Investigation and Suppression of External Alternating Field of HTS Excitation Coil in Homopolar Inductor Machine

In high-temperature superconducting homopolar inductor machine (HTS-HIM), the stationary high-temperature superconducting (HTS) excitation coil is directly exposed to complex external perpendicular alternating field (EPAF). In this situation, the ac loss including dynamic loss and magnetization loss will occur in the HTS coil carrying direct current, which is harmful to the operation of HTS-HIM. To avoid the thermal runaway quench of HTS coil caused by ac loss and ensure the safe and reliable operation of HTS-HIM, the EPAF acting on the HTS coil is investigated and suppressed in this article. First, the characteristics of the EPAF of HTS coil in HTS-HIM are obtained through theoretical and finite element analysis. Then, based on the distribution of EPAF and the special structure of HTS-HIM, a combined suppression method using two sets of U-shaped armature windings and L-shaped flux diverter is proposed and analyzed. The results show that the shielding factors of fundamental and dc components can be reduced to 25% and 31%, respectively.