Ten reasons for motor vibration

1. The rotor, coupler, coupling, and transmission wheel (brake wheel) are not balanced.

2. The iron core bracket is loose, the oblique key and the pin are loose, and the rotor is not tied tightly, which will cause the rotating part to be unbalanced.

3. The linkage part of the shaft system is misaligned, the center line does not coincide, and the centering is not correct. 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, the center line is destroyed due to deformation of the rotor fulcrum and foundation, and vibration is generated.

5. The gears and couplings connected with the motor are faulty, the gears are poorly engaged, the gear teeth are seriously worn, the wheel is poorly lubricated, the coupling is skewed, misaligned, the toothed coupling is toothed, the pitch is wrong, and the clearance is too Large or worn, it will cause a certain amount of vibration.

6. The structure of the motor itself is elliptical, the shaft 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, the foundation plate, a certain part of the foundation and even the entire motor installation foundation is insufficient.

7. Installation problem, the fixing between the motor and the base plate is not strong, the foot bolt is 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 transmitted by the motor is transmitted, such as the fan driven by the motor and the vibration of the pump, causing the motor to vibrate.

10. AC motor stator wiring error, winding-type asynchronous motor rotor winding short circuit, synchronous motor excitation winding turn-to-turn short circuit, synchronous motor excitation coil connection error, cage asynchronous motor rotor broken strip, rotor core deformation caused by stator and rotor air gap Both cause the air gap flux to be unbalanced and cause vibration.

Harm of motor vibration

The vibration of the motor will shorten the insulation of the winding and the bearing life, affecting the normal lubrication of the sliding bearing. The vibration force will expand the insulation gap, and the external dust and moisture will invade it, causing the insulation resistance to decrease and the leakage current to increase, even forming insulation breakdown. Waiting for an accident. In addition, the motor generates vibration, and it is easy to cause the cooler water pipe to crack, the welding point to vibrate, and damage to the load machinery, reduce the accuracy of the workpiece, cause fatigue of all mechanical parts subjected to vibration, and loosen the anchor screw. Or disconnected, the motor will cause abnormal wear of the carbon brush and the slip ring, and even severe brushing will burn the collector ring insulation, and the motor will generate a lot of noise. This situation usually occurs in DC motors.

Vibration causes and typical cases

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

1 electromagnetic reasons

1. Power supply: The three-phase voltage is unbalanced, and the three-phase motor is out of phase.

2. Stator aspect: the stator core becomes elliptical, eccentric, loose; the stator winding breaks, grounds breakdown, turn-to-turn short circuit, wiring error, stator three-phase current imbalance.

For example: Before the boiler room fan motor was repaired, it was found that the stator core had red powder. It was suspected that the stator core was loose, but it was not in the standard overhaul project, so it was not processed. The motor screamed when the test was overhauled. Troubleshoot after replacing a stator.

3. Rotor failure: the rotor core becomes elliptical, eccentric, and loose. The rotor cage strip is welded to the end ring, the rotor cage strip is broken, the winding is wrong, and the brush is in poor contact.

For example: during the running of the toothless saw motor of the sleeper section, the stator current of the motor is oscillated back and forth, and the vibration of the motor is gradually increased. According to the phenomenon, the rotor bar of the motor has the possibility of open welding and breaking. After the motor is disassembled, it is found that the rotor cage has 7 breaks. The two serious sides and the end ring have all been broken. If it is found to be untimely, it may cause a bad accident in which the stator is burnt.

2 mechanical reasons

1. The motor itself:

The rotor is unbalanced, the shaft is bent, the slip ring is deformed, the stator and rotor air gaps are uneven, the stator and rotor magnetic centers are inconsistent, the bearing is faulty, the basic installation is poor, the mechanical mechanism is not strong enough, the resonance is loose, the ground screw is loose, and the motor fan is damaged.

Typical case: After the factory condensate pump motor has replaced the upper bearing, the motor sloshing increases, and the rotor and stator have slight broom signs. After careful inspection, it is found that the motor rotor lift height is incorrect, and the rotor and stator magnetic centers are not up, re-adjust After the thrust head screw is provided, the motor vibration fault is eliminated. After the maintenance of the over-the-line lifting motor, the vibration has been too large, and there are signs of increasing gradually. When the motor is hooked, the vibration of the motor is still large, and there is a large amount of movement in the axial direction. The disintegration found that the rotor core is loose. There is also a problem with the balance of the rotor. After replacing the spare rotor, the fault is eliminated and the original rotor is returned to the factory for repair.

2. Coupling with the coupling: the coupling is damaged, the coupling is poorly connected, the coupling is not centered, the load is mechanically unbalanced, and the system is resonant.

❶The linkage part of the shaft system is misaligned, the center line does not coincide, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during the installation process. There is also a case where some of the center lines of the interlocking parts are coincident in the cold state, but after a period of operation, the center line is broken due to the deformation of the rotor fulcrum and the foundation, thereby generating vibration.

