Abstract

Dynamic characteristics of a turbine-set, regarded as a system: shafting-stator-foundation, have been analyzed for stimulated, transient and free vibrations.

1.  The increase of unit outputs of modern steam turbines has necessitated increasing of the turbine-set reliability, simuitaneously with the increased complicacy of their design. The shafting of a multi-case turbine forms, together with the bearings and the foundation, a highly complex dynamic system subject to various disturbances

1. Vibrations of a turbine set are caused by disturbing forces, the most important having been those resulting from imbalance of various origin i.e. from inaccurate balancing and assembling, thermal distortions and unequal settling of the foundation, mechanical and thermal rotor instability, unequal rotor rigidity etc.

1. The effects as specified above cause stationary stimulated vibrations. It shouid be pointed out that transient vibrations can occur, namely, flexural vibrations due to sudden imbalance (e.g. due to rotor blade breaking), and torsional vibrations due to short-circuit in the electric generator.

1. Flexible shafts of modern large turbine-sets operating at high pressure are likely to develop self-excited vibrations due to non-conservative forces of interaction of journals and oil film in bearings as well as due to non-conservative aerodynamic forces in the flow part of a turbine.

1. A method has been proposed that allows solving the mentioned problems of turbine-set dynamics; the method has been based on obtained general canonical equations of turbine-set vibrations.

1. Non-conservative circulating forces occurring in the oil film of bearings, in rotor blade rims, in stage seals above the shrouding and in labyrinth seals (of stators and outer seals) have been taken into account in the stability analysis; the mutual dependence of these forces has been presented. 

1. The influence of circulating forces can be changed in a wide range using appropriate designs of seals and other components of the flow part.

1.  Thę treshold output can be varied in a sufficiently wide range by means of constructional factors such as the selection of the seals above shroudings, clearance ratios in these seals, bearing type rotor rigidity and other.