Hairpin Winding with Direct Oil Cooling

Hairpin windings are often applied in propulsion motors of electrical vehicles. There are several reasons supporting the technology. In mass production, hairpin winding work can be effectively automated, rectangular conductors offer a high copper space factor, a relatively simple structure and improved thermal management capability. However, due to additional AC losses generated at higher operating speed, there is a risk of local hot spots within the stator slot region, which might lead to overheating risk and insulation damage. There is also a growing interest to produce higher and higher specific power machines. Therefore, a new cooling concept is proposed that further improves the thermal management of the hairpin winding and allows to increase the specific power of the machine. The proposed method is based on direct oil cooling (DOC) through the channel of the hollow conductor. Special inlets and outlets in each hairpin coil are arranged. Comparison of the proposed cooling arrangement with the traditional cooling of machine with hairpin winding is provided by applying finite element method (FEM).