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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