Impact of Design Aspects on the Vibrational Behaviour of the Stator End-Winding Region of Large Turbogenerators

In this paper, an investigation of the influence of design aspects and the optimization of material properties at the stator end-winding region of large turbogenerators is presented with respect to the vibrational behaviour. This study is motivated by increasing stresses on the electrical insulation system of the stator bars. Therefore, design aspects (number of strain blocks, weak support ring, etc.) and material properties (Young's Moduli of several materials) are varied in 3D-finite element analysis with the intention to minimize the acting strain. Thereby, designs, e.g. with a support ring with low stiffness, could lead to locally reduced strain values. But this positive effect is compensated by the shift of strain values along the axial plane. Thus, the stress is not fully reduced. Concerning the material properties, the copper and the electrical insulation system are the obvious candidates for optimization, but are not practically useful for modification. Other promising candidates for modifications are the glass-fiber reinforced materials. A decreasing of the stiffness could lead to locally reduced strain values.