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Ten reasons for motor vibration

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Ten reasons for motor vibration

来源: http://dntgm.com点击: Date: 2019-07-09 11 : 41Source : http : //dntgm.comClick :

There are many reasons for motor vibration and they are complicated. Motors with a large number of poles above 8 poles will not cause vibration due to motor manufacturing quality issues. Vibration is common in 2--6-pole motors, GB10068-2000, "Vibration Limits and Test Methods for Rotating Electrical Machines" stipulates the vibration limit values, measurement methods and determination criteria for rigid foundations of different high-center motors on a rigid basis. The standard can judge whether the motor meets the standard.

Harm of motor vibration

The vibration of the motor will shorten the winding insulation and bearing life, affect the normal lubrication of the sliding bearing, the vibration force promotes the expansion of the insulation gap, intrusion of external dust and moisture, causing the insulation resistance to decrease and leakage current to increase, and even insulation breakdown And other accidents. In addition, the motor generates vibration, and it is easy to cause the water pipe of the cooler to crack and the welding point to open. At the same time, it will cause damage to the load machinery, reduce the accuracy of the workpiece, cause fatigue of all mechanical parts subject to vibration, and loosen the anchor screws. Or, the motor will cause abnormal wear of the carbon brushes and slip rings, and even severe brush fires will burn the slip ring insulation, and the motor will generate a lot of noise. This situation often occurs in DC motors.

Ten reasons for motor vibration

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

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

3. The axis of the linkage part is misaligned, the center lines do not coincide, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during installation.

4. The center line of the linkage part coincides in the cold state, but after a period of operation, the center line is damaged due to the deformation of the rotor fulcrum and the foundation, which causes vibration.

5.The gears and couplings associated with the motor are faulty, the gears are poorly engaged, the gear teeth are worn seriously, the wheels are poorly lubricated, the couplings are skewed and misaligned, the toothed couplings have incorrect tooth shapes, tooth pitches, and excessive clearances. Large or severely worn, can cause some vibration.

6. Defects in the structure of the motor itself, the ellipse of the journal, the rotating shaft is bent, the gap between the shaft and the bearing pad is too large or too small, the rigidity of the bearing seat, the foundation plate, a certain part of the foundation, or even the entire motor installation foundation is insufficient.

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

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

9. The load dragged by the motor conducts vibration, such as the fan and water pump that the motor drags, causing the motor to vibrate.

10. Stator wiring of AC motor is wrong, rotor winding of winding asynchronous motor is short-circuited, inter-turn short circuit of field winding of synchronous motor, connection of excitation coil of synchronous motor is incorrect, rotor bar of cage asynchronous motor is broken, rotor core deformation caused by stator core, rotor air gap is not constant. Uniformity, resulting in air gap magnetic flux imbalance and vibration.

Causes of vibration and typical cases

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

I. electromagnetic reasons

1. Power supply: Three-phase voltage is unbalanced, and three-phase motor is running without phase.

2. On the stator side: the stator core becomes elliptical (public number: pump housekeeper), eccentric, and loose; the stator winding is broken, the ground is broken, the turns are short-circuited, the wiring is incorrect, and the stator three-phase current is unbalanced.

Example: Before the maintenance of the sealed fan motor in the boiler room, it is found that the stator core has red powder. It is suspected that the stator core is loose, but it is not an item within the scope of the standard overhaul, so it is not processed. The motor screams squeaks during the trial rotation after the overhaul. Troubleshooting after replacing a stator.

3. Rotor failure: The rotor core becomes elliptical, eccentric and loose. Rotor cage strips are welded to the end ring, rotor cage strips are broken, windings are incorrect, and brushes are not in good contact.

Example: During the operation of the sleeper segment toothless saw motor, it is found that the motor stator current swings back and forth, and the motor vibration gradually increases. According to the phenomenon, it is judged that the rotor cage of the motor may be welded and broken. After the motor is disassembled, it is found that the rotor cage is broken at 7 places. The severe two sides and the end ring have all been broken. If it is not found in time, a bad accident that may cause stator damage may occur.

2. Mechanical reasons

1. With regard to 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 not the same, the bearing is faulty, the foundation is poorly installed, the mechanical mechanism is not strong enough, resonance, the anchor screws are loose, and the motor fan is damaged.

