Investigation of Thermomechanical Stresses Inside the Motor’s Slot With Rectangular Winding During the Impregnation Process and Thermal Cycling

Some applications expose the electric motor to severe thermal cycling, which negatively impacts the motor winding mechanically. Such impact results in loss of adhesion, abrasion, cracking and wear of different components within the slot and the motor, leading to degradation or complete failure. Before relating the mechanical stress resulting from thermal stress to the failure of the motor, a deep investigation is carried out to understand the physical phenomena inside the slots as a reaction to heating and cooling. The first heating and cooling cycle in the life of a motor is the curing process of the impregnation material, and thereafter, many heating-cooling cycles occur during normal operation. In this paper, mechanical strain on hairpin winding resulting from the curing process of the impregnation material is investigated to get an understanding of residual mechanical stresses inside a motor after curing. An impregnated specimen is exposed to thermal cycling to study the resultant mechanical stress and its related parameters. The experimental results are compared to the simulation results, and they correspond well. Different impregnation materials are checked to allow choosing the suitable combination of materials that exposes the motor to the lowest stress.