There are many reasons for motor vibration, but also very complex. 8 or more pole motor will not cause vibration because of quality problems. Vibration is common in 2-6 pole motor, GB10068-2000, the vibration limit value and test method of rotating motor stipulates the vibration limit value, test method of high motor with different center on the rigid foundation and the judging standard of rigid foundation, according to this standard can judge whether the motor meets the standard.

The harm of motor vibration

The vibration of the motor will shorten the life of the winding insulation and the bearing, affect the normal lubrication of the sliding bearing, it causes the insulation resistance to decrease and the leakage current to increase, even the formation of insulation breakdown and other accidents. In addition, the motor vibration, but also easy to make the cooler pipe vibration crack, welding point vibration, at the same time will cause load mechanical damage, reduce workpiece accuracy, will cause all mechanical parts of the vibration fatigue, will make the anchor screw loose or broken, the motor will cause carbon brush and slip ring abnormal wear, and even serious brush fire and burn the collector ring insulation, the motor will produce a lot of noise, this situation in the DC motor also occurs from time to time.

Ten reasons for motor vibration

1. Rotor, coupler, coupling, transmission wheel (brake wheel) caused by imbalance. 

2. Loose core bracket, oblique key, pin failure loose, loose rotor binding will cause the rotation part of the imbalance. 

3. Linkage part of the shafting is not in the right, the center line does not coincide, centering is not correct. This fault is mainly caused by the installation process, bad alignment, improper installation.

4. The Central line of the linkage part is coincident in the cold state, but after running for a period of time, because of the deformation of the rotor fulcrum and the foundation, the Central line is destroyed, so the vibration is produced. 

5. The gears and couplings connected with the motor are out of order, the gears do not bite well, the teeth are worn badly, the wheels are not lubricated properly, the couplings are askew and misaligned, tooth shape, tooth pitch is not right, clearance is too big or wear is serious, can cause certain vibration. 

6. The defects of the structure of the motor itself, The Ellipse of the journal, the bending of the rotating shaft, the too large or too small clearance between the shaft and the bearing bush, the stiffness of the bearing block, the foundation plate, some parts of the foundation and even the whole motor installation foundation are not enough. 

7. Installation of the problem, the motor and the base plate between the fixed is not firm, anchor bolts loose, loose between the bearing seat and the base plate and so on. 

8. Too large or too small clearance between shaft and bearing bush can not only cause vibration but also cause abnormal lubrication and temperature of bearing bush. 

9. Motor-driven load conduction vibration, such as motor-driven fan, pump vibration, causing motor vibration. 

10. AC motor stator wiring error, winding asynchronous motor rotor winding short-circuit, synchronous motor excitation winding inter-turn short-circuit, synchronous motor excitation winding connection error, cage asynchronous motor rotor broken bar, the deformation of rotor core results in uneven air gap between stator and rotor, which results in unbalanced air gap flux and vibration.

Vibration causes and typical cases

There are three main reasons for vibration: electromagnetic reasons; mechanical reasons; mechanical and electrical reasons.

one. Electromagnetic reasons

1. Power supply: three-phase voltage imbalance, three-phase motor phase-missing operation. 

2. Stator: stator core becomes ellipse, eccentricity, looseness, stator windings break, grounding breakdown, turn-to-turn short circuit, wiring error, stator three-phase current imbalance. 

Example: before the repair of the sealed fan motor in the boiler room, it was found that there was red powder in the stator core, and it was suspected that the stator core was loose, but it did not fall into the scope of the standard overhaul, so it was not dealt with, after overhaul, the screech of the motor occurs during the trial run. Trouble shooting after replacing a stator.

3. Rotor fault: rotor core becomes ellipse, eccentric, loose. Rotor cage bar and end ring open welding, rotor cage bar fracture, wire winding error, bad brush contact, etc. . 

Example, the motor stator current oscillates back and forth and the motor vibration gradually increases during the operation of the toothless saw motor in the sleeper section, there are 7 faults in the rotor cage bar, and the serious 2 sides and end rings have all been broken.

TWO. Mechanical reasons

1. Motor itself: rotor imbalance, shaft bending, slip ring deformation, stator and rotor air gap is not uniform, stator and rotor magnetic center is not consistent, bearing failure, poor foundation installation, insufficient mechanical strength, resonance, loose anchor screws, motor fan damage. 

