There are many reasons for motor vibration and they are also very complicated. Motors with a large number of poles above 8 poles will not cause vibration due to quality problems in motor manufacturing.Vibration is common in 2--6 pole motors. GB10068-2000, "Rotating Motor Vibration Limits and Test Methods" stipulates the vibration limits, measurement methods and rigid foundation criteria for motors with different center heights on the basis of rigidity. The standard can judge whether the motor meets the standard.
electric motorThe harm of vibration
The vibration of the motor will shorten the winding insulation and bearing life, and affect the normal lubrication of the sliding bearing. The vibration force promotes the expansion of the insulation gap, causing external dust and moisture to invade it, resulting in a decrease in insulation resistance and an increase in leakage current, and even an insulation breakdown Wait for the accident.In addition, the vibration of the motor will easily cause the water pipe of the cooler to vibrate, and the welding point will vibrate. 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 if it is broken, the motor will cause abnormal wear of the carbon brushes and slip rings, and even serious brush fire will burn the collector ring insulation, and the motor will produce a lot of noise. This situation usually occurs in DC motors.
Ten reasons for motor vibration
1. It is caused by the imbalance of the rotor, coupler, coupling, transmission wheel (brake wheel).
2. The iron core bracket is loose, the oblique key and the pin are ineffective and loose, and the rotor is not tightly bound will cause the rotating part to be unbalanced.
3. The shaft system of the linkage part is not centered, the center line does not coincide, and the centering is incorrect.This kind of failure is mainly caused by poor alignment and improper installation during the installation process.
4. The center line of the linkage part coincides in the cold state, but after a period of operation, due to the deformation of the rotor fulcrum and foundation, the center line is destroyed again, and vibration occurs.
5. The gears and couplings connected to the motor are faulty, the gears are badly engaged, the gear teeth are worn out, the lubrication of the gears is not good, the coupling is skewed, misaligned, the gear coupling tooth profile, tooth pitch is wrong, the gap is too large Large or severe wear will cause certain vibration.
6. The structural defects of the motor itself, the shaft journal is elliptical, the rotating shaft is bent, the gap between the shaft and the bearing bush is too large or too small, the rigidity of a certain part of the bearing seat, foundation plate, foundation and even the entire motor installation foundation is insufficient.
7. Installation problems, the motor and the base plate are not firmly fixed, the foot bolts are loose, and the bearing seat and the base plate are loose.
8. Excessive or too small clearance between the shaft and the bearing bush 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 motor to vibrate.
10. Stator wiring error of AC motor, short circuit of rotor winding of winding asynchronous motor, short circuit of excitation winding of synchronous motor, wrong connection of excitation coil of synchronous motor, broken bar of rotor of cage asynchronous motor, deformation of rotor core, resulting in air gap between stator and rotor Even, resulting in an unbalanced air gap magnetic flux and causing vibration.
Causes of vibration and typical cases
There are three main reasons for vibration: electromagnetic reasons; mechanical reasons; electromechanical hybrid reasons.
XNUMX. Electromagnetic reasons
1. Power supply: the three-phase voltage is unbalanced, and the three-phase motor runs under phase loss.
2. Stator: Stator core becomes elliptical (public account: pump steward), eccentric, loose; stator winding has broken wire, ground breakdown, inter-turn short circuit, wiring error, stator three-phase current imbalance.
Example: The stator core was found to have red powder before the motor of the sealed fan in the boiler room was overhauled. It is suspected that the stator core is loose, but it is not within the scope of the standard overhaul, so it is not processed. The motor makes a harsh scream after the overhaul. Troubleshooting after replacing a stator.
3. Rotor failure: the rotor core becomes elliptical, eccentric or loose.The rotor cage bar and the end ring are open welding, the rotor cage bar is broken, the winding is wrong, the brush contact is poor, etc.
Example: During the operation of the toothless saw motor in the sleeper section, the stator current of the motor is found to swing back and forth, and the motor vibration gradually increases. According to the phenomenon, it is judged that the motor rotor cage bar may be welded and broken. After the motor is disassembled, it is found that the rotor cage bar has 7 fractures , The two sides and end rings of the serious two have all broken. If it is not found in time, it may cause bad accidents of stator burning.
