基于热稳定性能的主变压器油纸电容式套管介质损耗异常诊断

以一起500 kV主变压器油纸电容式套管介质损耗异常增长的故障诊断为例,介绍了基于热稳定性能的主变压器油纸电容式套管介质损耗异常诊断方法。通过热稳定性能试验,获取套管介质损耗随温度变化的规律;依据套管热稳定性能理论,诊断套管介损异常原因。该方法对于绝缘介质受潮缺陷诊断的有效性得到了验证。     

Dielectric Properties of Niobium and Lanthanum Doped Lead Barium Zirconate Titanate Relaxor Ferroelectrics

The lead barium zirconate titanate (PBZT) relaxor ferroelectrics are ideal for high voltage capacitor applications due to their high dielectric constant, stability under DC bias, and temperature stability. In this study the composition (Pb_0.65Ba_0.35)(Zr_0.70Ti_0.30)O₃ was selected as the base composition. It exhibited typical relaxor characteristics such as frequency dispersion and diffuse phase transition. The dielectric constant is 6000 at room temperature and remains almost constant under electric field as high as 20 kV/cm. To further enhance the dielectric properties, various amounts of niobium oxide and lanthanum oxide dopants were added to the base PBZT to alter the defect structure and hence the dielectric properties. It was found that the dielectric constant of 1% Nb-doped samples was increased by 20–25% while maintaining similar voltage stability. This increase was attributed to the abnormal grain growth in the Nb-doped sample, and the correlation between microstructure and dielectric constant was drawn through a grain size study. The La addition only caused a monotonic decrease of dielectric constant and slightly improved voltage stability.     

氰酸酯改性环氧树脂的研究

采用红外光谱对氰酸酯树脂(CE)改性环氧树脂的共固化反应进行分析,测试了环氧树脂固化物的介电常数(ε)、介质损耗因数(tanδ)和吸湿率,通过TG分析了固化物的热稳定性。结果表明:随着CE含量的增加,环氧树脂固化物的ε、tanδ下降;随着测量频率的增加,固化物的ε下降,tanδ上升。改性环氧树脂的吸水率降低,热稳定性变化较小,介电性能明显提高。     

The effects of chemical structure on the dielectric properties of polyetherimide and nanocomposites

Low dielectric constant polyetherimides have been synthesized by incorporating a bisphenol A dianhydride, BPADA, and 2,7-bis(4-aminophenoxy) naphthalene (BAPN), a phenylene ether diamine. The flexible ether and larger planar naphthalene structure of BAPN led to more spacing between polymer molecules, resulting in less efficient chain packing and an increase in the free volume, thus decreasing the dielectric constant. New PEI/silica hybrid nanocomposites were prepared from this novel polyetherimide via sol-gel process. The dielectric constants were further decreased with the incorporation of silica. These synthesized PEI and nanocomposites have high thermal stability and good mechanical properties.     

NOMEX合成纤维绝缘介质在直流电场中的空间电荷特性

为提升变压器内绝缘水平,延长变压器使用寿命,合成纤维绝缘纸因其优良的介电、机械、热稳定、抗潮等性能而被广泛应用在绝缘介质工程领域。采用电声脉冲（PEA）法测量分析以NOMEX纸为代表的油浸合成纤维绝缘纸在直流电场中的空间电荷注入、积聚、消散时的密度分布特性,并与传统油浸植物纤维素绝缘纸进行对比,结合材料频域介电谱特性研...     

Experimental investigations on insulating liquids for power transformers: Mineral, ester, and silicone oils

In this paper the dielectric strength, Electrostatic Charging Tendency (ECT), ageing stability, gassing tendency, heat transfer efficiency and stray gassing issue of mineral and silicone oils, synthetic and natural esters are analyzed and discussed.     

