Abstract
We have tested an axial-type motor that was fabricated using a disk-shaped Bi-2223 bulk rotor. Two-pole and three-phase copper coils were used for concentrated armature windings. Lock and load tests were performed as a function of temperature at a frequency of 60Hz. In order to examine the test results, the spatial harmonics of the air-gap magnetic flux density were measured at room temperature and 77.3K, and then analyzed by Fast Fourier Transformation. Hysteresis curves of the Bi-2223 bulk rotor were also measured in a rotating magnetic field at 77.3K. It was shown that the air-gap magnetic flux density includes large components of 5th and 7th harmonics due to the salient and concentrated armature windings, and these harmonics may be one of the main reasons for asynchronous torque as well as large slip operation. On the other hand, these harmonics are suppressed when the armature current is increased due to the heating with AC loss. Furthermore, it can be deduced from a comparison between the stational torque and the area of hysteresis loops that torque generation varies from hysteresis-dominant to induction-dominant mechanisms at the point the gradient of torque vs. armature current curve changes. These results are reasonably consistent with the temperature dependence of motor characteristics.