XNUMX. Mechanical reasons
1. The motor itself:
Unbalanced rotor, bent shaft, deformed slip ring, uneven air gap between stator and rotor, inconsistent magnetic center of stator and rotor, bearing failure, poor foundation installation, insufficient mechanical strength, resonance, loose anchor screws, motor fan damage.
Typical case: After replacing the upper bearing of the factory condensate pump motor, the motor shaking increased, and there were signs of slight bore sweeping in the rotation and stator. After careful inspection, it was found that the motor rotor was raised at the wrong height, and the rotation and stator magnetic center were not aligned. Readjust After the thrust head screw is equipped with a cap, the motor vibration fault is eliminated.The vibration of the cross-line hoisting ring hoisting motor has been large after overhaul, and there are signs of gradual increase. When the motor is off hook, it is found that the vibration of the motor is still large, and there is a large string movement in the axial direction. The disassembly found that the rotor core is loose , The balance of the rotor is also problematic. After replacing the spare rotor, the fault is eliminated, and the original rotor is returned to the factory for repair.
2. Coordination with coupling:
The coupling is damaged, the coupling is poorly connected, the coupling is not centered correctly, the load is unbalanced, and the system is resonant.The shaft system of the linkage part is misaligned, the center line does not coincide, and the centering is incorrect.This kind of failure is mainly caused by poor alignment and improper installation during the installation process.There is another situation, that is, the center lines of some linkage parts coincide in the cold state, but after a period of operation, due to the deformation of the rotor fulcrum and foundation, the center line is destroyed again, and vibration occurs.
For example:
a. Circulating water pump motor, the vibration has been too large during operation, there is no problem with the motor inspection, and everything is normal without load. The pump team thinks the motor is running normally, and finally checked that the motor alignment center difference is too large. After the pump team recalibrates , The motor vibration is eliminated.
b. After replacing the pulley in the boiler room induced draft fan, the motor will vibrate during trial operation and the three-phase current of the motor will increase at the same time. Check all circuits and electrical components for no problems. Finally, the pulley is found to be unqualified. After replacement, the vibration of the motor is eliminated, and the three-phase motor The current also returned to normal.
XNUMX. Reasons for motor mixing
1. Motor vibration is often due to uneven air gap, causing unilateral electromagnetic tension, and unilateral electromagnetic tension 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 rotor's own gravity or installation level and the wrong magnetic center, the electromagnetic tension caused by the rotor causes the axial series movement of the motor, which causes the motor vibration to increase. In severe cases, the shaft wears the root and causes the bearing temperature Rise rapidly.
The gears and couplings connected to the motor are faulty.This kind of failure is mainly manifested as poor gear engagement, severe gear tooth wear, poor lubrication of the gear, skewed and misaligned coupling, gear coupling tooth profile, incorrect tooth pitch, excessive clearance or severe wear, which will cause certain problems. vibration.
Defects in the structure of the motor itself and installation problems.This kind of failure is mainly manifested as the ellipse of the shaft journal, the bending of the rotating shaft, the excessive or small gap between the shaft and the bearing bush, the insufficient rigidity of the bearing seat, the foundation plate, a certain part of the foundation and the entire motor installation foundation, and the motor and the foundation plate are fixed. Weakness, loose foot bolts, looseness between the bearing seat and the base plate, etc.However, the gap between the shaft and the bearing bush is too large or too small can not only cause vibration, but also cause abnormal lubrication and temperature of the bearing bush.
The load driven by the motor conducts vibration.
For example: the vibration of the steam turbine of the steam 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?
To eliminate motor vibration, we must first find out the cause of the vibration. Only when the cause of vibration is found can we take targeted measures to eliminate motor vibration.
1. Before the motor is stopped, use a vibration meter to check the vibration of each part. For the parts with greater vibration, test the vibration value in three directions according to the vertical and horizontal axis. If the anchor screw is loose or the bearing end cover screw is loose, you can Fasten directly. After fastening, measure the vibration level to observe whether it is eliminated or reduced. Second, 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 cause the temperature of the motor to rise rapidly. Observe whether the pointer of the ammeter swings back and forth. The current swing occurs when the rotor is broken. Finally, check whether the three-phase current of the motor is balanced. If the problem is found, contact the operator in time to stop the motor to avoid burning the motor. damage.
