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Modélisations 2D et 3D, conception et réalisation d’un inducteur pour aimanter un ensemble de pastilles supraconductrices

Abstract : Today, superconductors are used in many applications, for example in cables, motors, alternators or for the generation of strong magnetic fields. Superconductors are available as tapes, wires or bulk materials. The process of magnetising superconductors results in bulk superconductors with a much higher trapped magnetic field than conventional permanent magnets. Proper magnetisation is the key to a very strong trapped magnetic field. The work developed in this thesis concerns the 2D and 3D modelling, design and realisation of an inductor to magnetise a set of superconducting pellets. Generally speaking, there are three techniques for magnetising superconductors: Zero Field Cooling (ZFC), Field Cooling (FC) and Pulsed Field Magnetization (PFM). We focus on PFM because it is a more compact and less expensive solution compared to the other techniques. The mentioned magnetisation process and all the phenomena involved have been solved based on the Finite Element Method (FEM) and using different formulations. In this work, we studied and compared in 2D and 3D the A-formulation, the H-formulation and an A-H formulation by coupling the different variables on the material boundaries. The comparison showed the advantages of the A-H formulation in modelling superconducting problems. Indeed, in some cases, we have shown that the use of the A-H formulation allows to reduce the simulation time. The model developed from this formulation is therefore an interesting tool for future dimensioning work and the development of superconductor applications at GREEN laboratory. We have also dimensioned and numerically studied a complete inductor model allowing one or more superconductors to be magnetised simultaneously. We study two configurations: prototype I for magnetising a single superconductor (2D problem) and prototype II for magnetising three superconductors (3D problem). Both configurations are solved by considering the electromagnetic and thermal phenomena as well as the coupling with the circuit equations feeding the inductor. The simulations showed that the temperature rise in the superconductor of about 10 Kelvin generated during the PFM magnetisation affected the trapped magnetic field. It was observed that the presence of one or more superconducting bulks did not affect the current pulse in the inductor. The maximum trapped field obtained numerically for prototype I was 706 mT and 736 mT for prototype II. The results obtained were then compared with the simulation results. However, some of the superconductors exhibited strong inhomogeneity in their properties, which resulted in a reduction in the experimentally observed trapped magnetic field. Hypotheses were made to try to reproduce numerically these inhomogeneities and their effects. However, this numerical calculation can only be done by 3D modelling without the possibility of using symmetries, and leads to a calculation time of up to several days. Experimentation with prototypes resulted in a maximum trapped magnetic field of 686 mT when one pellet was magnetised, while it was 606 mT when several pellets were magnetised simultaneously. Lowering the temperature by using another cryogenic fluid such as liquid hydrogen or another cooling system would increase this trapped magnetic field value to much higher values for the targeted electrical engineering applications.
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https://hal.univ-lorraine.fr/tel-03367055
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Submitted on : Wednesday, October 6, 2021 - 9:05:58 AM
Last modification on : Friday, October 29, 2021 - 8:07:05 PM
Long-term archiving on: : Friday, January 7, 2022 - 6:14:09 PM

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Jakub Kapek. Modélisations 2D et 3D, conception et réalisation d’un inducteur pour aimanter un ensemble de pastilles supraconductrices. Energie électrique. Université de Lorraine, 2021. Français. ⟨NNT : 2021LORR0113⟩. ⟨tel-03367055⟩

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