In the investigated high pressure steam turbine, with increasing steam flow rate the exciting aerodynamic forces rise and cause high, but limited vibration of turbine bearings. The tilting-pad journal bearing load and load angle are changing as the steam flow rate changes in turbine with partial arc admission, and accordingly the dynamic characteristics of bearings change.
The field experiments results at fossil fuel power plant presented. The aim of experiments was the partial arc steam admission optimization to reducing the effect associated with change of bearing load/load angle. At first, conventional (consecutive) order of valve opening was investigated. In this case, the bearing vibrations are rising while steam flow and valve outlet pressure are increasing. At some “critical point” the vibration level rises stepwise. Situation repeats symmetrically during turbine unloading/loading.
In the second part of experiments, the consecutive order of valve opening was changed to “diagonal” one. As a result, the bearing vibration weakly depends on the steam flow rate and its value is significantly lower. Long-term turbine operation shows that “diagonal” steam admission is optimal for this type of turbine.
From the analysis of the forces vectors follows that the “critical point” corresponds to static force, which acts in the direction between neighbor tilting-pads. It is contrary to operation and idle modes where this force is acting on pad. The static steam force is bigger and bearing loading is lower at the “critical point”. Numerical investigation of rotor-bearing threshold stability was performed for different bearing loading conditions with exciting aerodynamic steam forces. Two configurations of bearings were included into the model: LBP and LOP — at the “critical point”. Consecutive and so-called “diagonal” orders of valve opening were modeled. Threshold capacity is higher for the “diagonal” valve opening order.