In principle, thermal analyses of asynchronous machines can be divided into two classes. On the one hand, there are analytical methods and, on the other, numerical methods. The former are also known as thermal network calculations. They have the advantage that they require little computing capacity. Calculations can therefore be carried out quickly. The main task in the formation of such networks lies in the dimensioning of the resistors. These must be selected in such a way that the temperature behaviour within the machine is well mapped. Numerical simulations make it possible to analyse any geometry. However, the computational effort is significantly higher. Furthermore, considerably more time is required to generate the models. Both methods have been demonstrated in the preliminary investigations and the results verified using a low-voltage asynchronous machine.

Certain characteristic values of the machine to be analysed are essential for the development of analytical and numerical models. With this in mind, the machine from Elektromaschinenzentrale (EMZ) was measured both electrically and thermally. This was done at the Physikalisch-Technische Bundesanstalt (PTB). Based on the measurement, it is possible to determine the losses within the machine. These are incorporated into the models developed.

The calculated temperatures (of the thermal networks used) agree relatively well with the real measured values. Knowledge of the exact geometry is required here. The air gap width in particular is a very sensitive parameter with regard to the rotor temperature. Furthermore, it is shown how numerical simulations can support the creation of analytical networks. An independent numerical simulation also maps the internal thermal behaviour well. With regard to optimisation, numerical simulations are the method of choice. Weak points in the cooling system can be identified very easily. Parameter studies for improvement can also be implemented. The expertise gained will be used in follow-up projects to further exploit the potential of electrical machines.