| Popis: |
The utilization of slot wedges made of magnetic material in a synchronous and induction motor or generator makes possibility to increase the efficiency of the machine. In this paper, the experiences acquired in design, installation, testing and exploitation of the magnetic slot wedges on two relatively large hydrogenerators of rated output 34 MVA, 10.5 kV, 50 Hz, 187.5 min-1, cos = 0, 8, vertical form, are presented. The magnetic slot wedges with high mechanical strength and low average permeability of r = 2, 8 are embedded into open stator slots of the two hydrogenerators. The fixation of magnetic wedges in the stator winding slots is described in detail. The data referring to magnetic and mechanical properties of the installed magnetic wedges are presented. With magnetic slot wedges the magnetizing current in excitation winding required to generate the air-gap flux is lower than with non-magnetic slot wedges. The results obtained in the design stage and the comparison of on-site testing results of the generator with non-magnetic wedges and the same generator with magnetic wedges show an increase in efficiency. By installing the described magnetic wedges the surface losses in the generator rotor pole shoe iron were reduced by app. 20%, whereas the losses in the excitation winding were reduced by app. 8% due to the reduced air gap magnetizing current. In addition, the results obtained by analytical calculation and by measurement of the magnetic wedge influence on generator’s reactances are provided. Due to reduction of excitation current in no-load operation, synchronous reactances in direct and quadrature axis increase by app. 5% in the case of magnetic wedges. If an increase of reactances due to leakage reactance is taken into consideration, the total increase of synchronous reactances is app. 8%. |
