Precompressed and Stranded Aluminum Motor Windings for Traction Motors

There are benefits if copper windings are replaced with aluminum in applications that are cost- and mass-sensitive, such as automotive traction; these include the low cost of aluminum, low mass of aluminum, and the ease of motor recycling at the end of life. However, the relatively low electrical conductivity of aluminum compared to copper needs to be overcome. Precompressed motor coils have been shown to produce very high fill factors (> 75%), reducing dc-winding losses, therefore enabling the use of aluminum conductors. However, the single-stranded conductors used can be prone to high ac losses due to skin and proximity effects. Therefore, a method of manufacture of precompressed coils made from stranded/Litz wire is needed, allowing ac losses to be reduced to low levels. This paper describes the development and test of stranded, precompressed aluminum coils, which have been developed for use in an automotive traction application.