Theoretical And Experimental Study On Vibration Characteristics Of Misaligned Multi-rotor System

Shafting misalignment is a common fault of multi-rotor system.In this paper,the multi-rotor system of steam turbine generator set is taken as the research object,and the influence of misalignment on vibration characteristics of multi-rotor system is studied through theoretical and experimental methods.The static analysis model of multi-rotor system is established,the lift curve and internal force distribution curve of multi-rotor system are calculated,and the influence of alignment deviation on coupling internal force and bearing load is studied.It is found that when the double support shafting is misaligned,the coupling will produce larger shear force,and when the single support shafting is misaligned,the coupling will produce larger bending moment.Compared with the single support mode,the bearing load of double support mode is more affected by the elevation.The dynamic analysis model of multi-rotor system supported by sliding bearing is established,and the influence of alignment deviation on bearing dynamic characteristics,shafting modal characteristics and unbalance response characteristics of multi-rotor system is studied.It is found that there are coupling modes between rotors,and the misalignment will change the bearing stiffness near the coupling,which will affect the mode coupling.For double support shafting,the mode coupling is related to the relative stiffness of the bearings on both sides of the coupling.When the bearing on the light load side is raised,the stiffness of the bearings on both sides of the coupling is close,and the mode coupling is weakened.When the bearing on the heavy load side is raised,the bearing on the light load side tends to be empty,the shafting tends to be single support mode,and the mode coupling is enhanced.For single support shafting,only one side of the coupling has bearings.When the middle bearing is raised,the stiffness of the bearing increases and the coupling of the vibration mode weakens.When the end bearing is raised,the stiffness of the middle bearing decreases and the mode coupling increases.Compared with the double support shafting,the vibration coupling of single support shafting is stronger.When the single support shafting is misaligned,the vibration may not only appear in the inner span of the unbalanced rotor,but also have a greater impact on the outer span rotor.A multi-rotor system vibration test-bed is established,and the modal test of shafting is carried out by hammering method to study the influence of alignment deviation on the modal characteristics of shafting.The test results show that the vibration coupling of single support shafting is stronger than that of double support shafting.When the middle bearing of single support shafting is raised,the coupling of vibration mode and the transmission ability of vibration are weakened;When the end bearing is raised,the coupling of vibration modes between rotors is enhanced and the vibration transmission ability is enhanced.Taking 135 MW single support steam turbine generator unit as the research object,the experimental study on the influence of alignment deviation on the unbalance response characteristics of the unit is carried out,and the influence of alignment deviation on the vibration coupling between HP,IP and LP rotors of the steam turbine is analyzed.The research shows that the vibration caused by the unbalance of low-pressure rotor is transmitted to the high and medium pressure rotor due to the alignment deviation,which leads to the vibration coupling phenomenon that the vibration of the bearings at both ends is large and that of the middle bearing is small.According to the measured vibration data,the dynamic balance test of the low-pressure rotor is carried out,and the vibration of the steam turbine is reduced successfully.