Changes proposed for the IEC 60093 Standard concerning measurements of the volume and surface resistivities of electrical insulating materials

The IEC 60093 Standard, prepared by the International Electrotechnical Commission in 1980, sets up methods of measurements, determination and calculation of volume and surface resistivities of solid dielectrics. The document contains some editorial mistakes as well as content-related inaccuracies that require revisions. Besides corrections of obvious editorial mistakes it is suggested to introduce some content-related improvements. The most important remarks given in the paper are associated with the following problems: 1) shunting of the current meter by the resistance between guarding and guarded electrodes; 2) significant influence of the electrodes made of conducting rubber on volume resistivity measurement results; 3) errors associated with application of simplified expressions for resistivity calculations (volume resistivity for tubular samples, surface resistivity for samples with circular electrodes); 4) increase of the effective surface of the measuring electrode (margin width determination and consideration). Finally, proposals of alterations of particular clauses of the standard, supplemented with appropriate justifications, were given in the paper.     

A Field-circuit Coupled Method to Accurately Determine Intrinsic Complex Permittivity of XLPE Insulation Material

To identify the location of partial discharge occurring in a power cable, it is essential to obtain the intrinsic values of permittivity of cross-linked polyethylene (XLPE) material. This paper reveals that when the conventional two-parallel-electrode method is used, and due to the fringing effect, the measured permittivity of XLPE material pronouncedly differs from its intrinsic value, consequently significant measurement error could occur. An effective method based on the field-circuit coupled theory is presented in this paper to investigate the difference between the measured and intrinsic permittivity of XLPE insulation material. A capacitor constructed from a concentrically cylindrical XLPE sample is used. By assuming a certain value of the intrinsic permittivity for XLPE material, the electric field distribution in the XLPE material and the ambient is calculated. Then the total energy is determined, as well as the measurable permittivity. By assuming different values of intrinsic permittivity, corresponding measurable values of permittivity are determined, and a curve of measurable permittivity against its intrinsic value is then obtained, from which the intrinsic value can be found once its measurable value is obtained from experiment. The influence factors of the correction curve are analyzed, i.e. the sizes of sample and electrode. A measurement was carried out to verify this method.     

氧等离子体反应器中氧化铝电介质特性

绝缘电介质层是氧等离子体反应器中的重要组成部分,高性能的电介质材料保证了氧等离子体反应器能够高效、稳定的运行。本文对氧化铝电介质材料的特性以及氧等离子体反应器长时间工作后电介质材料的特性变化进行了研究。结果表明,α-Al_2O_3电介质层表面光滑平整、无缺陷,相对介电常数约为9.79,具有较高的体积电阻率和表面电阻率,损耗因数很小,有利于氧等离子体反应器效能的提升;长时间工作后的α-Al_2O_3电介质层基底表面结构、相对介电常数与体积电阻率基本不变,但其表面会附着一层由316L不锈钢电极表面溅射产生的黄褐色固态颗粒物,降低电介质层的表面电阻率。研究结果对优化氧等离子体反应器具有一定的意义。     

Area dependence of breakdown strength of polymer films: automatic measurement method

An automatic method for determining the breakdown strength of thin polymer films was evaluated. The equipment consists of a scanning electrode arm with which the breakdown voltage over the film sample is measured. The measurement electrodes were of solid brass and the ground electrode was of thin aluminum foil. Five different electrode areas between 0.045 and 9.3 cm² were used and 40-100 individual measurements per electrode area per sample were performed. All measurements were performed in air. The Weibull function parameters alpha and beta were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. the criteria for the automatic detection of the breakdowns, the effect of the electrode edge design, the DC ramp speed, partial discharges and humidity were analyzed. In order to control the reproducibility of the results, also another type of measurement setup was tested. It was concluded that the measured alpha-parameter values were stable and repeatable over a period of several years. The average beta-parameter values varied plusmn10-30%, more for the large than the small electrodes, and were also sensitive to changes in the sample, in the measurement conditions and the choice of the electrode system     

Correlation between tan δ diagnostic measurements and breakdown performance at VLF for MV XLPE cables

The main contribution of this paper is to investigate the correlation between Tan ? diagnostic measurements at 0.1 Hz (Very Low Frequency-VLF) and VLF breakdown performance for Medium Voltage (MV) cable samples through a laboratory test program. The cable samples used are a set of 15 kV, Cross-linked Polyethylene (XLPE), unjacketed cables removed from the field, the same service area, and having experienced similar operating conditions for almost four decades. The test program includes Tan δmeasurements at different voltage levels and a subsequent VLF extended step-withstand test. The VLF step test allows the evaluation of risk of failure during VLF Tan δtesting and assessment of the ultimate performance of the cables. The Tan ? diagnostic measurements are represented by the Tan δvalue and Tip-up, which are considered the classical metrics. However, the paper also suggests the use of a new additional diagnostic feature that takes into account the scatter in the Tan δmeasurements for a particular test voltage level.     

