Approximate Analysis of Transient Heat Conduction in the Stator of an Induction Motor during Auto-transformer Starting

For the development of electric machines, particularly induction machines, temperature limit is a key factor affecting the efficiency of the overall design during transient state. Since conventional loading of induction motors is often expensive, the estimation of temperature rise by tools of mathematical modeling becomes increasingly important and as a result of which computational methods are widely used for estimation of temperature rise in electrical machines. This paper describes the problem of two dimensional transient state heat flow in the stator of induction motor during auto-transformer starting. The stator being static is prone to high temperature and the study of thermal behavior in the stator is useful to identify the causes of failure in induction machines. The temperature distribution is obtained using finite element formulation and employing arch shaped elements in the r-θ plane of the cylindrical co-ordinate system. This model is applied to one 3-phase squirrel cage induction motor of 7.5 kW rating.