Bending of the casing of a 73-MW steam turbine running in a combined-cycle power plant

The 60-73 MW steam turbines in combined-cycle power plants tend to be made as a singlehull unit to ensure its reliability, efficiency, and high performance. In this case, the turbine casing is long, and its thermal deflections under working condition are large. Therefore, there are risks for fractures of the shaft and bearings. However, information on evaluating thermal deflections of turbine engine casings is lacking in the scientific literature. This study determines bending deformations of the casing of a 73-MW steam turbine running in a combined-cycle power plant. The study consists of two parts. In the first part, the displacement method developed by the authors on the basis of Moore’s method is used to determine the deflections of a cold turbine casing. In the second part, the deflections of the casing are calculated under working conditions. Numerical experiments were conducted using the SW Simulation module. The study showed that the bending deflection of the hot casing was well above the deflection of the cold casing and there was a real danger of interference of the rotor and casing. In order that the turbine should work properly, the rigidity of its casing must be increased, for example, by means of longitudinal ribs on the top. The calculations prove that using the ribs reduces bending deformations. The results of research can be used when developing steam turbines for combined-cycle power plants.

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