Characterisation of High-Temperature Superconducting Material under Rotating Magnetic Fields
- Publication Type:
- Thesis
- Issue Date:
- 2023
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High-temperature superconducting (HTS) materials enables the development of compact, lightweight, and efficient electrical machines, leading to significant size reduction and improved machine efficiency. A wide range of applications, including superconducting motors, generators, transformers, and technologies like superconducting fault current limiters and superconducting magnetic energy storage, have been explored. However, the commercialization of HTS technology faces challenges due to dissipative interactions occurring when these materials are exposed to alternating magnetic fields. This results in AC loss, also known as power dissipative loss, caused by the displacement of vortices within the material. This power dissipation can impose additional strain on cryocoolers. Factors such as geometric structure, magnetic field orientation, and current density distribution significantly impact this power dissipation. Thus, it is crucial to thoroughly study and characterize the electromagnetic behaviour of HTS bulk materials to ensure the feasibility of commercial superconducting applications. HTS materials only exhibit superconductivity at cryogenic temperatures, necessitating the inclusion of cryogenic cooling units, also known as cryocoolers, in practical and commercial applications. However, AC loss can compromise the stability of cryogenic systems and affect overall device efficiency. Therefore, a comprehensive understanding of the AC loss process and magnitude is essential for the design of new superconducting machines. While most studies have focused on measuring AC loss in one-dimensional alternating magnetic fields generated by transport currents or external magnetic excitations, this study investigates the properties of HTS materials, particularly AC loss, under rotating magnetic fields. Numerical modelling techniques based on finite element analysis (FEA) and H-formulation are employed to analyse the fundamental electromagnetic properties of HTS bulk materials and conductors. The study presents color-coded maps illustrating flux density distribution and examines the demagnetization of HTS-trapped field magnets under rotating magnetic fields. Moreover, a novel experimental setup is introduced to measure AC loss in HTS materials under rotating magnetic fields. The experimental results are compared with those obtained from FEA-based H-formulation, demonstrating consistency between them. The study also explores AC loss under various scenarios, such as different amplitudes and frequencies, and finds that losses are higher under rotating magnetic fields compared to one-dimensional alternating fields. The findings of this study provide a comprehensive understanding of the material properties of HTS when subjected to rotating magnetic fields, offering insights into the design of large-scale HTS applications. The results are valuable for further characterizing HTS materials and designing cryogenic cooling systems for HTS machines, advancing the practical implementation of HTS technology.
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