Electric fields of grounding electrodes with frequency dependent soil parameters

The profile of the electric field developed at the ground level above a horizontal grounding electrode due to the impression to the electrode of waves resembling lightning currents of first and subsequent strokes was calculated using an electromagnetic model. The simulation considered both assumptions constant values for soil parameters resistivity and permittivity and frequency dependent values. This dependence was given by an expression derived from field measurements. It was found that the frequency dependence of soil parameters is relevant, mainly at low conductivity soils and short front-time current waves, leading to a significant decrease of the electric field profile.     

真空环境下电介质表面电阻率测试方法及其影响因素

真空环境下直接测量电介质表面电阻率难度较大、成本较高、时间较长。为解决这一难题,提出了用测量电介质体积电阻率代替真空环境下电介质的表面电阻率的替代测试法;并从理论推导和试验验证两方面分析该替代测试法的可行性;最后以纯环氧板试样为实验对象,测量并分析了其电阻率与环境湿度、环境温度及大气压强的关系。结果表明:该替代测试法是可行的,且电介质表面电阻率与其表面薄涂层体电阻率成正比,厚度成反比;电介质电阻率随着环境湿度、环境温度的增大而减小,随着大气压强变化而变化很小。     

真空中不同温度下典型脉冲功率领域用有机绝缘材料介电特性的研究

针对脉冲功率领域最常采用的环氧树脂、交联聚苯乙烯和聚乙烯3种典型绝缘材料,设计了一套适用于真空中且可以控温的标准三电极系统。在真空中对不同温度和频率下的介电参数(介电常数、介质损耗、表面电阻率和体积电阻率)进行了测试,并研究了烘烤对其介电性能的影响。结果表明:在不同的温度和频率下,3种材料中聚乙烯的εr和tanδ最小,环氧树脂最大;交联聚苯乙烯的体积电阻率和表面电阻率最大,环氧树脂和聚乙烯次之。烘烤可在一定程度上降低绝缘材料的介电常数和电阻率。综合比较3种材料的电性能和耐热性能,其中交联聚苯乙烯的性能最好,适用于真空脉冲功率领域绝缘。     

电极系统对电机定子线棒绝缘介质损耗的影响

通过对测量电机定子线棒绝缘介质损耗(tan )的三电极系统的结构分析,建立了介质损耗测量电极系统的电路模型.在此基础上计算了各影响参数与线棒的介质损耗之间的关系.结果表明,测量电极与保护电极之间的间距、测量电极与保护电极之间的表面电阻率、主绝缘厚度、主绝缘的相对相容率均与线棒的介损有关,同时该理论计算值与试验结果的趋势...     

变压器油中腐蚀性硫浓度对绕组绝缘电气性能的影响

为了研究变压器油中腐蚀性硫含量对绕组绝缘性能的危害,通过在变压器绝缘油中添加二苄基二硫(DBDS),以得到三种浓度含腐蚀性硫的绝缘油样品,并将纸包铜绕组浸渍于绝缘油样品中,在130℃下开展加速热老化试验。在不同老化时间取样试品测量相关参数以研究绝缘纸上沉积物的特性、发展规律及其对绕组模型绝缘性能的影响。通过SEM观察铜导线与绝缘纸表面微观形貌变化规律,采用能谱分析技术确定绝缘纸表面沉积物质的元素及含量,利用Keithley6517B测试沉积量对绕组的体积/表面电阻率以及介质损耗参数影响规律。试验结果表明,油中的DBDS含量增加可明显加速铜片表面的腐蚀速度及绕组绝缘纸上腐蚀性物质的沉积,沉积于绝缘纸表面的物质会对绝缘的体积/表面电阻率、介质损耗造成明显的影响。以上研究对深入认识变压器油硫腐蚀机理及有效预防此类事故的发生具有重要意义。     

