From the perspective of the motor itself, the high vibration value of the motor is mainly related to the dynamic balance of the rotor. From the perspective of the motor's external conditions, the installation quality of the motor and the host, the alignment, the lack of rigidity of the foundation, the close natural frequency of the motor and the foundation, etc., can also cause the motor's vibration value to exceed the standard.

Note: When the vibration value of the motor is qualified during the no-load test but exceeds the standard after loading, problems other than the motor should be checked first.

(1) Motor bearing reasons. Some equipment manufacturers use the cold-beating method (rather than the method of heating the coupling and then hot-fitting) when installing the motor coupling, which causes damage to the bearing raceway and cage, causing the motor vibration value to exceed the standard. Incorrect hoisting methods during the user's on-site hoisting process (such as the motor falling to the ground quickly, collisions, etc.) can also cause damage to the bearing raceway and cage, causing the motor vibration value to exceed the standard. The motor is placed at the project site for a long time, the oil filling nozzle and oil filling pipe are missing, the motor bearing is rusted due to water ingress, and the grease deteriorates. The above factors will cause the motor vibration value to exceed the standard.

(2) The rigidity of the equipment foundation is insufficient . The rigidity of the common base is insufficient, or the rigidity of the concrete foundation under the common base is insufficient. After the motor is powered on, the vibration value measured exceeds the standard. At this time, it is necessary to solve the problem of excessive vibration value by reinforcing the foundation.

The national standard GB10068-2008 "Measurement and evaluation limit values of mechanical vibration of motors with a shaft center height of 56 mm and above" stipulates that rigid installation should meet the following requirements: the maximum vibration velocity measured in the horizontal and vertical directions on the motor foot (or on the base near the pedestal bearing or stator foot) should not exceed 25% of the maximum vibration velocity measured in the horizontal or vertical direction on the adjacent bearing.

(3) The flatness of the base is out of tolerance. The common base surface is not flat, the motor is placed on the base or the motor is tightened on the base, and the motor vibration value exceeds the standard after power is turned on. The vibration value is normal after loosening all or part of the motor foot bolts, and the vibration value exceeds the standard again when tightening again.  a. During the on-site installation of the motor, use a sledgehammer to hit the motor foot hard when aligning. b. The motor foot is not leveled and padded during alignment, and the motor foot bolts are tightened during installation. The above situations will cause the motor foot to deform, the bearing to be abnormally stressed, and the motor vibration value exceeds the standard after power is turned on.

When the motor base is processed in the factory, it is processed once on the milling machine, so there is no doubt that the motor foot is uneven when it leaves the factory. When the motor foot is found to be deformed (check with the naked eye, check with a feeler gauge, and check on the platform), the solution is to re-mill the motor foot flat surface.

(4) The deflection of the motor shaft changes. This usually happens in high-voltage two-pole motors and sliding bearing motors. After being placed for a long time at the user's site (warehouse) or out of use, the motor shaft is not rotated 180° regularly, causing the deflection of the motor shaft to increase (bend), and the motor vibration value exceeds the standard after power is turned on.

To solve the problem of excessive vibration values of such motors, it is generally necessary to re-balance the rotor to reduce the vibration value of the motor.

(5) The natural frequencies of the motor and foundation are close. If the overall natural frequency of the motor and foundation is close to the 1st or 2nd frequency of the motor (the avoidance rate is not enough), the vibration value will exceed the standard after the motor is powered on. This can be determined through vibration detection (spectrum analysis). At this time, it is necessary to solve the problem of excessive vibration value by strengthening the foundation.

(6) The vibration value of the motor is qualified when tested alone, but exceeds the standard when loaded. After the rotating parts (rotor) of the main engine and the motor rotor are connected, the alignment meets the standard requirements. However, due to the large residual imbalance of the entire shaft system, the exciting force generated causes the vibration value of the motor to exceed the standard. At this time, the coupling can be disengaged, and either of the two couplings can be rotated 180 degrees, and then the two couplings can be connected and tested. The vibration value will decrease. 

(7) Alignment problem. There is no problem with the coupling between the motor and the host, but the alignment deviation is large, causing the motor vibration value to exceed the standard.