Turbine-generator systems are subjected to sudden short circuits. The sudden change of electrical characteristics in these systems can incur very high excitation torques on the components. The excitation depends on the types of short circuits and the electrical properties of the generator, etc. Transient torsional vibration due to generator short circuit is investigated in this paper. Typical short circuit excitation functions are discussed. A modern gas turbine / generator / steam turbine system is used to illustrate the effects of modelling inaccuracies and parameter variations. The acceptance standards for such transient short circuit conditions are generally based on maximum torque transmitted or some kind of allowable shear stress. They cannot be accurately predicted by models which use 1–2 disks (stations) to represent a major machine in a train. Either a more refined model or a better reduction method is needed. Flexible couplings affect the transient torsional response and they must be included in the system vibration analysis. Their influence on the peak transmitted torque has been examined. The selection of couplings for turbine-generator systems in modern combined cycle power plants should be emphasized.

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