Experimental Investigation of an Extrusion Profile for Slot Liner Insulation of an Electric Traction Machine with Winding Direct Cooling

This study addresses the use of an alternative approach to ensure adequate slot insulation in electric traction drives. While the use of insulation composite materials, also called insulation papers, is state of the art and predominantly applied, a slot insulation with a closed, extrusion profile offers advantages especially for winding direct cooled electric machines. The results presented in this study provide an overview of the special features regarding electrical strength and the advantages of the slot insulation, referred to below as the insulation sleeve. The insulation sleeve is made of a PSU thermoplastic which is highly chemical resistant and can be used at temperatures of up to 180 °C. Its excellent resistance to cooling media enables it to be used in direct-cooled electric machines. In particular, the design of the profile allows higher cooling capacities to be achieved with the same installation space. Another advantage is the elimination of the overlap required for slot insulation papers, which can increase the copper fill factor or the cooling capacity. In the experimental investigations, the suitability of the insulation sleeve for use in an electric machine can be demonstrated. Significant increases in the breakdown voltage of more than 25% are achieved in the structure investigated, while at the same time the wall thickness is reduced. Comparable tests of the partial discharge inception voltage show no significant deviation between the two materials. The influence of defects within the insulation sleeve is also the subject of investigation. In addition, economies of scale mean that the insulation costs per slot can be sustainably reduced by using the insulation sleeve.