考虑地表高阻层的直流接地极跨步电压限值计算方法

为保证直流接地极附近人身安全,接地设计时必须满足跨步电压限值要求。针对水平双圆环形直流接地极,考虑在接地极上方地表铺设高阻层,研究在此条件下跨步电压限值的计算方法,并给出了新计算公式,最后基于边界元法对不同土壤条件下的直流接地参数进行研究分析。研究结果表明：直流接地极地表铺设高阻层能够有效提高人体耐受的跨步电压限值,建议铺设厚度为0.1~0.2 m;为明显提高跨步电压限值,选取的高阻层电阻率最好大于1 000 Ω·m。研究结果还表明,铺设高阻层对直流接地极的接地电阻、地电位升、地面跨步电压以及泄漏电流的分布影响很小,对金属设施的影响也基本可以忽略。     

Investigation of the High Frequency Properties of BST Thin Films—A Comparison of Three Different Commonly Used Methods

In this work three different commonly used high frequency measurement techniques for the determination of the electrical properties of BST thin films are compared. Two of the three setups determine the permittivity and the loss factor of planar sapphire capacitors by either measuring the reflection coefficient or the influence onto the resonance frequencies of two coupled microstrip resonators. The third setup utilizes the differential propagation constant of two identical coplanar wave guides (CPW) of different length to calculate the permittivity and the loss factor of the involved sapphire substrate. It is found that the latter method shows the best accuracy for the measurement of the permittivity and the loss factor of the sapphire substrates over a broad frequency range. Measurements of BST coated sapphire substrates are presented using this technique.     

Optical, electrical and electromechanical measurement methodologiesof field, charge and polarization in dielectrics

A selective review is presented of the use of optical, electrical, and electromechanical measurement methodologies of the electric field, charge, conductivity, and permittivity in dielectrics. Kerr electro-optic measurements are presented to demonstrate how volume charge distributions can distort the electric field distribution significantly and how the field and charge distributions depend on dielectric and electrode materials and geometry, and on voltage magnitude, polarity, and time duration. A new class of interdigital dielectrometry sensors is reviewed which from one side can measure profiles in dielectric permittivity and conductivity and related physical properties such as moisture content. Electromechanical devices such as the absolute charge sensor, a flow loop, and the couette charger (cc) with a rotating cylindrical electrode are reviewed for their applications in liquid flow electrification measurements     

Dielectric properties of nanostructured polypropylene-polyhedral oligomeric silsesquioxane compounds

This paper presents the results of the dielectric measurements conducted on polymer nanocompounds consisting of polypropylene (PP) and polyhedral oligomeric silsesquioxane (POSS). The material compounds were analyzed with a scanning electron microscope (SEM) and Raman-atomic force microscope (Raman-AFM). Ac and lightning impulse (LI) breakdown strength of the material compounds were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, octamethyl and isooctyl, were used in different quantities. The thickness of the samples was approximately 600 mum. Statistical analysis was applied to the results to determine the effects of the additive type and amount on the breakdown strength of polypropylene. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.     

精炼菜籽绝缘油的介电性能

为了研究植物绝缘油在变压器等充油高压电气设备中的应用,分析了精炼处理后菜籽绝缘油的主要介电性能,并进行了试验研究和理论分析,采用介电谱测试仪测量了菜籽绝缘油试品的相对介电常数和介质损耗因数,分析了两性能参数随试验温度、频率变化的规律,并参照相关标准对菜籽绝缘油的体积电阻率进行了研究。同时,测试了#25矿物绝缘油相应的介电性能参数。通过比较分析两类绝缘油介电性能参数温度谱、频率谱的试验结果发现,相对于矿物绝缘油,植物绝缘油具有良好的介电性能。     

Thermal, Mechanical and Dielectric Properties of Nanostructured Epoxy-polyhedral Oligomeric Silsesquioxane Composites

This paper presents the results of the thermal, mechanical and dielectric measurements conducted on polymer nanocomposites consisting of epoxy and polyhedral oligomeric silsesquioxane (POSS). The material composites were analyzed with a scanning electron microscope (SEM), an atomic force microscope (AFM) and a transmission electron microscope (TEM). Glass transition temperatures of the composites were measured with differential scanning calorimeter (DSC). Stress, strain, modulus and impact strength of epoxy nanocomposites were tested. Ac and lightning impulse (LI) breakdown strength of the composites were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, glycidyl and octaglycidyldimethylsilyl, were used in different quantities. Statistical analysis was applied to the measurement results to determine the effects of the additive type and amount on the properties of epoxy. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.     

