Performance Analysis of the Reheat-Stop-Valve Mechanism under Dimensional Tolerance, Misalignment and Thermal Impact

The reheat-stop-valve (RHSV) mechanism is a principal component in a steam turbine unit which controls the running state. Mechanical jamming and incompletence often occur during closing the mechanism. This paper proposes a method to quantitatively investigate the cumulative effect of dimensional tolerance, misalignment and thermal impact on the dynamic performance with shaft and bearing pairs in a RHSV mechanism. Finite element method is employed to study the effect of thermal impact on the clearance of the shaft and bearing pairs. Then, we calculate the clearance of the shaft and bearing pairs considering thermal impact and dimensional tolerance. Based on the non-linear clearance and misalignment, a model named compensation cone is developed to establish the multi-support mechanism of the shaft and bearings system. The method is demonstrated by applying to the RHSV mechanism in a supercritical steam turbine unit. The results indicate that the combined effect of dimensional tolerance, misalignment and thermal impact exerts great effect on the performance of mechanism.

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