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The 1-MW and 100-HP superconducting synchronous motors with high-temperature superconducting (HTS) rotor coils were developed and tested. Several electrical parameters, such as load angle and back electromotive force (EMF), are derived from the test result. In the case of the 1-MW motor, the full-load test could not be possible, at 3600-r/min rating speed, due to a vibration problem at the test bed. By using the electrical parameters obtained from the 1800-rpm test results, output power and efficiency characteristics are predicted. The load angle of a synchronous motor, which is generally denoted by δ, is defined as the phase angle difference between the back EMF and the stator terminal voltage. The generated torque is proportional to sin δ, and the maximum torque is generated when this angle is 90°. The superconducting synchronous machine has smaller load angle than a conventional one, due to smaller reactance of the stator coils. Therefore, it has larger maximum torque capacity than the conventional one. The developed motors connected to driving and load induction machines were tested. Through open-circuit test, back-EMF voltages were measured, and load angles were derived from load tests.

A superconducting motor shows several advantages, such as smaller size and higher efficiency, over a conventional motor, especially utilized in ship propulsion applications. However, the size reduction merit appears for large capacity, more than several MW. We develop a large capacity synchronous motor with a rotating high-temperature superconducting (HTS) coil, that is aimed to be utilized for ship propulsion, so it has a low rotating speed of about 200 rpm. The ship propulsion motor must generate high electromagnetic torque instead of low speed. Therefore, the rotor (field) coils have to generate a large magnetic flux that results in a large amount of expensive HTS conductor for the field coil. In this paper a 17 MW HTS motor for ship propulsion is designed with a cost-effective method because the HTS conductor cost is a critical factor in the construction of an HTS motor. Unlike conventional rotating machines, the superconducting motor consists of an iron-coreless structure. Most conventional motors can be designed with small error based on two-dimensional magnetic field analysis. However, the superconducting motor shows an even larger error between the two- and three-dimensional based designs. Thus, in order to improve the design accuracy, we have calculated the back electromotive force (EMF) using 3D magnetic field analysis. An output performance evaluation has also been carried out to obtain a design with higher efficiency.

Superconducting high gradient magnetic separation (HGMS) has advantages to treat wastewater because it can generate high magnetic field and achieve rapid purification. In this study superconducting HGMS was applied to remove impurities from the condenser water in thermal power plant. The condenser water contained mainly hematite and maghemite and it was highly magnetized than hematite. In the HGMS tests using a 6-T cryo-cooled Nb-Ti superconducting magnet, the turbidity of the condenser water was effectively reduced up to 99.6% and the result showed better performance than that of the 0.5-T permanent magnet test. The higher magnetic field was applied in the range of 1-6T, the more iron oxides were removed. The effect of magnetic filter configuration on the condenser water treatment was also investigated. Consequently superconducting HGMS system can be applicable to remove iron oxide impurities from condenser water in thermal power plant.

The Hall probe measurement system was used to measure the critical current distribution of superconducting coated conductor. The system consists of reel to reel moving apparatus, 7 array Hall probe, a rotary encoder and permanent magnet. The magnetic field profile across the width of superconducting coated conductor using Bean's critical state model was calculated. The effect of various parameters of the formulas on the magnetic field distribution and the effect of shape and size of artificial defects, which were formed on the surface of SmBa2Cu3O7-d(SmBCO) coated conductor using laser marking system, on the Hall probe magnetic field signal of the Hall probe measurement system was investigated.

It is environmentally important to recycle the wastewater, since paper factories use a large amount of water and equivalent amount of wastewater is generated. Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. In this respect, we prepared two types of superconducting magnets in order to apply HGMS parts for wastewater purification process. We made cryo-cooled Bi-2223 (HTS) superconducting magnet parts with room temperature bore in diameter of 70 mm and 200 mm in height. Also, cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The faster wastewater's flow rate was, the worse the degree of clarity in treated water was. The ability of wastewater treatment in the case of magnetic separation used with 10 of magnetite particles was better than that in the case of 5 of magnetite particles.