For example: a, circulating water pump motor, the vibration has been too large during operation, the motor is inspected without any problems, the idling is also normal, the pump class thinks that the motor is running normally, and finally the motor is found to have too much positive center difference, the pump class is looking for new. After the positive, the motor vibration is eliminated.

b. After changing the pulley of 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 without problems. Finally, the pulley is found to be unqualified. After the replacement, the motor vibration is eliminated, and the motor is three-phase. The current also returns to normal.

3 motor mixing reasons

1. Motor vibration is often uneven air gap, causing single-sided electromagnetic pulling force, and the single-sided electromagnetic pulling force further increases the air gap. This electromechanical mixing acts as motor vibration.

2. The axial movement of the motor is caused by the gravity of the rotor itself or the installation level and the magnetic center is not right, causing the electromagnetic tension to cause the axial movement of the motor, causing the vibration of the motor to increase. In severe cases, the shaft is ground and the temperature of the bearing is increased. Rapidly rises.

齿轮The gears and couplings associated with the motor are faulty. This kind of failure mainly manifests as poor gear occlusion, serious tooth wear, poor lubrication of the wheel, skewing and misalignment of the coupling, tooth profile of the gear coupling, incorrect tooth pitch, excessive clearance or serious wear, which will cause certain vibration.

缺陷 The structure of the motor itself is defective and installed. This kind of failure mainly manifests as the ellipse of the journal, the bending of the shaft, the gap between the shaft and the bearing bush is too large or too small, and the rigidity of the bearing seat, the foundation plate, a part of the foundation and even the entire motor installation base is insufficient, and the motor and the base plate are fixed. Not secure, the foot bolts are loose, and the bearing housing and the base plate are loose. The excessive or too small gap between the shaft and the bearing bush can not only cause vibration but also cause abnormal lubrication and temperature of the bearing bush.

The load that the motor drags conducts vibration. For example: steam turbine vibration of a turbine generator, fan driven by a motor, vibration of a water pump, causing motor vibration.

How to find the cause of vibration

In order 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 not stopped, check the vibration of each part with the vibration meter. For the vibration part, test the vibration value in three directions of vertical horizontal axis. If the ground screw is loose or the bearing end cover screw is loose, Directly tighten, measure the vibration size after tightening, observe whether there is elimination or lightening, secondly check whether the three-phase voltage of the power supply is balanced, whether the three-phase fuse is blown, and the 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 current meter pointer swings back and forth, and the current swing phenomenon occurs when the rotor breaks. Finally, check whether the three-phase current of the motor is balanced. If problems are found, contact the operating personnel to stop the motor running in time to avoid burning the motor. damage.

2. If the motor vibration is not solved after the surface phenomenon is processed, continue to disconnect the power supply, uncoupling the coupling, and mechanically disconnect the load connected to the motor. Single-turn motor, if the motor itself does not vibrate, the vibration source If the coupling is not looking for a positive or load machine, if the motor vibrates, it means that the motor itself has a problem. In addition, the power-off method can be used to distinguish whether it is an electrical cause or a mechanical cause. When the power is cut off, the motor will not vibrate immediately. Vibration reduction, it is an electrical cause, otherwise it is a mechanical failure.

Overhaul for 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 the welding part of the stator is welded, the winding is separated by phase, and the winding is short-circuited. If the fault is obvious, it can be insulated. The surface is burnt, or the stator winding is measured with an instrument. After confirming the short circuit between turns, the motor winding is re-routed.

For example: pump motor, the motor is not only vibrating, but the temperature of the bearing is also high. The small repair test found that the DC resistance of the motor is unqualified, and the stator winding of the motor has a phenomenon of open welding. After the fault is found by the elimination method, the motor runs normally.

2. Maintenance of mechanical reasons:

Check that the air gap is uniform. If the measured value is exceeded, re-adjust the air gap. Check the bearing, measure the bearing clearance, if it is not qualified to replace the new bearing, check the core deformation and looseness, the loose iron core can be bonded with epoxy resin glue, check the rotating shaft, repair the reaming of the curved shaft or directly straight shaft Then do a balance test on the rotor. During the trial operation of the blower motor overhaul, the motor not only has a large vibration, but also the bearing temperature exceeds the standard. After several days of continuous processing, the fault remains unresolved. When the team members helped to find out, the air gap of the motor was very large, and the level of the tile seat was not qualified. After the fault was found, the motor was successfully tested once after re-adjusting the gaps.

3. The load mechanical part is checked normally, and the motor itself has no problem. The cause of the fault is caused by the connection part. At this time, check the basic level of the motor, the inclination, the strength, whether the center is correct, and whether the coupling is damaged. Whether the motor shaft extension is in compliance with the requirements.