Stator winding proximity loss reduction techniques in high speed electrical machines

Eddy-current losses in the stator windings of high speed machines may constitute a significant amount of the total stator copper losses, if they are not adequately dealt with. Many measures, such as using Litz-wire, discrete parallel strands or only partially filling a slot, reduce both the electrical and thermal performance or increase the cost and should only be used when necessary. This paper systematically analyzes and compares the effects of such measures with 2D FEA, applied to an example high speed permanent magnet machine, providing insight into tradeoffs between the various methods. It is shown that, among others, only partially filling the slot can be equally effective as using multiple parallel strands, and that the advantages of parallel strands are limited by uneven current sharing across the strands. If all proposed methods are combined, the resulting design offers similar performance to a machine with Litz-wire.