宮城 大輔

A Cable-in-Conduit-Conductor (CICC) is a composite conductor consisting of many superconducting strands twisted in multiple steps. The CICC has the characteristics which make it suitable for fusion magnets, but lower critical current than expected have been observed in some experiments. The resistance distribution between the strand and the copper sleeve in a "Wrap Joint" is expected to be inhomogeneous and to affect the current distribution and the critical current in the CICC. We measured the DC resistance distribution between the strand and the copper sleeve in a simple model Wrap Join at liquid helium temperature and observed an inhomogeneous resistance distribution. A 3-D strand path calculated by considering the manufacturing process of CICC and an algorithm from previous work were used to evaluate the resistance distributions between the strand and the copper sleeve. The calculated and measured resistance distributions showed the same overall trends. The homogeneity of the resistance distribution between the strand and the copper sleeve is strongly dependent on whether the strand is in direct contact with the copper sleeve or not. Maximizing the number of direct contacts between the strand and the copper sleeve of the "Wrap Joints" was effective for reducing any possible current imbalances.

Purpose - In the laminated core of transformer, motor, etc. each electrical steel sheet is usually insulated in order to reduce the eddy current loss. Raw steel sheets without insulation are sometimes used in a small core of electrical machines and electronic equipments, because the cost of iron core can be reduced if cheap steel sheets without insulation are used in the core. The purpose of the paper is to show how the contact resistance between sheets of laminated core affects the interlaminar eddy current and to show the criterion for judgment of the necessity of insulation. Design/methodology/approach - The eddy current losses of core made of SPCC (cold rolled steel sheets) of different widths with and without insulation under various conditions are analyzed by using the finite element method (FEM) considering the contact resistance. The equivalent circuit for such a laminated core without insulation is shown. The experimental investigation is also carried out. Findings - A criterion for the judgment of insulation is examined. It is shown that the increase of eddy current is affected by the ratio (this corresponds to the criterion) of the resistance of steel and the contact resistance. Originality/value - The paper clarifies a criterion for the necessity of insulation between sheets of laminated core. It is shown that a similar tendency to the measured value of eddy current loss can be obtained by utilizing the modeling method of laminated core.

From the point of view of environment and energy problems, the renewable energies have been attracting attention. However, fluctuating power generation by the renewable energies affects the stability of the power network. Thus, we propose a new electric power storage and stabilization system, Advanced Superconducting Power Conditioning System (ASPCS), in which a Superconducting Magnetic Energy Storage (SMES) and a hydrogen-energy-storage converge on a liquid hydrogen station for fuel cell vehicles. The ASPCS proposes that the SMES coils wound with MgB2 conductor are indirectly cooled by thermosiphon circulation of liquid hydrogen to use its cooling capability. The conceptual design of cooling scheme of the ASPCS is presented. (C) 2013 Elsevier B. V. All rights reserved.

In order to use effectively renewable energy sources such as wind and photovoltaic power generations, we propose a new system, called Advanced Superconducting Power Conditioning System (ASPCS), that is composed of superconducting magnetic energy storage (SMES), fuel cell-electrolyzer (FC-EL), hydrogen storage, dc/dc and dc/ac converters, and controller. The new system compensates the fluctuating electric power generations with SMES having characteristics of quick response and large I/O power and with hydrogen energy having characteristics of large storage capacity. The ASPCS will be combined with a liquid hydrogen station for FC vehicles. The SMES is a key component of the ASPCS to compensate the fast fluctuations of the renewable energy generations that cannot be compensated by prediction using the Kalman filtering method. The design study of the 50 MJ SMES coil was performed with an MgB2 conductor to be operated at 5 T maximum and 20 K by using liquid hydrogen of the FCV stations. The stability and ac losses of the coil were estimated in this study.

It has been observed that the measured critical currents of cable-in-conduit-conductors (CICC) in some experiments are smaller than the expected ones. One of the reasons is the occurrence of unbalanced current at steady state caused by uneven contact resistances between strands. Because the contact resistance between strands is dependent on the contact length, the number of contacts and the loop length between strands, we need information about all strands' locations in the CICC. Therefore, we developed an evaluation method that describes the locations of every strand in the CICC in consideration of the twist disorder based on manufacture processes and elastic potential energy. Moreover, we compared the contact number and length between strands obtained by our calculated strands' positions with measured ones. We found that both results are in good agreement and clarified the validity of our calculation method of all strands' positions in the CICC.

