Yong Zhou

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.

The development of an external rotor permanent magnet synchronous motor (ERPMSM) with integer slots involving winding temperature rise and vibration noise was presented in this paper. Based on analyzing the characteristics and influence of different winding forms, a 710 kW 76.5 RPM ERPMSM with different pole slots with 72s/60p and 108s/36p for a coal-mine belt conveyor was calculated and analyzed using electromagnetic field and temperature and fluid field,and the structure mechanics of the PMSM with 108s/36p was also analyzed. Finally, the new prototype was developed and tested. The test results show that the maximum temperature of the winding is 94 °C, and the Vibration intensity is 1.12 mm/s, which is less than the relevant standard value. Major performance comparison tests also meets design expectations, it was verified that the low-speed high torque ERPMSM with integer slots has lower winding temperature and vibration noise.

This study introduces the results of preparing and testing a persistent current system including persistent current switch (PCS), large-scale HTS magnet, and joints. The transition state of PCS between superconductivity and normal was controlled by changing its temperature. The magnet with inductance of 2.5 H was excited to 136 A at 37 K and worked in persistent current mode. The joint resistance and magnetic field attenuation rate of the PCS system were calculated to be 1×10 ^-6 Ω and 1.24 mT/h, respectively. If HTS magnets in machine are in persistent current mode, slip-ring just works at charging the magnet period. In the long run, by reducing working hours of the slip-ring, the HTS machine can be saved from frequent maintenance.

Vibration and noise are the key performance of marine propulsion motors. With the increase in the power level of marine propulsion motors, it is more and more important to study the vibration level and vibration isolation of marine propulsion motors. A 20 MW HTS motor (HTSM) with air-core stator and superconducting rotor is conceptually designed for marine electric propulsion in this study. Combined with the generation and transmission of the vibration, the full-band low-vibration design was carried out by the system acoustic design, the electromagnetic acoustic design, and the co-design of structure and electromagnetic from the perspective of excitation source and transmission path. A design method for low vibration design of HTSM was obtained, which can provide a reference for the follow-up development of large-capacity low-vibration HTSM.

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.

To shorten the cooling time of the superconducting rotor, reduce the thermal leakage of the cold mass, enhance the working stability of high-temperature superconducting (HTS) magnets, and reduce the amount of HTS wires, a novel warm rotor for a 200 kW HTS generator (HTSG) with radial support rods, tangential racetrack rings, and modular HTS magnets was successfully developed. There are 12 HTS magnets in 6 poles of the HTSG, all of which can work stably without quench, and the performance of the magnets meets the expectation. The vacuum, thermal insulation, and cryogenic systems of the generator run stably, which meet the needs of continuous operation at full load. The manufactured warm rotor and the original iron-core stator of the existing 200 kW HTSG were assembled into a new 200 kW HTSG, the assembly process was completed at Wuhan, and then finished the performance test. The test results show that the output power of the HTSG reaches 203.4 kW and the torque reaches 3885 N.m when the field current reaches 24 A and the speed is 500 r/min, which achieved the target power.

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.

The refined FEA model of Roebel transposed wires to analyze the stress and vibration of the HTS machines with air-core stators is unreasonable and needs more computing resources. The homogenization method based on representative unit cell (RUC) was used to equate the mechanical parameters and then simplify the model of the transposed wire in this study, the study process was as follows. First, the manufacturing process of the Roebel transposed wire was introduced. On this basis, an RUC consisting of repetitive microstructures along the length direction was used to establish the RUC of the wire. The FEA results showed that the mechanical parameters decreased with the increase in the thickness of its insulation and temperature. Especially, Young's modulus along the z-axis of the wire was less affected by the thickness of the insulation than that along the x-axis and the y-axis. Finally, tensile tests along the z-axis and modal analysis of the transposed wire were used to verify the homogenization method. The results showed that the first four-order bending modes and natural frequencies of the wire were consistent with the test results, and the errors were all within 5%.

With the continuous advancement of science and technology, the application of high-temperature superconductivity has developed rapidly. The high-temperature superconducting (HTS) motor replacing the copper coil in the traditional motor with HTS winding is increasingly used in power equipment, and the effective thermal management of HTS winding is vital in ensuring the life and effective operation of the HTS motor. In this study, five enhancement structures of indirect oil cooling channels were designed to improve the heat dissipation capacity of the HTS motor winding, and the enhancement effects of the different structures were comprehensively evaluated through numerical simulation using Fluent software 2022R1. The best enhancement structure was selected through structural optimization. The results showed that the Nusselt number of the gap-type enhanced structure was higher than that of the V- and staggered-type structures at the same flow velocity and 68% higher than that of the bare pipe. At the same inlet flow velocity and with a pressure drop limit of 30 kPa, the performance evaluation criterion value of the gap-type structure was 39% and 63% higher than that of the staggered- and V-type structures, respectively. The gap type is the optimal enhancement structure and can effectively improve the heat dissipation of the HTS winding coil.

For a 2.4 MW high-temperature superconducting (HTS) motor, a rotating cold mass support with good strength and stiffness was required. In this research, arch-shaped support was ultimately suggested by the good performance of strength, deformation, thermal leakage, and manufacturability. The arch-shaped support, which was made of Glass-Fiber Reinforced Plastic (GFRP), had a good capability for resisting multiple physical field loads and heat insulation at the same time. Tests were carried out and proved that the compressive strength of the support could reach 322.85 MPa and the average coefficient of thermal conductivity of the support was less than 0.43W/(m•K) at room temperature. According to the results of the stress and deformation study, the tangential deformation of the arch support won't significantly vary when the direction of rotation changes. Additionally, when electromagnetic and thermal loads were introduced, arch support performed better at resisting radial and tangential deflection, which was beneficial for maintaining the electromagnetic and mechanical environment of the motor and safeguarding HTS magnets.