Coupled Fluid-Thermal Analysis And Rotor Thermal Stress Calculation For Induction Motors Operating With Broken Bars

The induction motor has the advantages of simple structure, low maintenance cost and long service life, and is widely used in daily life, factory equipment, port wharves, oil fields, coal mines and other fields. With the development of the national economy, the capacity of the single motor is keeping increasing, and the heat load is also a corresponding increase, which has a direct effect on the machine operation reliability and service life. So the research on heating and cooling of induction motor is becoming increasingly important. Taking a squirrel-cage induction motor Y802-2as an example, 3D fluid-flow and heat-transfer of the motor at the healthy state, one broken bar fault and two adjacent broken bars fault state are calculated in this paper.And based on the temperature result,thermal stress of the rotor were studied. This research can provide the basis for the fault diagnosis of the motor, and it can also provide references for analysis of other induction motors.Firstly, considering the ventilation structure and characteristics of heat-transfer of the motor, the outer approximate infinite fluid field and 3D finite-element structure models of the motor are established, and particular care has been devoted to the rotating fluid domains. By the finite volume method, the motion and energy coupled equations are solved, and the flow state of fluid and the variation of the fluid field parameters are obtained.Secondly, based on Fourier's theorem and Newton's heat transfer law, a numerical method is used for calculating the heat transfer coefficient of the motor surfaces. The steady thermal field of the motor with full load is calculated and the temperature distribution and heat flux distribution in the key position of the motor are obtained,so that the influence of the number of broken bar on the motor thermal profile can be investigated in depth. The temperature results from simulation analysis are compared with the experimental results, which proves the efficiency of the proposed model and method.Finally, the thermal stress analysis of the motor rotor is carried out with thetemperature result as the load. The deformation, the stress component and the displacement curves of the squirrel-cage in three cases are solved, and based on that,we propose the most probably broken location due to the thermal load and the further bar breakage is predicted. The thermal stress analysis of rotor provides the basis for fault diagnosis of induction motor.