Typical case: After replacing the upper bearing of the condensate pump motor in the factory, the motor sloshing increased, and the rotor and the stator showed slight signs of rifling. After careful inspection, it was found that the lift height of the motor rotor was incorrect, and the rotor and stator magnetic center were not aligned. Readjust After the thrust head screw is capped, the motor vibration fault is eliminated. After the maintenance of the over-the-line hoisting motor, the vibration has always been too large, and there are signs of gradually increasing. When the motor is dropped, it is found that the motor vibration is still very large, and there is a large series of axial movement. The disassembly shows 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. Cooperating with the coupling:

The coupling is damaged, the coupling is poorly connected, the coupling is not accurately located, the load is unbalanced, and the system is resonant. The axis of the linkage part is misaligned, the center lines do not coincide, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during installation. There is also a case where the centerline of some linkage parts coincides in the cold state, but after a period of operation, the centerline is damaged due to the deformation of the rotor fulcrum and the foundation, resulting in vibration.

E.g:

a. Circulating water pump motor, the vibration has always been too large during operation, the motor inspection is no problem, and no load is normal. The water pump class believes that the motor is operating normally. Finally, it is checked that the motor has too much centering error. , Motor vibration is eliminated.

b. After the replacement of the pulleys of the induced draft fan in the boiler room, vibration occurs during the trial operation of the motor and the three-phase current of the motor increases. After checking all the circuits and electrical components, there are no problems. Finally, the belt pulley is unqualified. The current returned to normal.

Three. Motor mixing reasons

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

2.Axial series motion of the motor. Due to the gravity or installation level of the rotor itself and the magnetic center being incorrect, the electromagnetic pull force causes the axial series motion of the motor, which causes the motor vibration to increase. In severe cases, the shaft wear roots cause the temperature of the shaft. Rise quickly.

The gear and coupling connected to the motor are faulty. Such failures are mainly manifested by poor gear meshing, severe gear tooth wear, poor wheel lubrication, skewed and misaligned couplings, tooth couplings with incorrect tooth pitch, tooth pitch, excessive clearance, or severe wear, all of which can cause certain problems. vibration.
Defects in the structure of the motor and installation problems. This kind of failure is mainly manifested by the ellipse of the journal, the rotating shaft is bent, the gap between the shaft and the bearing pad is too large or too small, the rigidity of the bearing seat, the foundation plate, a part of the foundation, or the entire motor installation foundation is insufficient, and the motor and the foundation plate are fixed. Insufficient, loose foot bolts, loose between bearing seat and foundation plate, etc. Too large or too small clearance between the shaft and the bearing pad can not only cause vibration, but also cause abnormality in the lubrication and temperature of the bearing pad.

The load dragged by the motor conducts vibration.

For example, the turbine of a turbine generator vibrates, and the fan and 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 stops, use a vibration meter to check the vibration of each part. For the parts with large vibrations, test the vibration values in three directions, vertical and horizontal axis. If the anchor screws are loose or the bearing end cap screws are loose, you can Directly tighten, measure the vibration after tightening, and observe whether it has been eliminated or reduced. Secondly, check whether the three-phase voltage of the power supply is balanced and whether the three-phase fuse is blown. Single-phase operation of the motor can not only cause vibration, It will also cause the temperature of the motor to rise rapidly. Observe whether the pointer of the ammeter is swinging back and forth. When the rotor is broken, the current swing phenomenon occurs. Finally, check whether the three-phase current of the motor is balanced. Contact the operating staff to stop the motor operation in case of problems. damage.

2. If the vibration of the motor is not resolved after the surface phenomenon has been solved, continue to disconnect the power supply, disengage the coupling, and mechanically separate the load connected to the motor. For single-turn motors, if the motor itself does not vibrate, explain the source of vibration. It is caused by the misalignment of the coupling or the load machinery. If the motor vibrates, it indicates that the motor itself has a problem. In addition, the power failure method can be used to distinguish between electrical and mechanical reasons. If the vibration is reduced, it is an electrical reason, otherwise it is a mechanical failure.

Overhaul for the cause of the failure

1. Maintenance for electrical reasons:

The first is to determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it indicates that there is an open welding phenomenon at the welding part of the stator connection. Open the winding and split the phase to find out. In addition, if there is an inter-turn short circuit in the winding, if the fault is obvious, it can be found from the insulation Scorching marks are seen on the surface, or the stator windings are measured with an instrument, and after confirming the inter-turn short-circuit, the motor windings are taken offline again.