Superconductivity synchronous motors compared with conventional motors can reduce the motor size and enhance the motor efficiency for low-speed and high torque applications under the space constraints for propulsion system. Especially, homopolar superconductivity synchronous motors (HSSMs) need less superconductor and lower magnetic flux density in superconductor field coil than air-cored superconductivity synchronous motors (ASSMs). In addition, mechanical structure is more simplified and stability is increased because the superconductor field coil of HSSMs is not rotated in operation. In this paper, we present the outline of HSSMs including structure, characteristics and operational principles with the conceptual design of HSSM.

A 1 MW class superconducting synchronous rotating machine has been designed as a draft based on 2-dimensional (2D) magnetic field distribution considering several conditions such as superconducting wire length, machine efficiency, size and so on. By the way from 2D design it is not possible to consider the effect of end coils and end portions of stator iron yoke especially in superconducting machine with air-cored structure which increases magnetic field difference between 2D and 3D analysis. In this paper electrical design based on the 3D magnetic field distribution is conducted to get more proper design result and reduce design errors from 2D design approach. As the machine has larger capacity, the superconducting machine will show the advantages more and more over the conventional machine. Although the advantages at 1MW rating are not so great, the 3D design approach to get more optimized result would be very helpful for larger superconducting synchronous machine design. Through 3D analysis such as EMCN (equivalent magnetic circuit network) method and Flux-3D FEM (finite element method), we could get smaller machine size, higher efficiency, and smaller Bi-2223 HTS (high temperature superconducting) wire length than the 2D design result. Moreover influence of an important parameter, synchronous reactance, has been analysed on the machine performances such as voltage variation and output power.

In large scale applications, such as SMES, motors and generators, High Temperature Superconducting (HTS) magnets are constructed with many stacks of the double-pancake coils connected in series. In spite of its higher thermal stability, HTS magnet can experience a severe quench, which can resulted from a very small portion. From HTS magnet design point of view, it is very important to predict the possibility of occurrence quench in the designed magnet to provide a suitable quench protection device. In this paper a highly instrumented HTS race track double-pancake coil was prepared to examine the quench development characteristics. It is wound using the Bi-2223 tape. Many voltage taps, cryogenic thermocouples and heater were installed in the winding. Conduction cooling method is adapted for the convenience of temperature. Quench development in the coil was measured under different operating current. The experimental details and results are presented in this paper.

This paper proposes an effective parametric design for high temperature superconducting (HTS) synchronous motors with 3D equivalent magnetic circuit network (EMCN) method. Proposed design process consists of 5 steps which are electric design, mechanical design, characteristic analysis for field and armature, and motor characteristic analysis. Especially, in order to predict the performance of HTS synchronous motors, the variation of output power characteristics according to the variation of back electromotive force (BEMF) and inductance is analysed in electric design. Reliability of proposed design process and developed program is verified through the comparison of the results of commercial program using 3D finite element analysis (FEA) method.

This paper proposes an effective design process for 1 MW HTS superconducting motor by using 3-dimensional equivalent magnetic circuit network method (3D EMCN) and response surface methodology (RSM). During the process, 3D EMCN is used with a simplified 3D analysis model to get electric parameters in short time. RSM is used for the motor optimal design to improve power density. The usefulness of this method is verified through the comparison of the performances of the optimal geometry and those of the initial geometry

A 100 HP rated synchronous motor with superconducting rotating field winding has been designed based on the formulated equations established from 2 dimensional magnetic field distributions in a cylindrical coordinate. The cross-section was drawn based on calculated design results via Fortran program and then modeled with FEM (finite element method) to investigate the machine performances. First of all, the magnetic field distributions are analyzed in many ways according to the field directions and the armature currents. Especially after the rotating field winding is arranged with BSCCO-2223 high-temperature superconducting (HTS) pancake coils, the exerted magnetic field normally on the HTS tape is calculated through FEM. And the machine output power is calculated according to the torque angles that lie between the field and the armature main flux lines. Moreover, this paper includes the eddy-current loss variations of a copper damper located between the field and the armature coils. Finally, 3 dimensional magnetic field distribution is also calculated via FEM. The radial components of magnetic field are compared along the center line of an armature conductor section between 2 dimensional and 3 dimensional results. By the comparison we make sure that about 30% of machine output is added from the end effect of HTS field coil and more accurate design approach is possible.

