Finite element analysis of the starting behaviour of large salient pole machines

The incorporation of improved mechanical models into a transient electromagnetic finite element (FE) analysis of an asynchronous start of a hydroelectric generator is presented. In most cases, the rotor´s dynamic characteristics are neglected during FE simulations of the starting sequence. However, rotary oscillations can exhibit a profound impact on the generation of electromagnetic torque. Therefore, omitting the oscillations might result in considerable errors. In order to improve this situation, an analytic model of the rotor´s oscillatory behaviour was implemented. This model replaces the constant moment of inertia commonly used in electro-magnetic codes. From the combination of the mechanical rotor model and the transient FE analysis, better estimates of the torque ripples and the resulting mechanical stress levels can be obtained