Research On Torsional Vibration Of The Shafts Of Large Turbo-generator Sets

Torsinal vibration of the shafts of large turbo-generator sets is of great important to ensure the safe and economic operation of the power units. It is related with many theoretical and technicality problems.1. A DEH model based on the Matlab is set up and it is link to a model of a turbo-generator shaft. The influence of the control system to the torsional vibration of the shaft is researched. It is indicated from the researches that, when the parameters of the links of the control system are changed to reduce the sensitivity of the control system, the disturbance of the torsional vibration is increased. And when the parameters of the links of the control system are changed to increase the sensitivity of the control system, the torsional vibration are oppositely limited a certain extent. If the control system is enough sensitiveness, the unstable torsional vibration will be occur.2. Torsional natural frequencies, modal shapes and responses of two-phase circuit disturbance are all calculated, and the impact of temperature distribution to torsional vibration of rotors is summarized. The research of torsional vibration of large steam turbo-generator shaft system before this paper do not take into account the effect of steam flow intergrad process. In this paper, the research results about the effect of steam flow to torsional vibration of shafts after the control valves fast closing are presented. The model of shaft system is continuous mass model. The combined math model of a digital electro-hydro control system, thermal cycle system and a infinite electric network is considered. The simulation of a 300MW steam turbo-generator shaft system which is divided into 233 shaft sections show that the disturb and exciting become stronger to shaft and torsional vibration when taking into account the temperature distribution and the steam flow intergrad process. So the effect of steam flow to shaft torsional vibration must be think of in safety evaluation of the shaft systems.3. A tridimensional model of a Jeffcot rotor is reported. A new motion equation of the torsional vibration with rotation and the conception of the natural frequency with rotation of torsional vibration is presented. The natural frequencies of rotors with different geometrical structures and different speeds are computed based on the finite-element method, and the factors affecting the coefficient of the natural frequency with rotation are analyzed. It is shown that the effect of the centrifugal force is equivalent to the increase of the torsional stiffness of a rotor. So the value of the natural frequency with rotation is larger than that of the natural frequency without rotation. The natural frequency, which can be calculated from an empirical equation proposed in this study, is relative to the rotation speed, the diameter and the thickness of the disk. A rule is put forward to estimate a rotor which must or not be taken account of the centrifugal force.4. Based on the dynamic state, the torsional vibration model of a shaft is educed. A new motion equation of the torsional vibration is presented, in which the centrifugal force is considered. The natural frequencies of the shafts with different geometrical structures and different speeds are computed based on the finite-element method, and the factors affecting the coefficient of the natural frequency with rotation are analyzed. The torsional vibration of a 300MW turbo-generator set is researched and the conclusion that the centrifugal force can be ignored in the research of the torsional vibration of the turbo-generator sets is gained.5. A test-bed is designed to simulate the torsional vibration of the shaft of a 300MW turbo-generator set. And the torsional vibration is excitated by the three-phase short circuit and the load throw-off on the test-bed. The results indicate that the characteristic calculated as the torsional vibration model in this paper is the same as which of the actual shaft.