Ten reasons and solutions for abnormal vibration of motor

Ten causes of motor vibration

1 rotor, coupler, coupling, drive wheel (brake wheel) imbalance caused by.

2. Loose core support, loose oblique key, pin failure, loose rotor binding will cause unbalance of the rotating part.

3. The shafting system of the linkage part is not centered, the center line does not coincide, and the centering is not correct. This fault is mainly caused by improper installation or improper installation during the installation process.

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 the foundation, resulting in vibration.

5. The gear and coupling connected 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 and misplaced, the tooth shape of the gear coupling, the tooth distance is wrong, the gap is too large or the wear is serious, will cause certain vibration.

6. Defects in the structure of the motor itself, such as the journal ellipse, the bending of the rotating shaft, the gap between the shaft and the bearing bush is too large or too small, and the stiffness of the bearing seat, the foundation plate, a part of the foundation and even the whole motor installation foundation is not enough.

7. Installation problems, the motor is not firmly fixed between the foundation plate, the foot bolt is loose, the bearing seat and the foundation plate is loose, etc.

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. The load conduction vibration driven by the motor, such as the vibration of the fan and water pump driven by the motor, causes the motor vibration.

10. Ac motor stator wiring error, linear winding asynchronous motor rotor winding short circuit, synchronous motor excitation winding inter-turn short circuit, synchronous motor excitation coil connection error, cage type asynchronous motor rotor broken bar, rotor core deformation caused by constant and rotor air gap imbalance, resulting in air gap flux imbalance resulting in vibration.

The harm of motor vibration

The vibration of the motor will shorten the life of winding insulation and bearings, affect the normal lubrication of sliding bearings, and promote the expansion of the insulation gap, so that the dust and moisture of the outside world 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, vibration welding points, at the same time can cause load mechanical damage, 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, brush can appear even serious fire and burned collector ring insulation, The motor will make a lot of noise, which usually happens in DC motors.

Vibration causes and typical cases

There are three main causes of vibration: electromagnetic reasons; Mechanical reasons; Electromechanical mixing reasons.

1, electromagnetic reasons

(1) Power supply: three-phase voltage is not balanced, and three-phase motor runs out of phase.

(2) stator: stator core change ellipse, eccentric, loose; The stator winding has broken wire, ground breakdown, inter-turn short circuit, wiring error, stator three-phase current imbalance.

For example, red powder was found in the stator core before the overhaul of the sealed fan motor in the boiler room. It was suspected that the stator core was loose, but it was not within the scope of the standard overhaul, so it was not dealt with. After the overhaul, the motor made harsh screams during the test turn, and the fault was removed after the replacement of one stator.

(3) rotor fault: rotor core change ellipse, eccentric, loose. Rotor cage bar and end ring open welding, rotor cage bar fracture, winding error, brush poor 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:

Rotor imbalance, shaft bending, slip ring deformation, uneven air gap between stator and rotor, magnetic center inconsistency between stator and rotor, bearing failure, poor foundation installation, mechanical mechanism strength is insufficient, resonance, foundation screw loosening, motor fan damage.

Typical case: After replacing the upper bearing of the factory condensate pump motor, the motor shaking increases, and there are slight signs of sweeping the rotor and stator. 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 readjust the spare cap of the thrust head screw, the motor vibration fault is eliminated. After maintenance, the vibration of the cross-wire hoist motor has been relatively large, and there is a sign of gradual increase. When the motor fell off, it was found that the vibration of the motor was still large, and there was a large series movement in the axial direction. After disassembly, it was found that the rotor core was loose, and the rotor balance was also problematic.

(2) with coupling: coupling damage, coupling connection is poor, coupling center is not allowed, load mechanical imbalance, system resonance, etc.

The linkage part of the shafting is not centered, the center line does not coincide, centering is not correct. This fault is mainly caused by improper installation or improper installation during the installation process. There is another situation, that is, some linkage part of the center line in the cold state is consistent, but after running for a period of time due to the rotor fulcrum, foundation and other deformation, the center line is destroyed, resulting in vibration.

