绝缘材料介电谱测量的接触法和非接触法误差分析

理论分析了几何尺寸测量误差和复电容测量误差对接触法和非接触法介电谱测量误差的影响,并对二者的误差进行了比较,然后对电极间隙距离、试样介电常数对介电谱测量误差的影响进行了仿真分析.基于介电谱仪测量得到高温硫化硅橡胶的介电谱,分析了几何尺寸(试样厚度)测量误差对接触法和非接触法测量结果准确性的影响.结果表明:非接触法受几何尺寸和复电容测量准确性的影响比接触法要大,对仪器测量的准确性要求较高,容易产生比接触法更大的误差.非接触法的相对介电常数测量误差随试样相对介电常数的增加先快速增大然后逐渐稳定;试样相对介电常数不大于5时,随着电极间隙距离的增加,相对介电常数的测量误差快速增大.非接触法适用于几何尺寸和介电常数测量准确性足够高的场合.     

高压IGBT封装硅凝胶材料高温和热老化绝缘特性研究

在高压IGBT器件中，新兴的宽禁带半导体芯片逐渐代替了传统的硅基半导体芯片，其高功率密度特性会导致电力电子模块的工作温度急剧上升。硅凝胶作为高压IGBT器件的封装用绝缘材料，其绝缘性能面临高温和热老化的挑战。为了研究高温和热老化对硅凝胶材料热稳定性和绝缘性能的影响，本文基于硅凝胶材料的高温试验与热老化试验，测试了高温和长期热应力作用对硅凝胶材料介电性能、体积电导率和击穿强度的影响，对硅凝胶的高温特性和热老化特性进行分析。结果表明：随着温度的升高，硅凝胶的复介电常数实部降低、介质损耗增加、直流电导率升高、击穿强度降低；随着热老化时间的增加，硅凝胶的复介电常数实部增加、介质损耗先减小后增大、直流电导率先增大后减小、击穿强度降低。     

特高压直流干式套管用环氧及环氧/皱纹纸复合材料介电特性研究

为研究引入皱纹纸对环氧材料介电特性的影响,通过介电谱及热刺激去极化电流(thermally stimulated depolarization current,TSDC)测量技术,对特高压直流干式套管用环氧及环氧/皱纹纸材料复介电常数、TSDC特性进行了测量分析。提出了基于相对介电常数一阶导数的改进差分进化优化算法,该方法能有效分析环氧材料内各介电弛豫过程。试验结果表明:皱纹纸的引入使环氧复合材料复介电常数实部、虚部均变大(高温中频区除外),其高温直流电导率也显著增大。与纯环氧相比,环氧/皱纹纸复合材料α(温度低于175℃时)、β、δ过程的弛豫时间均减小;δ过程弛豫强度减小、β过程弛豫强度显著增大;δ过程活化能减小,δ过程活化能增加;环氧/皱纹纸复合材料中陷阱深度较浅、但陷阱密度显著增加。以上结果,可为干式套管绝缘材料配方评估、工艺改进提供方法及理论指导。     

基于FDS的变压器油浸纸老化程度与水分含量评估方法

搭建了频域介电谱(FDS)技术测试试验平台,测试了不同老化程度和不同水分含量油浸纸样品的复介电常数,并对测试结果进行对比分析。分析结果表明:绝缘纸聚合度的降低使油浸纸样品的复介电常数实部和虚部在低频段增大,而在高频段基本不变;绝缘纸水分含量的增加使油浸纸样品的复介电常数实部在10~2 Hz以下的频域范围内增大,虚部在整个测试频域范围内增大,且虚部曲线随水分含量的增大呈现向右平移趋势。提出利用复介电常数虚部的等效下降幅度作为绝缘纸聚合度映射特征量,以此评估油浸纸的老化状态。拟合出特征频率10~(-4) Hz处复介电常数实部与水分含量的关系式,以此提出一种适用于不同老化程度和油浸纸水分含量的频域介电特征量评估方法。     

油纸绝缘频域介电谱特性与聚合度的关联影响规律研究

为研究绝缘纸聚合度与油纸绝缘频域介电谱特性间的关联影响规律,搭建了油纸绝缘频域介电响应测试平台,测试了新绝缘油、低含酸量绝缘油、高含酸量绝缘油、一定老化程度绝缘油分别与不同聚合度绝缘纸所组成的油纸绝缘的复介电常数以及新绝缘油分别与低含水量、高含水量绝缘纸组成的油纸绝缘的复介电常数,并对测试结果进行了对比分析。分析结果表明:绝缘纸聚合度通过影响水分和酸在油纸间的分布情况而对油纸绝缘复介电常数产生关联性影响。利用频域介电谱法诊断油纸绝缘中水分或小分子酸含量时,应考虑聚合度影响两者在油纸间的分布情况后对油纸绝缘频域介电谱特性产生的关联性影响。     

基于VC++的介质复介电常数变温测量系统软件设计

本文针对介质电参数测量自动化与精确化的需要,综述了高Q谐振腔法测量介质复介电常数的基本方法,设计了一套基于VC 的、可兼容多种矢量网络分析仪与多种形式谐振腔的介质复介电常数变温测量软件系统,并论述了具体的开发设计过程.利用不同的方法测量多组介质片对软件进行测试,测量结果表明,该方法可以提高测量效率和精度,为介质复介电常数测量提供了一种有效的手段.     