In the electromagnetic field computation in consideration of nonlinear magnetic anisotropy, the solution by the Newton-Raphson method has some problems which are an asymmetric matrix and poor convergence characteristic. We applied the Fixed-Point method to the electromagnetic field computation in consideration of nonlinear magnetic anisotropy and examined the usefulness of the Fixed-Point method through comparing the Fixed-Point method with the ordinary Newton-Raphson method. The Fixed-Point method with a symmetric matrix is quite faster than the Newton-Raphson method with an asymmetric matrix. Therefore, the Fixed-Point method is a very useful technique in nonlinear magnetic anisotropy problems.

Purpose - The purpose of this paper is to propose the speed-up of the fixed-point method by updating the reluctivity at each iteration (this is called a modified fixed-point method). Design/methodology/approach - A modified fixed-point method, which updates the derivative of reluctivity at each iteration, is proposed. It is shown that the formulation of the fixed-point method using the derivative of reluctivity is almost the same as that of the Newton-Raphson method. The convergence characteristic of the newly proposed fixed-point method is compared with those of the Newton-Raphson method. Findings - The modified fixed-point method has an advantage that the programming is easy and it has a similar convergence property to the Newton-Raphson method for an isotropic nonlinear problem. Originality/value - This paper presents the formulation and convergence characteristic of the modified fixed-point method are almost the same as those of the Newton-Raphson method.

Cable-in-Conduit-Conductor (CICC) is used for the international thermonuclear fusion experimental reactor (ITER) toroidal field (TF) coils. But the critical current of the CICC is measured lower than expected one. This is partly explained by unbalanced current distribution caused by inhomogeneous contact resistances between strands and copper sleeves at joints. Current density in some strands reaches the critical under unbalanced current, and the quench is occurred under smaller transport current than expected one. In order to investigate the contact resistances, we measure the three-dimensional positions of all strands inside the CICC for Large Helical Device (LHD) poloidal field (PF) outer vertical (OV) coil, and evaluate contact parameters such as number and lengths of strands which contact with a copper sleeve. Then, we simulate the strand positions in the CICC using the numerical code which we developed, and compare the contact parameters which evaluated from the measured strand positions and the simulated ones. It is found that the both results are in good agreement, and the developed numerical model is useful for evaluation of the contact parameters. We apply the code to various CIC conductor joints to obtain optimal joint parameters. ? 2012 The Japan Society of Plasma Science and Nuclear Fusion Research.

The pulse width modulation (PWM) inverter has been used for the control of a motor since the rotating speed can be changed efficiently and easily. In order to estimate the iron loss in an iron core with sufficient accuracy under a PWM inverter excitation, it is necessary to understand correctly the influence of operating condition and circuit parameter on iron losses. In this paper, we measured magnetic properties of the nonoriented electrical steel sheet excited by a single-phase full-bridge PWM inverter using a ring specimen that corresponds to a magnetic circuit of an actual motor core. The effect of the carrier frequency and circuit resistance on the iron loss and the behavior of minor loops was examined. It is shown that the iron loss is increased when the circuit resistance is increased due to the generation of minor loops. Therefore, the circuit resistance should be decreased in an actual motor system.

Permalloy is used in a magnetically shielded room to inhibit the penetration of externalmagnetic field, etc. The flux density in permalloy used in the shielded room is of the order of a few mT or lower. In order to examine the performance of such a shielded room, the dc magnetic properties at low flux density is necessary. In this paper, we developed a measurement method of dc (5 mHz) magnetic properties of permalloy under such a low flux density. It is shown that the dc magnetic properties could be measured more than 4 mT by paying the attention to the degaussing of specimen and applying the correction of drift and offset of measurement system.

