Manufacturing Process and Design Requirements of Litz Wire with Focus on Efficiency Improvement of Traction Motors

Enameled wire is a basic material for coil winding technologies. The manufacturing process varies and parameters depend on the final product. One competitive product for traction motors is profiled litz wire, which comprises of twisted enameled wire strands. Product design and manufacturing of litz wire is complex with many options. Profiled rectangular litz wire can substitute the solid rectangular enameled wire within the continuous hairpin technology. Due to thinner individual wires alternating current (AC) losses in electric traction motors can be reduced to improve efficiency and power density. Compared to solid wire, it has a lower a filling factor, which results in higher direct current (DC) resistance, however the overall weight is also reduced. Depending on the drive cycle, AC losses can overcome DC losses in low operating points. In contrast to that the AC losses can be significantly reduced at high frequencies compared to solid wire. A litz wire design can be simulated using litz wire models for analytical computing. Analysis of real traction motor parameters display benefits of litz wire windings compared to solid wire hairpin windings. This paper gives insights on the litz wire technology and its manufacturing process. Furthermore, it describes state of the art design parameters for the use of litz wire in electric motors. Finally, a simulation-based motor study presents the potential of performance increase by litz wire windings compared to solid wire windings.