High power density all-superconducting rotating machines have potential in electrical aircraft. However, superconductors in the armature windings of such rotating machines carry AC currents under rotating magnetic fields and AC loss generated in these components poses a great challenge for the cooling system. Therefore, AC loss reduction is one of the critical tasks underpinning their practical deployment in such an application. Low-cost, round MgB2 wires are one of the promising candidates for reduced AC loss due to their multifilamentary structure, fine filament size and tight twist. Magnetization loss due to a changing magnetic field is likely to be the dominant loss in the armature windings and this has two main loss components: hysteresis loss in the MgB2 filaments and coupling loss in the resistive matrix which may become the dominant loss component at high frequency. Previous AC loss simulations have focused on MgB2 wires with a magnetic matrix operating at low frequency and 4.2 K [1-4], which may be far from the real operating conditions for aviation. Therefore, it is necessary to simulate magnetization loss in non-magnetic low-loss MgB2 wires operating under realistic operating conditions.
In this work, as the first step, we carried out 3D FEM simulations of non-magnetic 2-filament MgB2 wires based on the H-formulation. The amplitude of the AC magnetic field varies from 0.1 T to 2 T and frequency is up to 200 Hz. The matrix resistivity, filament size and twist pitch (10 mm and 30 mm) are also varied to study their impact on each loss component. The measured Jc (B, T) data of a non-magnetic MgB2 filament manufactured by HyperTech Research is assumed as an input parameter. The magnetic field and critical current density distributions are analysed to better understand the magnetization loss characteristics.
[1] Escame Guillaume, et al., Superconductor Science and Technology 30, no. 3 (2017): 034008.
[2] Escamez Guillaume, Frédéric Sirois, Valtteri Lahtinen, Antti Stenvall, Arnaud Badel, Pascal Tixador, Brahim Ramdane, et al., IEEE Transactions on Applied Superconductivity 26, no. 3 (2016): 1-7.
[3] Escamez Guillaume, et al, IEEE Transactions on Magnetics 52, no. 3 (2015): 1-4.
[4] Zhao Junjie, et al., Cryogenics 84 (2017): 60-68.
This work was partly supported by CSC (Chinese Scholarship Council) and was partly supported by the New Zealand Ministry of Business, Innovation and Employment (MBIE) Strategic Science Investment Fund “Advanced Energy Technology Platforms” under contract No. RTVU2004. We also acknowledge HyperTech Research for providing information on the MgB2 wires.