Unexplainable rotor oscillations occured at an industrial steam turbine with air condenser shortly after startup of the plant, but already at specified load points. These oscillations led to immediate shutdowns and were not explainable with conventional reasons at that time. After several oscillation measurements and analysis a hypothesis was developed to explain the oscillation phenomena: The reason of the oscillations is an aggregation of condensate in a labyrinth seal of one or more turbine stages which acts like additional bearings and shifts the eigenfrequencies of the whole system.

This work presents an analytical steady-state heat transfer model to explain, how condensation can occur in high-pressure sections of a steam turbine. With this model it is possible to take into account heat exchange in single turbine stages. The occurring heat fluxes are calculated row by row in each stator and rotor blade row. A new approach for considering the heat fluxes due to heat conduction between guide blades and guide blade carrier is presented. Due to the absence of measured surface temperatures the determination of convective heat transfer coefficients plays a major role in this work.

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