汽轮发电机端部电动力的有限元计算

本文采用有限单元法，在考虑了汽轮发电机端部结构涡流及媒质非线性的情况下，借助于现有的短路电流计算理论，计算了汽轮发电机定子绕组端部电动力的分布，并就端部磁屏蔽对电动力的影响作了计算分析，在此基础上编制了适用于微机系统的端部场及电动力计算专用软件，软件通用性好，使用方便，并能直观地显示计算结果。     

Experiment of force‐balanced coil for magnetic energy storage

Higher magnetic field is of great advantage to superconducting magnetic energy storage because it promises a compact device. However, it does not affect the serious problem of huge electromagnetic forces caused by high magnetic fields and large coil current. Electromagnetic stresses, reaching as much as several hundred bars, thus become a major factor in determining whether a large‐size strong magnetic field system can be established. In order to solve this problem, we have proposed the force‐balanced coil (FBC) concept that reduces the huge centering electromagnetic forces by balancing them with the hoop forces caused by the toroidal current. Then we designed and fabricated a small‐size superconducting FBC system to demonstrate the FBC concept. It was successfully excited up to near rated current. It is shown that the FBC system has the potential for simplifying the supporting structures and making the facility compact. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 82–91, 1999     

大型电力变压器铁心电磁振动数学模型

描述了电力变压器铁心电磁振动的数字模型建立过程,讨论了如何从能量守恒和功能转换的角度描述表征磁致伸缩现象的磁场力,并导出了变压器铁心电磁振动的数学模型.     

导波雷达液位测量装置在大型火力发电厂的应用

导波雷达液位计采用了TDR(时域反射)原理,电磁波传播不受介质密度、介质粘度、介质蒸汽、液面波动、液面泡沫的影响,对液位的测量精确,并且能耗低,在大型火力发电厂液位测量方面有广阔的应用前景。     

H∞ control approach to a magnetic levitation system by 4-point attraction with nonlinear characteristics

An H_∞ control system design for a magnetic levitation system by 4 points attraction is presented. In the levitation system, a vehicle which runs as the secondary in a reluctance-type linear motor is levitated by four pairs of attraction forces and guided by two pairs of attraction forces. Because it has contactlessness, in the field of semiconductor products, its application is favorable for ultraclean environments in microscopic processing. In the control system design, the influence of both disturbances and uncertainties in the model is considered. The main disturbances stem from the position sensors. The uncertainties are divided into electromagnetic and mechanical ones: the former are due to the gain change in the current amplifier, the influence of leakage flux and linearization error in the magnetic circuit, and the latter are due to the changes of the mass and the moment of inertia of the vehicle. Therefore, the designed controller is indispensable to guarantee robustness of this system for both stability and performance. The controller design is based on the standard H_∞-optimal control problem. As the novel features in this paper, the low sensitivity and the robust stability for this system design is obtained. Further, there are two-poles on jω-axis in the controlled model, and an integrator is included in the controller so that equivalently there are three poles on the jω-axis in the model. Finally, several experiments, comparisons and simulations are carried out to verify the low sensitivity and robustness of the designed control system.     

Approximate Expressions for Maximum Values of Transient Magnetic Fields and Electromagnetic Forces Imposed on Windings in Superconducting Generators

As superconducting generators have a number of advantages, the investigations for such machines have actively been carried out throughout the world. In the superconducting generator, it is very important to support the field winding and to protect it from quenching. On the other hand, since the armature winding is of air core, the evaluation of eddy current loss in the winding and the way it is supported arc inevitable. Thus, the magnetic fields and the electromagnetic forces acing on both the field and the armature windings at the early stages of the machine design should be known. In previous papers the transient behavior of magnetic fields and electromagnetic forces acting on the windings of a superconducting generator based on a computer simulation for a sudden 3-phase fault have been discussed in part. However, the behavior of magnetic fields and electromagnetic forces during transient period is very complicated and many calculations are required to determine their maximum values. In this paper, for practical use at the early stages of the machine design, approximate expressions are derived to calculate the maximum values of the magnetic fields and electromagnetic forces on the windings in the case of a 3-phase fault. To check these expressions numerically, a 1000-MVA superconducting generator was conceptually designed. The numerical results obtained by using these expressions agree well with the computer simulation results.     

