Effect of the Bending Radius on the Breakdown Strength of Rectangular PAI/PEEK Insulated Winding Wire of Electric Motors

The high efficiency and mass production of electric motors for e-mobility solutions raised the hairpin technology in motor manufacturing. The reliability of these machines depends on the insulation quality of the windings, which can be investigated by the breakdown test of winding wires according to existing standards. In this study, two groups of U-shaped samples prepared from rectangular wire covered with double-layer polyamide-imide (PAI) and polyetheretherketone (PEEK) insulation were prepared with 25 mm and 50 mm bending diameters. The samples were tested by 50 Hz A.C. progressive stress. The results show that the breakdown voltage of the sample group with a smaller bending diameter is significantly lower than that of samples with a greater bending diameter. The result of the study shows that the breakdown voltage of rectangular cross-section conductors with layered insulation is very sensitive to the bending radius. This affects the long-term reliability of rotating machines wounded with hairpin technology.