Speaker
Description
High-Temperature Superconducting (HTS) Coated Conductors (CCs) can be sliced and stacked together and utilised as Trapped Field Stacks (TFSs) for electric motors and generators after magnetisation. However, TFSs are vulnerable to higher-order harmonic waves within the air gap of electric machines, which stem from the stator's alternating arrangement of slots and teeth, leading to a phenomenon of magnetic moment collapse and decay in the trapped magnetic field within the TFSs, when the TFSs face a transverse field applied orthogonally to their initial magnetisation direction. This is known as cross-field demagnetisation.
To mitigate the demagnetisation issues, the diamagnetism of superconductors has been employed as a potential preventive method. To investigate their ability to shield TFSs against external alternating current (AC) field, superconductors has been added as side tapes around a TFS in a 2D electromagnetic-thermal coupled numerical model, which has been built for a Fractional Slot Concentrated Winding (FSCW) machine, with its traditional Permanent Magnets substituted by stacks of HTS tapes on the rotor surface. This model was developed using the Finite Element Method (FEM) and validated against experimental data. The HTS stacks were magnetised through Pulsed Field Magnetization (PFM), and once magnetised, they function as TFSs to produce rotor fields. The trapped magnetic field, current distribution within the TFSs, and temperature dynamics of the TFSs as well as the current distribution in the side tapes have been examined to demonstrate the shielding effect. The shielding effect has been demonstrated to be stronger with a higher number of layer number of side tapes. This study will contribute to understanding the shielding capabilities of HTS CCs in practical superconducting machines and aid in designing HTS TFS rotors.
