Challenges in Electric Machine Stator Manufacturing and Their Influences on Thermal Performance

Thermal performance of electric machines strongly depends on their insulation system and the corresponding impregnation process. A series of experiments was carried out on individual stator segments with concentrated winding to study thermal behavior and impregnation goodness. Variables include different impregnation processes, resins, and slot liner materials. A custom-made thermal test rig was used to measure the thermal conductance of each segment. Unexpected results led to further characterisation including cross-section microscopy and CT-scanning of the internal structure of the segments. Air pockets in the gap between the inner layer of winding and the tooth were observed. Their influence was investigated by calibrating a Lumped Parameter Thermal Network (LPTN) model at steady state operation. The simulations explained why the segments without slot liners showed increased thermal conductance. It also showed why varying the slot liner materials, the resins or the impregnation processes had limited influence on the thermal conductance. This paper highlights that repeatable positioning of conductors in the slots as close to the tooth as possible and high impregnation goodness around the slot liners are key manufacturing challenges for high stator thermal performance.