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There are many reasons for motor vibration

Update:27 Jul 2018
Summary:

There are many reasons for motor vibration and it is co […]

There are many reasons for motor vibration and it is complicated. Motors with more than 8 poles and large numbers do not cause vibration due to motor manufacturing quality problems. Vibration is common in 2--6 pole motors, GB10068-2000, "Rotating Motor Vibration Limits and Test Methods" stipulates different heights on the basis of rigidity..
There are many reasons for motor vibration and it is complicated. Motors with fan motor  more than 8 poles and large numbers do not cause vibration due to motor manufacturing quality problems. Vibration is common in 2--6 pole motors, GB10068-2000, "Rotating Motor Vibration Limits and Test Methods" stipulates the vibration limit, measurement method and rigid foundation determination criteria for different center high motors on a rigid basis. The standard can determine whether the motor meets the standard.

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 a severe brushing will burn the collector ring insulation, and the motor will generate a lot of noise. This situation usually occurs in the DC motor.

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 flawed, 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, the foundation plate, a part of the foundation and even the entire motor installation base 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 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.

Vibration causes and typical cases

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

I. Electromagnetic reasons

1. Power supply: Three-phase voltage is unbalanced, and 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, and the stator three-phase current is unbalanced.

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: in 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 opening and breaking. After the motor is disassembled, it is found that the rotor cage has 7 breaks. The two serious sides and the end rings have all been broken. If they are not found in time, the accident of burning the stator may occur.