Manufacture of Hollow Coils for a Current-Dense Aerospace Generator

The adoption of hollow bar-type conductors in the stator coils of an electrical machine offers the potential to realise high power and torque densities, due to the higher current densities enabled by direct cooling. However, when working with these conductors, integrating layer changes and forming end windings that are as compact as possible while respecting minimum bend radii are significant manufacturing challenges. A design study of a medium sized power and torque dense electrical machine, with hollow conductor windings provided a meaningful baseline to determine a hollow conductor coil topology. An equivalent stator core with a conventional stranded winding, illustrates the potential machine level performance benefits of a hollow conductor winding. Predictions show that by adopting $4 \text{mm} \times 4 \text{mm}$ hollow square section conductors, operating at a current density of $35 \mathrm{A} / \text{mm}^{2}$, the power density of the machine active components can be increased by $\approx 70 \%$. We present work done to design and form coils for this machine including a novel, helix winding, concept that results in both the start and end of each coil being on the outside of the end windings, helping minimise end winding space requirements. The work shows a viable approach to working with hollow conductors of this size.