Study On Torsional Vibration Of Turbo-generator Shafts With Electro-mecllanical Coupling

As the series capacitor compensation device and high voltage direct current (HVDC) transmission system are widely used, the structure of power network becomes more and more complex. The subsynchronous oscillation and torsional vibration of turbo-generator shafts become increasingly prominent. Serious electro-mechanical coupling will directly cause serious damage to large turbine generator rotor shaft and result in major accidents, which harms the safe operation of the electric power system. The torsional vibration of turbo-generator shafts with electro-mechanical coupling is studied in this paper. The primary contents are as follows:Firstly, to remove the limitations of traditional Prony algorithm (TPA) and the small disturbance method, a modified segmentation Prony algorithm (MSPA) is presented here. By dividing the whole observation window into several segments according to certain rules and then utilizing data in all of the segments, the overall sample function matrix is constructed and the averaging-error effect of the whole observation window is taken into account. Meanwhile, a new approach of extracting oscillation modes is presented by means of Kaiser window FFT analysis and a concept of energy class. The MSPA and time domain simulation method are integrated and used in analysis of subsynchronous oscillation (SSO). Their results can be confirmed and complemented by each other. Simulation results show that the MSPA not only enhances SPA’s computational efficiency and the credibility of results, but also avoids the lost of oscillation modes existing in modified PA (MPA) which uses singular value decomposition to determine the rank of Prony model.Secondly, from the view of whole system, different kinds of electric power system model are built by using Matlab/Simulink software. The torsional vibration caused by traditional big disturbance, the subsynchronous resonance caused by series capacitor compensation device and the torsional vibration caused by HVDC are simulated and analyzed. Meanwhile, the effects of different operation modes and faults on subsynchronous oscillation and torsional vibration are discussed. The results can provide guidance and reference for practical operation of power system.Lastly, in view of mechanical side, this paper takes a660MW supercritical steam turbine unit as the research subject. The natural characteristics and dynamic responses of the shaft are calculated by using finite element method. The effects of temperature distribution and the shaft damping on natural characteristics and dynamic responses are analyzed, and some significant results are obtained. Morlet wavelet, which can analyse non-stationary signal and obtain the best resolution both in frequencies domain and in time domain, is introduced and applied to analyse torsional vibration signals. The method has too many strongpoints compared with the traditional methods.