Coupled Torsional Vibration and Fatigue Damage of Turbine Generator Due to Grid Disturbance

Abstract

Crack failures continually occur in shafts of turbine generator, where grid disturbance is an important cau.se. To estimate influences of grid disturbance, coupled torsional vibration and fatigue damage of turbine generator shafts are analyzed in this work, with a case study in a 600MW steam unit in China. The analysis is the following: (i) coupled system is established with generator model and finite element method (FEM)-based shafts model, where the grid disturbance is signified by fluctuation of generator outputs and the shafts model is formed with lumped mass model (LMM) and continuous mass model (CMM), respectively: (ii) fatigue damage is evaluated in the weak location of the shafts through local torque response computation, stress calculation, and fatigue accumulation: and (Hi) failure-prevention approach is formed by solving the inverse problem in fatigue evaluation. The results indicate that the proposed scheme with continuous mass model can acquire more detailed and accurate local responses throughout the shafts compared with the scheme without coupled effects or the scheme using lumped mass model. Using the coupled torsional vibration scheme, fatigue damage caused by grid disturbance is evaluated and failure prevention rule is formed.

Online Evaluation of Turbo-Generator Shaft Fatigue Damage Caused by Subsynchronous Oscillation

“…However, such methods are mainly used for offline torque calculation, and the coupling effects between mechanical and electromagnetic subsystems cannot be considered. After the modeling of the shafts, generator, transformer and other equipment, the whole system can be solved, the torque can be calculated offline, and certain commercial software platforms, e.g., PSCAD/EMTDC and MATLAB/ SIMULINK can be used to solve the shaft torque by this method [6], [15], [23], [24]. A method of computing torque in real time was presented in [25]- [27].…”

“…In recent years, in China, SSO faults have increasingly happened. For example, in 2008, cracks caused by SSO and torsional vibration were detected in generator shaft and couplings between a low-pressure cylinder and generator of a 660 MW unit [6]. SSO occurred when a 600 MW subcritical unit was connected to the grid in India in 2013, and the oscillations caused fatigue damage and cracks in the low-pressure rotor of the unit.…”

“…For the repairs of abrasion defects in a 600 MW steam turbine, torsional stresses and fatigue were analyzed offline [13]. Reference [6] developed a coupled model to calculate the interaction between the turbine generator and the grid, and fatigue damage was evaluated in the weak location of the shaft. The impact pole slipping resulting from a delayed fault clearance has on peak shaft torque and on accumulative fatigue life expenditure of the shaft was examined in [14].…”

Finite element analysis of an actively controlled heavy rotor using a PVDF piezoelectric layer as a sensor and actuator

“…The coupling joint between various turbines and generator are most probable sections to be failed during the faults. 15 So, under actively controlled system, the vibrations produced during various electrical faults in coupling elements 35, 74 and 110 are simulated numerically. To establish the stability of the system, the relative angular displacement vs relative angular velocity plots of elements 35, 74 and 110 are shown in Figure 11.…”

“…Further, various researchers use lumped mass model to analyze the torsional vibration in big turbo-generator rotor under unloaded state of the generator. 4,7,10,14,15,16 The variation in the electromagnetic torque of generator cause torsional vibrations in turbo-generator rotor. Therefore, it is essential to measure these torsional vibrations so that further effective control mechanisms can be developed.…”