Superconducting racetrack coils have worse quench characteristics due to the different structure from solenoid coils. Racetrack coils also have round curvatures along their end portions; however, a large difference in their structures from solenoid coils exists in the straight portions, which is considered as a cause of the worse performance. In the round portions, there exists strong continuous constraint along the windings against the winding movement via the Lorentz force during coil excitation because of winding tension. On the contrary, in the straight portions, there is almost no constraining. Thus, the windings are apt to move more easily than at the round portions. As a result, especially in the case of a dry magnet, they show worse characteristics than their solenoid counterparts. For the compensation of this mechanism, we propose to improve the quench currents of racetrack coils. We have ground the straight sides of a racetrack coil bobbin into a rounded shape with a negligible effect on coil performance. By experiments, we confirmed that the proposed one had a higher quench current. Moreover, after we applied the proposed idea to the four field coils of an actual 30 kVA superconducting generator, we obtained very good output voltage and current waveforms.

Superconducting racetrack coils have different shapes from those of ordinary solenoid coils which have the same curvature along the windings. So they have different or worse performance from the viewpoint of quench characteristics due to the different structures. Racetrack coils also have round curvatures along their end portions; however, the main difference of their structures from solenoid coils exists in the straight portions. It is considered that the worse performance is due to the straight portions. In the round portions, there exists strong continuous constraint along the windings against the movement toward the perpendicular direction during coil excitation. On the contrary, in the straight portions, there is almost no constraining. As a result, especially in the case of dry magnet, they show even worse characteristics than solenoid counterparts. For the compensation of this worse performance, we proposed one idea to improve quench characteristics of racetrack coils. We manufactured one racetrack coil with an ordinary shape and the other with the proposed idea. By experiments we made sure that the proposed one had a higher quench current. Moreover, after we had made an application of the proposed idea to the four field coils of an actual 30 kVA superconducting generator, we could get very good output voltage and current waveforms.

The superconducting motor shows several advantages such as smaller size and higher efficiency against conventional motor especially utilized in ship propulsion application. However, this size reduction merit appears in large capacity more than several MW. We are going to develop a 17-MW class synchronous motor with a rotating HTS (high-temperature superconducting) coil that is aimed to be utilized for ship propulsion, therefore it has a slow rotating speed of about 200 rpm. The ship propulsion motor must generate high electromagnetic torque instead of low-speed. Therefore, the rotor (field) coils have to generate large magnetic flux that results in large amounts of expensive HTS conductor for the field coil. In this paper, a 17-MW HTS motor for ship propulsion is designed with smaller manufacturing cost by HTS field coil length reduction because the HTS conductor cost is a critical factor in the construction cost of an HTS motor. Furthermore, the output performance of the machine is simulated based on the equivalent circuit model of the synchronous motor with back electromagnetic field values from three-dimensional magnetic field calculation. The simulation results are used to design higher efficiency motor.

Iron oxide is widely used for the adsorption of oxyanion and anionic pollutants in water. Incorporation of aluminum expands available Fe oxide surface that can contact with pollutants because amorphous Al oxide exhibits extremely large surface area with porous morphology. Magnetic Fe-Al binary oxide was prepared by adjusting temperature during sintering of the oxides and investigated the feasibility of the magnetic adsorbent for chromate removal from aqueous solution with permanent and superconducting magnets. The Fe-Al oxide was highly magnetized (31.4 emu/g) after sintering at 500 °C. It is considered that the highly magnetized Fe-Al oxide with comparably large surface area can be a good magnetic adsorbent. The initial chromate solution with the adsorbent had 110 NTU of turbidity. After the superconducting magnetic separation with 0.5, 1, and 4 T, the turbidity of the solution decreased to 31.8, 12.3, and 7.7 NTU, respectively. The Fe-Al oxide is an effective magnetic adsorbent that can not only adsorb anionic pollutants, but also be separated by superconducting magnetic separation system.