In order to investigate superconducting properties such as long decay time constants, current imbalances and critical current degradations, we need detailed information about all strand locations in the cable-in-conduit conductor (CICC), and hence we develop a new estimation method to obtain all strand locations. It is very difficult to estimate all strand positions because all strands in the real CICC are squeezed into the conduit and are not regularly arranged but displaced. In order to estimate these strand displacements due to the compression, we introduce mechanical potential energy among strands, and hence we search the minimum energy locations which should be realized in the conductor. In order to calculate this process, we perturb all strands from the original locations and continue these processes by using a genetic algorithm until the potential energy is minimized. This analytical method is very useful to simulate all strand positions and allows us to investigate all the electromagnetic phenomena in the CICCs. ? 2011 IEEE.

It is an urgent issue to reduce global carbon-dioxide in the world, and hence the renewable energy, that is environmentally friendly, should be supplied as a large amount of the electric power. Since installation of a large amount of the fluctuating renewable energy, such as wind turbine and photovoltaic, will cause the power utility network unstable, we propose an advanced superconducting power conditioning system (ASPCS) that is composed of Electrolyzer-Hydrogen-FC (EL - H-2 - FC) and SMES cooled with liquid hydrogen (LF2) from a LH2 station for vehicles. The ASPCS has a function of compensating the fluctuating renewable energy with SMES that has quick response and large I/O power, and with EL - H-2 - FC that has moderate response and large capacity. The SMES is wound with MgB2 superconductor with a critical temperature of 39 K from an economical point of view, because it is cooled with LH2 through a thermo-siphon system to keep safety against a flammable gas. The ASPCS effectively fulfills a power balance by applying a statistical prediction method of Kalman filter algorithm. The capacity of SMES is optimized by using the trend prediction for a number of wind power data. The overall electric efficiency of the ASPCS is evaluated for a typical wind generator.

In order to use effectively renewable energy sources, we propose a new system, called Advanced Superconducting Power Conditioning System (ASPCS), that is composed of SMES and Fuel Cell-Electrolyzer (FC-EL) in connection with a liquid hydrogen station for vehicles. The new system will compensate the fluctuating renewable energy sources with SMES having characteristics of quick response and large I/O power, and with FC-EL having characteristics of moderate response and large storage capacity. The SMES coil with an MgB2 conductor operated at 20 K is cooled with a thermo-siphon cooling system by using cryogen from the liquid hydrogen station. The necessary minimum storage capacity of SMES is estimated as 50 MJ for compensating output power of 1 MW. A four-pole SMES coil is designed by using stranded cable concept. The design study of the SMES coil composed of the MgB2 conductor and the thermo-siphon cooling system is reported.

The optimization method using the ON/OFF sensitivity analysis has an advantage that an epoch-making construction of magnetic circuit may be obtained. Therefore, it is attractive for designers of magnetic devices. We have already developed the ON/OFF method for the optimization of a static magnetic field problem, and the effectiveness is verified by applying it to the optimization of magnetic recording heads. In this paper, the ON/OFF sensitivity method is extended to the optimization of the eddy current problem using the adjoint variable. The newly developed ON/OFF method is applied to the determination of the optimal topology of the yoke of the billet heater for rolling wire rod. As a result, the optimal shape of yoke, which we could not imagine beforehand can be obtained. It is shown that the local heating of the yoke was reduced without decreasing the heating efficiency.

A critical consideration in the optimal design of magnetically shielded rooms is the manner in which an external magnetic field, which should be shielded, is imposed on a target area. In this paper, we examined the possibility of applying the B-s method (the method of which the magnetic field B-s in the analyzed region is given) to the shielding problem with a measurement-based magnetic field, which includes an irrotational field component as noise, and, therefore, is inconsistent with Maxwell's equations. We show that the B-s method has a well-defined physical meaning for such an irrotational field component. Furthermore, we explain why the convergence and the accuracy of the B-s method are better than those of the A method.