A. The vibration of the circulating pump motor has been too large in operation, and there is no problem in the inspection of the motor, and everything is normal in the no-load condition. The pump team thinks that the motor is running normally, and finally it is found that the center of the motor is too different.

B. After replacing the belt pulley of the induced draft fan in boiler room, the motor will vibrate during the trial operation and the three-phase current of the motor will increase. After checking all the circuits and electrical components, it is found that the pulley is unqualified.

3. Motor mixing reasons

(1) Motor vibration is usually caused by uneven air gap, resulting in unilateral electromagnetic pull, which in turn further increases the air gap. This electromechanical hybrid effect is manifested as motor vibration.

(2) The axial series movement of the motor, due to the gravity of the rotor itself or the installation level and the wrong center of the magnetic force, the electromagnetic pull caused by the axial series movement of the motor, causing the vibration of the motor to increase, and the shaft grinding root occurs in serious cases, so that the temperature of the bearing bush rises rapidly.

(3) the gear and coupling connected with the motor are faulty. This fault is mainly manifested as poor gear occlusion, serious gear tooth wear, poor wheel lubrication, coupling skew, dislocation, tooth coupling tooth shape, tooth distance is wrong, gap is too large or wear is serious, will cause certain vibration.

(4) structural defects and installation problems of the motor itself. This fault is mainly manifested in the journal ellipse, shaft bending, shaft and bearing bush clearance is too large or too small, bearing seat, foundation plate, some part of the foundation and even the entire motor installation foundation stiffness is not enough, the motor and the foundation plate is not firmly fixed, foot bolts loose, bearing seat and foundation plate loose, etc. 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.

(5) Load conduction vibration driven by motor. For example, the vibration of the steam turbine of the turbine generator, the vibration of the fan and water pump driven by the motor, and the vibration of the motor.

How to find the cause of vibration

In order to eliminate 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 motor vibration.

1, the motor did not stop until, 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 if the power of three-phase voltage balance, Three-phase fuse burn out phenomenon, the single phase operation can not only cause vibration of motor, still can make the motor temperature rise quickly, observe whether ammeter pointer is swinging back and forth, the rotor broken bar in current oscillation phenomena, the last check whether motor three phase current balance, found that the problem timely contact operators to stop the motor running, so as to avoid burning 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, In addition, the power failure method can be used to distinguish between electrical reasons and mechanical reasons. When the power failure occurs, the motor does not immediately vibrate or the vibration is reduced, which indicates that it is electrical reasons, otherwise it is mechanical failure.

Repair according to the cause of the failure

1. Maintenance of electrical causes:

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: pump motor, the motor not only vibrates large bearing temperature is also high in operation. Minor repair test found that the DC resistance of the motor is not qualified, and the stator winding of the motor has opened welding phenomenon. After the fault is found and eliminated by the elimination method, the motor runs normally.

2. Maintenance of mechanical reasons:

Check whether the air gap is uniform. If the measured value exceeds the standard, adjust the air gap again. Check the bearing, measure the bearing clearance, if unqualified, replace the new bearing, check the deformation and loosening of the core, the loose core can be bonded and cemented with epoxy resin, check the rotating shaft, repair welding and remachining of the bending rotating shaft or direct shaft, and then do balance test on the rotor. During the trial operation after the fan motor 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. When helping to deal with the problem, my team found that the air gap of the motor was very large and the level of the pedestal was also unqualified. After finding out the cause of the fault and readjust the gaps of each part, the motor succeeded in a test run.

3. The mechanical part of the load is normal:

There is no problem with the motor itself. The cause of the fault is caused by the connection part. At this time, it is necessary to check whether the basic horizontal plane of the motor, tilt degree, strength, center alignment is correct, whether the coupling is damaged, and whether the motor shaft winding degree meets the requirements.