Pre-compressed and stranded aluminium motor windings for traction motors

There are benefits if copper windings are replaced with aluminium in applications which are cost and mass sensitive, such as automotive traction; these include the low cost of aluminium, low mass of aluminium and the ease of motor recycling at end of life. However the relatively low electrical conductivity of aluminium compared to copper needs to be overcome. Pre-compressed motor coils have been shown to produce very high fill factors (>75%), reducing DC winding losses, therefore enabling the use of aluminium 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 pre-compressed 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, pre-compressed aluminium coils which have been developed for use in an automotive traction application.