International Journal of Applied Electromagnetics and Mechanics

Guest-editorial to the special issue on ASAEM 2003

The design and analysis of electrical machines often require analytical models for performance assessment and system simulation. Inductance is one of important parameters of these models. In this paper, the calculation methods of apparent and incremental inductances are introduced for a transverse flux linear motor (TFLM), which has a peculiar coil shape. To consider nonlinearity of the inductances according to current and magnetic materials, nonlinear analysis is performed by 3-dimensional equivalent magnetic circuit network (3D EMCN). The calculation method has been verified by test results.

This paper studies two post-assembly magnetization methods for permanent magnet motors. One is stator winding magnetization method (SWMM) for ferrite magnets. The other is magnetizing fixture magnetization method (MFMM) for magnets having large coercive force like NdFeB magnets. They are applied to three types of permanent magnet motors: SPM type of BLDC motor, LSPM type motor and IPM type of BLDC motor. In case of line start permanent magnet motors(LSPM), the eddy current produced in the rotor bars seriously disturbs magnetizing. Therefore, the magnetization processes are analyzed by using the time stepping finite element method. As a result, it is clarified that the SWMM is proper for the SPM type motor using ferrite magnets and the MFMM is proper for the LSPM and IPM type motors using NdFeB magnets.

It is necessary to install three single-phase shunt reactors in the middle of a 500 kV transmission lines with long distance for compensation of capacitive reactive power of the lines. However, unlike traditional shunt reactors installed in substation, except the high voltage reactor windings, as a kind of special single-phase shunt reactor, there are the low voltage auxiliary windings to be placed in its core or yokes in order to supply few lower-voltage loads for some low voltage devices. In this paper, based on the finite element analysis of three-dimensional nonlinear magnetic field, the self and mutual inductances of the shunt reactor with auxiliary windings are calculated. Further, the Volt-Ampere curves of the shunt reactor with and without loads are also numerically analyzed. The numerical results are verified by measurements of a model and two prototype shunt reactors.

In this paper, the Halbach magnetized linear generator for charging the battery of a mobile apparatus is proposed and characteristics of the generator are investigated. Magnetic characteristics are analyzed by modified Space Harmonic Method and EMF calculation result is also included.

A new ferromagnetic shape memory alloy consisting of Fe-Cr-Co-Ni-Si-Mn has been developed by means of the melt spinning technique. The alloy has both the shape memory effect and the comparatively high-magnetic permeability itself. The shape memory effect can be improved with annealing upon the alloy but at the same time it loses good ferromagnetic properties. This paper discusses shape memory characteristics measured by differential scanning calorimeter (DSC) and thermo-mechanical analyzer (TMA). Improvement of the shape memory effect is observed in samples containing manganese from 5% to 6% (weight percent), after annealing at temperature over 800°C.

This paper presents measured results of the two-dimensional vector magnetic properties in electrical steel sheets under high frequency excitation conditions. The relationship among the maximum flux density, the magnetizing direction, the exciting frequency, the axis ratio of the rotating flux density(the ratio of the maximum flux density and the minimum flux density), and the iron loss is clarified. The results obtained from the non-oriented electrical steel sheet (35A550) and for the grain-oriented electrical steel sheet (35G155) are compared in this paper.

The feasibility of in-situ Eddy Current Monitoring (ECM) under high temperature environment is discussed. For the purpose, an ECM experiment was conducted at a System Safety Benchmark Facility (SSBF), which was designed and constructed for assessing the crack growth behavior of welded pipes in a Boiling Water Reactor (BWR) environment. The target for the monitoring was a large-scale pipe specimen made of austenitic stainless steels 304, 304L and 316L, connected by weld joints of nickel based alloy 182 within the SSBF. Slits were prepared at the Heat Affected Zones (HAZs) and weld lines from the inner surface of the pipe specimen. Eddy Current Testing (ECT) probes were arranged on the outer surface of the pipe specimen at the positions where the slits had been introduced. After exerting the load, it was observed that the ECM experimental signals changed. Subsequently, the numerical simulation of eddy current signals based on the experimental conditions was carried out. As a result of comparison between experimental and numerical eddy current signals, it is shown that the in-situ ECM system makes it possible to observe crack propagation in a BWR environment.

The NDT method using electromagnetic waves has availability for crack detection in large pipes or structures in nuclear power plants. The purpose of this study is then, to develop a new method to determine the crack size and location with high speed and accuracy. Through this study, it has been shown that the transmitted wave carries a lot of information on crack depth and the obtained signals of reflected wave below the cut-off frequency depend on the crack position. Experimental results indicate that there exists attractive possibility in the new NDT method.

In this paper, new progress on the ECT-based crack sizing techniques is presented. At first, a fast and accurate forward simulator, which is indispensable in the inversion of ECT signals, is briefly introduced. Several schemes for inversion of crack signals are presented then for EDM cracks, stress corrosion cracks (SCC) respectively. In addition, scheme and reconstruction results for multiple cracks, deep cracks and cracks in the welding part are also given. From the numerical results, it is demonstrated that sizing of single crack from ECT signals has become possible even for a natural crack or a crack as deep as 10 mm. For multiple cracks, more effort is necessary for its modelization and reconstruction.

From the application of genetic algorithm (GA) to the optimal design of some electromagnetic devices, it is found that its convergence speed is directly affected by the similarity of crossover codes. Based on the analysis for crossover operation a crossover-controlled genetic algorithm (CCGA) is presented. For increasing the interrupting capability at no load current, a permanent magnetic field is drawn into the arc-rotated interrupter of sulfur hexafluoride circuit breaker. Under the condition of same angular frequency at any point on arc, the desirable flux density is determined. On the basis of finite element analysis the optimal magnetic field distribution is obtained by applying CCGA. As a result 18.6 percent of CPU time taken by GA is saved and the interrupting performances at no load and short circuit currents are improved.

In this paper, μ + □ evolution strategy (ES) was applied to brain electrical source localization problems using electroencephalography (EEG). The results by the ES were compared to those by simulated annealing (SA) and genetic algorithm (GA), which have been typically used for the brain source localizations. Monte-Carlo simulation and phantom experiment study demonstrated that the use of ES could enhance both accuracy and computational efficiency.

This paper deals with the improvement of starting characteristic for Moving Magnet type Linear Oscillatory Actuator (MM-LOA) using a spring damper. MM-LOA is applied to variable loads such as vacuum pumps and compressors. However, it has the characteristic of over-displacement in starting state because of the low inertia of mover. To improve the starting characteristic, a spring damper has been adopted in a mechanical system. The design parameters have been computed by 2-D Finite Element Analysis (2-D FEA). In addition, dynamic characteristic analysis has been performed by time differential method. The propriety of improved starting characteristic is verified by a comparison of analyzed results with those of experiments.