Experimental and theoretical discussion on step-out characteristics of high temperature superconducting induction/synchronous motor

Abstract

This paper presents experimental and theoretical results of step-out characteristics of a 20 kW class High Temperature Superconducting Induction/Synchronous Motor (HTS-ISM). A fabricated motor (3-phase, 8-pole, rotor windings: HTS, stator windings: Cu) is investigated, and its maximum quasi-synchronous output is 20 kW at line voltage of 400 V. The step out condition and its behaviour is investigated for different combinations of the input voltage and the drive frequency at 77 K (atmospheric liquid nitrogen). It is shown that tested results of torque versus primary current characteristics agree well with the theoretical expression by compensating with no-load currents. However, the corresponding step-out current differ each other when air-gap magnetic flux density, which is in proportion to (voltage/frequency), increases. Based on electromagnetic field analysis, it could be concluded the reason for the above discrepancy is the magnetic saturation of the iron core. Furthermore, step-out occurs at the phase angle of 45 degree regardless of which is whether or not the step-out current is affected by the above magnetic saturation. These results are really important for the consideration of stable rotation condition of the HTS-ISM.