Recently, because of the development of the power electronics technology, PWM inverters have been used to drive motors for achieving precise and energy efficient control. The precise estimation of the increase in iron loss due to high harmonic components of flux, including carrier frequency, is important in the design of motors excited by a PWM inverter. We measured the iron losses of non-oriented electrical steel sheets that were excited by using a single-phase full-bridge PWM inverter and examined the influence of carrier frequency and circuit resistance on the iron losses. We showed that the iron loss increased because of the generation of minor loops when the circuit resistance was high. Therefore, the circuit resistance should be decreased in an actual motor system. © 2012 The Institute of Electrical Engineers of Japan.

In the laminated core of transformers, motors, etc., each electrical steel sheet is usually insulated in order to reduce the eddy current loss. It has been reported that the insulation is not necessary in such a laminated core in some conditions. However, few studies have been performed in quantitative and systematic examination of the relationship between the insulation and eddy current. In this study, the eddy current losses of a core made of SPCC (colded rolled steel sheets) of different widths with and without insulation under various conditions are analyzed by using the finite element method (FEM) and considering the contact resistance. The equivalent circuit of a laminated core without insulation is presented, that can be used for determining the necessity of insulation. It is shown that the increase in the eddy current is affected by the ratio of the resistance of steel to the contact resistance. An experimental investigation is also carried out. © 2012 The Institute of Electrical Engineers of Japan.

Neodymium-iron-boron (Nd-Fe-B) magnets exhibit exceedingly high maximum energy products and remanences. Their coercivities, however, decrease rapidly with increasing the temperature, and the magnets are easily demagnetized at elevated temperatures. To reduce the effects of temperature, the coercivity at the room temperature is enhanced by the addition of the dysprosium (Dy), which causes a reduction in remanence. The Grain Boundary Diffusion process is a technology to enhance coercivities while suppressing a large reduction in remanences. Dy that is effective for the coercivity enhancement is supplied from the magnet surface and diffused into the magnets through the grain boundary phase, and then put at the grain surface. When the Grain Boundary Diffusion process is applied to relatively large magnets, the partial coercivities near the magnet surface, where higher coercivities are generally required, can be enhanced effectively. In other words, the magnets exhibit nonuniform coercivity. We have conceived a simple and effective method for estimating the demagnetization curves of such nonuniform coercivity magnets. In this paper, the validity of the estimation method was examined. © 2012 The Institute of Electrical Engineers of Japan.

A multi-laminated HTS tape conductor has been recently developed to fabricate large pancake coils such as SMES. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of different inductances of all tapes. The pancake coil has been widely used for large magnet, because the pancake coil is tightly wound and endures large electromagnetic force. The tape transpositions at both ends of the pancake coil are effective for the coil fabrication, because it cannot damage the conductor. It is very important to analyze current distribution in the multi-laminated tape conductor used for the pancake coil. In this paper, we analyze the current distribution in the tape conductor by using circuit model, and then propose a relationship between the laminated tape number of the conductor and the pancake coil number to obtain the homogeneous current distribution. We fabricated the double pancake coil based on the relation, tested it to verify the relation and demonstrated the homogeneous current distribution in the conductor.

Various kinds of HTS bulk motors are proposed and have been developed. Generally, those motors are driven by semiconductor inverters and currents fed to the armature windings contain high harmonics. Therefore, the bulks are exposed to high harmonics magnetic fields and AC losses are produced in the bulks. The AC losses deteriorate the efficiency of the motors and cause temperature rise of the bulks which decrease the trapped magnetic fluxes of the bulks. Usually, electro-magnetic shielding devices are inserted between the bulks and armature windings. However, the shielding devices degrade compactness of the motors. Therefore, it is important to have knowledge of the influence of the high harmonics magnetic fields on the AC losses and trapped magnetic fluxes of the bulk for optimum design of the shielding devices. In this work, the authors experimentally study the influence of high harmonics magnetic fields. (C) 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.

In order to reduce global carbon-dioxide in the world, we propose an Advanced Superconducting Power Conditioning System (ASPCS) which is composed of 5 MW renewable energy resources and 1 MW hybrid storage system. The hybrid storage system is composed of FC-H-2-EL and SMES which is installed adjacent to a LH2 station for vehicles. Since the SMES can be operated at 20 K which is a saturated temperature of LH2, we can use MgB2 superconductors. In the ASPCS, 100 MJ storage capacities of the SMES should be required. This paper focuses on studies into a conceptual design of SMES toroidal coil composed of the MgB2 and indirectly cooled by LH2. (C) 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of ISS Program Committee.

