Influence of damper winding topology on additional rotor Joule losses in converter-fed synchronous machines for hydropower plants

Salient-pole synchronous machines have been a common technology in pumped storage hydropower plants for decades. With the help of a full-scale converter, the electric machine can be operated at variable speeds, which is becoming increasingly important due to the growing number of fluctuating renewable energy sources in the grid. Due to the converter’s switching behavior when connected to the stator winding, additional harmonic currents are induced in the damper and field windings via the magnetic field in the air gap. This study aims to qualitatively investigate the influence of different damper winding topologies on the induced voltage and resistance factor of the field winding as well as on the total additional AC Joule losses in the rotor windings related to the converter. The machine design is based on a real research hydro generator. In addition to the reference machine, three other rotor topologies are investigated: one with a short-circuited ring between the field winding and the pole shoe, one with a larger gap between the pole shoe and the field winding, and one with a wider pole shoe. For each of the topologies, three different damper bar arrangements are investigated. The calculations are based on FEM simulations that cover a frequency range from 0.01 Hz to 15 kHz and consider load-point-dependent saturation caused by the fundamental harmonic. This paper is important for the future design of variable speed salient-pole synchronous machines in pumped storage hydropower plants, as the results show the potential to significantly reduce additional AC Joule losses in the rotor windings.