Litz Wire Strand Shape Impact Analysis on AC Losses of High-Speed Permanent Magnet Synchronous Motors

Litz wires are commonly used in high-frequency applications in order to reduce the impact of skin and proximity effects. Recently, this winding type has become more popular in high-speed electrical machines. Although many research papers have already highlighted the benefits and the practical limitations that derive from their utilization, less attention has been paid to the impact of the wire's cross-section shape. Thus, this design characteristic is investigated in the present work by comparing the losses in litz wires with circular, square and rectangular cross-section. At first, the stator copper losses (including DC resistance losses, proximity- effect and skin-effect losses) of a high-speed permanent magnet synchronous motor are calculated through 2D finite element analysis. Then, the obtained results of different litz wire strand shapes are presented and thoroughly discussed. Finally, some useful conclusions are drawn.