Converter Fed Synchronous Generator System for Medium and Large Power Plants

Converter fed synchronous generators have the following advantages: The turbine can operate at any speed, independant of the frequency of the power system, the part load efficiency may be improved if the speed can be adjusted. The generator is protected and isolated. The stability is improved. This scheme is applicable to hydro, steam and wind generation. The paper gives details on a converter fed 650 MW unit with steam turbine having a synchronous generator with two 3-phase windings at 30° to each other which directly feeds a 12-pulse HVDC link. The usual converter transformer, var-compensators and current harmonics filters on the generator side are eliminated. The study shows the advantages and disadvantages of the system. The system stability is considerably improved compared to the conventional design. As the steam turbine can be operated only with constant speed, the improvements in the efficiency of the thermal system are limited. A cost reduction can be achieved only with a higher turbine speed. Details are given on the total system losses and the total system costs in comparison to the conventional design.