Vertical electric dipole near a flat imperfectly conducting ground

Contents A vertical electric dipole is situated above a flat imperfectly conducting ground. The exact solution for the reflected field consists of two parts. One part is the field of the image of the exciting dipole, the other part is due to a series of multipoles centred at the image of the exciting centre.

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Vertikaler Dipol über nichtperfekt leitenden Halbraum

Übersicht Ein vertikaler elektrischer Dipol ist über einen nichtideal leitenden Halbraum angeordnet. Die exakte Lösung für das gespiegelte Feld besteht aus zwei Anteilen. Der erste Anteil resultiert aus dem Bild des erregenden Dipols, während der zweite Anteil von einer Dipolreihe hervorgerufen wird, dessen Zentrum mit dem Bild des erregenden Dipols zusammenfällt.

     

一种计算任意形状孔缝平均电极化率密度的方法

孔缝耦合是电磁干扰最主要的途径,如何计算孔缝耦合对排查电磁干扰十分很重要。现有文献中解析计算任意形状孔缝平均电极化率密度的方法是基于超几何函数理论的。该方法虽然能够较为精确地计算出任意形状孔缝的平均电极化率密度,但由于超几何函数对于非数学专业的工程人员来说过于复杂,因此这种计算孔缝平均电极化率密度的方法很少被应用于电磁场工程实践中。针对这一问题,提出了一种新的解析公式,在不损失精度的前提下,大大简化了计算,可以显著提高孔缝耦合问题的解决效率。核心思想是将任意孔缝的平均电极化密度计算问题转化计算无数小圆孔平均电极化率密度的算术平均值,进而推导出一个简单函数沿孔缝边缘进行线积分的解析式,应用该解析式即可十分方便地计算出任意形状孔缝的平均电极化率密度。     

The behavior of charged conducting particles in electric fields

The presence of metal particles within a gas-insulated switchgear (GIS) might initiate a sparkover and lead to fatal failure of an electric power transmission system. In order to investigate the behavior of a particle in a GIS, the model electrodes and the measuring system are constructed. The motion of a particle was investigated by using a CCD camera and a high-speed video camera. Different shapes of elongated particles were made from 0.1-mm and 0.25-mm diameter wires. The measured values of lift-off field strength of a particle lying on the electrode agreed quite well with the theoretical predictions. The initial raising up of a particle usually started at the sharper edge, as expected. There were two types of different modes of particle motions: one is the bouncing motion between two electrodes or one electrode, and the other is the standing motion on the electrode. An interesting thing is that the standing motion is on the upper electrode, when a negative voltage is applied to the upper electrode. This phenomenon could be explained from the difference of positive and negative corona currents starting from both edges of a standing particle     

非车载充电机高精度电能计量研究与应用

针对我国在电动汽车领域内直流充电的应用现状,文章论述了对直流电能进行精确计量的重要性和必要性.通过分析非车载充电机计量的精度和损耗根源,对计量连接装置的结构进行了改良并设计出相应的计量模块.为了降低在充电过程中分流器长时间通入大电流时给充电桩的电量计量准确性带来的不利影响,文章提出了一种提升计量准确性的优化方法:用高精...     

Accurate evaluation of the induced current in a circular cylindrical shield of finite length

The aim of this paper is to analyze the of shielding of electromagnetic fields excited by an impressed current surrounded by a perfectly conducting cylinder of finite length. The induced currents are derived by means of an effective expansion in a Neumann series, and approximated formulas are also given.     

Ultrafast control of hole spin by electric field in semiconductors

Ultrafast and coherent transitions induced by electric field between spin states of the valence band in semiconductors are considered. It is shown that using optimized femtosecond electric fields one can, in principle, control a selected component of the hole spin. The feasibility of hole spin switching is illustrated using the well-known Luttinger-Kohn Hamiltonian for valence bands of tetrahedral and zinc-blende semiconductors. The presented results may be useful in the development of the ultrafast semiconductor spintronics.     

Accurate modeling of interelectrode resistance and powerdissipation in electric glass melters

An accurate technique for modeling the interelectrode resistances as well as the potential and power density distributions in electric glass melters is presented. The model also provides necessary data for sizing the supply transformers associated with such melters. The solution technique involves only algebraic equations, and therefore can be implemented by simple computer software. An example melter with a two-phase supply and eight electrodes was simulated using the proposed three-dimensional modeling technique. Because of the general nature of the proposed model, this technique provides a valuable as well as reliable and easily implemented design tool for melters with multiphase power supplies and general electrode configurations     

电热小家电材料的绿色性评价和选择方法

绿色制造是社会可持续发展的重要保障,绿色材料是绿色制造中不可或缺的一部分.针对电热家电材料选择的不确定性和主观性,提出了一种包含绿色性评价和基于绿色性材料选择的混合多标准决策问题解决方法PGT(a hybrid PIV contain GPMBWM and TFMN),该方法包含了对材料进行选择的邻近指数值法和对评价标...     

Analysis of the electric field and force in an arrangement of a conducting sphere and a plane electrode with a dielectric barrier

This paper presents an analysis of the electric field and dielectrophoretic force in an arrangement consisting of an uncharged conducting sphere and a plane electrode with a dielectric barrier. The electric field is calculated by using the method of multipole images using an iterative algorithm proposed for calculating the images of the dielectric barrier of finite thickness. The calculation results show electric field intensification due to the presence of the dielectric barrier having higher permittivity, /spl epsiv//sub S/, than that of the surrounding medium, /spl epsiv//sub E/; however, if the barrier is separated from the conducting sphere by at least the sphere radius, its influence is negligible. Inside the dielectric barrier, the electric field on the axis of symmetry becomes more uniform and the average field significantly increases with decreasing its thickness. For a case where dielectric barrier is sufficiently thin, the electric field at the contact point and the force on the conducting sphere vary approximately as power functions of /spl epsiv//sub S///spl epsiv//sub E/.     

