The vibration of the motor will shorten the life of the winding insulation and the bearing, and affect the normal lubrication of the sliding bearing. The vibration force promotes the expansion of the insulation gap, allowing external dust and moisture to intrude into it, resulting in a decrease in insulation resistance and an increase in leakage current, and even the formation of insulation breakdown. wait for the accident.

In addition, the motor generates vibration, which is easy to crack the cooler water pipe, and the welding point vibrates. At the same time, it will cause damage to the load machine, reduce the accuracy of the workpiece, cause fatigue of all the mechanical parts subjected to vibration, and loosen the anchor screws. Or broken, the motor will cause abnormal wear of the carbon brushes and slip rings, and even serious brush fires will burn the collector ring insulation, and the motor will generate a lot of noise, which generally occurs in DC motors.

 

Ten Causes of Motor Vibration

 

1. Caused by the imbalance of rotor, coupler, coupling, transmission wheel (brake wheel).

2. The iron core bracket is loose, the oblique keys and pins are invalid and loose, and the rotor is not tied tightly, which will cause the unbalance of the rotating part.

3. The shaft system of the linkage part is not centered, the center lines are not coincident, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during the installation process.

4. The center line of the linkage part is coincident in the cold state, but after running for a period of time, due to the deformation of the rotor fulcrum and the foundation, the center line is damaged again, resulting in vibration.

5. The gears and couplings connected to the motor are faulty, the gears are poorly meshed, the gear teeth are seriously worn, the lubrication of the wheels is poor, the couplings are skewed and dislocated, the toothed couplings have incorrect tooth shape and pitch, and excessive clearance. Large or serious wear, will cause a certain amount of vibration.

6. Defects in the structure of the motor itself, the journal is elliptical, the shaft is bent, the gap between the shaft and the bearing bush is too large or too small, and the rigidity of the bearing seat, foundation plate, part of the foundation and even the entire motor installation foundation is not enough.

7. Installation problems, the motor and the base plate are not fixed firmly, the foot bolts are loose, the bearing seat and the base plate are loose, etc.

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

9. The load driven by the motor conducts vibration, such as the vibration of the fan and water pump driven by the motor, causing the motor to vibrate.

10. The stator wiring of the AC motor is wrong, the rotor winding of the wound asynchronous motor is short-circuited, the excitation winding of the synchronous motor is short-circuited between turns, the excitation coil of the synchronous motor is connected incorrectly, the rotor of the cage-type asynchronous motor is broken, and the deformation of the rotor core causes the air gap between the stator and the rotor to fail. Evenly, the air gap magnetic flux is unbalanced and vibration is caused.

Vibration causes and typical cases

There are three main reasons for vibration: electromagnetic reasons; mechanical reasons; electromechanical mixing reasons.

 

1. Electromagnetic reasons

1. In terms of power supply: the three-phase voltage is unbalanced, and the three-phase motor runs without phase.

2. In the stator: the stator core becomes elliptical, eccentric, and loose; the stator winding is broken, grounding breakdown, inter-turn short circuit, wiring error, and the three-phase current of the stator is unbalanced.

Example: Before the overhaul of the sealed fan motor in the boiler room, red powder was found in the stator iron core, and it was suspected that the stator iron core was loose, but it was not an item within the scope of standard overhaul, so it was not handled. Troubleshoot after replacing a stator.

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

For example: During the operation of the toothless saw motor in the sleeper section, it was found that the stator current of the motor oscillated back and forth, and the motor vibration gradually increased. According to the phenomenon, it was judged that the rotor cage of the motor may be welded and broken. After the motor was disassembled, it was found that the rotor cage was broken in 7 places. , the two serious two sides and end rings have all broken, if not found in time, there may be a bad accident that may cause the stator to burn.

 

2. Mechanical reasons

 

1. The motor itself

The rotor is unbalanced, the rotating 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 installation is poor, the mechanical structure is not strong enough, resonance, the anchor screw is loose, and the motor fan is damaged.

 

Typical case: After replacing the upper bearing of the condensate pump motor in the factory, the vibration of the motor increased, and the rotor and stator showed slight signs of sweeping. After careful inspection, it was found that the rotor of the motor was lifted to the wrong height, and the magnetic centers of the rotor and stator were not aligned. Readjust After the thrust head screw is replaced with a cap, the motor vibration fault is eliminated. After the overhaul, the vibration of the cross-line hoist motor has been too large, and there are signs of gradual increase. When the motor is dropped, it is found that the motor vibration is still very large, and there is a lot of axial movement. It is found that the rotor core is loose. , There is also a problem with the rotor balance. After replacing the spare rotor, the fault is eliminated, and the original rotor is returned to the factory for repair.

