ROEBEL WINDINGS FOR HYDRO GENERATORS
Examensarbete för masterexamen
Roshanfekr Fard, Poopak
Large-scale generators tend to have high power. Normally, the armature winding of these generators consist of multiple strands insulated separately and transposed (using Roebel transposition) in order to suppress losses caused by eddy currents and circulating currents. As the generator reaches high power density, circulating currents in the armature winding are large, and hence the loss must be estimated accurately in generator design. Calculation of such losses requires the distribution of circulating currents, which differs from strand to strand. The Roebel bar optimum structure allows increasing machine efficiency, and consequently energy savings. In this thesis, the circulating currents in a Roebel transposed diamond coil have been studied. The Roebel transposition in the active part of the generator have been 180° and 360°. Moreover the circulating currents for a traditional Roebel bar (no transposition at the end region) and for a Roebel bar with transposition at the end region has been carried out. Finally the values of circulating currents and the losses due to these currents for these Roebel bars have been compared. The study has been carried out using models of the winding developed in a FEM-program package. A 2D model of the active part has been drawn in MagNet. From the flux linkages that are taken from the program the circulating currents has been calculated analytically. A 3D model of the end region of the winding has been drawn in MagNet and the fields of this region has been studied. The circulating currents in half a coil has been investigated from the results obtained from the 2D and 3D simulations. The conclusions of the study are that using 360 transposition in the active part reduces the circulating currents almost to zero. 180 transposition reduces the circulating current. The study further concludes that using transposition in the end region reduces the circulating currents in the bar. Finally the study concludes that the minimum circulating current loss is achieved in case of 360 transposition in the active part (slot region) and transposition in the end region. It is also shown a cost-effective well chosen manufacturing process.
Elkraftteknik , Electric power engineering