电容型电气设备介质损耗角的在线监测

在线监测容性设备的介质损耗是判断其绝缘状况的有效手段。作者通过与容性设备末屏串联分压电容的方法提取工频电压信号，采用绝对测量和过零比较法相结合的新方法测量介质损耗角；对影响测量精度的相关问题进行了分析，并提出了解决办法；引入了横向比较法和趋势分析法等绝缘诊断策略。试验结果证明所提出的方法能满足测量的可信度、准确度和稳定度要求，可实现介质损耗角的在线监测。     

同轴线管介质阻挡放电的伏安特性

采用一维流体力学模型对大气压下氦气同轴线管介质阻挡放电动力学特性进行数值模拟研究,获得了保持放电稳定性的方法。通过求解一维电子、离子、亚稳态原子连续性方程、动量方程和电流连续性方程,计算出同轴线管介质阻挡放电的放电电流和气体电压。分析讨论了不同放电模式下同轴线管介质阻挡放电的伏安特性。     

Low loss flexible SrTiO<Subscript>3</Subscript>/POE dielectric composites for microwave application

Flexible, high dielectric constant and low dielectric loss composites for microwave application fabricated with SrTiO₃ (STO) ceramic filler dispersed inside a thermoplastic polyolefin elastomer (POE) polymer matrix have been studied in this paper. The dielectric property and the mechanical property of STO/POE composites filled with different volume fraction of ceramic filler were investigated. The results indicated that with the increase volume fraction of ceramic filler, both the permittivity and the dielectric loss of composites increased. Good frequency stability within a wide range was observed in all the samples. For the composites containing 40 vol% STO, the composites has a tensile strength of 2.75 MPa with an elongation of about 90% at break value. The permittivity and the dielectric loss of the composites were 11.0 and 0.01 in microwave frequency, respectively. A microstrip transmission line on the composites containing 40 vol% STO as a microwave substrate is designed and measured after bending at different angles, meanwhile the transmission coefficients of the microstrip transmission line were unchanged when bending angle is less than 60°. This indicates that the STO/POE composites have the promising characteristics for potential applications in microwave substrate, flexible dielectric waveguide and related flexible microwave devices.     

Dielectric resonators and filters

High-performance DRs and filters are widely used in wireless and satellite communication systems due to their superior characteristics, such as high unloaded Q, excellent temperature stability, and smaller size compared to their air-filled counterpart. Temperature-stable high-Q dielectric materials with a wide range of dielectric constants from 20 to 100 are available. The properties of a DR such as resonant frequency and unloaded Q can be accurately determined by full-wave EM simulations. TEoi single-mode filters offer the advantages of design simplicity and flexibility in layout options over HEn dual-mode filters, while dual-mode filters have significiint advantages in the mass and volume of the products. Mixing the TEoi and HE\ modes, dielectric loaded resonator filters achieve the advantages of dual-mode HEn DR filters and the excellent spurious performances of the TEqi mode ring resonator filters.     

热老化条件下LDPE/TiO2纳米复合材料介电特性研究

电力电缆在运行过程中普遍存在的热老化现象容易加速绝缘失效,限制设备使用寿命,甚至引发电力系统故障。纳米粒子掺杂改性可以提高聚乙烯基体材料的热稳定性,开展相关研究可以为提高电缆绝缘寿命提供解决方案。以低密度聚乙烯(LDPE)/二氧化钛(Ti O_2)纳米复合材料为研究对象,分别研究了热老化条件下纳米粒子质量分数、老化时间、老化温度对材料介电特性的影响。实验结果表明,掺杂Ti O_2纳米粒子能够改善LDPE基体材料的介电特性,当Ti O_2纳米粒子填充质量分数为0.5%时,纳米复合材料介电特性最佳。老化时间和老化温度是影响材料介电特性劣化的两个重要因素,随着老化时间推移和老化温度提高,纳米复合材料的介电性能劣化现象越明显。对聚乙烯材料进行纳米改性的同时降低电缆运行环境温度,对提高电缆绝缘寿命具有重要意义。     

