Oil Rotor Cooling Comparison for Electrically Excited Synchronous Machine

Electrically Excited Synchronous Machines have recently gained attention in electric vehicle applications due to their magnet-free design; however, they necessitate effective rotor cooling due to field current heat dissipation. This study uses conjugate heat transfer simulations in Ansys Fluent to compare three oil cooling strategies for a 36 kW electric motor under nominal heat dissipation. These cooling strategies are evaluated within the same framework, highlighting their relative effectiveness under identical operating conditions. The model accounts for material anisotropy in the windings and combines analytical calculation and numerical simulation to determine the equivalent thermal conductivity representing the material's anisotropic heat conductivity. The results show that spray cooling reduces the winding hotspot temperature by 95.2°C; however, the increased pressure drop requires additional power consumption. Inner rotor cooling achieves an additional temperature reduction of 13.9°C, demonstrating superior thermal performance without a significant increase in driving power.