Three-D numerical thermal analysis of electric motor with cooling jacket

Abstract

The need of a sustainable clean future has paved the way for environmental friendly electric vehicle technology. In electric vehicles, overloading is limited by the maximum temperature rise in the electric motor. Although an improved cooling jacket design is of vital importance in lowering the maximum temperature of the motor, there has not been as much study in the thermal analysis of motors compared to electromagnetic design studies. In this study, a three-dimensional steady state numerical method is used to investigate the performance of a cooling jacket using water as the primary coolant of a three-phase induction motor with special emphasis on the maximum temperature and the required pumping power. The effective thermal conductivity approach is employed to model the stator winding, stator yoke, rotor winding and rotor yoke. Heat transfer by induced air is treated as forced convection at the motor ends and effective conductivity is obtained for air in the stator-rotor gap. Motor power losses, i.e., copper and iron losses, are treated as heat generation sources. The effect of bearings and end windings is not considered in the current model. Pressure and temperature distributions under various coolant flow rates, number of flow passes and different cooling jacket configurations are obtained. The study is successful in identifying the hot spots and understanding the critical parameters that affect the temperature profile. The cooling jacket configuration affects the region of maximum temperature inside the motor. Increasing the number of flow passes and coolant flow rate decreases maximum motor temperature but results in an increase in the pumping power. Of the cooling jacket configurations and operating conditions investigated, a cooling jacket with six passes at a flow rate of 10 LPM with two-port configuration was found to be optimal for a 90-kW induction motor for safe operation at the maximum output.