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.

No abstract

Harmonic flux penetrating solid conductive material causes eddy currents inside. It seems plausible that its magnitude does not exceed the exciting magnetomotive force (mmf). However, under certain circumstances the opposite occurs. This article deals with a special case in which the eddy current is approximately 13% higher than the exciting mmf. An analytical field solution, a finite element calculation and a measurement proving this phenomenon are presented. A special flux linkage is turned out to be the reason for this phenomenon. Finally, another example with higher pronounced mmfexceeding in a coil is presented.