Generally, motors with more than 8 poles will not cause vibration due to motor manufacturing quality problems. Vibration is common in 2-6 pole motors, GB10068-2000.

“Vibration Limits and Test Methods for Rotating Motors” stipulates the vibration limits, measurement methods and rigidity foundation judgment standards for motors with different center heights on a rigid foundation. Based on this standard, it can be judged whether the motor meets the standard.

Harm of motor vibration

Motor vibration will shorten the life of winding insulation and bearings, affect the normal lubrication of sliding bearings, and expand the insulation gaps, causing dust and moisture to invade, resulting in reduced insulation resistance and increased leakage current, and even insulation breakdown and other accidents.

In addition, motor vibration can easily cause the cooler water pipes to crack and the welding points to vibrate, while causing damage to the load machinery, reducing the accuracy of the workpiece, causing fatigue of all mechanical parts that are vibrated, and loosening or breaking the anchor screws.

Motor vibration can also cause abnormal wear of carbon brushes and slip rings, and even serious brushing and burning of collector ring insulation. The motor will generate a lot of noise, which usually occurs in DC motors.

Causes of vibration

There are three main situations:

Electromagnetic reasons; Mechanical reasons; Electromechanical mixed reasons.

I. Electromagnetic reasons

1. Power supply: three-phase voltage is unbalanced, and the three-phase motor runs in a phase-missing state.

2. Stator: the stator core becomes elliptical, eccentric, and loose; the stator winding is broken, grounded, short-circuited, and the wiring is wrong, and the stator three-phase current is unbalanced.

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

2. Mechanical reasons

1. The motor itself

The rotor is unbalanced, the 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 is poorly installed, the mechanical structure is not strong enough, the resonance, the anchor screws are loose, and the motor fan is damaged.

2. In terms of coordination with the coupling

The coupling is damaged, the coupling is poorly connected, the coupling is not accurately centered, the load machinery is unbalanced, the system resonates, etc. The shaft system of the linkage part is not centered, the center line does not overlap, and the centering is incorrect. The main cause of this failure is poor alignment and improper installation during the installation process.

There is also a situation that the center lines of some linkage parts overlap when they are cold, but after running for a period of time, the center line is destroyed again due to the deformation of the rotor fulcrum, foundation, etc., resulting in vibration.

If the motor vibration is not resolved after the surface phenomenon is treated, continue to disconnect the power supply, untie the coupling, separate the load machinery connected to the motor, and turn the motor alone.

If the motor itself does not vibrate, it means that the vibration source is caused by the coupling not being aligned or the load machinery. If the motor vibrates, it means that there is a problem with the motor itself. In addition, the power-off method can be used to distinguish whether it is an electrical reason or a mechanical reason. When the power is cut off, the motor stops vibrating or the vibration is reduced immediately, which means that it is an electrical reason, otherwise it is a mechanical failure.

3. Repair according to the cause of the fault

(1) Repair of electrical causes:

First, determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it means that there is a weld break at the stator connection welding part. Disconnect the winding phases for search. In addition, check whether there is a short circuit between turns in the winding. If the fault is obvious, you can see the burn marks on the insulation surface, or use an instrument to measure the stator winding. After confirming the short circuit between turns, the motor winding is taken off the line again.

(2) Repair of mechanical causes:

Check whether the air gap is uniform. If the measured value exceeds the standard, readjust the air gap. Check the bearings and measure the bearing clearance. If it is unqualified, replace it with a new bearing. Check the deformation and looseness of the core. The loose core can be glued and filled with epoxy resin glue. Check the shaft. Re-weld the bent shaft or directly straighten the shaft, and then perform a balance test on the rotor.

The motor vibration of the sliding bearing is related to the assembly quality of the bearing. Check whether there are high points in the bearing, whether the oil inlet of the bearing is sufficient, the bearing tightening force, the bearing clearance, and whether the magnetic center line is appropriate.

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 uneven and bad; if the axial vibration is large, the bearing assembly quality is poor.

This is just a simple judgment. It is necessary to consider the actual cause of the vibration based on the on-site conditions and the above-mentioned factors.

The vibration of the Y series box motor 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 to stick.

Pay attention to the bearing temperature. If the locating bearing heats up faster than the non-locating bearing, the machine should be stopped immediately. This is because the axial vibration caused by the insufficient axial stiffness of the machine base should be reinforced.

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.

3. Electromechanical hybrid reasons

Under normal circumstances, it is not necessary to perform dynamic balancing on the motor during maintenance, except for extremely special cases, such as flexible foundation, rotor deformation, etc., in which case on-site dynamic balancing or return to the factory for processing is required.