Research On AC Losses Of Superconducting Tapes

In recent years,the development trend of superconducting materials used in power equipment is increasing.The zero resistance property of superconducting material can greatly reduce the loss of power equipment,greatly improve its working efficiency,and better achieve the goal of high efficiency and energy saving.However,the application environment of superconducting materials is more stringent.Low temperature superconducting requires liquid helium environment and high temperature superconducting requires liquid nitrogen environment.Therefore,the structural design of power equipment is also challenged.At the same time,because of the complex electromagnetic environment in power equipment,the magnetic field environment of different directions and different amplitudes will have a greater impact on the AC losses of superconducting materials.The existence of AC losses will also lead to the instability of the operation of superconducting power equipment and reduce work efficiency.Therefore,it is of great practical significance to study the AC losses characteristics of superconducting materials,especially the changes of AC losses characteristics of superconducting materials under different magnetic fields.At present,compared with low temperature superconducting materials,high temperature superconducting materials have a wider range of applications and better application prospects in power equipment.In this thesis,the anisotropy of critical current and AC losses of HTS were studied,and the racetrack background magnet for testing the characteristics of HTS was designed and fabricated.Firstly,the classification and basic characteristics of HTS materials were described.The critical current anisotropy and its mathematical model of HTS were introduced.The generation principle and classification of AC losses of HTS were described in detail.The mathematical models of AC losses of HTS in self-field and DC field were introduced and calculated numerically by using relevant data.According to the electromagnetic characteristics of HTS,the mathematical model of HTS AC losses simulation calculation was deduced based on H-Formulation,and the corresponding partial differential equation was modeled and simulated.In the simulation calculation,not only the influence of AC losses varying with the transmission current in the self-field was studied,but also the DC field is added to the model to study the effect of HTS in the specific amplitude and angle.In order to measure the critical current and AC losses characteristics of the tape in the field,a new type of racetrack background magnet was designed and fabricated in this thesis.Firstly,the space magnetic field distribution of Helmholtz coil with racetrack type was numerically analyzed to obtain the coil size when the space magnetic field distribution was optimized.At the same time,in order to make the tape better placed in the magnet for different field intensity and angle measurement research,this thesis also designed the magnet coil skeleton,including angle conversion,tape fixation,coil fixation and so on.It can provide background magnetic field with certain magnetic intensity for long tape,and had the function of changing the angle between magnetic field and tape.Based on the racetrack background magnet,the critical current test platform was built firstly,and the E-I characteristic curve of the sample tape was measured and fitted.The critical current value of the tape was obtained by the electric field criterion method.The critical current characteristics under different magnetic field intensity and angles were compared and analyzed.Meanwhile,based on the principle of lock-in amplifier measurement method,an AC losses test platform was built to measure the self-field loss of tape without external field,and the effects of different magnetic field amplitudes and angles on the AC losses characteristics of tape under DC external field were also measured and analyzed.The measured results were compared with the analytical values of the mathematical model and the simulation results obtained from the simulation model to verify the correctness of calculation formula and the simulation model of AC losses of HTS tapes in the self-field and after field.