Effects of electrical leakage currents on MEMS reliability and performance

Electrostatically driven MEMS devices commonly operate with electric fields as high at 10/sup 8/ V/m applied across the dielectric between electrodes. Even with the best mechanical design, the electrical design of these devices has a large impact both on performance (e.g., speed and stability) and on reliability (e.g., corrosion and dielectric or gas breakdown). In this paper, we discuss the reliability and performance implications of leakage currents in the bulk and on the surface of the dielectric insulating the drive (or sense) electrodes from one another. Anodic oxidation of poly-silicon electrodes can occur very rapidly in samples that are not hermetically packaged. The accelerating factors are presented along with an efficient early-warning scheme. The relationship between leakage currents and the accumulation of quasistatic charge in dielectrics are discussed, along with several techniques to mitigate charging and the associated drift in electrostatically actuated or sensed MEMS devices. Two key parameters are shown to be the electrode geometry and the conductivity of the dielectric. Electrical breakdown in submicron gaps is presented as a function of packaging gas and electrode spacing. We discuss the tradeoffs involved in choosing gap geometries and dielectric properties that balance performance and reliability.     

Labyrinthine Instability in Dielectric Fluids

The dual to recent work of the labyrinthine instability in magnetic fluids is demonstrated with analysis and measurements using dielectric fluids. Here polarizable fluid layers are placed within an initially uniform electric field tangential to the fluid interface separating two dielectric fluid layers. To eliminate electric space charge effects, alternating electric fields must be applied at a frequency much greater than the larger reciprocal dielectric relaxation time of the fluids. Past theory and measurements have shown that a flat interface in a uniform tangential field is stable if the interface is of infinite extent. If the fluid interface has a finite thickness in the direction of the applied field, reaction fields cause nonuniform field components tangential to the fluid interface. Above a critical magnitude the resultant field destabilizes the fluid interface forming labyrinthine patterns. An interfacial stability analysis and an energy minimization method are compared to measurements.     

The Enhanced Dielectric and Insulating Properties of Al2O3 Modified Ta2O5 Thin Films

Future-generation memory devices will require materials with higher dielectric constants compared to conventional dielectric materials such as silicon oxide and silicon nitride. Tantalum oxide (Ta₂O₅) is one of the most promising high dielectric constant materials because of its ease of integration into conventional VLSI processes compared to other complex oxide dielectrics. The dielectric constant and thermal stability characteristics of bulk Ta₂O₅ samples were previously reported to enhance significantly through small substitutions of Al₂O₃. However, this improvement in the dielectric constant of (1 – x)Ta₂O₅-xAl₂O₃ was not clearly understood. The present research attempts to explain the higher dielectric constant of (1 – x)Ta₂O₅-xAl₂O₃ by fabricating thin films with enhanced dielectric properties. A higher dielectric constant of 42.8 was obtained for 0.9Ta₂O₅-0.1Al₂O₃ thin films compared to that reported for pure Ta₂O₅ (25–30). This increase was shown to be closely related to a-axis orientation. Pure Ta₂O₅ thin films with similar a-axis orientation also exhibited a high dielectric constant of 51.7, thus confirming the orientation effect. Systematic study of dielectric and insulating properties of (1 – x)Ta₂O₅-xAl₂O₃ thin films indicate improved leakage current properties and reliability characteristics such as temperature coefficient of capacitance and bias stability with increase in Al₂O₃ concentrations.     

基于加窗插值谐波分析法的容性设备介损角测量研究

谐波分析法是容性设备介损角在线提取的常用方法,而谐波分析法的基础——离散傅里叶变换(DFT)存在的频谱泄露和栅栏效应会影响介损角测量的效果。本文通过对不同窗函数数谱分析及比选的基础上,提出了基于汉宁窗插值算法的容性设备介损角提取方法。首先获取电压、电流信号离散序列,求取汉宁窗修正式,并修正基波频率,然后求取修正后的电压电流相角,最后公式计算求出介质损耗角。通过仿真验证,表明了该算法具有较高精度且稳定性较好,对于基波频率波动、采样频率变化及白噪声均有较好的测量效果。     

Multifunctional SrTiO3/NiZn ferrite/POE composites with eletromagnetic and flexible properties for RF applications

