Hun-June Jung

Fundamental experiments of axial-type BSCCO-bulk superconducting motor model

An axial type HTS hysteresis motor has the same structure as a conventional axial flux type permanent magnet synchronous motor. The permanent magnet rotor of a conventional permanent magnet synchronous motor is replaced by a rotor made from HTS materials with the objective of increasing power densities and reducing losses. The behavior of a BSCCO bulk rotor has been tested in rotating magnetic fields produced by two poles and three phase motor coils fed by a PWM inverter at 77 K. To characterize the torque output capability of the HTS hysteresis motor, speed versus torque and current versus torque are tested. Experimental results for the HTS hysteresis motor are presented.

Performance of axial-type motor with Bi-2223 HTS bulk rotor

We fabricated and tested an axial-type motor with a Bi-2223 bulk to investigate its applicability. The motor was immersed in liquid nitrogen with zero-field cooling method. Load and locked rotor tests were carried out in a rotating magnetic field at 60 Hz frequency. Load tests showed that the fabricated motor does not reach synchronous speed, and torque declines with increasing rotational speed. These properties are similar to those of induction motor with high rotor resistance. On the other hand, locked rotor test indicates that the torque vs. magnetic field characteristics is qualitatively described by the area of hysteresis loop which is measured on a bulk surface with a hall sensor. That is, the fabricated motor shows both characteristics of conventional induction and hysteresis motors.

Characteristics of axial-type HTS motor under different temperature conditions

We tested an axial-type Bi-2223 bulk motor under different magnetic field and temperature conditions. Distributed armature windings with a pole number of four were used in order to compensate for the harmonic components in the air-gap magnetic flux density. The temperature was varied by evacuating the metal cryostat with a rotary vacuum pump. The fabricated motor demonstrated hysteresis characteristics when the temperature of the system was decreased and the magnetomotive force was adjusted to appropriate values. Then, synchronous speed at no-load condition was fulfilled. On the other hand, slip of rotational speed as well as inductive torque was induced when temperature and magnetic conditions were not satisfied. These results can be explained based on the pinning properties and AC loss inside the bulk rotor.

Investigation of magnetic characteristics in HTS bulk materials for motor applications

Magnetic characteristics of a Bi-2223 bulk rotor that was used for the HTS motor was investigated at 77.3 K. Spatial distribution of the magnetic flux density in the air-gap of axial-type HTS motor was measured in a rotating magnetic field at 60 Hz frequency. Numerical simulation based on 3D finite element method was also performed. It was shown that the pinning property of the bulk rotor influences the harmonic components of the air-gap flux density as well as motor characteristics.

Synchronization of an axial-type Bi-2223 bulk motor operated in liquid nitrogen

We fabricated and tested an axial-type Bi-2223 bulk motor that was operated in liquid nitrogen. The rotating characteristics were tested as a function of temperature, which was controlled by evacuating the metal cryostat with a rotary vacuum pump. The tests were performed for different air-gap lengths. It was found for the first time that the synchronization was realized when the operating temperature as well as the armature current was set to the appropriate range. Furthermore, the no-load test results showed that the rotating speed had no hysteretic characteristics through the increasing and decreasing process of the armature current even after the motor was pulled-in, and this result indicated that there were no trapped fluxoids in the bulk rotor.

Electromagnetic characteristics of Bi-2223 disk in a rotating magnetic field

Abstract The electromagnetic characteristics of disk shaped Bi-2223 bulk used for the rotor of an axial-type motor were studied in a rotating magnetic field. The magnetization of the Bi-2223 disk was measured by means of the Hall sensor that was mounted on the disk. It was shown that the fabricated axial-type motor generates standstill torque in proportion to the area of magnetization loops at weak applied field. Therefore, it can be deduced that the generated torque originates from hysteresis property of the bulk at this field region. Furthermore, the characteristics of Bi-2223 disk were also measured by varying the temperature with rotary vacuum pump in order to examine the dependency of the pinning property upon the torque characteristics, and the results are to be presented.

Preliminary test results of radial-type sintered Sm-123 bulk motor

We designed and fabricated a radial-type motor with a high temperature superconducting bulk rotor. The fabricated motor has 3-phase and 4-pole armature winding, and then generates rotating magnetic field at the speed of 1800 rpm under the condition of 3-phase, 60 Hz electric power. Sintered Sm-123 bulk was utilized for the solid rotor in this study. The performance of the sintered Sm-123 bulk motor was evaluated by no-load, locked-rotor and load test. Test results showed that the motor generated a little torque and rotated with large slip, even if the motor was applied 165 V/sub rms/ of the phase voltage (the stator current is 18 A/sub rms/). Because of small magneto-motive-force and spatial harmonic components in the air-gap, magnetic flux was prevented from penetrating into the HTS bulk rotor. Therefore, the screening current in the rotor flowed only at the surface of the rotor and generated torque is remained in a little value.

Comparative Study of Axial-type Bi-2223 Bulk Motor with the Use of Different Stator Windings

Using high temperature superconducting (HTS) bulk materials, some types of bulk motors have been proposed and developed [1, 2, 3, 4]. We have been studying the characteristics of electric motors with the use of Bi-2223 bulk disk rotor [5, 6, 7, 8]. In order to do some preliminary researches, the stator of the motor has been constructed to be two-pole and three-phase concentrated armature winding wound around salient magnetic poles. The synchronous speed of the rotating magnetic field is in principle 3600 rpm. The test results, however, showed that the motor rotated with large slip and the torque decreased with increasing speed. As one of the main reasons for the results, we suppose the effect of the space harmonics of the air-gap magnetic field distribution. It is well known that magnetic space harmonics have the detrimental effect to motor performances. Therefore, the investigation of this effect is essential in order to realize the high performance HTS motor.