Free vibration analysis of a large hydroelectric generator and computation of radial electromagnetic exciting forces

Major causes of vibration in electrical machines come from electromagnetic sources. A serious problem may arise when the frequencies of the periodic exciting force are identical with, or close to, one of the natural frequencies of the machine. This paper presents a 2D modal analysis which calculates the natural frequencies and mode shapes of the stator and rotor of a large hydroelectric generator. The structural model takes into account the shape of the stator teeth and rotor poles. Moreover, a 2D electromagnetic transient simulation is performed in order to predict the frequencies and mode shapes of the electromagnetic exciting force. This advanced electromagnetic numerical simulation takes into account the winding sequence and the geometry of the rotor and stator given by the manufacturer. The purpose of this work is to validate a multiphysics tool for the future and recognize its advantages over the classical method.