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​Causes of motor vibration and problem solving methods

Date:2023-12-05   Author:XINDA MOTOR

Motors are widely used in various industries, but many problems will occur during use. Among them, motor vibration is easily encountered in daily production and life. Motor vibration will accelerate the wear of motor bearings and greatly shorten the normal service life of the bearings. At the same time, motor vibration will cause the winding insulation to degrade.

Due to vibration, the wire binding at the end of the motor is loosened, causing the end windings to rub against each other, reducing the insulation resistance, shortening the insulation life, and in severe cases, causing insulation breakdown. In addition, motor vibration will cause damage to the machinery being driven and affect the normal operation of surrounding equipment.

1. Causes of motor vibration

1. Vibration caused by electromagnetic reasons

In terms of power supply: the three-phase voltage is unbalanced, and the three-phase motor runs with a lack of phase.

Regarding the stator: the stator core becomes elliptical, eccentric, and loose; the stator winding has disconnection, ground breakdown, inter-turn short circuit, wiring errors, and the stator three-phase current is unbalanced.

Rotor failure: The rotor core becomes oval, eccentric, and loose. The rotor cage bar and end ring are open welded, the rotor cage bar is broken, the winding is wrong, the brush contact is poor, etc.

2. Vibration caused by motor mixing

Motor vibration is often due to uneven air gaps, causing unilateral electromagnetic pulling force, which in turn further increases the air gap. This electromechanical hybrid effect manifests as motor vibration.

The axial movement of the motor is due to the electromagnetic pulling force caused by the gravity of the rotor itself or the incorrect installation level and magnetic center, causing the axial movement of the motor, causing increased vibration of the motor, and in severe cases, shaft wear and tear, causing the temperature of the bearing to rise rapidly. high.

>>The gears and couplings connected to the motor are defective. This kind of failure mainly manifests as poor gear meshing, severe gear tooth wear, poor lubrication of the opposite wheel, skewed and misaligned couplings, incorrect tooth shape and pitch of the gear coupling, excessive clearance or severe wear, all of which will cause certain problems. vibration.

>>Structure defects and installation problems of the motor itself. This kind of failure mainly manifests as elliptical journal, bent shaft, too large or too small gap between shaft and bearing, insufficient stiffness of bearing seat, foundation plate, certain part of the foundation and even the entire motor installation foundation, and the fixed connection between the motor and the foundation plate. Not firm, the foot bolts are loose, the bearing seat and the foundation plate are loose, etc. If the gap between the shaft and the bearing bush is too large or too small, it can not only cause vibration but also cause abnormalities in the lubrication and temperature of the bearing bush.

>>The load driven by the motor conducts vibration

For example: the vibration of the turbine of the steam turbine generator, the vibration of the fan and water pump driven by the motor, causing vibration of the motor.

3. Vibration caused by mechanical reasons

>>The motor itself:

The rotor is unbalanced, the rotating shaft is bent, the slip ring is deformed, the stator and rotor air gaps are uneven, the stator and rotor magnetic centers are inconsistent, bearing failure, poor foundation installation, insufficient strength of the mechanical mechanism, resonance, loose anchor screws, and damaged motor fans.

Typical case: After replacing the upper bearing of the condensate pump motor in the factory, the shaking of the motor increased, and the rotor and stator showed slight signs of sweeping. After careful inspection, it was found that the motor rotor was lifted to an incorrect height, and the magnetic centers of the rotor and stator were not aligned. Readjustment After the thrust head screws are replaced with caps, the motor vibration fault is eliminated. After the overhaul of the cross-wire hoist motor, the vibration has been relatively large, and there are signs of gradual increase. When the motor was dropped, it was found that the vibration of the motor was still very large, and there was a large amount of axial movement. After disassembly, it was found that the rotor core was loose. , there was also a problem with the rotor balance. After replacing the spare rotor, the fault was eliminated and the original rotor was returned to the factory for repair.

>>Coupling aspects:

Damage to the coupling, poor coupling connection, inaccurate coupling centering, unbalanced load machinery, system resonance, etc. The shaft system of the linkage part is misaligned, the center lines do not coincide, and the centering is incorrect. The main cause of this failure is poor alignment and improper installation during the installation process. Another situation is that the center lines of some linkage parts are coincident in the cold state, but after running for a period of time due to the deformation of the rotor fulcrum, foundation, etc., the center lines are destroyed again, resulting in vibration.

For example: a. The circulating water pump motor has been vibrating too much during operation. There is no problem with the motor inspection, and everything is normal under no load. The water pump team thinks that the motor is running normally. Finally, it is found that the motor alignment center is too wrong, and the water pump team starts to find it again. After correcting, the vibration of the motor is eliminated. b. After replacing the pulley of the induced draft fan in the boiler room, the motor vibrated during trial operation and the three-phase current of the motor increased. After checking all circuits and electrical components, it was found that there was no problem. Finally, it was found that the pulley was unqualified. After the replacement, the vibration of the motor was eliminated. At the same time, the three-phase current of the motor increased. The current also returns to normal.

2. How to deal with motor vibration problems

1. Maintenance of electrical reasons:

The first step is to determine whether the three-phase DC resistance of the stator is balanced. If it is not balanced, it means that there is an open welding phenomenon in the stator connection welding part. Disconnect the winding and separate the phases to search. In addition, whether there is an inter-turn short circuit in the winding. If the fault is obvious, it can be found from the insulation If you see scorch marks on the surface, or use an instrument to measure the stator winding, and confirm the short circuit between turns, take the motor winding offline again.

For example: a water pump motor. During operation, the motor not only vibrated and the bearing temperature was high, but also the minor repair test found that the DC resistance of the motor was unqualified and the stator winding of the motor had open welding. After troubleshooting was used to find and eliminate the fault, the motor ran normally.

2. The load mechanical part is checked normally, and there is no problem with the motor itself. The cause of the failure is the connection part: at this time, check the basic level, inclination, strength, center alignment of the motor, and whether the coupling is damaged. Whether the motor shaft extension meets the requirements, etc.

3. Maintenance of 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 cemented with epoxy resin glue; check the rotating shaft, repair the bent rotating shaft or directly replace it with a new shaft. , and then perform a balance test on the rotor; check the bearings and measure the bearing clearance. If there is a journal defect, restore the original size and reassemble the bearing.