Research On The Structural Vibration Of Turbo-generator Set And Its Influencial Factors

In the past,the vibration analysis of turbo-generator sets was mainly concentrated on the rotating parts,the degree of emphasis on the vibration of the structural components was insufficient.However,the structural components are used as one of the key components of the turbo-generator set.The vibration faults of the structural components of the turbo-generator set also involves the safety,stability,and economy of the power plant.Especially,structural vibration faults have occurred on large-scale turbo-generators in recent years such as 300 MW,600 MW,and 1 000 MW turbo-generator sets which have seriously affected the safe operation of the unit.Firstly,the division of the shafting unit,the differential equation of motion of the rigid disk,the differential equation of motion of the elastic axis,and the unbalanced mass force in the dynamic equation are introduced in detail.The finite element dynamic model of a rotor-bearing system for a turbo-generator set under rigid support is established.By analyzing the influence of the flexible support on the dynamic characteristics of the system,the equivalent oil film stiffness and damping coefficient of the system under flexible support can be obtained.The finite element dynamic model of the rotor-bearing system of the turbo-generator set under flexible support can be obtained by replacing the oil film parameters with the equivalent oil film parameters.Secondly,the phenomenon of structural vibration occurred on two large generators are analyzed.The structural vibration phenomena of large sacle gas-steam combined cycle unit generator and ultra supercritical turbine-generator are analyzed separately.Due to the typical characteristics,the low-pressure cylinder is used as an example for calculation and analysis.The vibration response characteristics of the bearing pedestal vibration and the shaft vibration with the support stiffness are thoroughly studied based on the established finite element model.The results show that the support stiffness has a greater impact on the bearing pedestal vibration and shaft vibration.Under the same size excitation force,when the support stiffness is larger,the shaft vibration is larger and the bearing seat vibration is smaller.When the support stiffness is smaller,the bearing pedestal vibration is larger and the shaft vibration is smaller.Finally,the phenomenon of double resonance peak appearing in both the actual unit and calculation is explained using the dynamic vibration absorber theory.It is shown that as the bearing is located on the exhaust cylinder,the support stiffness is low.The natural frequency of the bearing is reduced to less than 50 Hz.When the natural frequency of the bearing is exactly the same as the natural frequency of the rotor,vibration absorbing phenomenon occurs.In the case,bearing turns to be a vibration absorber.Shaft vibration transfers to the bearing.During run up process,there are double vibration resonance peaks nearby bearing and shaft natural frequency.It causes the double resonance peak phenomenon.And starting from the theory of the tuned mass damper and combining the advantages of particle damping,an energy dissipation device for the generator stator which called sand damping dynamic vibration absorber is proposed by replacing the tuning mass with sand.The effectiveness of the new vibration absorber for vibration suppression of the generator stator is calculated and analyzed.