地表相对介电常数对雷暴云定位影响分析与研究

地表并非均匀介质的理想导体,传统的一维大气电场分量无法准确的对雷暴云进行定位,而利用大气电场三维场强分 量进行雷暴云定位时,电场的场强、雷暴云的高度角测量往往会受到地表及空气介电常数的影响,产生定位误差。 为解决雷暴 云定位精度低的问题,分析了三维大气电场对于地表相对介电常数的敏感特性,结合镜像法,利用空中电荷电场分布、雷暴云电 荷结构等原理,建立了雷暴云定位模型,分析得到大气电场场强、高度角与环境相对介电常数的关系。 实验结果表明,地表相对 介电常数越大,所测得的电场水平分量与雷暴云高度角越大,地表相对介电常数与大气电场水平分量的相关系数为-9. 5,呈负 相关,相关性强,因此要获得准确的雷暴云高度及方位,还须实时的地表相对介电常数进行修正。     

Electrohydrodynamic Flow in Optoelectrostatic Micropump: Experiment Versus Numerical Simulation

This paper deals with optoelectrostatic pumping of conductive liquids in microchannels. In this technique, the fluid is heated by laser irradiation and exposed to an external ac electric field. If the fluid permittivity and conductivity vary with temperature, the electric body force is generated, and pumping effect can be achieved. A numerical model of this phenomenon is presented, and it is based on the finite-element analysis of the electric, thermal, and flow fields. The numerical predictions are compared with the experimental data, with a reasonable qualitative agreement.      

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     

Silicone rubber dielectrics modified by inorganic fillers for outdoor high voltage insulation applications

The paper discusses the mechanisms by which inorganic fillers in silicone rubber dielectrics enhance the properties of thermal conductivity, relative permittivity, and electrical conductivity making them useful in outdoor high voltage insulation applications. The addition of alumina trihydrate or silica fillers to silicone elastomers, forming binary composites with enhanced thermal conductivity, is discussed in relation to filler type, particle size, shape, and concentration, and its use as a housing material for non-ceramic insulators to minimize material erosion at dry band arcing sites by lowering hot spot temperature. Also discussed is the enhanced relative permittivity of silicone dielectrics that is obtained through the addition of barium titanate powder which can be further increased with the addition of aluminium powder forming a tertiary composite, resulting in a significant grading of the surface electric field when applied as a housing material to high voltage bushings. Controlled electrical conductivity of silicone dielectrics is discussed through the use of antimony-doped tin oxide filler binary composites and when applied as a housing material to outdoor bushings, the pollution performance is greatly enhanced.     

脉冲电场诱导细胞内外膜电穿孔模型与跨膜电位的仿真

基于经典的球形单细胞3层介电模型,同时考虑细胞核对跨膜电位的影响,提出了更为合理和接近实际的球形单细胞的多层介电模型,给出了稳恒电场和任意时变脉冲电场作用下细胞膜和核膜跨膜电位的计算方法。仿真结果表明:当脉宽减小时核膜跨膜电位增加,而脉宽增大时细胞膜跨膜电位增强;当脉宽在100-500ns范围时能有效实现肿瘤细胞膜和核膜电穿孔,同时不影响正常细胞。计算结果与实验吻合得很好,为肿瘤的电化学疗法和基因疗法的临床应用提供了理论指导。     

低介电常数绝缘纸的制备及其击穿性能

为提高油浸式变压器绕阻中纸-油-纸复合绝缘系统的击穿电压,实验室制备了能降低绝缘纸介电常数的微纳米级SiO2空心微球以及含不同质量分数SiO2(wSiO2)空心微球的实验用绝缘纸手抄片。测量浸油后的含不同质量分数SiO2空心微球绝缘纸的介电常数,wSiO2=5%空心微球的绝缘纸介电常数最低,比未加SiO2空心微球的绝缘纸介电常数低34%。用双层电介质场强公式分析绝缘纸介电常数以及复合绝缘系统中油隙厚度对油、纸中场强分配的影响。设计纸-油-纸复合绝缘系统模型,用COMSOL仿真软件对模型进行计算,得出模型中纸、油中电场为均匀电场,双层电介质场强公式可用于纸-油-纸模型的理论分析。最后,用含不同质量分数SiO2空心微球的绝缘纸组成纸-油-纸复合绝缘系统进行电击穿实验,介电常数越低的绝缘纸组成的纸-油-纸复合绝缘系统击穿电压越高,介电常数最低的wSiO2=5%空心微球的绝缘纸组成的纸-油-纸复合绝缘系统比未加SiO2空心微球的绝缘纸组成的纸-油-纸复合绝缘系统的击穿电压高15.5%。     

Electric Field Effects on the Equilibrium and Small Signal Stabilization of Electrofluidized Beds

A continuum analysis is developed of electric field coupling to a charge-free fluidized bed of polarizable particles, with the electric field at an arbitrary angle to the gas flow. The electric force density and stress tensor is derived from the principle of virtual work and includes polarization and electrostriction forces but neglects Coulombic free charge forces. Effective medium theory for various particle structures derives the effective bed permittivity as a function of particle voidage and is used with the energy method to derive the electric. force density acting on the particles. Necessary force-free boundary conditions at the top free surface of the bed are developed. A linear stability analysis is used to find the conditions for electric field stabilization. Experiments with Rochelle salt show elimination of bubbling with collinear electric field and flow but never complete stabilization with crossed field and flow as predicted by the analysis. There is qualitative agreement between the stability analysis and measurements. Numerical differences are attributed to particle viscosity, which was not included in the fluid model.     

