3-D Simulation of AC Loss in a 114-Filament MgB 2 Wire at 20 K

In future electric aircraft applications employing all-superconducting rotating machines, round multifilamentary magnesium diboride (MgB2) wires are a preferrable material for lowering AC loss, due to their small filaments at the macron level and tight twist pitch. Our previous work has investigated AC loss behaviour in a 54-filament MgB2 wire with a filament radius of 12.5 μm, where the filament size was found not ideal for loss reduction. In this work, 3D AC loss simulations of a twisted, non-magnetic 114-filament MgB2 wire with a 5 μm filament radius at 20 K are performed using H-formulation. Three types of AC losses are studied: (1) transport loss only (Qt0, with current levels up to 90% of its self-field critical current Ic0), (2) magnetization loss only (Qm0, with AC field amplitudes and frequencies up to 2 T and 200 Hz, respectively), (3) total AC loss carrying AC current exposed to AC field (Qtotal, with AC field also up to 2 T and current levels up to 40% of Ic0). Simulation results show that, for the Qm0, the simulated hysteresis loss Qh of a 5-mm twist pitch, 114-filament wire at 50 Hz and 200 Hz matches the analytical hysteresis loss equation for a cylindrical superconductor, scaled by 114 (the number of filaments), when Bm ≤ 0.5 T. Increasing the twist pitch (5 mm Vs 10 mm) and filament size (5 μm in the 114-filament wire Vs 12.5 μm in the 54-filament wire) leads to a higher Qm0 due to the coupling effect. Moreover, the simulated Qtotal of the 114-filament wire range from 0.22 to 7.48 W/cm3 for i ≤ 0.4 and Bm ≤ 0.5 T operated at 200 Hz.