An investigation into the mechanical and electrical losses of permanent magnet disc machines
The subject of the thesis is the investigation of the loss-mechanisms in high-speed permanent magnet disc generators. Such electrical machines can be directly coupled to gas
turbine engines and run at speeds of up to 60000 revolutions per minute. The work focuses
particularly on the losses occurring in the stator of the machine, which are:
1. Ohmic resistance losses
2. Eddy current losses
3. Circulating current losses
4. Pumping losses of coolant fluid
Numerical modelling was used to gain a theoretical understanding of the loss-mechanisms
involved. Validation of these results was carried out by means of experiments conducted
on several purposely built test rigs. The results of the experiments were then correlated to
the numerical solutions so that the prediction of the losses for different geometries can be
obtained with a high degree of certainty. For the numerical analysis, commercial software
was used for thermal and flow problems, but for the electro-magnetic problems a new
computer code using the object oriented language C++ was developed.
Besides this, the magnitude and relation of eddy-currents and circulating currents in Litz
cables was investigated in depth by modelling the Litz cables macroscopic properties in
detail, which allowed the investigation of the effect of the cable bundling configuration.
It was shown that the design of these machines is always bound onto the operating
conditions as the magnitude of the different losses do not allow the ideal combination
of properties to be found for a range of load points but only for given operating point.