水分对变压器油和绝缘纸频域介电谱特性的影响

频域介电谱法作为一种无损的电气诊断技术,非常适用于变压器油纸绝缘状态的现场诊断。考虑到水分对变压器油纸绝缘系统的巨大危害,运用Concept80宽频介电谱测试系统,研究了水分对矿物绝缘油和不同种类油浸绝缘纸介电特性的影响规律,并对比了相同水分质量分数油浸普通绝缘纸、绝缘纸板和热稳定纸的介电性能。研究表明:矿物油-纸绝缘试品的介电性能受水分的影响极大;矿物油的直流电导率随着水分质量分数的增加呈指数规律增大,在10-3～10-1Hz范围内,油浸绝缘纸的复相对介电常数实部随其水分质量分数增加呈线性规律增大。因此,可利用油品介质损耗因数(直流电导率)和油浸绝缘纸复相对介电常数实部对变压器油、油浸绝缘纸的水分质量分数分别进行诊断。     

基于曲线拟合的变电设备快速频域介电谱测试研究

基于介质响应测试技术的频域介电谱(FDS)是一种现场常用的无损分析方法,通过检测材料在频域内介电常数的变化规律,可以得到油纸材料的受潮与劣化情况。受检测信号周期限制,现有的FDS方法在低频部分耗时极长。研究了一种基于曲线拟合的快速频域介电谱测试方法,通过理论计算与试验,研究了正弦电压波形采样参数对曲线拟合优度的影响,并确定了波形采样周期比、波形采样点位置、波形采样是否连续、正弦电压波形幅值等关键波形参数的最优范围。最后搭建了快速FDS测试平台,对绝缘纸板及试验变压器进行测试,并与商用仪器IDAX-300进行比较,测试误差小于1%,但测试速度提高5倍。     

材料εr和μr的带线测量法及误差分析

以带线系统为测试夹具,利用网络分析仪在微波频率下测量材料的复介电常数和复磁导率。分析了影响测试精度的主要误差因素,并建立误差的数学模型。     

温度和频率对XLPE电缆泄漏电流的影响

为了研究温度与频率对XLPE电缆泄漏电流的影响,采用粒料制作了XLPE片状试样,并对XLPE试样的复介电常数、电导率以及介电模量进行了测试,测试的温度和频率范围分别为20~200℃、10-2~105Hz。结果表明:复介电常数的实部随着频率升高快速降低,下降趋势随着温度升高而变缓;交流电导率与频率的关系遵循幂律定律,且其直流电导区域符合Arrhenius法则;介电模量谱很好地表征了介电松弛现象,能观察到被直流电导与电极极化淹没的损耗峰值,且随着温度的升高,损耗峰值向高频方向移动;XLPE绝缘的松弛极化的增强会造成介电常数以及松弛极化损耗的增大,在相同状态下,电缆泄漏电流会随着温度、频率的升高而增加。     

基于最小二乘法的变压器油纸绝缘频域介电谱法的研究

为了分析油纸绝缘系统的介电频谱与微水含量、温度之间的关系,在实验室搭建了频域介电谱法的测试平台。根据油纸绝缘系统的Debye弛豫模型,推导出了复电容实部与虚部的计算公式,并利用最小二乘法对测试数据进行曲线拟合,得到弛豫模型中的参数值,找出参数值的变化规律,并根据其来评估变压器的绝缘状况。结果表明:油纸复合绝缘系统复介电常数的实部和虚部都随温度和微水含量的增大而增大;温度和微水会影响等效模型中的参数,将弛豫参数的变化规律应用于变压器的状态评估有一定的可行性。     

航天器热试验加热电缆绝缘自动测试系统的设计

为实现航天器热试验外热流模拟装置与航天器之间绝缘性能的检测,对加热电缆绝缘自动测试技术进行研究,设计了一套基于PXI的航天器热试验加热电缆绝缘自动测试系统.该系统采用继电器矩阵技术设计了加热电缆输入通道切换装置,基于PXI总线仪器实现了多芯电缆自动扫描以及对地绝缘电阻的测量,并采用VC++ 6.0开发了系统上位软件.测试结果表明,该系统能够在短时间内完成最多8根加热电缆的对地绝缘检测,结果准确、运行可靠,大大提高了加热电缆绝缘电阻测试的自动化水平.     