Electrorheological properties of anisotropically filled elastomers

We report the results of numerical simulations for the change of both mechanical and electrical properties of elastomers with anisotropically filled polarizable particles under capacitively graded electric and mechanical fields. Such composites have potential applications in electromechanical control. We have used numerical techniques to study the effect of particle shape, permittivity/conductivity ratio, and spatial arrangement on the shear modulus as a function of the electric field. We also investigated the influence of the high field and nonlinear conductivity in the polymer matrix. The results indicate that electrostatic energy and changes therein, which result in electro-rheological effects, are concentrated between particles, and that the electrostatic interaction between the particles is concentrated in a very narrow regime at the tip of the particles, The interaction increases with the electric field intensity until the field between the particles is high enough to cause nonlinear electrical conduction in the polymer, resulting in a redistribution of the electric field and electrostatic energy     

Electric field behavior near a contact point in the presence ofvolume conductivity

The electric field behavior, in particular the field intensification at a contact point, is very important in complex dielectric systems with gaseous or vacuum insulation. The paper describes the electric field behavior at and near a contact point in various arrangements with a zero contact angle when volume conductivity is present in the solid dielectric. Contact conditions are separated into line, point, and surface contact. The effect of volume conductivity is investigated analytically, and numerically by using the boundary element method. The electric field behavior near a contact point principally depends on the absolute value of complex relative permittivity, and volume conductivity usually promotes the field intensification. In the arrangements of point contact or line contact, the position of peak electric field shifts from a contact point when the volume conductivity is higher than a certain value, while in the arrangement of surface contact, the position is usually more or less remote from the contact point, whether volume conductivity is present or not     

UHV交变电场在人体中感应电流计算分析

为研究1000 kV特高压(UHV)架空线路工频电磁场对人体健康及环境的影响,计算了人体位于UHV线路下方时,交变电场在人体内的感应电流及其影响因素和线路最小对地高度。探讨了设计规程中高压线路最小对地高度应保证线路下方距地1m高处的电场强度<10kV/m的合理性。结果表明,人体的电导率和介电常数的大小对工频电场在人体内感应电流密度的大小并无明显影响;按照线路下方距地1m高处的最大电场强度<10kV/m的原则来确定UHV线路的最小对地高度,感应电流密度不会超过安全值。     

The effect of water treeing on the electric field distribution ofXLPE. Consequences for the dielectric strength

This paper describes the influence of water trees on dielectric properties of flat samples cut from a HV crosslinked polyethylene (XLPE) cable insulation. In order to obtain experimental results in a short period of time, we used accelerated aging conditions of voltage and frequency as well as different techniques for producing a multitude of artificial water tree inception points. The average value of the water tree permittivity and a law for the time-dependence of permittivity inside the treed degraded areas were deduced from measurements of capacitance and water tree lengths. On the basis of the experimental knowledge of permittivity and water tree length, we determined with analytical numerical methods, the distribution of the electric field for different shapes of treed regions. Because of the increase in length and permittivity of the water tree, the electric field in front of the degraded area is amplified, which is an important factor of risk leading to the electric breakdown     

Study of normal and malignant white blood cells by time domaindielectric spectroscopy

The aim of this paper is to present a comprehensive theoretical and experimental study by means of time domain dielectric spectrometer (TDDS) of static and dynamic dielectric properties of normal and malignant blood cells. The successful use of the TDDS method as a tool of human cell study required a special protocol and algorithms for all stages of cell preparation, measurements and data treatment. The routine developed in this study was used in the experimental analysis of nine lines of malignant, transformed and normal lymphocytes. It was shown that dielectric permittivity, capacitance and conductivity values of the cell membrane are higher for normal lymphocytes in comparison with malignant ones     

Three-Dimensional Numerical Simulation of Circulation and Heat Transfer in an Electrically Boosted Glass Melting Tank

A three-dimensional numerical methodology to simulate the effect of electric boosting on glassmelt circulation and heat transfer in a glass melting furnace is presented. Due to a small, characteristic Hartmann number, the ponderomotive forces in the momentum equation were neglected. The voltage and electric current fields within the melt were determined by solving real and imaginary parts of the electric potential. The Joulean heat dissipation was determined and coupled to the energy equation of the melt. Other relevant processes, such as batch-melting and heat transfer from combustion space, were integrated into a system model. Merits of electric boosting were examined by obtaining some representative results and comparing model predictions with and without electric boosting.     

