3D numerical simulation of magnetization loss in multifilamentary MgB₂ wires at 20 K

Abstract

High-power density all-superconducting rotating machines have potential for application in electrical aircraft motors.
However, superconductors in the armature windings of such rotating machines carry AC currents under AC/rotating magnetic fields, resulting in AC losses For. reducing AC loss, low-cost, round magnesium diboride (MgB2) wires are one promising material due to their multifilamentary structure, fine filament size and tight twist. To date, previous 3D AC loss simulations have focused on MgB2 wires with a magnetic matrix operating at low frequency and 4.2 K, which are not relevant to aviation applications. In this work, 3D simulations of magnetization loss at 20 K of twisted 2-filament and 54-filament wires with a non-magnetic matrix are carried out using the finite element method, based on the H-formulation, with AC field amplitudes from 0.1 T to 2 T and frequencies up to 200 Hz. The measured Jc(B, 20 K) and n(B, 20 K) data of a non magnetic MgB- 2 wiremanufactured by Hyper Tech Research is assumed as input parameters. For the 2-filament wire, the operational frequency,the twist pitch, the filament size, the matrix resistivity, and inter-filament gap have been varied to systematically study their impacts on magnetization loss and its loss components (hysteresis loss, coupling loss and eddy currents). The simulation results show that the 2-filament wire with a 5 mm twist pitch and a higher resistivity matrix operated at 50 Hz has the lowest magnetization loss through decoupling the filaments. Furthermore, a lower coupling loss at 200 Hz for field amplitudes exceeding 1 T is observed, this is because critical coupling frequency fc shifts to small values with increasing field amplitudes. For the 54-filament MgB2 wire, the magnetization loss of a 5 mm twist pitch and a higher resistivity matrix wire operated at 50 Hz is estimated. The simulations show that the hysteresis loss of the 54-filament wire can be well predicted by the analytical hysteresis loss equation for a cylindrical superconductor multiplied by 54 (the number of filaments) because the filaments are in an uncoupled state. Good agreement is also observed between the simulated coupling loss and the analytical coupling loss equation from Wilson book for a circular-arranged multifilamentary superconducting wire.