变压器油纸绝缘频域介电特征量与绝缘老化状态的关系

为了更好地将频域介电谱技术用于无损诊断变压器油纸绝缘老化状态,通过频域介电谱测试了不同老化程度油纸绝缘试品的频域介电特征量。研究了油纸绝缘试品的相对介电常数、介质损耗因数、电容、体积电导率与频率和绝缘纸老化状态的关系,在分析温度对油纸绝缘试品频域介电特征量影响规律的同时,提出了求解油浸绝缘纸活化能的新方法。结果表明:油纸绝缘试品在10 3～100Hz的频域介电特征量能反映其老化状态;不同老化程度油纸绝缘的电容C(DPt)或相对介电常数r(DPt)在10 3Hz、10 2Hz、10 1Hz的值分别与绝缘纸聚合度差值(DP0 DPt)存在二次多项式函数关系;利用油纸绝缘试品tan曲线求解出的油浸绝缘纸(DP=880)活化能为96.65kJ/mol,利用"频温平移因子"可将已知测试温度下的频域介电特征量推广到未知温度,解决了测试温度不同对FDS结果带来的影响。     

Effect of Discharge Electrode Parameters on the Flow Velocity Profile of the Wire?rod Type Electrohydrodynamic Gas Pump Exit

Experimental investigation has been conducted to study the effects of corona wire diameter, pipe length, and corona polarity on outlet flow velocity distribution profile of a wire-rod type electrohydrodynamic (EHD) gas pump. Upon applying negative or positive dc high voltage between a wire electrode (outer diameter (o.d.) 60 μm, 200 μm, or 300 μm) and a rod electrode (o.d. 3 mm) in atmospheric air, corona discharge occurs and EHD gas flow is generated in the direction from the wire electrode to the rod electrode through a cylindrical pipe (inner diameter (i.d.) 20 mm). For both polarities, the discharge current and average flow velocity increase monotonically on increasing the applied voltage before the onset of spark discharge. Using wire electrodes with a smaller diameter, stable corona discharge between corona onset and spark onset is generated in a wider voltage range, and the discharge current becomes larger, resulting in a higher flow velocity. The maximum average flow velocity of 2.0 m/s, corresponding to a flow rate of 38 l/min, was achieved with a wire of diameter 60 μm by applying a voltage of ?16 kV.     

纳米ZnO/低密度聚乙烯复合材料的介电特性

聚合物纳米复合材料因其优良的介电、机械等性能在电介质领域得到广泛的应用。纳米粒子改性聚乙烯基绝缘材料具有很好的研究价值及工程意义。该文主要研究了表面经分散剂处理的纳米ZnO粒子添加剂与低密度聚乙烯(LDPE)共混物的介电特性。结果表明5%含量的纳米ZnO添加剂能有效提高聚乙烯基复合材料的体积电阻率和交流击穿强度。同时纳米添加剂虽增加了体内的残余电荷,但能有效抑制电极同极性电荷的注入。另外由于聚合物纳米复合材料的界面特异性,使得介电常数随着纳米ZnO含量的增加呈先减小后增大趋势,而损耗值却线性增加。纳米ZnO/聚乙烯复合材料介电性能提高归因于纳米粒子与聚乙烯分子间类同于深陷阱的界面效应。     

Application notes - basic parameters of coplanar-strip waveguides on multilayer dielectric/semiconductor substrates, Part 1: high permittivity superstrates

A simple method and closed-form analytic formulas for symmetric CPS based on single layer substrate (infinite and finite thickness) and multilayer lossy dielectric (semiconductor) substrate, where the permittivity of the superstrate layers decrease away from the strips, are proposed. Since the line models are given analytically, the dependencies of the line parameters may be analyzed and optimized in wide ranges of sizes, permittivities, and losses (substrate resistivity). In general, the formulas are reversible. The measured line parameters may be used to calculate the permittivity and loss tangent (resistivity) of one of the substrate layers if the parameters of the other layers and strips are known. The method may be easily extended to include larger number of substrate layers.