Computation of temperature distribution in the rotor of an induction motor during star-delta starting in two dimensional rectangular co-ordinates

In developing electric motors in general and induction motors in particular temperature limits are 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 two-dimensional transient thermal model in rectangular co-ordinates using finite element formulation and triangular 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 the rotor of one squirrel cage TEFC machine of 7.5 kW during star-delta starting. The temperature distribution has been determined considering convection from the outer air gap surface.