Study On Torsional Vibration And Suppression Thchnology Of Fan Shaft Under Electromechanical Coupling

Energy conservation and consumption reduction have become the basic ideas for the development of the power industry.In order to reduce production costs,many power plants began to carry out frequency conversion transformation of auxiliary equipment such as induced draft fans.However,after the transformation of the equipment,there are frequent failures such as coupling fracture and shafting damage,which seriously affects the economic and safety of the unit operation.In this paper,the method of establishing and solving the equation of motion for multidegree-of-freedom system is introduced.The lumped mass model is established with a 1000 MW supporting induced draft fan shaft system and the inherent characteristics of the shafting system are calculated.This paper studies the working mechanism of three-phase asynchronous motor and vector frequency conversion system.Based on this,the electromechanical coupling model of induced fan driven by vector frequency conversion system is established and the calculation and analysis software of torsional vibration is developed.The research shows that the various harmonics will cause the motor to output pulsating torque,if the frequency is close to the natural frequency of the shaft torsional vibration,the harmonic torsional resonance will be induced;and when the parameters of the motor and frequency conversion system are not properly matched,the selfexcited current will be generated in system and the self-excited instability of the electromechanical coupling system will be further induced.Taking the induced draft fan of 1000 MW unit as an example,this paper calculates and analyzes the speed increasing process.Through the spectrum analysis of the rotational speed,torque,current,etc.It is found that the torque pulsation during the acceleration process is caused by the harmonic torsional resonance and the self-excited instability.In order to suppress the large-scale pulsation of the torque,this paper proposes a technical solution to replace the diaphragm coupling with a high-elastic rubber coupling,and designs the parameters of the elastic coupling.Then the field test before and after the coupling transformation is carried out.The test results before the coupling transformation are in good agreement with the results obtained from model calculation,and the results after the coupling transformation shows that the phenomenon of torque pulsating is effectively suppressed during the start and stop of the fan.Finally,this paper analyzes the fatigue life of the fan shaft.It is found that the stress before the shafting transformation exceeds the torsion fatigue limit,which leads to the damage of the shafting,and the stress after the transformation meets the needs of the safe operation.