Studies On Temperature Rise And Levitation Characteristics Of High Temperature Superconducting Bulk Under Magnetic Levitation Dynamic Excitations

The high temperature superconducting(HTS)maglev,with the self-reliant innovation feature,is an important technical reserve in the field of high-speed maglev in China.With the start-up of the HTS maglev engineering prototype vehicle and test line,the engineering process is imminent.However,research on key problem of temperature rise(TR)of HTS bulk under the geometric irregularity incentive and magnetic field irregularity incentive of the permanent magnet guideway(PMG)and other incentives is about the theoretical analysis only,few experimental data report this study.And the experimental research on dynamic levitation force has not associated with the essential problem of HTS bulk TR.In this thesis,the TR and levitation force of HTS bulk under various dynamic excitations are taken as the main starting point,the TR characteristics and levitation force performance of HTS bulk under small/large amplitude and low/high frequency magnetic field excitations,and more uncontrollable and extreme risk excitations were studied.The risk conditions and parameters were summarized,and the engineering reference suggestions were put forward.First,according punch method the HTS bulk was modified,the TR detection system was built for HTS bulk,which can realize high precision detection of multi-point temperature data.Base on this system,the HTS bulk TR characteristics were studied under the features of PMG irregularity(small amplitude,low frequency),and the effects of rotating speed(RS),field cooking height(FCH)and long-time operation condition on the TR of HTS bulk were analyzed.The results showed that the geometry of PMG is relatively flat,the amplitude of magnetic field fluctuation is small and the frequency of magnetic field fluctuation is low.Under this excitation,there is only a faint TR inside the HTS bulk.The magnetic thermal effect of the system composed of PMG and HTS bulks was proved firstly to be stable and reliable.Secondly,based on the annular Halbach array,the TR charactericsics and levitation force behavior of HTS bulk under large amplitude and high frequency magnetic excitation were studied,the effects of different conditions on the TR and levitation preformance were analyzed.The results showed that: firstly,the change of TR inside HTS bulk is consistent with the change of levitation force in time,and the TR and levitation force reach saturation at certain magnetic field parameters.Secondly,the influence of RS,FCH,WH,and step-to-step acceleration on the TR and levitation force of HTS bulk is different,the best choices of FCH and WH for HTS maglev need to be combined with the fluctuation amplitude and frequency of the external magnetic field.Thirdly,82 K is the inflection point of the risk attenuation of levitation force of HTS bulk,and 87 K is the turning point where the HTS bulk cannot show the flux pinning characteristics.Fourthly,when the magnetic field fluctuation frequency changes from low frequency to high frequency,the oscillation of levitation force changes from weak vibration to strong vibration.Finally,two magnetic-heat-force coupling models of HTS maglev were established in COMSOL Multiphysics software,and a better coupling model based on H-method was selected through comparison and verification,so as to accurately simulate the force and heat behaviors of HTS bulk under the PMG irregularity excitations and other external excitations.The features of several typical excitation types,such as geometric irregularity,magnetic field irregularity and other external excitations,were discussed respectively.The reasonable mathematical method was adopted to characterize and calculate.The special conditions with dangerous TR were summarized,and the effective methods to reduce and weaken the oscillation were proposed.Based on the influence of magnetic properties of Halbach PMG on levitation force and TR,one idea of PMG optimization was proposed.In summary,this thesis mainly studied the TR and levitation force responses of HTS bulk under dynamic excitations,and summarized the features of dangerous working conditions with HTS maglev characteristic,all the above results support references for the engineering application of HTS maglev.