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The welding residual stress and its influence on the warm rotor of an HTS motor was analyzed in this study. First, the thermo-elastoplastic FEA and the heat source model were introduced. Second, the influences of weldpass number, welding current, and groove types on the welding residual stress of the T-joint were analyzed. Then, the T-joint sample was manufactured and the residual stress was tested by the X-ray diffraction to verify the correctness of the FEA method. Last, the dynamic performance of the shaft was analyzed by the co-simulation analysis of welding and vibration. The results showed that the welding residual stress decreased with the increase in the number of weld passes and welding current had little effect on that. Compared with the V-shaped groove, the K-shaped groove and J-shaped groove were more suitable for the T-joint. Besides, the residual stress was superimposed with the stress caused by the working load and then weakened the strength of the T-joint. Moreover, the dynamic performance of the shaft was analyzed by the co-simulation analysis of welding and vibration. The relative error of the first three-order natural frequencies with residual stress and without that was less than 3.5%, which indicates that the residual stress had little effect and can be ignored.

Temperature rise determines the lifetime of the motor. Wuhan Institute of Marine Electric Propulsion has conceptualized and designed a 20 MW high-temperature superconducting motor (HTSM) with an oil-cooling air-core stator and a superconducting rotor. This paper describes the design and analysis process of the cooling system of this stator: Firstly, We simplified the full structure of the HTSM and established the model of the oil-cooling air-core stator for thermal analysis. Second, We analyzed and compared the cooling effect of different oil inlet forms under different thermal loads and coolant flow, and sequentially determined the optimized inlet form. The analysis results show that the average and maximum temperature of the oil and coil increase with a higher thermal load, or a smaller oil flow. Underrated operating conditions (240 kW@60 m3/h), the maximum temperature of the coil is 72 °C, and the maximum temperature of the cooling oil is 65 °C, meeting the temperature rise requirement. Finally, we present a structural solution for a compact oil-cooled air-core stator that can increase the torque density of the HTSM.

Although very important, the mechanical properties of high-temperature superconducting (HTS) magnets are not as highly valued as their excellent electromagnetic performance such as high current transmitting and high magnetic density. The modal characteristics of HTS magnets under multi-physical loads may cause adverse structural responses, which may cast a negative impact on the electromagnetic performance of the magnets and even hinder the normal operation of the entire machine. To figure out the modal characteristics of the HTS magnets in the working environment, a series of analyses were conducted in this paper using Finite Element Analysis (FEA) and modal experimental methods. FEA models for an HTS motor magnet were established, and the accuracy of the models was verified with experimental data. Based on that, the influence of thermal and electromagnetic loads on the modal characteristics of the HTS magnet was further studied. The results indicate that electromagnetic loads hardly cause any changes in the modal frequency of the HTS magnets, but the thermal load can significantly reduce the modal frequency by 13.97%. This study provides an important basis for the design and vibration analysis of HTS motors in the future and supplements the research on the mechanical properties of HTS magnets.