In order to analyze magnetic characteristics of magnetic devices, it is necessary to accurately measure magnetic properties of an electrical steel sheet in arbitrary directions. In this paper, we developed a 2-D-single-sheet tester (SST) using diagonal exiting coils in order to improve the measurement accuracy under high flux condition. The measurement region of flux density B and magnetic-field strength H is examined for the accurate measurement. The magnetic properties of grain-oriented electrical steel sheet under alternating magnetic flux and rotating magnetic flux are measured using our system. The accuracy of measurement in the case of grain-oriented sheet is examined by comparing the measured results using 2-D-SST with those by using an ordinary SST under alternating flux excitation. The effect of positioning error of orthogonal B and H coils on measurement accuracy is also discussed.

In order to accurately design magnetic devices that are used at high temperature, it is necessary to understand the behavior of several magnetic materials at high temperature. However, the precise measurement of magnetic properties at around Curie temperature is difficult, because the permeability is near to that of air and the preparation of measuring setup having an insulation which can be used at around 800 degrees C is not easy. In this paper, the magnetic properties of several magnetic materials until Curie temperature are measured. It is shown that the change of iron loss of cold rolled steel sheet SPCC with the temperature is more remarkable than that of electrical steel sheet.

Reduction of the cooling cost and the securing of thermal stability are important problems to put HTS power cables to practical use. It is in particular very important in an HTS cable design to estimate the temperature rise by the AC loss and the over current precisely. The detailed behavior of the ac loss and the temperature distribution in a co-axial multi-layered BSCCO HTS power cable are analyzed by the magneto-thermal coupled method considering the temperature dependence of the critical current density and the Cu electrical resistance. Moreover, the temperature rise by the ac loss and the ohmic loss in each layer under the over current is calculated and the cooling necessity from the inside of a Cu former is examined.

For the design of an Interior Permanent Magnet (IPM) motor with small torque ripple and large driving torque, the optimal design method called the ON/OFF method is attractive, because a new magnetic circuit, which we could not imagined beforehand, may be obtained. In this paper, a non-parametric optimization technique to find a new magnetic circuit which minimizes a torque ripple and maximizes a driving torque of IPM motor is examined. The effectiveness of the ON/OFF method for the optimal design of a motor is examined by applying it to the design of the verification model of the IPM motor established by the technical committee of IEE of Japan. Factors affecting torque ripple and driving torque of the obtained optimal motor core are also discussed.

The dc B-H curve or hysteresis loop of a magnetic material is necessary even in dynamic field analysis. Conventional methods for measuring magnetic properties require special shape specimens like a plate or a rod of specified dimensions. In this paper, we developed a novel technique for measuring the dc magnetic properties of specimens with various shapes using an electromagnet and a special probe having two Hall elements with very small active area. It is also shown that the magnetic field is not uniform near the specimen, and the magnetic field strength H on the surface of the specimen can be obtained by extrapolation. In addition, the dc excitation due to the earth's magnetic field can be avoided by setting small gaps between the specimen and pole pieces. The magnetic properties of an electrical steel sheet and a cylindrical specimen of a soft magnetic composite can be measured using the proposed technique. It is shown that the measured result using the proposed system is almost the same in comparison to a single sheet tester. © 2011 American Institute of Physics.

The optimization method using the ON/OFF sensitivity analysis has an advantage that an epoch-making construction of magnetic circuit may be obtained. Therefore, it is attractive for designers of magnetic devices. We have already developed the ON/OFF method for the optimization of a static magnetic field problem, and the effectiveness is verified by applying it to the optimization of magnetic recording heads. In this paper, the ON/OFF sensitivity method is extended to the optimization of the eddy current problem using the adjoint variable. The newly developed ON/OFF method is applied to the determination of the optimal topology of the yoke of the billet heater for rolling wire rod. As a result, the optimal shape of yoke, which we could not imagine beforehand can be obtained. It is shown that the local heating of the yoke was reduced without decreasing the heating efficiency.