Shaft Crack Analysis and Diagnosis for the 600MW Steam Turbine Generator

Abstract

In order to find the cause of the shaft crack appeared in a 600MW steam turbine generator, several measurements are taken. The shaft assembly consists of three parts: shrink-fitted coupling, shaft and key which are used to transfer torque between coupling and shaft. First, the natural frequency of the shaft system is calculated. The result shows that the vibration signal contains the frequency nears the second natural frequency of the steam turbine shaft system. Second, stress field near the damaged coupling and shaft is analyzed using finite element method. The torque under different operation condition is calculated before stress analysis and applied to the shaft assembly, then. And, local stress concentrations position calculated is proved to be coincident with the place crack initiation. Finally, the cause of the fault is analyzed: at least three causes have found to be having something to do with the crack fault.

Crack Growth Prediction of the Steam Turbine Generator Shaft

“…The initial stress caused by interferences between the shaft and coupling is significant. However, the local stress at the end of the keyway may be much higher than other positions, the contact stresses under different loads were analyzed in [8], with the elastic material property.…”

“…Such problems firstly happened in 1970s in USA with severe crack accidents of the turbine generator shafts [6][7]. The shaft crack accidents were also emerged in a power plant in China including two 600MW steam turbine generator units [8]. Torsional interaction phenomena were monitored between the turbine generator and the network in the operation history.…”

“…Torsional interaction phenomena were monitored between the turbine generator and the network in the operation history. Several factors are determined to be the root causes including the contact stresses and the network disturbances [8].…”

“…To determine the root causes of the crack failures, the stress analysis was analyzed using Finite Element Method (FEM) in many researches as well as the fatigue accumulation of the local part to determine the remaining useful life [4,[8][9]. Furthermore, the crack initiation and propagation are to be analyzed to determine the failure position, extend the useful life and avoid catastrophic failures, which are less researched.…”

Analysis on Torsional Vibration Characteristics of Steam Turbine Generator Shafts

“…The calculation accuracy of finite element method which was very complicated to model was very high. Comparatively, transfer matrix method which was easy to make programs had been widely used in actual project [1][2][3][4][5] . This article explained the four-terminal network method, Riccati transfer matrix method and finite element method respectively, and the applications of three methods in inherent characteristics analysis of turbine generator units.…”