Typical case: after the motor of condensate pump is replaced with the upper bearing, the motor sloshing increases, and the rotor and stator have slight signs of sweeping. After careful inspection, it is found that the motor rotor lifting height is not right, when the magnetic center of the rotor and stator is not aligned, the motor vibration fault can be eliminated by readjusting the screw cap of the thrust head. After overhaul, the vibration of the cross-wire coil hoist motor has been on the high side, and there are signs of gradual increase. When the motor falls off the hook, it is found that the vibration of the motor is still very big, and there is a large series movement in the axial direction, rotor balance is also a problem, replacement of the standby rotor after the elimination of the fault, the original rotor back to the factory repair.

 2. With the coupling: coupling damage, poor coupling connection, coupling center is not accurate, load mechanical imbalance, system resonance. Linkage part of the shafting is not in the right, the center line does not coincide, centering is not correct. This fault is mainly caused by the installation process, bad alignment, improper installation. There is another situation, that is, some linkage part of the center line in the cold is consistent, but after running for a period of time due to rotor fulcrum, foundation deformation, the center line was destroyed, and thus produce vibration.

 For example: A, circulating water pump motor, running vibration has been on the high side, motor check no problem, no load is also all normal, pump class that motor operation is normal, finally check out the motor center difference is too much, the vibration of the motor is eliminated after the new alignment of the pumps. 

B, after replacing the belt pulley of the induced draft fan in the boiler room, the motor vibrates during the trial operation and the three-phase current of the motor increases, after replacement, the vibration of the motor is eliminated and the three-phase current of the motor is restored to normal.

3. Motor mixing reason 

1).The vibration of the motor is usually caused by the unevenness of the air gap, which leads to the single-side electromagnetic tension, and the single-side electromagnetic tension makes the air gap further increase. 

2). The axial serial motion of the motor, due to the electromagnetic pulling force caused by the gravity or the installation level of the rotor itself and the wrong magnetic force center, causes the axial serial motion of the motor, and causes the vibration of the motor to increase, causes the bearing bush temperature to rise rapidly. The gears and couplings connected with the motor are defective. This kind of fault mainly displays as bad gear bite, serious gear tooth wear, bad lubrication to the wheel, the coupling is askew, dislocation, the tooth shape of the tooth type coupling, the tooth pitch is not correct, the clearance is too big or the wear is serious, will cause a certain amount of vibration. Defects in the structure of the motor itself and installation problems. This kind of fault mainly displays as the shaft neck ellipse, the rotating shaft bends, the clearance between the shaft and the bearing bush is too big or too small, the bearing seat, the foundation plate, some parts of the foundation and even the entire motor installation foundation rigidity is insufficient, motor and foundation plate fixed between the weak, loose anchor bolts, bearing pedestal and foundation plate between the loose and so on. The clearance between shaft and bearing bush is too large or too small, which can not only cause vibration but also cause abnormal lubrication and temperature of bearing bush. Motor-driven load conduction vibration. 

For example: steam turbine generator vibration, motor-driven fan, pump vibration, causing motor vibration.

How to find the cause of vibration?

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

1. Before stopping the motor, check the vibration of each part with the vibration meter, and test the vibration value in detail in three directions of vertical and horizontal axis for the parts with large vibration, then it can be fastened directly, and after fastening, we can measure its vibration, and observe whether it can be eliminated or reduced, and then check whether the three-phase voltage of the power supply is balanced and whether the three-phase fuse has the phenomenon of burning off, the single-phase operation of the motor can not only cause vibration, but also make the temperature of the motor rise rapidly, finally, check whether the three-phase motor current balance, found problems in time with the operator to stop the motor operation, so as not to burn the motor. 

2. If the vibration of the motor is not resolved after the surface phenomenon is treated, then continue to disconnect the power supply, uncouple the coupling, so that the motor is mechanically separated from the load to which it is connected, single-rotating motor, if the motor itself is not vibrating, if the motor vibrates, it means that there is something wrong with the motor itself. In addition, the power-off method can be used to distinguish the electrical cause from the mechanical cause, when the power failure moment, the motor immediately do not vibration or vibration to reduce, it is electrical reasons, otherwise mechanical failure.

Carry out maintenance according to the cause of failure

1. Maintenance for electrical reasons:

The first is to determine whether the three-phase DC resistance of the stator is balanced, if not, it shows that there is a phenomenon of open welding in the welding part of the stator connection, and to look for the broken winding phases, and whether there is a turn-to-turn short circuit in the winding, if the fault is obvious, the scorch mark can be seen on the insulation surface, or the stator windings can be measured by the instrument. 

