Influence of clearances in joints of thermal expansions system on reliability of multi-cylinder steam turbine

The results of studies are presented identifying structural causes resulting in malfunctions in operation of the thermal expansion system (TES) of steam turbines. A model is developed and used as a basis for analysis of interaction between the turbine cylinder, the bearing housing and the bed frame taking place as the cylinder is affected by shear forces and moments from connected pipelines. Possible options have been studied for the contact in a pair «longitudinal key — groove in the bearing housing». It is shown that the most unfavorable for TES is the «diagonal» type of contact. The results of the simulation show the effect of the ratio of values of the gaps in the TES keyed connection on the probability of «diagonal» contact and jamming of bearing housings on longitudinal keys. The technique is presented of building «a stability diagram» aimed at evaluation of resistance of the turbine cylinder TES to external impact. As an example, results are shown of stability studies for a high-pressure cylinder and a front bearing housing with dimensions corresponding to those of the T-175/210-130 turbine. It is proved that to ensure reliability when designing new or upgrading existing turbines one should take into account the effect of the ratio of clearance values in the elements of the thermal expansions system. The values of the selected clearances in joints of the TES elements must exclude the possibility of jamming of bearing housings on longitudinal keys. It is shown that an increase in the clearance in transversal key joints during the turbine operation increases the probability of jamming. It is proved that to ensure reliable TES operation, every major overhaul of the turbine must involve performing work on restoration of clearances in transversal key joints or using «swivel» keys, which are not exposed to variation of clearances changes under mutual angular displacements of the turbine cylinder feet and corresponding support surfaces of bearing housings.

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