High-Temperature Superconductors (HTS) considerably accelerate the development of superconducting machines for electrical engineering applications such as fully electrical aircraft. This present contribution is an overview of different superconducting materials that can be used as magnetic screens for the inductor of high specific power electrical machines. The impact of the material properties, such as the critical temperature ($T_c$) and the critical current density ($J_c$), on the machine performances is evaluated. In addition, the relevance to flux modulation machines of different HTS bulk synthesis methods are addressed.

The use of high-temperature superconducting (HTS) cables in power systems increases the transmission capacity, whereas reducing the volume of the installation. In addition, in high current applications, HTS cables considerably reduce power losses, right-of-ways and total system mass. This paper presents different multi-physics studies to be performed to accurately design the direct current (DC) HTS cables for the future railway network planned by the French company SNCF. The process used to design DC cables for high operating current (between 5 kA and 20 kA at 1750 V) made of commercial (RE)BaCuO tapes is presented. In this design process, the critical current density dependence J _c(B, θ, T) of the superconducting tapes, the thermal properties of the materials used as well as different cable cooling configurations are considered. Finally, we discuss the selection of the appropriate cooling configuration to ensure adequate cooling of the cable.

This article presents a 3-D semi-analytical model of a partially superconducting axial flux modulation machine for the computation of the flux density distribution, the torque, and the eddy-current losses in the armature. The modulation of the superconducting coil magnetic field by the superconducting bulks is calculated by solving the Maxwell’s equations in scalar potential with the variable separation method. Using Fourier series analysis and the convolution theorem, the bulk region is modeled by a domain with a spatially variable magnetic permeability. This variable permeability enables considering a diamagnetic bulk as well as a more complex magnetic behavior using the Bean model. The results of the proposed model are compared with 3-D finite-element models and good agreement is obtained for a significantly reduced computation time. The proposed model appears to be a suitable tool for optimization and sizing processes.

This article presents a 3-D semi-analytical model of an axial-flux reluctance coupling. Thanks to the separation of variables method, Fourier series analysis and the convolution theorem (i.e. Cauchys product), the salient-pole region is modelled by a spatially variable magnetic permeability. Additionally, an iterative algorithm is implemented to account for the magnetic saturation of the iron teeth. The results of the proposed model are compared with a previously published 2-D semi-analytical model, 3-D finite-element method and experimental results. The proposed method appears to be an appropriate tool for the design process of reluctance couplings in cases where the salient poles are saturated.

High temperature superconductors (HTSs) are enablers of extensive electrification for aircraft propulsion. Indeed, if used in electrical machines, HTS materials can drastically improve their performance in terms of the power-to-weight ratio. Among the different topologies of superconducting electrical machines, a flux modulation machine based on HTS bulks is of interest for its compactness and light weight. Such a machine is proposed in the FROST (Flux-barrier Rotating Superconducting Topology) project led by Airbus to develop new technologies as part of their decarbonization goals driven by international policies. The rotor of the machine will house large ring-segment-shaped HTS bulks in order to increase the output power. However, the properties of those bulks are scarcely known and have barely been investigated in the literature. In this context, the present work aims to fill out partially this scarcity within the framework of FROST. Thus, a thorough characterisation of the performances and homogeneity of 11 large REBaCuO bulks was carried out. Ten of the bulks are to be utilized in the machine prototype, originally keeping the eleventh bulk as a spare. A first set of characterisation was conducted on the eleven bulks. For this set, the trapped field mapping and the critical current were estimated. Then, a series of in-depth characterisations on the eleventh bulk followed. It included critical current measurement, X-ray diffraction, and scanning electron microscopy on different millimetre-size samples cut out from the bulk at various locations. The X-ray diffraction and scanning electron microscopy showed weakly oxygenated regions inside the bulk explaining the local drop or loss in superconducting properties. The objective was to determine the causes of the inhomogeneities found in the trapped field measured on all the bulks, sacrificing one of them, here the spare one. To help obtain a clearer picture, a numerical model was then elaborated to reproduce the field map of the eleventh bulk using the experimental data obtained from the characterisation of its various small samples. It is concluded that further characterisations, including the statistics on various bulks, are still needed to understand the underlying reasons for inhomogeneity in the trapped field. Nonetheless, all the bulks presented enough current density to be usable in the construction of the proposed machine.

This article presents the superconducting machine demonstrator realized within the frame of project FROST (Flux-barrier Rotating Superconducting Topology) which started in 2020. This demonstrator is a 250 kW partially superconducting machine adopting the so-called flux modulation topology which employs a superconducting static coil fed with DC current to produce a magnetic field which is modulated by a rotor composed of superconducting bulks. Both these components are the machine inductor which generate a torque by interacting with a three-phase conventional copper wound armature. This article presents the machine expected performances as well as an overview of the demonstrator assembly.