The motor is widely used in all walks of life, and there will be many problems in use. Among them, the motor vibration, which is easily encountered in daily production and life, will accelerate the wear of the motor bearing, greatly shorten the normal service life of the bearing, and at the same time, the vibration of the motor will reduce the winding insulation.
Due to vibration, the binding wire at the end of the motor is loose, resulting in mutual friction between the end windings, reduced insulation resistance, shortened insulation life, and serious insulation breakdown. In addition, the vibration of the motor will cause damage to the driven machinery and affect the normal operation of the surrounding equipment.
1、 Causes of motor vibration
1. Vibration caused by electromagnetic reasons
Power supply: unbalanced three-phase voltage, three-phase motor phase operation.
Stator: the stator core becomes elliptical, eccentric and loose; the stator winding is broken, ground broken, turn to turn short circuit, wrong wiring, and the three-phase current of the stator is unbalanced.
Rotor failure: the rotor core becomes elliptical, eccentric and loose. Open welding of rotor cage bar and end ring, broken rotor cage bar, wrong winding, poor contact of brush, etc.
2. Vibration caused by motor mixing
The vibration of the motor is often caused by the uneven air gap, which causes the unilateral electromagnetic tension, and the unilateral electromagnetic tension further increases the air gap. This kind of mechanical and electrical mixed effect is manifested as the vibration of the motor.
The axial series movement of the motor results from the electromagnetic pull caused by the gravity or installation level of the rotor itself and the incorrect magnetic center, which causes the axial series movement of the motor, and increases the vibration of the motor. In serious cases, the bearing bush roots are worn, which makes the temperature of the bearing bush rise rapidly.
>>There is something wrong with the gear and coupling connected with the motor. This kind of fault is mainly manifested as bad gear engagement, serious wear of gear teeth, poor lubrication of wheels, deflection and dislocation of coupling, incorrect tooth shape and pitch of gear coupling, excessive clearance or serious wear, which will cause certain vibration.
>>Defects of motor structure and installation problems. This kind of fault is mainly manifested in the ellipse of the journal, the bending of the shaft, the too large or too small clearance between the shaft and the bearing bush, the insufficient rigidity of the bearing seat, the foundation plate, some part of the foundation and even the whole motor installation foundation, the insecure fixation between the motor and the foundation plate, the loose foot bolts, the loose between the bearing seat and the foundation plate, etc. However, too large or too small clearance between the shaft and the bearing pad can not only cause vibration, but also cause abnormal lubrication and temperature of the bearing pad.
>>Load conduction vibration of motor drive
For example, the vibration of steam turbine of steam turbine generator, fan and water pump driven by motor will cause motor vibration.
3. Vibration due to mechanical reasons
>>Motor itself:
The rotor is unbalanced, the shaft is bent, the slip ring is deformed, the air gap between the stator and the rotor is uneven, the magnetic center of the stator and the rotor is inconsistent, the bearing is faulty, the foundation is installed poorly, the mechanical mechanism is not strong enough, resonance, the anchor screw is loose, and the motor fan is damaged.
Typical case: after the replacement of the upper bearing of the condensate pump motor in the plant, the motor shaking increases, and the rotor and stator show slight signs of bore sweeping. After careful inspection, it is found that the lifting height of the motor rotor is not correct, and the magnetic center of the rotor and stator is not aligned. After readjusting the thrust head screw and the backup cap, the motor vibration fault is eliminated. After maintenance, the vibration of the cross line lifting ring hoist motor is always large, and there is a sign of gradual increase. When the motor drops the hook, it is found that the vibration of the motor is still large, and there is a large series of axial movements. After disassembly, it is found that the rotor core is loose, and the rotor balance is also problematic. After replacement of the spare rotor, the fault is eliminated, and the original rotor is returned to the factory for repair.
>>Cooperation with coupling:
Coupling is damaged, coupling connection is poor, coupling alignment is not correct, load mechanical imbalance, system resonance, etc. The shaft system of the linkage part is out of alignment, the center line is not coincident, and the centering is not correct. This kind of fault is mainly caused by the poor alignment and improper installation in the installation process. In another case, the center lines of some linkage parts are coincident in cold state, but after a period of operation, due to deformation of rotor fulcrum and foundation, the center line is damaged again, resulting in vibration.
For example: a. the vibration of circulating water pump motor is always too large during operation. There is no problem in the motor inspection, and everything is normal without load. The water pump team thinks that the motor operates normally, and finally checks that the motor alignment center difference is too much. After the water pump team re aligns, the motor vibration is eliminated. b. After replacing the belt pulley of induced draft fan in boiler house, the motor vibrates during the trial operation and the three-phase current of motor increases. Check all circuits and electrical components and find out that the belt pulley is unqualified. After replacement, the motor vibration is eliminated and the three-phase current of motor returns to normal.
2、 Treatment of motor vibration
1. Maintenance of electrical reasons:
First, determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it means that the welding part of the stator wiring has the phenomenon of open welding. Disconnect the winding and find out the phase separation. In addition, check whether the winding has the phenomenon of turn to turn short circuit. If the fault is obvious, you can see the scorch trace from the insulation surface, or measure the stator winding with an instrument. After confirming the turn to turn short circuit, put the motor winding back to the line.
For example, during the operation of the water pump motor, the motor not only vibrates the temperature of the large bearing but also has a high temperature. It is found that the DC resistance of the motor is unqualified and the stator winding of the motor has the phenomenon of open welding. After the fault is found and eliminated by the elimination method, the motor operates normally.
2. The mechanical part of the load is checked to be normal, and the motor itself has no problem. The cause of the fault is caused by the connecting part: at this time, it is necessary to check whether the foundation level, inclination, strength, center alignment of the motor are correct, whether the coupling is damaged, and whether the elongation of the motor shaft meets the requirements.
3. Maintenance for mechanical reasons:
Check whether the air gap is uniform. If the measured value exceeds the standard, readjust the air gap. Check the deformation and looseness of the iron core. The loose iron core can be filled with epoxy resin adhesive. Check the shaft, repair the bent shaft or replace the shaft directly, and then carry out the balance test on the rotor. Check the bearing, measure the bearing gap. If there is any defect in the journal, restore the original size, Refit the bearing.