For example: water pump motor, the motor not only vibration large bearing temperature is also high minor repair test found that the motor DC resistance is not up to standard, motor stator winding welding phenomenon, with the elimination of trouble to find the elimination, the motor is in good working order.

2. Maintenance for mechanical reasons:

Check the air gap is uniform, if the measured value exceeds the standard, re-adjust the air gap. Check the bearing, measure the bearing clearance, if it is not up to standard to replace the new bearing, check the deformation and looseness of the iron core, loose iron core can be bonded with epoxy, check the rotating shaft, repair and weld the bending shaft or direct shaft, then balance test the rotor. During the trial operation after overhaul, the motor not only vibrates greatly, but also the bearing bush temperature exceeds the standard. After continuous treatment for several days, the fault is still not solved. My team in helping to deal with the staff found that the motor air gap is very large, tile base level is not up to standard, fault reasons found, re-adjust the clearance of each part, the motor test-run a success.

3. The mechanical part of the load check is normal, the motor itself is no problem:

The cause of the fault is caused by the connecting part, at this time to check the motor foundation level, tilt, strength, center alignment is correct, whether the coupling is damaged, motor shaft stretch is in line with the requirements, etc. .

The process of dealing with motor vibration

1.the motor and load off, air test motor, detection of vibration value. 

2.Check the vibration value of motor base, according to GB 10068-2006, the vibration value of base base should not be more than 25% of the corresponding position of bearing, if more than this value shows that motor base is not rigid base. 3. If only one or two of the four footings have excessive vibration, the vibration will pass if the footings are loosened, indicating that the footings are not properly cushioned, re-center and tighten the anchor bolts.

4.Fasten all four foundation bolts on the foundation, and the vibration value of the motor still exceeds the standard. At this time, check if the coupling installed on the shaft extension is level with the shaft shoulder, such as uneven, the exciting force produced by the redundant key on the shaft extension can cause the motor horizontal vibration to exceed the standard. In this case, the vibration value will not be too much, and often after the host docking vibration value can be reduced, should persuade the user to use, the two-pole motor in the factory test according to GB10068-2006 in the shaft extension key slot installed in the half key. The extra keys do not add an additional exciting force. If need to handle, need to cut off redundant key only extra length general can.

5.such as the motor air test vibration is not over the standard, with the load vibration over the standard, there are two reasons: one is a large deviation; The other is that the residual unbalance of the rotating parts (rotor) of the main engine and the residual unbalance of the rotor of the motor are in the phase overlap, after docking, the residual unbalance of the whole shafting at the same position is large, the generated exciting vibration force causes the vibration. At this point, you can take the coupling off, the two couplings of either rotation 180 ° C, and then docking machine, vibration will be reduced. 

6.vibration speed (intensity) not exceed the standard, vibration acceleration exceed the standard, can only replace the bearing. 

7.because of the poor rigidity of the rotor of the two-pole high-power motor, the rotor will be deformed for a long time without use, and may vibrate when it is rotated again. This is the reason for the poor storage of the motor. Every 15 days to the motor barring, each barring at least 8 turns more than. 

8.The motor vibration of sliding bearing is related to the assembly quality of bearing bush. Check whether the bearing bush has a high point, whether the oil feeding into the bearing bush is enough, the bearing bush tight force, the bearing clearance and the magnetic force center line are suitable.

9. Under normal circumstances, the reason of motor vibration can be judged simply from the vibration values in three directions: large horizontal vibration, unbalanced rotor; large vertical vibration, uneven installation foundation; large axial vibration; Poor assembly quality of bearings. This is only a simple judgment, according to the field situation, combined with the above-mentioned factors for comprehensive consideration, to find the real cause of vibration. 

10.Y series box motor vibration should pay special attention to axial vibration, such as axial vibration is greater than radial vibration, bearing of the motor great harm, will cause shaft hold accident. To observe the bearing temperature, such as positioning bearings than non-positioning bearings faster temperature rise, should be stopped immediately. This is because the base of the axial stiffness caused by insufficient axial vibration, the base should be reinforced. 

11.After the rotor is dynamically balanced, the residual unbalance of the rotor is fixed on the rotor and will not change. The vibration of the motor itself will not change with the change of location and working condition, vibration problems can be handled well at the user site. In general, the overhaul motor does not need to do the motor dynamic balance check, in addition to very special circumstances, such as flexible foundation, rotor deformation, etc. , must do on-site dynamic balance or back to the factory treatment.

Source: internet (for study only, intrusion and deletion)