Cooling of rotating machines. Parametric studies

The design of rotating electrical machines must ensure that the sizing carried out, taking into account electrical objectives, also satisfies thermal constraints. This involves calculating the detailed temperature field in order to verify its adequacy with the permissible temperature rise [1]. This is governed, in particular, by the winding insulation qualified by its class [4]. It is also essential to determine and classify the heat dissipation paths precisely, and to measure the respective role of each transfer mode in the management of dissipated heat flows.

The file provides an extensive survey of general laws and suitable convection correlations, plus some thermophysical data on the materials and fluids commonly encountered in this context.

To illustrate the practical application of this information, the reader will find here examples of the results of thermal studies of typical open and closed electrical machines whose behavior, from the thermal point of view, is radically different. These results are based on three-dimensional numerical modelling, validated by comparison with dedicated experimental tests carried out on finely instrumented machines [10] [12] [13]. The electrical machines on which the analyses presented here are based are two asynchronous motors with caged rotors, one open with axial ventilation and the other closed and cooled by external ventilation. These motors cover a wide range of motor structures and applications. The conclusions drawn from these analyses can be transposed relatively easily.