Performance Estimation of a Traction Machine with Direct Cooled Hairpin Winding

Hollow and profiled conductors, which can be categorized as direct cooled conductors, are selected to develop a design proposal of an electrical machine with direct cooled hairpin type of winding. The objectives of this work are 1) investigating the benefits of direct heat removal when using hollow and profiled conductors, and 2) analyzing high frequency capability of these types of windings. Firstly, the winding layouts for a discontinuous hair-pin and a continuous wave winding are drawn in order to visualize the formation of end-turn region and the access points for the coolant. Secondly, the cooling characterization is carried out on basis of a test cell and corresponding 3D FE conjugate heat transfer model. Thirdly, power loss characterization is carried out with focus on AC losses in the winding over the operation range of interest. And finally, a conventional machine where the winding is made a solid rectangular conductor is compared to direct cooled conductors. The exploitation of direct cooled conductors causes higher power losses for the same current as the conductor material is removed for the cooling and thereby improving the thermal management as the coolant removes directly the heat. Consequently, the intermittent torque density, also power capability is increased but that at the cost of a higher tension in the construction materials, specifically in the insulation system, when intensive parallel cooling is applied across the machine winding involving overhangs and the conductors in the slot.