Assessment of cooling integration with direct cooled windings

This paper presents and assesses the cooling integration of medium size electrical machines with distributed hair-pin type of windings. By introducing a hollow or profiled conductor the generated heat can be removed right where it is created. The cooling duct in conductor that can be connected either to series or parallel cooling flows increases DC resistance up to 1.5 times when comparing commercially available small hollow conductors. Any added heating power is compensated by cooling and added pumping power that can bring the continuous operation to a new peak level though at lower efficiency. This article targets production oriented calculations and experiments for conjugate heat transfer analysis where the advantage of direct cooled hair-pin type of windings is compared to more conventional rectangular solid conductors. A machine design, which is suitable for traction application, is selected to investigate the power losses in the machine winding and experimental work on direct cooled test cells is used to support the thermal design and evaluate the benefits of the cooling integration