Impact of Slot Liner Compression on the Total Thermal Resistance of the Stator-Winding Assembly in Electric Motors

The increasing demand for high-performance electric motors, driven by the rapid adoption of electric vehicles, necessitates effective thermal management techniques that improve their safety, efficiency, and reliability. Heat must be transferred from the current-carrying copper windings to the metallic stator body through an electrically insulating material called the slot liner. However, little research has focused on the interactions between the slot liner and the windings. This study examines the impact of slot liner compression on the thermal resistance across the stator-winding assembly considering two common slot liners: Nomex® 410 and Kapton® MT+. A mock stator-winding assembly was developed by stacking a grooved copper piece that mimics the windings, a slot liner, a rigid silicon piece that imitates the stator, and a reference material used to quantify heat flow. Steady-state temperature gradients are induced across the stack, infrared (IR) microscopy captures the resulting two-dimensional temperature maps, and the total thermal resistance across the assembly is calculated. Tests are repeated at several levels of compression. With increasing compression, the area-normalized thermal resistance of the winding-stator interface with a Nomex® 410 slot liner decreases by 14.9% (from 94 to 80 cm2K/W) and, with Kapton® MT+, it decreases by 68.0% (from 50 to 16 cm2K/W). This research provides insight into the effects of slot liner material and compression level on the thermal management of electric motors. Reducing the total thermal resistance reduces temperatures within the windings, resulting in longer component lifespans and more efficient motors.