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Abstract. Numerical methods of calculating the electromagnetic forces and of simulating the oscillation behavior of the stator end winding are introduced. The end winding oscillations of different turbo generators under forced vibrations are computed in a combined simulation. Also eigenfrequencies and eigenmodes are determined. The obtained results are surveyed by measurements. Numerical simulation of oscillation behavior is found a useful tool in end winding design although model parameter identification still offers improvement potential.

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Purpose -Operation of synchronous machines in the power range of several 10 MW with variable speed up to 7,000 rpm using a current converter is, thanks to the development of power switches, possible and economically reasonable today. However, current harmonics, produced by converter, generate additional losses, especially eddy current losses on the rotor surface are produced by the converter, which strongly depend on the rotor permeability. The purpose of this paper is to show that an accurate machine modeling is required, in order to consider the nonlinearity of electromagnetic processes inside. Design/methodology/approach -This paper concentrates on the determination of the rotor surface losses in a three-phase turbogenerator feeding a current converter. Saturation of rotor steel is taken into account using a transient finite element method model of the machine, coupled with a converter model. Findings -A detailed analysis of the damper currents and losses in a turbogenerator operating with a frequency converter is presented. The effectivenes of damper winding modifications, concerning the eddy current loss reduction in the rotor surface, is depicted. Practical implications -The introduced modelling technique presents an accurate electromagnetic modelling of an I-converter-fed synchronous generator with massiv poles, which is fed by a current converter and so has to sustain additional eddy current losses in the rotor surface. In this way, the amount and distribution of these losses are evaluated more accurately which allows a more efficient design of the damper winding as well as machine cooling system. Originality/value -Some researchers have made contributions to the analysis of current converter-fed synchronous machine, regarding terminal behaviour of the machine. This paper focuses on eddy current losses on the rotor surface, considering the time and space dependent saturation aspect in the machine, particularly in the rotor.