Thermal effects of resin in round-wire and hairpin windings - a numerical study

Efficient thermal management is critical for achieving high power density and reliability in electrical machines. The impregnation of windings with resin using trickle impregnation and potting processes significantly improves the overall thermal performance. This paper presents a numerical analysis of the impact of resin on thermal characteristics of round-wire and hairpin windings under same copper volume. Detailed three-dimensional CFD models are developed to represent the geometric features of both winding types with and without two common resins, Voltatex 4200 and Demak XE 663, which are used for trickle impregnation and potting, respectively. Simulations account for conjugate heat transfer between conductors, resin, slot liners and surrounding back iron under representative operating conditions. Temperature distributions are evaluated and compared. The effect of resin thermal conductivity on winding temperature is also studied in detail. Results demonstrate that replacing air pockets with resin of thermal conductivity as low as 0.2 W/m·K substantially enhances conductive heat transfer within the winding pack, leading to lower peak temperatures in both configurations. However, the degree of improvement is higher in round-wire winding due to variations in packing factor and resin distribution. Filling the middle inter-coil air pocket in round-wire winding has a negligible impact on the winding temperature.