Analysis and optimization of abnormal vibration for a gas-steam combined cycle power unit

XUE Zhaoao; YANG Shichun

doi:10.19471/j.cnki.1673-6397.2026.01.011

Abstract：To address the abnormal vibration issues occurring during the trial or production operation of a gas-steam combined cycle generator units,a 9F-class gas-steam combined cycle generator unit is taken as an example.The single-mass,single-degree-of-freedom vibration modes of components such as the foundation plate,columns,and frame in response to disturbance force excitation are analyzed.The generation,transmission,and excitation response processes of the disturbance force are outlined,along with the main causes of abnormal vibration.By comparing the measured results of shaft vibration(relative displacement)and bearing vibration(absolute velocity)with standard limits,the characteristics of abnormal vibration are determined,and corresponding vibration reduction measures are implemented.The results show that the single degree of freedom and natural frequency of the horizontal radial vibration,horizontal axial vibration,and vertical vibration of the base plate of the columns and frame play an important role in the vibration of the generator unit.The vibration of the generator unit's shaft system is a superposition of multiple vibrations;monitoring shaft vibration and bearing vibration can effectively identify abnormal vibrations.Through investigation of the adverse factors causing the abnormal vibrations,it is found that mass eccentricity of the gas turbine rotor is the main cause.Based on the dynamic balancing test,a rectification plan is developed(adding a 700 g counterweight with a key phase of∠60° to the 7th bearing side of the gas turbine;adding an 800 g counterweight with a key phase of ∠240° to the 8th bearing side of the gas turbine;and adding a 1 038 g counterweight with a key phase of ∠220° to the compressor disc of the gas turbine),which effectively solve the abnormal vibration problem.This analytical method can provide a reference for the diagnosis and control of abnormal vibrations in similar generator units.