Numerical analysis of three dimensional steady state heat conduction in the rotor of an induction motor by finite element method

In developing electric motors in general and induction motors in particular temperature limits is a key factor affecting the efficiency of the overall design. Since conventional loading of induction motors is often expensive, the estimation of temperature rise by tools of mathematical modeling becomes increasingly important. Excepting for providing a more accurate representation of the problem, the proposed model can also reduce computing costs. The paper develops a three-dimensional steady state thermal model in polar co-ordinates using finite element formulation and arch shaped elements. A temperature-time method is employed to evaluate the distribution of loss in various parts of the machine. Using these loss distributions as an input for finite element analysis, more accurate temperature distributions can be obtained. The model is applied to predict the temperature rise in the rotor of a squirrel cage 7.5 kW totally enclosed fan-cooled induction motor. The temperature distribution has been determined considering convection from the outer air gap surface and annular end surface for both totally enclosed and semi enclosed structures.