Electromagnetic forces in three-phase rigid busbars withrectangular cross-sections

A three-phase busbar arrangement with straight rigid conductors carrying short-circuit currents is investigated. Calculations are made assuming steady-state AC current with a peak value equal to the peak value of the short-circuit current. This assumption is used in the related IEC Standards 865/92. In this paper, the electromagnetic forces and current densities are calculated by solving the electromagnetic field diffusion equation numerically, using finite elements. The results are compared with results calculated according to the IEC Standards 865/86, as well as with the corresponding technical revision IEC 865/92. The comparison involves arrangements with rectangular cross-sections, as used in AC indoor installations of medium and low voltage. The forces calculated, especially in cases of multiple sub-conductors per main conductor, were greater than those calculated according to the above Standards. In older Standards this difference is up to fifty per cent, while in the revision this difference is smaller. The differences are probably due to proximity effects     

Bloelectromagnetics Research Activities in Europe [Health Effects]

A recent report issued by EMF-NET offers a lengthy list of European projects on the biological effects of power line and wireless communication electromagnetic fields. The list also includes projects on potential risks related to exposure in the working environment. The EMF-NET project is an initiative of the EC and is titled "Effects of the exposure to electromagnetic fields: from science to public health and safer workplace." This four-year project, which is to conclude in 2008, is one of the most ambitious and all-encompassing programs funded by the EC to date. It targets exposures from a wide range of nonionizing electromagnetic-energy-emitting devices, sources, and systems - including power lines, cellular mobile phones, base stations, broadcasting antennas, and household electrical appliances such as mixers and induction ovens (IH hobs) - as well as various electromagnetic equipment found in industry environments and health care facilities     

神经网络法优化接触器电磁系统

将人工神经网络优化方法引入接触器电磁系统的优化设计中,利用人工神经网络强大的非线性逼近能力和高效率的并行计算功能进行优化.采用改进BP算法前馈神经网络法,建立了接触器反力特性中拐点位置的动态吸力和激磁电流为输入神经元,以电磁系统的尺寸作为输出神经元的前向三层的神经网络,并以CJX1型接触器为样本,通过变步长法训练神经网络.网络训练成熟后,可对接触器的外型尺寸进行优化.采用神经网络法减少了大量的三维电磁场计算,可以得到很高的优化速度,很快得到结果.经优化后的接触器可减小电磁系统的体积.     

Limiting power characteristics of direct-current electromagnetic motors

Dynamic electromagnetic forces are determined at the energy efficiency limit for an electromagnetic motor. It is shown that the methods for calculating electromagnetic forces and traction forces are the same. The limiting electromagnetic forces are simulated using the FEMM software package.     

Conceptual design of a novel arcless controlled switch

A new current controlled switch is introduced in this paper and its conceptual design approach is described. The device works based on the motion of a liquid conducting medium and uses the built in electromagnetic quantities instead of external feedback signals to control the desired quantities. At first, the proposed electromagnetic structure of the device and the design criteria are introduced. After that the resulted Lorentz force on the moving conducting medium is calculated using FEM software and the motion equations of this conducting medium are solved using a numerical method. Accordingly the design criteria, which are converted to a set of mathematical and physical constraints, can be checked in each time step and the structure or quantities can be modified where needed. Finally some modifications are applied to the design and the switch operation is simulated for some different operating points.     

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     

An arcless controlled switch

A new current controlled switch is introduced in this paper. The switch has inherent control on the current and operates based on the motion of a conducting medium through a set of transition contacts. Basic theory concerning controlled motion of the conducting medium through a liquid metal (LM) interface is exposed followed by experimental study. The structure of the device and the design basis are described and the Lorentz force on the moving conducting medium is calculated using FEM software. Acting major role in the device operation, the forces on the conducting medium have been characterized and the motion equations of this conducting medium are solved using a numerical method. Accordingly, the design criteria, which are converted to a set of mathematical and physical constraints, are checked and the structure or quantities are modified where needed. Finally, a specimen is made and the switch operation is studied.     

