Ten causes of motor vibration

1. Unbalance of rotor, coupler, coupling and transmission wheel (brake wheel).
2. Loose core support, inclined key, loose pin failure, loose rotor binding is not tight will cause the rotating part of the imbalance.
3. The shaft system of the linkage part is not centered, the center line is not coincident, and the centering is not correct. The main reason for this failure is the installation process, to the bad, improper installation caused.
4. The center line of the linkage part is consistent in the cold state, but after running for a period of time, the center line is destroyed due to the deformation of the rotor fulcrum and foundation, and so on, so the vibration is generated.
5. The gear and coupling associated with the motor are faulty, the gear bite is bad, the gear tooth wear is serious, the wheel lubrication is bad, the coupling is skewed, misplaced, the tooth shape of the gear coupling, the tooth pitch is wrong, the clearance is too large or the wear is serious, will cause a certain vibration.
6. Defects of the structure of the motor itself, ellipse of the shaft neck, bending of the rotating shaft, too large or too small gap between the shaft and the bearing bush, and insufficient stiffness of the bearing seat, foundation plate, some part of the foundation and even the entire motor installation foundation.
7. Installation problems, the motor and the foundation plate is not fixed firmly, the bottom bolt is loose, the bearing seat and the foundation plate is loose, etc.
8. The clearance between the shaft and the bearing bush is too large or too small, which can not only cause vibration but also cause abnormal lubrication and temperature of the bearing bush.
9. The load driven by the motor conducts vibration, such as the vibration of the fan and water pump driven by the motor, which causes the vibration of the motor.
10. AC motor stator wiring error, winding asynchronous motor rotor windings short circuit, synchronous motor wound winding turns short circuit, synchronous motor excitation coil connection error, cage asynchronous motor rotor bar broken, rotor core deformation resulting in uneven stator and rotor air gap, resulting in air gap flux imbalance resulting in vibration.

Harm of motor vibration
The vibration of the motor will shorten the life of the winding insulation and bearing, affect the normal lubrication of the sliding bearing. The vibration force will promote the expansion of the insulation gap, so that the external dust and water will invade it, resulting in the reduction of insulation resistance and the increase of leakage current, and even the formation of insulation breakdown and other accidents. In addition, vibration motor, vibration and easy to make the cooler water pipe crack, the vibration welding contact, can cause mechanical damage to the load at the same time, reduce the precision of workpiece, can cause all the mechanical parts by vibration fatigue, can make the anchor bolt is loose or broken, motor and can lead to abnormal wear of carbon brush and slip ring, can appear even serious brush fire and burned collector ring, insulation of the motor will make a big noise, this kind of situation usually also have occurred in the dc motor.

Vibration causes and typical cases
There are three main reasons for vibration: electromagnetic reasons; Mechanical reasons; Mechanical and electrical mixing.
1. Electromagnetic reasons
(1) Power supply: the three-phase voltage is unbalanced, and the three-phase motor runs without phase.
(2) stator: stator core becomes ellipse, eccentric and loose; The stator winding has broken line, ground breakdown, interturn short circuit, wiring error, and the stator three-phase current is not balanced.
For example: red powder was found in the stator core of the sealed fan motor in the boiler room before overhaul, and it was suspected that the stator core was loose, but it was not within the scope of the standard overhaul, so it was not handled. The motor squealed during the test run after overhaul, and the fault was removed after replacing a stator.
(3) rotor failure: rotor core ellipse, eccentric, loose. Open welding of rotor cage bar and end ring, broken rotor cage bar, wrong winding, bad brush contact, etc.

Example: sleeper section toothless saw swing motor found in the operation of the motor stator current, the motor vibration increases gradually, according to the phenomenon of judging the motor rotor cage bar has the possibility of the welding and cracking, found that after the collapse of motor rotor cage bar fracture, there are 7 serious 2 on both sides of the root and end ring fracture, has been found not in time is likely to cause loss of the stator of bad accidents.

2. Mechanical reasons
(1) The motor itself:
The rotor is unbalanced, the rotating shaft is bent, the slip ring is deformed, the stator and rotor air gap is uneven, the stator and rotor magnetic force center is inconsistent, the bearing failure, the foundation is poorly installed, the mechanical mechanism is not strong enough, the resonance, the foundation screw is loose, the motor fan is damaged.
Typical case: after the motor of the condenser water pump was replaced with the bearing, the motor swaying increased, and the rotor and stator showed slight signs of sweeping. After careful inspection, it was found that the lifting height of the motor rotor was wrong, and the magnetic center of the rotor and stator was not in alignment. After readjusted the backup cap of the thrust head screw, the motor vibration fault was eliminated. After maintenance, the vibration of the cross-line hoisting ring motor has been relatively large and showed signs of gradual increase. When the motor was hook off, it was found that the vibration of the motor was still very large and there was a large series movement in the axial direction. It was found that the rotor core was loose and the rotor balance had problems after disintegration.
(2) with the coupling: coupling damage, coupling connection is poor, the coupling center is not allowed, load mechanical imbalance, system resonance, etc.
Linkage part of the shaft is not centered, the center line is not coincident, centering is not correct. The main reason for this failure is the installation process, to the bad, improper installation caused. In another case, some linkage center lines are coincident and consistent in cold state, but after running for a period of time, because of the deformation of the rotor fulcrum and foundation, the center lines are destroyed and vibration is generated.