 

2. Matching with the coupling

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

 

For example: a. The vibration of the circulating water pump motor has been too large during operation. There is no problem in the motor inspection, and the no-load is normal. The pump team thinks that the motor is running normally. Finally, it is found that the alignment center of the motor is too far away. After positive, the motor vibration is eliminated.

b. After replacing the pulley of the induced draft fan in the boiler room, the motor will vibrate during the test run and the three-phase current of the motor will increase. Check all the circuits and electrical components. Finally, the pulley is found to be unqualified. After the replacement, the vibration of the motor is eliminated, and the three-phase current of the motor is The current also returned to normal.

3. Reasons for motor mixing

1. Motor vibration is often caused by uneven air gap, which causes unilateral electromagnetic pulling force, and unilateral electromagnetic pulling force further increases the air gap. This electromechanical hybrid effect is manifested as motor vibration.

2. The axial movement of the motor is caused by the electromagnetic tension caused by the gravity of the rotor itself or the installation level and the wrong center of the magnetic force, causing the motor to move axially, causing the motor to vibrate more. rise rapidly.

The gears and couplings connected to the motor are faulty. This kind of failure is mainly manifested in poor gear engagement, serious gear tooth wear, poor lubrication of the wheel, skew and misalignment of the coupling, incorrect tooth shape and pitch of the toothed coupling, excessive clearance or serious wear, which will cause certain damage. vibration.

Defects in the structure of the motor itself and installation problems. This kind of fault is mainly manifested as ellipse journal, bending shaft, too large or too small gap between shaft and bearing bush, insufficient rigidity of bearing seat, foundation plate, part of foundation and even the entire motor installation foundation, fixed between motor and foundation plate It is not strong, the foot bolts are loose, the bearing seat and the base plate are loose, etc. Excessive or too small clearance between the shaft and the bearing bush can not only cause vibration, but also make the lubrication and temperature of the bearing bush abnormal.

 

Load-conducted vibration dragged by the motor

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

How to find the cause of vibration ?

 

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

 

1. Before the motor is stopped, use a vibration meter to check the vibration of each part. For the parts with large vibration, test the vibration value in three directions in the vertical, horizontal and axial directions. If the anchor screws are loose or the bearing end cover screws are loose, you can Directly tighten, and measure the vibration size after tightening to observe whether it is eliminated or reduced. Secondly, check whether the three-phase voltage of the power supply is balanced, and whether the three-phase fuse is blown. The single-phase operation of the motor can not only cause vibration, but also It will also make the temperature of the motor rise rapidly. Observe whether the pointer of the ammeter swings back and forth. When the rotor is broken, the current swings. Finally, check whether the three-phase current of the motor is balanced. If there is a problem, contact the operator to stop the motor in time to avoid burning the motor. damage.

 

2. If the vibration of the motor is not resolved after the surface phenomenon is treated, continue to disconnect the power supply, untie the coupling, and mechanically separate the load connected to the motor. If the motor itself does not vibrate, it means the source of vibration It is caused by the misalignment of the coupling or the load machine. If the motor vibrates, it means that there is a problem with the motor itself. In addition, the power failure method can be used to distinguish whether it is electrical or mechanical. When the power is cut off, the motor will not vibrate immediately or If the vibration is reduced, it is an electrical reason, otherwise it is a mechanical failure.

 

Repair the cause of the failure

1. Maintenance of electrical reasons:

The first is to determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it means that there is an open welding phenomenon in the welding part of the stator connection. Disconnect the winding to find out the phases. In addition, whether there is a short circuit between turns in the winding. If burn marks are seen on the surface, or measure the stator winding with an instrument, after confirming the short circuit between turns, take the motor winding off the wire again.

For example: water pump motor, during operation, the motor not only vibrates greatly, but also the bearing temperature is too high. The minor repair test 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 runs normally.

