Propagation Characteristics of End-Winding Insulation Fatigue Damage in Variable Frequency Motor Under Multi-Field Coupling

During the operation of large motors fed by inverter, the variable frequency current may affect the stress state of the winding conductor and insulation, which will further affect the propagation characteristics of insulation damage. In this article, the 3-D magnetic-thermal-mechanical coupling damage evolution model is established by using the finite element method (FEM), where the effects of variable frequency current excitation are considered. The complex distribution states of the frequency conversion and periodic stress inside the insulation layer are determined. The stress intensity factor (SIF) and modified Paris equation in fracture mechanics are introduced to describe the influence of frequency (50–350 Hz) on the propagation degree and trend of insulation damage. The fatigue propagation characteristics of motor end insulation damage under multi-field coupling variable frequency stress are quantitatively studied. The final results show that the fatigue growth rate of insulation damage at the knuckle part is affected seriously by the variable frequencies, which reach the maximum at about 200 Hz. The results of this research may provide theoretical references for the detection, diagnosis, and residual life prediction of stator insulation for variable frequency electrical machines.