Influence of Specimen Selection on Lifetime Prediction of Low Voltage Electrical Machines Under Variable Temperature Aging

To a great extent, electric machine (EM) lifetime is affected by electrical failures that compromise the integrity of the windings electrical insulation system (EIS). During EMs operation, the EIS suffered various stresses, such as, thermal, electrical, mechanical and ambient (TEAM), which lead the deterioration and decrease the dielectric property of EIS. However, under rated operating conditions, the entire degradation process can take several years before insulation breakdown occurs. Thus, accelerated lifetime tests (ALT) are conventionally performed on various high stress level. Furthermore, the suitable specimen topology should be chosen according to the ALT task objectives, which is also crucial to the resulted lifetime values. In this paper, ALTs at variable temperature profile are performed using two types of specimens (i.e., coils and motorettes). Then, the collected lifetime data are analyzed by statistical tools and the underlying stress mechanism is discussed. Finally, the thermal-mechanical stress is pointed out as the primary factor contributing to lifetime prediction mismatch.