Influences of Stator Conductor Spatial Positions on Transient Potential Distributions in Electric Machines fed from Wide-Bandgap Inverters

This thesis presents a novel method to addressing the challenges arising from steep-fronted voltage impulses on the dielectric strength of insulation systems in stator windings, with a focus on the spatial arrangement of conductors in the stator slots. The motivation for this research stems from the increasing prevalence of voltage impulses with high gradients, which can lead to more pronounced inter-turn voltage stress, particularly in the line-end coils of electric machines. Studies have shown that under repetitive voltage impulses, the turn-to-turn insulation is subjected to greater stress than the ground insulation, leading to potential insulation breakdowns. Consequently, this research focuses on understanding the high-frequency behavior of voltage impulses in the stator winding and the influence of conductor positioning. The study begins with an analysis of different pulse voltage stresses using an inverter based on silicon carbide power semiconductors and investigates the impacts of different insulated wires on the partial discharge inception voltage. To explore these transient phenomena further, high-frequency models representing stator windings are developed, beginning with a single-coil structure and subsequently extending to a three-phase winding model. Each step is validated through experimental measurements.