The electrification of powertrains could pave the way for fresh perspectives and new opportunities for electric traction machines. As in the case of traditional drive systems, it is essential to fulfill the requirements of power, torque, efficiency, and comfort when designing electric machines. External factors such as temperature, humidity, mechanical factors (e.g., vibrations) and chemical stresses significantly impact the performance of drive systems when electrification is deployed in vehicles. In this case, the insulation of the copper winding and the oil-based fluid, which are part of the cooling circuit are heavily stressed. The increased electrical stress results in partial discharges and other loads, leading to the damage and failure of the entire system. This study focuses on the experimental investigation of the degradation mechanism of polyalphaolefin-based cooling oil (PAO oil) under the influence of a high-intensity electric field. To explore the effects of aging, we propose a novel accelerated experimental approach. The laboratory tests involve inducing localized partial discharges within a specially designed aging cell containing a small quantity of PAO oil. We reveal the effect of a repetitive pulse electric field (high-voltage pulse train) on the dielectric properties of the fluid and compared it with thermal cycling; rapid formation of oxidation products is detected. Finally, we propose a theoretical mechanism for aging-product formation and provide practical confirmation by Pyrolysis Gas Chromatography/Mass Spectrometry (Pyrolysis CG-MS) and Evolved Gas Analysis (EGA).
Koshelev et al. (2026) studied this question.