615 / 2019-01-20 22:59:02

Numerical calculation of flow path clearance at HIP under natural conditions for a 1000MW nuclear steam turbine

numerical calculation; high-intermediate-pressure casing; finite element model; flow path clearance

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In nuclear power plants, it’s very common that rubbing fault happens between dynamic and static components of steam turbine. But it’s extremely difficult to diagnose this phenomenon accurately. A strong abnormal vibration of the unit may happen when the rubbing fault occurs, which will affect the safe and stable operation of the nuclear power units.
In this paper, the high-intermediate-pressure(HIP) casing of one certain 1000MW nuclear steam turbine is taken as an object. Based on Pro/E and ANSYS WORKBENCH software, the deformation of the HIP casing is calculated during the whole installation process and the change of flow path clearance is analyzed. Firstly, a finite element(FE) model of the nuclear steam turbine HIP casing is established. Five different calculation conditions are used to simulate the installation process. After placing the lower casing, we place the lower diaphragm, the rotor, the upper diaphragm, and the upper casing in turn. Secondly, the deformation of HIP casing in the cold state is calculated. Finally, the flow path clearance of different states is calculated, including tip clearance, diaphragm clearance, flange clearance, gland seal clearance. Compared with the operational monitoring data, the trend of change is analyzed during the whole installation process.
According to the calculated data, the value of tip clearance and diaphragm clearance increases first and then decreases. The results show that the maximum value appears when the upper casing is installed. After tightening the bolts, the lower casing is lifted up, but the whole casing shows a sinking trend. These specific data can be of reference value to the steam turbine design, manufacture and installation department. It provides a lot of guidance for engineers during the overhaul of steam turbine.