An overview of electrical properties for stress gradingoptimization

The scope of the following paper is to present, both from a theoretical and a practical point of view, some aspects involved in stress grading in the general configuration where insulated HV conductors pass through a grounded screen. The difference between capacitive and resistive materials is discussed; particular attention is devoted to the rules governing the potential and the field distribution in both cases. The case of a capacitive varnish with nonlinear permittivity is discussed and a comparison with materials of constant permittivity is made. The experimental behavior of nonlinear semiconducting materials used in practice are examined and a discussion is given on the possible use of resistive materials of constant conductivity. Finally, practical considerations are listed as basic rules for optimizing the grading effect     

Calculation of a Valve Magnetic System of Maximum Current Release of a Circuit Breaker

Circuit breakers are one of the most widespread electrical devices in control and distribution systems that use electric energy fluxes, providing protection from short circuits and current overloads. First and foremost, circuit breakers should provide a high operation speed at shutdown, which can be achieved with low weight and significant electromagnetic forces. For approximate determination of magnetic system dimensions, network analysis methods are used. In addition, the model of magnetic field structure can be substantially simplified. The conductivity of air gaps between the ferromagnetic elements of a magnetic system can be described by a modified method of probable paths of magnetic flux, and the resistance of ferromagnetic elements (magnetic potential drop) is taken into account by means of a mathematically expressed magnetization curve (for steel of 10895 grade).     

变压器油纸绝缘系统低频介电参数方程

油纸绝缘系统频域介电谱的低频部分更有利于诊断、评估绝缘系统的老化状态与水分含量,为了将频域介电响应法更好地应用到工程中,针对变压器油纸绝缘系统低频激励下的介电响应进行了研究。首先分析了绝缘电介质(油隙、油浸纸)在低频激励下的电极极化过程,进而提出以电导率、离子迁移率等为参量的绝缘电介质的介电参数方程;然后基于变压器油纸绝缘系统的XY几何等效模型,构建变压器油纸绝缘系统低频介电参数方程;最后通过试验对所构建的介电参数方程进行验证。研究结果表明:油纸绝缘系统介电参数计算值与试验值相符合,建立的介电参数方程能够有效地表征变压器油纸绝缘系统频域介电响应低频部分的介电参数。     

气液滑动弧放电降解4-氯酚溶液的研究

用10kV高压产生直接与废水接触的气液滑动弧放电非平衡等离子体降解水中4-氯酚。实验研究表明:由于液滴的存在改变了电极间的介电常数和局部电场,气液滑动弧放电的电压波形比纯气流滑动弧放电更加不规则,起弧电压更低:从溶液COD降解效果来看,当不锈钢作为电极材料时, 4-氯酚降解效果比铝和铜电极材料好;当空气作为载气时,经过76min的等离子体处理,溶液的COD值由1679.2mg／L降到190mg／L,相当于COD降解率为88．68％;增大气液混合比能够提高4-氯酚的降解效果;同时检测了H2O2和O3的生成量和溶液pH、电导率的变化。     

非线性均压材料的设计理论与参数调控

具有非线性电学参数的材料,其电导率或介电常数能够随着空间电场做出自适应的改变,从而达到智能改善绝缘介质空间电场分布均匀性的效果,可用于缓解高压设备局部集中的高电场。目前,国内外已经能够制备出具有高稳定水平的非线性电导特性的材料,如以氧化锌压敏微球为填料,以绝缘材料为基体的复合物。该文详细综述了国际上对于非线性电导材料均压的设计理论,介绍了如何根据实际改善电场分布的需求选择非线性均压材料的参数。在此基础上,总结国际上学者对于在材料制备过程中调控材料非线性参数以满足均压设计需求的研究工作。本文也对非线性均压材料在应用于实际高压设备方面的进展做了简单介绍。     

Changes in electrical impedance of biological matter due to the application of ultrashort high voltage pulses

Time domain-based impedance measurements were used to study the changes in electrical parameters of biological samples following the application of ultrashort high voltage (HV) pulses. Pulses with very short duration (300 ns) caused a significant drop in post pulse resistance of the plasma membrane only at high field strengths in excess of 20 kV/cm. The conductivity of the plasma membrane returned to almost pre-pulse values within less than 10 ms after the field was applied. Further steps of recovery, attributed to pore shrinking and resealing with an exponential decay of the conductivity, as is expected in electroporation, were not observed. An increase in medium conductance, as recorded minutes after the pulse, arises mainly from cell damage. Although pore formation is a possible effect of the high electric field, our results suggest further disturbance of the membrane-like micelle formation or even the creation of large defects, forced by mechanical tension within the cell membrane.     

Numerical Modeling of Insulating Particles Trajectories in Roll-type Corona-Electrostatic Separators

The trajectories of the insulating particles in roll-type corona-electrostatic separators depend on the configuration of the electrode system, the applied high voltage, the roll speed, the size of the particles and the relative humidity of the ambient air. The aim of this work was to point out how numerical modeling can be of use in the study of the effects of these factors. Particle charging is modeled using the Pauthenier?s equation for spheres in uniform electric field. The equation of particle discharging was obtained after an experimental study of the surface potential decay of a granular layer of insulating material in contact with an electrode. The trajectories are computed based on the balance equation of the electrical and mechanical forces that act on such charged particles. The numerical results are in good agreement with the experimental findings.