Comparison of Optimized Hairpin and Pull-in Winding High-Speed Electrically Excited Synchronous Machines for Traction Applications

This paper presents an in-depth comparison of the overall efficiency and different loss components of high-speed traction electrically excited synchronous machines (EESMs), designed for hairpin and pull-in winding technology. Stator copper losses and iron losses are both critical for the efficiency of EESMs in the high-speed region. In addition to DC copper losses, AC losses originating from skin and proximity effects along with circulating currents are imperative for the computation of operational efficiency. In this work, the aforementioned loss components are evaluated for both hairpin and pull-in winding EESM variants. Moreover, a brief overview of the Zooming FEM analysis which is used to compute AC copper losses in pull-in winding is presented. The machine designs used for comparing the two winding technologies are specifically optimized for them, resulting in a tangible comparison from a holistic point of view. The results discussed in this paper provide an insight into the selection of stator winding technology for high-speed EESMs with a target of achieving maximum operational efficiency.