented 0.68PMN–0.32PT single crystal and ceramics at cryogenic temperature. Two abnormal loss peaks, which are frequency dependent, are presented for all the samples. One of abnormal loss peaks locates in the range from 50 to 80 K and the other was observed in the range from 200 to 300 K. The difference of the abnormal loss between the single crystal and ceramics were compared. It is assumed that the dielectric loss anomalies at cryogenic temperature are related to the change of domain structure and phase structure parameter induced by temperature.     

Breakdown behavior of oil-impregnated polypropylene as dielectricin film capacitors

The dielectric breakdown behavior of thin metalized PP films for use in HV capacitors was studied as function of temperature with and without rape-seed oil as impregnation medium. The impregnating oil penetrates into the amorphous regions of the dielectric. With oil impregnation, the dielectric breakdown strength of the PP film is increased by >25%. A correlation between the breakdown strength and the degree of impregnation was found. With increasing temperature the breakdown strength of PP films decreases. Moreover, the measurements showed abrupt changes of slope in the breakdown strength at defined temperatures. From these results a correlation was established between the dielectric breakdown strength of PP films and temperature induced structure changes. It was shown that the abrupt changes of slope in the breakdown strength occurring at defined temperatures are due to the additives contained in the PP capacitor films used. Finally, guidelines for further development of impregnated PP films as dielectrics for high power capacitor applications are presented     

Microstructure and Properties of Solution Deposited, Nb-Doped PZT Thin Films

Nb doped PZT films with Nb concentrations of 0, 5, 8 and 12 mol% are being processed via chemical solution deposition on platinized Silicon substrates. An original processing route including seed layer and additional PbO coating is presented whereby homogeneous, pyrochlore free microstructures with 111/100 texture are obtained. The temperature dependence of the dielectric constant shows diffuse peaks corresponding to the paraelectric to ferroelectric transition. The transition temperature is found to decrease from 325°C to 220°C with increasing Nb content. Nb is however found to lead to a substantial increase in the dielectric constant in comparison to non-doped PZT. The dependence of the dielectric constant on DC bias field is also reported. Strong asymmetries towards positive values both in the values of the dielectric constant and coercive fields are obtained at room temperature, and become replenished at 100°C. This is interpreted in terms of space charge effects on the pinning of domain walls. Furthermore, the loss tangent shows a relaxation peak which shifts to higher frequencies with increasing Nb content, and suggests that Nb-doping affects the dielectric properties of the interfacial layer. Finally, Nb addition is found to lead to slant hysteresis loops with lower remnant polarization and coercive field.     

Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 from co-precipitation method

High dielectric Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were firstly prepared by co-precipitation method at low temperature. X-ray diffraction results revealed that pure phase of NBCTO was achieved by calcination at 950 °C for 2 h. Thermo-gravimetric analysis on a dried NBCTO precursor was carried out to study the thermal decomposition process. The microstructure and dielectric properties of NBCTO ceramics sintered at different temperatures were investigated. The results indicate that the sintering temperature has a sensitive influence on the microstructure and dielectric properties. Higher sintering temperature gave rise to increased dielectric constant and dielectric loss of NBCTO samples, and the sample sintered at 975 °C for 8 h exhibits high dielectric constant of 8.3?×?10³ and low dielectric loss of 0.069 at 10 kHz. The dielectric properties were further discussed by the impedance spectroscopy.     

Improved Temperature Stability of Microwave Properties in Tunable Devices Using Substituted Ba 1− x Sr x TiO 3

An improvement in ferroelectric device technology has become possible through optimization of the properties of the ferroelectric materials used to make the devices. The improvements discussed herein impact true time delay line and phase shifter performance by enhancing control over dielectric constant and extending the temperature range of tunability and device operation. Figures of merit were obtained for substituted-Ba 1 m x Sr x TiO 3 materials which have lower, less varying dielectric constant and adequate, less varying tunability at 1 MHz over the mil spec ( m 50 °C to 100 °C) range. For the sample whose figure of merit varies the least, dielectric constant and losses at 20 GHz and room temperature are reported. Dielectric constant and losses at 1 kHz are discussed.