Optimization of a 900 mm Tilting-Pad Journal Bearing in Large Steam Turbines by Advanced Modeling and Validation

Modernization of steam turbine components can extend power plant lifetime, decrease maintenance costs, increase service intervals, and improve operational flexibility. However, this can also lead to challenging demands for existing components such as bearings, e.g., due to increased rotor weights. Therefore, a careful design and evaluation process of bearings is of major importance. This paper describes the applied advanced modeling methods and performed validation for the optimization of a novel 900 mm three-pad tilting pad journal bearing that showed high temperature sensitivity to the fresh oil supply temperature. The bearing was developed to cope with increased rotor weights within the low pressure (LP) steam turbine modernization at two 1000 MW nuclear power plants. With a static load of 2.7 MN at a speed of 1500 rpm, it represents one of the highest loaded applications for tilting pad bearings in turbomachinery worldwide. After identification of the reasons for the sensitivity, advanced modeling methods were applied to optimize the bearing. For this purpose, a more comprehensive bearing model was developed considering the direct lubrication at the leading pad edge and pad deformation. The results of the entire analyses indicated modifications of bearing clearances, pad length, thickness, and pivot position. The optimized bearing was then implemented on both units and proved its excellent operational behavior at increased fresh oil supply temperatures of up to 55 °C. In conclusion, the application of advanced modeling methods proved to be the key success factor in the optimization of this bearing, which represents an optimal solution for turbomachinery.