Refined Structural Design and Thermal Analyses of a High-Speed Wound-Field Generator for the More Electrical Aircraft

Wound-field synchronous machines are widely used as generators to cover the electric energy demands in various low-speed applications. The main advantages over their rare earth permanent magnet counterpart are the ease of control, the inherent fault tolerance, the low cost, the use of more sustainable materials, etc. However, permanent magnet machines are well known to provide higher power density and efficiency values, which make them the usually preferred choice as generator on board of aircraft. This is also enabled by the more robust structure of the rotor which allows operations at relatively high speeds. Contrarily, the rotor of the wound-field machine comprises salient poles, making it unsuitable for high-speed operations. This paper aims at investigating the structural and thermal performance of a high-speed wound-field generator for aircraft applications. The electromagnetic aspects, extensively dealt with in a previous publication of the authors, are not discussed in this paper. On the other hand, 2D and 3D finite-element structural analyses, as well as computational fluid dynamics evaluations, are carried out. From a structural point of view, the centrifugal forces acting on the end windings were managed by adding a layer of non-magnetic material at the periphery of the rotor. From a thermal point of view, removing the rotor cage previously designed as a retaining system allowed the enabled axial flow to cool down the rotor. The results revealed the designed motor to be suitable for the application at hand.