Fault Analysis Of Fan Driven By Variable-frequency And Research On Vibration Reduction Technology

In order to saving energy and reducing auxiliary power ratio,many power plants are transforming induced draft fan to be driven by variable-frequency energetically.Vector control is one of the most widely used motor speed technology,its economy is also very significant.Vector control technology brought a lot of security problems at the same time that increasing energy efficiency,such as shaft broken,coupling diaphragm rupture,blade crack and so on which seriously threaten to the operation of units.This paper conducted thoroughly research on shaft fault problems after induced draft fan transformed to driven by variable frequency.First of all,studied the structure and working principle of three-phase asynchronous motor,especially some parameters like rated power,stator voltage,stator current and electromagnetic output torque of the motor,and analyzed the production of motor harmonic.In addition,the vector frequency conversion system are researched including the vector control principle,inverter and pulse width modulation method and so on,also analyzed the reason of inverter’s harmonic.After that,simplified and established the mechanical model of several units by using the method of concentrated mass,the shafting torsional inherent frequency and the corresponding vibration model were analyzed.The harmonic resonance mechanism of induced draft fan driven by variable frequency is given.In this paper,field tests were carried out on several induced draft fans which driven by variable frequency,researched the mechanism of harmonic resonance.Test objects consist two static blade adjustable axial flow fans of 600 MW unit and two test rigs driven by vector control.Through the analysis of the four units’ parameters during in the process of acceleration such as amplitude,frequency,waveform of torque,verified mechanism of harmonic resonance,and the solution of suppressing harmonic resonance is presented.In addition,this paper researched induced draft fan which driven by variable frequency may occur electromechanical system self-excited instability.In the MatLab/Simulink environment,established the electromechanical coupling system of induced draft fan driven by vector control motor.Simulation and calculate the acceleration process of induced draft fan and thorough analysis parameters of the process of acceleration,like voltage,current,electromagnetic torque and shaft transmission torque and others.At the same time,the test carried out on a static blade adjustable axial flow fan of a 1000 MW unit,the fan shaft fracture and the coupling problem of diaphragm rupture appeared repeatedly after motor transforming to vector control.Torque test data are analyzed,the characteristic parameters and the simulation results fit well.Confirmed that afte the transformed of the fan did happen self-excited instability phenomenon,then the measure to restrain the self-excited instability is presented.