Numerical simulation of the electric field distribution intribo-powder coating of conducting cylindrical objects

The successful implementation of powder coating technology requires detailed investigation of different factors, which can improve, or disturb, the process. The two most important are the air entrainment force and the electric deposition force acting on the powder particles. The authors present a numerical model for predicting the electric field distribution between a tribe gun and a cylindrical object. It is assumed, that the particle distribution is governed primarily by the air flow and that the only source of the electric field is the space charge of the tribocharged particles. Simplified models for the field lines and design configuration have been assumed and the electric field is determined by means of the charge simulation method     

浅谈大屏幕系统在电力调度中的应用

以广东电网公司江门供电局调度中心的大屏幕系统为例,介绍大屏幕系统的结构和各种功能,探讨该系统在电力调度中的使用以及与电力调度自动化主站系统的联接等问题,认为大屏幕系统的应用将极大地提高电力调度水平。     

用于检测厚铝板缺陷的体波EMAT优化方法

针对电磁超声换能器(electromagnetic acoustic transducer,EMAT)的换能效率低,易受外界环境噪声影响导致回波信号较小、信噪比较低的问题,提出一种使用正交试验的优化方法进行改进。该方法基于电磁场涡流效应、质点弹性动力学的波动方程及有限元法,建立了一个检测厚铝板单平底孔缺陷、收发一体的体波EMAT二维有限元模型。该模型应用正交试验和极差分析法,通过对比不同结构下的缺陷回波电压信号强弱程度,分析磁铁和线圈的结构参数对其的影响,获得了优化的模型结构参数值。同时,得出在本结构下磁铁与线圈的最佳宽度比。通过实验验证了优化结果的有效性,缺陷回波电压峰-峰值的实验与仿真结果相符。     

潜油电泵机组及井下传感器状态监测技术研究

建立了基于电力线载波通信的井下多参数状态监测系统结构,提了基于RBF网络时序预测的传感器状态监测方法,引入最近邻聚类算法的思想,提出了一种K-均值聚类算法初始中心选取方法.该方法能够根据样本序列的变化,自动调整初始聚类中心半径的大小,保证精确度的同时可提高计算速度,提出了一种根据故障传感器输出特性参数的变化对井下传感器故障类型进行分类的新方法,对提出的状态监测系统及传感器监测方法及技术的有效性进行了实验研究.实验结果验证了所提出方法的有效性.     

Adequacy evaluation of a small area in a large composite powernetwork

A methodology is presented which can be used to conduct adequacy studies, considering both the continuity and the quality of power supply as failure criteria on a small area in a large power network. The technique is simple and can be used with existing computer programs to determine the adequacy performance of a power network. It also considers all credible outages that can affect the adequacy of the small area in a power system. The main disadvantage is that the efficiency of the method depends on the size of the small area as compared to the size of the entire power network. The efficiency also depends on the network topology, the type of buses in the small area, and the load-curtailment philosophy. Some of these issues are illustrated by applying the methodology to the IEEE Reliability Test System. A qualitative comparison of the proposed method with two other methods that can be used to determine the adequacy of large power networks is presented     

中小电机市场发展空间凸现

中小型电机是量大面广的产品,耗用的电能占全国总发电量的60％以上,广泛应用于工业、农业和国民经济其他部门。     

小型风力发电系统手持式用户终端开发

为了给用户提供一种监测和管理风电系统的直观手段,设计了一款手持设备,采用32位ARM芯片stm32作为MCU,彩色TFT触摸屏作为人机交互媒介,通过CLASS 1蓝牙模块与风电系统数据采集器进行无线通讯,获取风电系统的实时运行状态,将信息以图表方式反馈给用户;并将功率信息存储到闪存芯片中,以便用户按年、月、日发电量分别进行查询。实验结果及工业产品应用表明,该手持终端操作简便,稳定可靠,风电系统发电量历史数据图表响应快速,用户体验流畅。     

The breakdown electric field between two conducting spheres by themethod of images

The determination of the breakdown electric field of air between two identical conducting spheres is a good example of the use of the method of images to solve a practical problem in engineering electromagnetics. The sparkover electric field is computed from published or measured data for the breakdown voltage by using the theoretical solution for the image charges. Thus students are exposed to a sophisticated method of images solution involving two sets of infinitely many charges. Additional educational benefits include an enhanced appreciation for the properties of air as an insulator, for the limits of the electroquasistatic approximation, for the numerical convergence properties of infinite series, and for the history of science. Instead of using published tables, an exposure to high-voltage engineering to obtain measured breakthrough data is an option if a suitable laboratory is available     

安全性评价在电力生产中发挥作用的探讨

阐述了黑龙江省电力有限公司所属发供电企业开展安全性评价的过程，分析了开展这项工作以来发生设备事故、一类障碍的情况，从中总结出安全性评价在发供电企业电力生产过程中的作用。     

Accurate evaluation of the magnetic field strength of largesubstation air-core reactor coils

A circular cylindrical conductor segment is a basic modeling element of substation air-core reactor coils. The analytical expressions for evaluating the stationary and quasi-stationary magnetic field strength of a segment are derived. In the derivation, a surface source model is developed to substitute the given volume current distribution by equivalent surface sources. The magnetic flux density of sample coils is calculated by using the derived equations. The results are compared with those obtained by the finite element method. Good agreement is observed. The derived equations are very useful for solving problems that involve the accurate calculation of the magnetic field distribution around a coil, the magnitude of forces on a coil, the current distribution in the conductors of a coil and the inductive properties of a coil