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Investigation of Partial Discharge Activity in the Slot of a Hairpin-wound Stator

The reliability of electric vehicles is a key aspect for the entire market. Namely, the lifetime of the electric motor is critical. Therefore, it is necessary to know the stress, ageing factors and the condition of the motor. Higher frequency harmonics, steep slew rates and increasing voltage levels driven by state-of-the-art inverters increase the electric stress imposed on the motor winding insulation, which may lead to partial discharges (PD). If PD occurs, the lifetime of the electrical machine can be reduced to unacceptable levels. Hence, the qualification and lifetime evaluation of inverter-fed machines are of high relevance. It is difficult to identify the exact cause of PD when a complete stator is tested because of its complex structure. In order to investigate PD phenomena in the turns of a hairpin-wound stator, a miniaturized test block representing a single slot of the stator is constructed, in which multiple conductors can be placed. The winding configuration is based on a symmetric three-phase delta connected winding in which, each phase has three parallel paths, i.e., conductors from multiple parallel paths of the same phase are present in each slot in various combinations. The aforementioned test setup is used to investigate the partial discharge inception and extinction voltages (PDIV and PDEV) of various turn-to-turn configurations.