Multifunctional dielectric composites with electromagnetic and flexible properties for RF applications were investigated. A kind of low loss flexible dielectric and magnetic composite with SrTiO₃ (STO) ultrafine particles and NiZn ferrite (NZO) ultrafine particles embedded in a Thermoplastic Polyolefin Elastomer (POE) matrix was fabricated using the extrusion technology. The dielectric and magnetic properties of the as-prepared composites with different volume fraction of ceramic fillers were studied. The results indicate that when the volume of the ceramic fillers is fixed, the permittivity of the composites increase while the dielectric loss, permeability and magnetic loss decrease with the increasing of the ratio of STO to NZO. The cut-off frequencies of the composites are all above 1 GHz. The good frequency stability of the electromagnetic properties within a wide frequency range was observed. All the composites show very good flexibilities. With the increasing of the volume fraction of ceramic fillers, the tensile strength and elongation decrease. The obtained multifunctional flexible magnetic-dielectric composites are good candidates for the applications of the capacitor-inductor integrating devices in RF communications such as electromagnetic interference filters and antennas.     

Galerkin analysis of electrothermal instabilities in plane liquidlayers

The stability of a horizontal layer of poorly conducting dielectric liquid subjected to a unipolar injection of ions and a thermal gradient is studied. Ions arising from injections and dissociation are supposed to have the same nature. Ionic mobility and electric permittivity are allowed to vary linearly with temperature. The linear stability analysis has been carried out by means of a Galerkin method with one and two trial functions. A single trial function provides useful analytical relations between parameters for the neutral stability surface. A second trial function is necessary to account for the existence of overstability in the absence of a thermal gradient and to achieve better accuracy in the solution     

基于希尔波特-黄变换的介损数字测量算法

准确提取基波电压和电流信号是检测介质损耗因素的关键。提出了一种新的介质损耗因数检测算法,采用希尔波特-黄变换(HHT)对试品电压和电流信号进行检测,通过经验模态分解法(EMD)提取信号的固有模态函数(IMF),再进行Hilbert变换,得到各自的瞬时频率,由瞬时频率进行介质损耗因数的准确检测。该算法无需同步采样,可以实时提取测量电压、电流信号的基波成分。仿真结果表明,HHT受采样数据长度、频率跟踪误差的影响较小,在非同步采样的情况下,具有良好的应用特性,能有效提高介质损耗因数检测的准确度。     

Integration of MnZn-ferrite tapes in LTCC multilayer

For co-firing of MnZn-ferrite tapes and LTCC dielectric tapes, the sintering shrinkage curves and the coefficient of thermal expansion of ferrite and dielectric tapes were matched. Highly densified embedded ferrite without any cracks could be manufactured by co-firing at 900 °C in nitrogen atmosphere. However, the permeability of MnZn-ferrite co-fired between dielectric tapes is significantly reduced (μ´=100) compared to that of the separately sintered ferrite (μ´=500). Changes in the phase stability and microstructure of MnZn-ferrite were investigated to explain the permeability reduction in the embedded ferrite. It is supposed that early densification of the dielectric tapes on the top and bottom of the ferrite layer prevent the gas exchange during sintering which is necessary for (Mn,Zn)Fe₂O₄ spinel formation. As a result, high amount of Fe₂O₃ secondary phase and a Mn-rich spinel phase with low permeability remain in the embedded ferrite layer.     

同轴谐振腔测量片状介质材料的介电常数

基于同轴谐振腔,提出一种测量低损耗片状介质材料相对介电常数的方法。结合麦克斯韦方程组和电磁场边界条件,分析部分填充介质的同轴谐振腔内TEM谐振模,推导填充介质同轴谐振腔的本征方程。采用多项式拟合法简化计算模型。本文通过计算分析,设计一个空腔工作频率在1.8183 GHz的同轴谐振腔进行研究。在HFSS电磁仿真软件中进行仿真分析,研究填充介质材料的厚度和放置高度对测量结果的影响,仿真测量结果与理论模型结果一致。在实验中搭建测量系统实现全自动测量。实验测量同轴谐振腔空腔的谐振频率为1.8183 GHz。对FR4介质材料的相对介电常数进行测量。经过多次测量表明测量系统稳定性良好。实验结果符合实际标称值,与仿真误差小于5%,证明该方法的可行性和准确性。