Load Test Analysis of High-Temperature Superconducting Synchronous Motors

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.