Systematic Investigation of the Grooving Process and its Influence on Slot Insulation of Stators with Hairpin Technology

Due to the increasing electrification of the automotive drive train, production systems for electric motors grow in importance. In order to produce the required quantities at reasonable costs there is a particular need for developing new stator production plants. A trend towards using shaped coils in stators, so called hairpins, is emerging as this technology promises great automation potentials as well as high copper fill factors. Due to the axial insertion of the hairpins into the lamination stack the requirements for the slot liner shape change in contrast to the widely used winding technologies. Thus, new slot liner shapes, such as ‘B’-, ‘O’- or ‘S’-shapes, can be used. The shapes replace the previous ‘U’- shaped slot liner as well as the slot cover. In order to maintain a high fill factor, the shapes have to fit closely to the lamination stack. For this purpose, the insulation paper must be grooved and then folded into the desired shape. To map the new slot liner shapes, the grooving process and its influence on slot insulation must be understood in detail. In this paper the grooving process and its effect on breakdown voltage of the slot liner are examined. First, an overview about different insulation materials for slot liners is given. Second, a test rig setup to adjust different depths and widths of grooving is introduced. Additionally, a further test rig setup for conducting breakdown voltage tests on slot liners is presented. Based on these test rigs, experiments are carried out to determine how the grooving process parameters affect the breakdown voltage of the slot liners. As a result of the investigation a characterization of the grooving process regarding the breakdown voltage for the examined insulation paper is presented.