2. If the motor vibration is not resolved after the surface phenomenon is processed, continue to disconnect the power supply, untie the coupling, and mechanically separate the load connected to the motor. Single-turn motor. If the motor itself does not vibrate, the source of vibration is indicated It is caused by the coupling failure or the load machinery. If the motor vibrates, it means that the motor itself has a problem. In addition, the power-off method can be used to distinguish between electrical and mechanical reasons. When the power fails, the motor will not vibrate or immediately If the vibration is reduced, it is an electrical cause, 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 and separate the phases for searching. In addition, whether there is a short circuit between the windings. If you see burnt marks on the surface, or measure the stator winding with an instrument, and after confirming the short circuit between the turns, take the motor winding off the wire again.
For example: water pump motor, the motor not only vibrates, but the bearing temperature is too high. Minor repair tests found that the motor's DC resistance is unqualified, and the motor stator winding has open welding. After the fault is found and eliminated by the troubleshooting method, 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, measure the bearing clearance, if it is unqualified, replace with a new bearing, check the deformation and looseness of the iron core, the loose iron core can be glued and filled with epoxy resin, check the shaft, repair the curved shaft, rework or direct the straight shaft , And then do a balance test on the rotor.During the trial operation after the blower motor was overhauled, the motor not only vibrated greatly, but the temperature of the bearing bush exceeded the standard. After several days of continuous treatment, the fault remained unresolved.My team members found that the air gap of the motor was very large and the tile seat level was not up to standard. After finding the cause of the fault, after re-adjusting the gaps of various parts, the motor was successfully tested.
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, check the basic horizontal plane, inclination, strength, center alignment of the motor, whether the coupling is damaged, and whether the motor shaft extension winding meets 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 shall 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 there is only one or two diagonal vibrations exceeding the standard of four feet, loosen the anchor bolts, the vibration will be qualified, indicating that the foot pad is not solid enough, and the anchor bolts are tightened to cause vibration of the machine base. Cushion the 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. If it is not flat, it is caused by the extra key on the shaft extension. Exciting force will cause the motor's horizontal vibration to exceed the standard.In this case, the vibration value will not exceed too much, and the vibration value can often decrease after being docked with the host. The user should be convinced to use it. The two-pole motor is installed in the shaft extension keyway according to GB10068-2006 in the factory test. : Pump Butler).The extra keys will not increase the excitation force.If you need to deal with it, just cut off the extra keys to make them longer.
5. If the air test vibration of the motor does not exceed the standard, and the load vibration exceeds the standard, there are two reasons: one is the large deviation of alignment; the other is the residual imbalance of the rotating parts (rotor) of the main engine and the residual of the motor rotor The phases of the unbalance are overlapped, and the residual unbalance of the entire shaft system at the same position after docking is large, and the generated vibration force is large to cause vibration.At this time, you can disconnect the coupling, rotate either of the two couplings by 180°C, and then connect the test machine, the vibration will decrease.
6. 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 turned again. This is the reason for the improper storage of the motor. Normally, the two-pole motor is in storage.The motor should be cranked every 15 days, and the crank should rotate at least 8 times each time.
8. The motor vibration of the sliding bearing is related to the assembly quality of the bearing bush. Check whether the bearing bush has high points, whether the bearing bush has enough oil, the bearing bush tightness, the bearing bush clearance, and the magnetic center line are suitable.
9. Under normal circumstances, the cause of motor vibration can be simply judged from the vibration values in three directions. The horizontal vibration is large, and the rotor is unbalanced; the vertical vibration is large, and the installation foundation is not flat; the axial vibration is large, and the bearing assembly is large. low quality.This is just a simple judgment. It is necessary to find the true cause of the vibration based on the site conditions and the above-mentioned factors.
10. The vibration of Y series box-type motors should pay special attention to the axial vibration. If the axial vibration is greater than the radial vibration, it will cause great harm to the motor bearing and cause the shaft holding accident.Pay attention to the bearing temperature. If the locating bearing heats up faster than the non-locating bearing, stop immediately.This is because of axial vibration caused by insufficient axial rigidity of the machine base, so the machine base should be reinforced.
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 changes in location and working conditions. The vibration problem can be handled at the user site. of.Under normal circumstances, it is not necessary to perform dynamic balance verification on the motor for maintenance. Except for very special conditions, such as flexible foundations, rotor deformation, etc., it must be dynamically balanced or returned to the factory for treatment.
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