2. Maintenance of mechanical reasons:

Check that the air gap is uniform, and readjust the air gap if the measured value is out of specification. Check the bearing, measure the bearing clearance, if it is unqualified, replace it with a new bearing, 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, re-process or directly straighten the shaft , and then perform a balance test on the rotor. During the trial operation after the overhaul of the blower motor, the motor not only vibrated greatly, but also the temperature of the bearing bush exceeded the standard. After several days of continuous treatment, the fault remained unresolved. When my team members helped to deal with it, they found that the air gap of the motor was very large, and the level of the tile seat was not qualified. After the cause of the failure was found and the gaps of each part were readjusted, the motor had a successful trial run.

3. The mechanical part of the load is checked normally, and the motor itself has no problem:

The cause of the failure is caused by the connection part. At this time, it is necessary to check the basic level, inclination, strength of the motor, whether the center alignment is correct, whether the coupling is damaged, and whether the motor shaft extension and winding meet the requirements.

 

Steps to deal with motor vibration:

 

1. Disconnect the motor from the load, test the motor empty, and check the vibration value.

2. Check the vibration value of the motor foot. According to the national standard GB10068-2006, the vibration value of the foot plate should not be greater than 25% of the corresponding position of the bearing. If it exceeds this value, the motor foundation is not a rigid foundation.

3. If only one of the four feet or two diagonally vibrate exceeding the standard, loosen the anchor bolts, and the vibration will be qualified, indicating that the bottom of the feet is not well padded. After the anchor bolts are tightened, the machine base will deform and vibrate. Place the bottom feet firmly, re-align them, and tighten the anchor bolts.

4. Fully tighten the four anchor bolts on the foundation, and the vibration value of the motor still exceeds the standard. At this time, check whether the coupling installed on the shaft extension is level with the shaft shoulder. Exciting force will cause the motor to vibrate horizontally beyond the standard. In this case, the vibration value will not exceed too much, and the vibration value will often decrease after docking with the host. Users should be persuaded to use it. The two-pole motor is installed in the half key in the shaft extension keyway according to GB10068–2006 during the factory test. Extra keys will not add extra excitation force. If you need to deal with it, just truncate the extra keys to make it more than the length.

5. If the vibration of the motor does not exceed the standard in the air test, and the vibration with the load exceeds the standard, there are two reasons: one is that the alignment deviation is large; The phase of the unbalanced amount overlaps, and the residual unbalanced amount of the entire shafting at the same position after the butt joint is large, and the generated excitation force is large and causes vibration. At this time, the coupling can be disengaged, and either one of the two couplings can be rotated by 180°C, and then the test machine can be connected, and the vibration will decrease.

6. If the vibration speed (intensity) does not exceed the standard, and the vibration acceleration exceeds the standard, only the bearing can be replaced.

7. Due to the poor rigidity of the rotor of the two-pole motor, the rotor will be deformed if it is not used for a long time, and it may vibrate when it is rotated again. This is the reason for the poor storage of the motor. Under normal circumstances, the two-pole motor is stored during the storage period. The motor should be cranked every 15 days, and the crank should be rotated at least 8 times each time.

8. The motor vibration of the sliding bearing is related to the assembly quality of the bearing bush. It should be checked whether the bearing bush has a high point, whether the oil inlet of the bearing bush is sufficient, the bearing bush tightening force, the bearing bush clearance, and whether the magnetic center line is appropriate.

9. In general, the cause of motor vibration can be simply judged from the vibration values ​​in three directions. If the horizontal vibration is large, the rotor is unbalanced; if the vertical vibration is large, the installation foundation is not flat; if the axial vibration is large, the bearing is assembled. low quality. This is just a simple judgment. It is necessary to find the real cause of the vibration according to the site conditions and the factors mentioned above.

10. Special attention should be paid to the axial vibration for the vibration of the Y series box-type motor. If the axial vibration is greater than the radial vibration, it will cause great harm to the motor bearing and will cause a shaft-holding accident. Pay attention to observe the bearing temperature. If the locating bearing heats up faster than the non-locating bearing, it should be stopped immediately. This is due to the axial vibration caused by insufficient axial rigidity of the machine base, and the machine base should be reinforced.

11. After the rotor is dynamically balanced, the residual unbalance of the rotor has been solidified on the rotor and will not change. The vibration of the motor itself will not change with the change of location and working conditions. The vibration problem can be handled well at the user’s site. of. Under normal circumstances, it is not necessary to perform dynamic balance verification on the motor when overhauling the motor. Except for very special cases, such as flexible foundation, rotor deformation, etc., it must be done on-site dynamic balance or returned to the factory.

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Post time: Jun-17-2022