基于IPM的脉冲电磁场发生系统

本文介绍了一种脉冲电磁场发生系统，由单片机控制的智能功率模块（IPM），产生大功率脉冲电泳，带动线圈产生所需要的脉冲电磁场，重点阐述了系统的硬件构成及其各部分的主要作用和系统软件的设计过程。     

Dielectrophoresis of Lossy Dielectrics

Dielectrophoresis of a solid particle in a liquid medium is usually studied under the assumption that the dielectrics are ideal. Real dielectrics, however, exhibit nonzero conductivities, and the results are sometimes unpredictable. The particular case of a lossy dielectric sphere in a lossy dielectric liquid is considered. The dielectrophoretic motion following the application of a dc field is studied, and it is shown that the motion is strongly affected by conductivities. From the results it can be deduced, for instance, that the separation of solid particles in liquid media can be based on differences of conductivities rather than differences of permitivities of the two media.     

采用磁性槽楔的笼型感应电机电磁振动特性研究

针对笼型感应电机运行过程中产生电磁振动的问题,探讨磁性槽楔对电机电磁振动的影响。以一台笼型感应电机为例,对同一电机分别采用普通槽楔与磁性槽楔进行磁场、电磁力及电磁振动的计算分析。基于瞬态磁场结果,对电机采用两种槽楔的气隙磁场进行了分析和比较,并得到了两种情况下电机所受电磁力。以电磁力为载荷,研究了电机的电磁振动并给出了振动位移曲线。运用频谱分析的方法,从时域及频域特征量的角度,定量分析了磁性槽楔对电机电磁振动的影响,最后结合实验对理论分析结果进行验证。同时计算电磁振动的方法亦可为研究同类型电机的振动问题提供参考。     

Electromagnetic transport and confinement of liquid metals

Applications in which electromagnetic forces are used to stir, transport, dispense, and/or confine liquid metal are described. Applications include the electromagnetic trough, the electromagnetic mould, pedestal melting, thin strip casting, and levitation casting. Fundamentals relating to the production of electromagnetic forces are reviewed, a number of important applications are discussed, essential design limitations are identified, and the question of modeling for design purposes is considered. It is shown that with present technology, electromagnetic confinement methods cannot be expected to support ferrostatic heads in excess of 10-25 cm. This limit imposes a constraint on the development of new applications, such as the extension of the electromagnetic mold to steel casting and the use of electromagnetic confinement in the strip-casting process     

High-efficiency sterilizer by high-voltage pulse usingconcentrated-field electrode system

Recently, a sterilization method of microorganisms in liquid food using pulsed electric fields (PEFs) has been reported by some researchers. Considering the application to the food industry, the energy efficiency of the method becomes important. It is reported that microorganisms suspended in aqueous solution were killed linearly (logarithmic) by the PEF process using a parallel-plate electrode configuration. The PEF is generated by capacitor discharge through a switch (using stationary, rotary, vacuum tube, and semiconductor, etc.). The survivability ratio decreases with increasing operating temperature and increasing capacitance value of the capacitor. Although many kinds of microorganisms suspended in liquid foods were treated by the PEF system, the energy efficiency was still low in the case of high-conductivity liquid. The authors developed a new electrode system for concentrating the electric field in a liquid food medium. The new electrode configuration made it possible to raise the energy efficiency for the pulsed sterilization process compared to that for conventional parallel-plate or concentric-cylinder electrode systems     

梯度折射率介质内二阶辐射传递方程及其有限元求解

梯度折射率介质内的辐射传递方程可以看作是一类特殊的对流型方程，对流项的存在能够引起解的非物理振荡。该文给出了一个梯度折射率介质离散坐标形式的二阶方程，同时发展了基于此离散坐标形式二阶方程的有限元法用于求解多维半透明梯度折射率介质内的辐射传递问题，最后通过5个算例进行验证。结果表明，与一阶梯度折射率介质辐射传递方程相比，二阶方程具有更好的数值特性，可以有效消除强对流特性引起的非物理振荡现象。基于二阶方程的有限元法可以精确且稳定地求解多维半透明梯度折射率介质内的辐射传递。     

Electromagnetic forces in three-phase leads

The electromagnetic field of two parallel conductors with alternating currents is examined by using the separation of variables method. The influence of the skin effect on the electrodynamic force acting on these conductors is investigated. The electromagnetic forces in three-phase leads are presented, and their graphs are given. The particular cases for small and strong skin effects are also considered.