Evaluation of AC Losses in Multifilament MgB 2 Wires Under Rotating Magnetic Fields Using 3-D Finite Element Analysis

There is a growing interest in researching the application of high-temperature superconductors to AC electrical equipment and systems. In particular, fully superconducting rotating machines with high power densities are attracting attention in aerospace and other industrial fields. However, AC losses occur when an AC current flows through and a rotating magnetic field is applied to the armature windings of a fully superconducting rotating machine. Therefore, it is important to evaluate AC losses in superconductors. On the other hand, there is an increasing demand for low-cost MgB2multi-filament wire with twisted, round, thin filaments, to reduce AC losses. Until now, three-dimensional (3D) numerical analysis for estimating AC losses in multi-filamentary round wires, such as MgB2, has faced long calculation times and poor convergence. In this study, we constructed 3D numerical analysis models of superconducting multi-filament wires under rotating magnetic fields using the finite element method (FEM) based on theA-Vformulation. AC loss calculations were performed for 2-filament and 36-filament wires, varying parameters such as the maximum magnetic flux density, the electric conductivity of the matrix, and the twist pitch. The validity of the model was confirmed as the numerical analysis results agreed with the theoretical values when the filament coupling was weak. Furthermore, the FEM analysis results showed that AC loss calculations could be performed for the cases with both weak and strong filament coupling. The proposed 3D numerical analysis model can be extended to the calculation of AC losses in superconducting multi-filament wires with complex shapes.