基于电热加速老化试验的XLPE电缆绝缘性能研究

为了掌握电缆绝缘性能与温度之间的关系,在实验室对运行年限不同的10 kV高压XLPE电缆进行电热加速老化试验,测量不同的载流量下电缆分别在空气和沙土中的温度变化数据。试验测量数据和温升曲线表明,运行中电缆的温度变化与所加载的流量和周围环境介质均有关系,运行年限相同的电缆在空气中的温度变化较在沙土中的要大,运行年限越久的电缆不论在空气中还是在沙土中温升都较快。基于电热加速老化试验方法研究运行年限不同的电缆的温度变化情况,为电缆绝缘性能的判断提供参考依据。     

毫米波段电介质测试系统的建立和应用

本文介绍一个毫米波段利用锯齿波调制的速调管振荡器、隔离器、开式腔、光栅尺、检波器、高灵敏度示波器、采集电路、微机组成的测试系统。它既可测量一般电介质复介电常数，也可以测量高介电常数低损耗电介质的复介电常数。它具有工作稳定可靠、灵敏度高、测量精度高，速度快，并兼有图形及数据处理。本文将给出五种样品的测试数据结果。     

Startup of air-cooled condensers and dry cooling towers at low temperatures of the cooling air

The problems of startup and performance of air-cooled condensers (ACC) and dry cooling towers (DCT) at low cooling air temperatures are considered. Effects of the startup of the ACC at sub-zero temperatures are described. Different options of the ACC heating up are analyzed, and examples of existing technologies are presented (electric heating, heating up with hot air or steam, and internal and external heating). The use of additional heat exchanging sections, steam tracers, in the DCT design is described. The need for high power in cases of electric heating and heating up with hot air is noted. An experimental stand for research and testing of the ACC startup at low temperatures is described. The design of the three-pass ACC unit is given, and its advantages over classical single-pass design at low temperatures are listed. The formation of ice plugs inside the heat exchanging tubes during the start-up of ACC and DCT at low cooling air temperatures is analyzed. Experimental data on the effect of the steam flow rate, steam nozzle distance from the heat-exchange surface, and their orientation in space on the metal temperature were collected, and test results are analyzed. It is noted that the surface temperature at the end of the heat up is almost independent from its initial temperature. Recommendations for the safe start-up of ACCs and DCTs are given. The heating flow necessary to sufficiently heat up heat-exchange surfaces of ACCs and DCTs for the safe startup is estimated. The technology and the process of the heat up of the ACC with the heating steam external supply are described by the example of the startup of the full-scale section of the ACC at sub-zero temperatures of the cooling air, and the advantages of the proposed start-up technology are confirmed.     

Engineered sintering aids for PbO-based electroceramics

Borate- and silicate-based glasses that devitrify on heating to form ferroelectric lead titanate have been developed. Their potential for use as sintering aids in PbO-based electroceramics has been evaluated by studying the densification of PbTiO₃ (PT) with increasing wt.% addition of glass powder. When ≥3 wt.% of a borate-based glass was added, ≥94% theoretical density was achieved at 1,100 °C but for a silicate-based glass system 10 wt.% glass addition was required to achieve the same density. As the wt.% glass content increased the maximum and room temperature permittivity decreased and there was also a decrease in T _c and the c/a ratio. The decrease in T _c is believed to be due to increased clamping from neighbouring grains as the density of the PT increases. The decrease in maximum and room temperature permittivity is related to the presence of secondary phases.     

Application of functionally graded material for solid insulator in gaseous insulation system

Functionally graded materials (FGM) have spatial distribution of a material property in order to achieve efficient stress control. An application of the FGM to a solid insulator (spacer) for a gaseous insulation system, like gas insulated switchgear, is expected to improve electric field (E-field) distribution around the spacer. In this paper, we describe the applicability of the FGM spacer to gas insulated power equipment. In the FGM spacer, we gave spatial distribution of dielectric permittivity to control the E-field distribution inside and outside the spacer. This paper includes following key results for the applications of the FGM. Firstly, E-field simulation results when applying the FGM by a finite element method are presented, in which we show the effective reduction of the maximum field strength by applying the FGM. Next, a fabrication technique of the FGM spacer sample with not only step-by-step but also continuous changes of permittivity is presented by use of centrifugal force. Finally, dielectric breakdown tests using FGM samples which are accurately controlled the spatial distribution of permittivity are carried out under lightning impulse voltage applications. The test result indicates the increase of breakdown voltage (BDV). From these results, we verified the applicability and the fabrication technique of FGM spacer for improvement of the dielectric strength in the gaseous insulation system.     

双复纤维长径比对其吸波性能的影响

采用电加热和化学气相沉淀(CVD)法合成双复纤维材料,研究了双复纤维含量一定的条件下长径比对吸波性能的影响.结果表明,双复纤维长径比的增大导致复磁导率和复介电常数都有所增大,其中复介电常数的实部显著增大,而且双复纤维长径比为15∶1左右时,吸波效果较好,吸收峰为-19.1dB,11.2～1 8GHz范围反射率低于-5d...     

Thick film heater elements and temperature sensors in moderndomestic appliances

This paper describes the use of thick film heating elements in domestic appliances, and comparison is made of performance and cost between thick film and traditional heaters. Thick films are created by screen printing pastes, usually containing glass and metal powders, onto a flat substrate. A brief explanation of thick film technology is given. This technology has been used for many years in the electronics industry to produce circuits containing conductors, resistors and dielectrics. The structure of a thick film resistor makes it ideal for heating applications, and it may be deposited on a number of substrate materials. Experimental data demonstrating that thick films make effective and reliable heating elements and temperature sensors are presented. The combination of a thick film heating element with thick film temperature sensor on an insulated steel substrate is described