Ensuring the stability of steam turbine rotors. Part 1. The principle of choosing the parameters of plain bearings in high-power turbine units during design and repair

Abstract

Plain bearings and their dynamic properties primarily determine the reliable operation of shaft lines in high-power turbine units, since not only disturbing hydrodynamic forces, but also damping forces are concentrated in the oil layer of the bearings. What is decisive is not the forces themselves, but the work performed by these forces over the displacements and velocities of these displacements. First of all, it is necessary to ensure the design loads on the bearings during operation, which is achieved by optimal alignment of the rotors at the half-couplings. Firstly, in the power industry, the culture of correctly determining rotor alignment at half-couplings is disappearing, and repair errors are superimposed on manufacturing imperfections. Secondly, bearings with maximum stiffness anisotropy and optimal degree of ellipticity should be used. Unfortunately, manufacturing plants often follow old books on mechanics, which propose setting a side clearance of the order of one thousandth of the diameter, and this has found its way into old repair documentation. At the same time, theory and field adjustments show that the clearance in the elliptical plain bearing of a large rotor should not be less than 0.002 of the diameter, or the relative clearance with respect to the trunnion radius should be about 0.004. The alignment of the rotors at the half-couplings must take into account the different lift of the rotor journals in adjacent bearings. The need to choose the degree of ellipticity of small-diameter bearings for high-pressure rotors of high-power turbines is especially noted.