For example: water pump motor, the motor not only vibrates the large bearing temperature but also is too high during the small repair test. It is found that the DC resistance of the motor is unqualified, and the stator windings of the motor are opened. After the fault is found and eliminated by elimination, the motor runs normally.

2. Maintenance for mechanical reasons:

Check whether the air gap is uniform. If the measured value exceeds the standard, readjust the air gap. Check the bearing and measure the bearing clearance. If the bearing is not qualified, replace the new bearing, check the core deformation and looseness. The loose core can be filled with epoxy glue, check the shaft, repair the reworked bent shaft or directly straight the shaft. , And then perform a balance test on the rotor. During the trial operation after the blower motor was overhauled, the motor not only vibrated greatly, but the bearing bush temperature exceeded the standard. After several days of continuous processing, the fault was still not resolved. When the team members assisted in processing, they found that the air gap of the motor was very large, and the level of the tile seat was unqualified. After the cause of the fault was found, the gap of each part was readjusted, and the motor was successfully tested once.

3. The inspection of the load mechanical part is normal, and the motor itself has no problems:

The cause of the failure is caused by the connection part. At this time, check the basic horizontal plane, inclination, strength of the motor, whether the center is correct, whether the coupling is damaged, and whether the motor shaft extension meets the requirements.

Steps to deal with motor vibration

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

2. Check the vibration value of the motor foot. According to the national standard GB10068-2006, the vibration value at the foot plate must 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 diagonal vibrations exceeds the standard, loosen the anchor bolts and the vibration will be qualified, indicating that the feet are not properly cushioned, and the foundation bolts will cause deformation of the base to cause vibration. Firm the bottom feet, realign them, and tighten the anchor bolts.

4. Fully tighten the four foundation 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. If it is not flat, the extra keys on the shaft extension are generated. Excitation force will cause the horizontal vibration of the motor to exceed the standard. In this case, the vibration value does not exceed too much, and the vibration value can often decrease after docking with the host. The user should be convinced to use it. The two-pole motor is installed in the shaft extension keyway with a half key (public number according to GB10068-2006) during factory test : Pump Butler). The extra keys will not add extra excitation force. If you need to deal with it, you just need to trim the extra keys to the extra length.

5. If the vibration of the motor does not exceed the limit in the air test, there are two reasons for the vibration of the load: one is the large deviation of the correction; the other is the residual imbalance of the rotating part (rotor) of the host and the residual of the motor rotor. The phases of the unbalance amount overlap, and the residual unbalance amount of the entire shaft system at the same position after the docking is large, and the generated vibration force is large to cause vibration. At this time, you can disengage the coupling, rotate either of the two couplings by 180 ° C, and then connect the test machine, and the vibration will decrease.

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

7. Due to the poor rigidity of the rotor of the two-high-power motor, it will be deformed for a long time without use, and it may vibrate when it is turned again. This is the reason for the poor storage of the motor. Under normal circumstances, the storage period of the two-pole motor. Every 15 days, the motor should be cranked, and at least 8 revolutions should be made each time.

8. The vibration of the sliding bearing motor is related to the quality of the bearing bush assembly. It should be checked whether the bearing bush has a high point, whether the bearing oil is enough, the bearing bush tightness, the bearing gap, and the magnetic centerline are appropriate.

9. In general, the cause of the motor vibration can be judged simply from the vibration value in three directions. The horizontal vibration is large and the rotor is unbalanced. The vertical vibration is large and the installation foundation is not good. The axial vibration is large and the bearing is assembled. low quality. This is just a simple judgment. According to the site conditions, combined with the factors mentioned above, consider the real cause of vibration.

10. For the vibration of Y series box motor, special attention should be paid to the axial vibration. If the axial vibration is greater than the radial vibration, it will cause great harm to the motor bearings and cause a shaft-holding accident. Pay attention to the bearing temperature. If the locating bearing heats up faster than the non-locating bearing, stop the machine immediately. This is because the axial vibration caused by insufficient axial rigidity of the machine base should be strengthened.

11. After the rotor is dynamically balanced, the residual imbalance 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. It can handle the vibration problem at the user's site. of. Under normal circumstances, the motor does not need to be checked for dynamic balance when servicing the motor. Except for very special cases, such as flexible foundations and rotor deformation, on-site dynamic balancing or return to the factory must be performed.


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