Electrical machines like transformers, motors and generators have a high efficiency; however the electrical losses reach such high levels that the produced losses must be removed through an appropriate method. The life expectancy of the winding isolation strongly depends on temperature, an increase of the temperature level by 5 to 8 K results in a halving of the life expectancy. As the winding resistance is temperature dependant, an improvement of the cooling would bring about a decrease on the copper losses. Due to the high material costs, it is desirable to use this to its limit: through a more efficient cooling process the current density can be increased and as a result the same machine size can reach a higher power. The flow and thermal processes in a large motor or generator are highly complicated and they cannot be well described with the older methods. Measurements inside a fast rotating rotor are very complicated due to the high circumferential speed. The 3D Computational Fluid Dynamics is the correct alternative for the analysis, concept and for the detailed design of electrical machines as it allows to precisely predict the flow structure around the stator coil ends, the distribution of the cooling medium, the pressure losses, the heat transfer coefficients and temperature distribution. Without an extreme simplification of the geometry, a coupled thermal and flow calculation for the complex geometry of a stator in the coiler head is only possible with software based on Cartesian mesh like FloEFD. |