A. The vibration of the circulating pump motor has been too large in operation. The motor has been checked without any problems and all is normal without load. The pump team thought that the motor was running normally, and the final inspection found that there was too much difference in the alignment center of the motor.

B. After the pulley is replaced by the induced draft fan in the boiler room, the vibration of the motor occurs during the test run and the three-phase current of the motor increases. All the circuits and electrical components are checked and there is no problem. Finally, it is found that the pulley is unqualified.

3. Reasons for motor mixing
(1) Motor vibration is often uneven air gap, causing unilateral electromagnetic pull, and unilateral electromagnetic pull and further increase the air gap, this electromechanical mixing is manifested as motor vibration.
(2) the motor axial series, due to the rotor itself gravity or installation level and magnetic center is wrong, caused by electromagnetic tension, causing the motor axial series, motor vibration increase, serious cases occur shaft grinding tile root, so that the temperature of the bearing bush rapidly increased.
(3) There is something wrong with the gear and coupling connected with the motor. This fault is mainly shown as bad gear bite, serious tooth wear, poor lubrication of the wheel, coupling skew, dislocation, gear coupling tooth shape, tooth pitch is wrong, clearance is too large or serious wear, will cause a certain vibration.
(4) defects in the structure of the motor itself and problems of installation. This fault is mainly manifested as the ellipse of the journal, the bending of the shaft, the clearance between the shaft and the bearing bush is too large or too small, the stiffness of the bearing seat, the foundation plate, a part of the foundation and the entire motor installation foundation is not enough, the fixation between the motor and the foundation plate is not firm, the bottom bolt is loose, the loosening of the bearing seat and the foundation plate, etc. And the clearance between the shaft and the bearing bush is too large or too small can not only cause vibration but also make the lubrication and temperature of the bearing bush abnormal.
(5) the load driven by the motor conducts vibration. For example, the vibration of the turbine generator, the vibration of the fan and water pump driven by the motor, causes the vibration of the motor.


How to find the cause of vibration
In order to eliminate the motor vibration, we must first find out the cause of vibration. Only by finding the cause of vibration, can we take targeted measures to eliminate the motor vibration.

Before 1, the motor did not stop, with vibration table to check each vibration situation, for larger parts according to the vertical vibration level three axial direction vibration numerical tests in detail, if it is loose bolts or bearing end cover screw loosening, can direct fastening, measuring its vibration size after fastening, observe whether there is to eliminate or reduce, secondly to check whether balanced three-phase voltage, three-phase fuse burn out phenomenon, the single phase of the motor running can not only cause vibration, will cause the motor temperature rise quickly, observe whether ammeter pointer is swinging back and forth, the rotor broken bar in current oscillation phenomenon, Finally, check whether the three-phase current of the motor is balanced, and contact the operator to stop the motor running in time if any problems are found, so as not to burn the motor.

After 2, if the surface treatment, the motor vibration is unresolved, continued to disconnect the power supply, loose coupling, the motor is connected with the load of mechanical separation, single motor, if you don't vibration motor itself, explain the source of vibration is caused by the coupling is not find or load machine, if the motor vibration, then there is something wrong with the motor itself, it also can take power method to distinguish is electrical, or mechanical reasons, when a power outage, motor vibration or vibration reducing immediately, then is electrical reason, otherwise is a mechanical failure.

Carry out maintenance for the cause of the failure
1. Maintenance of electrical reasons:
First is whether the measured stator three phase dc resistance balance, such as imbalance, explain the stator wire welding parts have open welding phenomenon, disconnect phase winding points to look up, whether there is another winding interturn short circuit phenomenon, such as fault obvious can see from the surface of the insulating sear, or use the instrument measuring the stator winding, after confirm the turn-to-turn short circuit, the motor winding to logoff.
For example: water pump motor, the motor not only vibrates greatly in operation, but also has high bearing temperature. A minor repair test found that the DC resistance of the motor is not qualified, and the stator winding of the motor has open welding phenomenon. After the fault is found and eliminated by the elimination method, everything is normal for the motor.

2. Maintenance of mechanical reasons:
Check if the air gap is even. If the measured value exceeds the standard, readjust the air gap. Check the bearing, measure the bearing clearance, if unqualified replace the new bearing, check the deformation and loosening of the iron core, the loose iron core can be glued with epoxy resin for filling, check the rotating shaft, repair welding of the bending rotating shaft for reprocessing or direct straight shaft, and then do a balance test on the rotor. During the trial operation of the blower motor after overhaul, the motor not only had large vibration, but also the temperature of the bearing bush exceeded the standard. After several days of continuous treatment, the fault was still not solved. Our team found that the air gap of the motor was very large and the level of the tile base was not up to standard. After finding out the cause of the fault and readjust the clearance of each part, the test run of the motor was successful.

3. The mechanical part of the load is checked normally:
The motor itself is not a problem, the cause of the failure is caused by the connection part, then to check the basic plane of the motor, tilt, strength, center alignment is correct, whether the coupling is damaged, whether the motor shaft extension winding is in line with the requirements.