Comparison Between the Salient-Pole Synchronous Machine and the Doubly Fed Induction Machine With Regard to Electromagnetic Parasitic Forces and Stator Vibrations

Pumped-storage hydro power plants have been mainly equipped with fixed-speed salient-pole synchronous machines (SPSM). However, the upgrade from fixed-speed technology to variable-speed technology, using doubly fed induction machines (DFIM) brings many benefits in terms of stability and efficiency. This article deals with a DFIM obtained by replacing the rotor of an existing SPSM. The original SPSM had a fractional-slot winding. Although this winding configuration was not causing any problem in the SPSM, it leads to vibration issues in the case of the DFIM. It is shown how this special winding is responsible for electromagnetic forces leading to vibrations and why these vibrations were unnoticed in the case of the SPSM. The influence of the operation point (speed, power factor) on the force magnitude and resulting vibrations is studied. Using a simple and efficient algorithm, it is shown how the winding can be reconnected in order to lower the exciting force.