In variable-speed pumped-storage power plants, a promising solution is to connect the synchronous hydrogenerator to the grid via a full-rated frequency converter. In this case, the nominal frequency of the hydrogenerator can be chosen independently from the grid. The purpose of this paper is to investigate how the nominal frequency affects generator efficiency using the converter-fed synchronous machine topology. The nominal speed of rotation is varied between 275 rpm and 600 rpm, while the nominal frequency used is between 20 and 85 Hz. An analytical model of the salient pole synchronous generator is used. The weight of active materials, iron losses, copper losses and mechanical losses are calculated for the different nominal frequencies and speeds of rotation. Based on this, generator efficiency curves are calculated and presented.