Study On The Coupled Lateral-torsional Vibration And Safety Analysis Of Rotating Machinery With Variable Frequency Drives

With the increasing demand for energy saving and emission reduction,many rotating machinery and equipment use variable frequency operation mode.However,complex vibration phenomena frequently occur on variable frequency operation units,causing accidents such as shaft cracks and coupling damage,which seriously affects the economics and safety of unit operation.In this paper,the dynamic model of the complex gear rotor system was established,and the harmonic output characteristics of the vector frequency conversion system were analyzed.A gear rotor test rig with variable frequency drive(VFD)was taken as the research object to establish a finite element model of gear rotor system lateral-torsional vibration analysis,and its inherent characteristics were calculated.A gear rotor test rig with VFD was taken as the research object to study the harmonic torsional resonance mechanism of the gear rotor system with VFD.The influence of the harmonics of the variable frequency motor on the pulsating torque was analyzed,and the torque test analysis was carried out on the field test rig.Through theoretical analysis and experimental research,it was found that when the output harmonic frequency of the inverter coincides with the natural frequency of the gear rotor system,it would cause harmonic resonance phenomenon,resulting in the pulsation of the motor torque;The phenomenon of pulsating torque also occurred many times,when there were multiple harmonic resonance points in the electromechanical system;The pulsating torque frequency was basically all the first-order torsional vibration frequency,and the frequency locking phenomenon would occur at multiple resonance speeds.A gear rotor test rig with VFD was taken as the research object to study the effect mechanism of the variable frequency motor output pulsating torque on the coupled lateral-torsional vibration of the gear rotor system,and the influence of the pulsating torque frequency on the coupled vibration was analyzed.The tests of the coupled lateral-torsional vibration were carried out on the field test rig to further verify the effect of pulsating torque on the coupled vibration.Through theoretical analysis and experimental research,it was found that the harmonic output pulsating torque of the inverter was the fundamental cause of the coupled lateral-torsional vibration;When the frequency of the pulsating torque coincides with the natural frequency of the gear rotor system,it was easy to cause the coupled lateral-torsional vibration.The coupled vibration phenomenon at the gearbox is most obvious.The safety analysis method of shaft system with VFD based on the combination of virtual and real test method is proposed,and the torsional S-N curve is fitted and corrected.A gear rotor test rig with VFD was taken as the research object to carry out field testing and response calculation of the shear stress of the gear rotor system,and the fatigue life of the shaft and diaphragm coupling was calculated and analyzed.Through theoretical analysis and experimental research,it was found that the fatigue life of the dangerous section of the gear rotor test rig and the coupling cannot meet the normal life requirements;In the safety analysis of the shaft system,the fatigue life of the entire shaft system cannot be represented only by the stress of the test section,calculating the fatigue life of dangerous cross-sections and important connecting parts can more comprehensively represent the fatigue life of the system.