Determination of Critical Parameters in Electrical Machine Thermal Models

In this paper, the authors discuss the problem concerning the determination of some thermal parameters which are very complex to compute. These parameters play an important role in thermal networks usually adopted for electrical machine thermal analysis. In particular, in this paper, the following thermal parameters are analyzed: equivalent thermal resistance between external frame and ambient, equivalent thermal conductivity between winding and lamination, forced convection heat transfer coefficient between end winding and end-caps, radiation heat transfer coefficient between external frame and ambient, interface gap between lamination and external frame, air cooling speed, and the bearings effective thermal resistance. While the information given in this paper is mainly related to induction motors, it is also of general use for the designers of other types of machine. The reported results have been validated using induction motors with power ranges from a few kilowatts up to 1 MW.