Vibration
Vibration
(OP)
Hi,
We are experiencing severe vibration problem with a 500 k W 2 pole 400 V 50 Hz squirrel cage electric motor. The motor is driven by a VSD. The motor was uncoupled from the drive and run at nominal speed, the vibration was 2-3 mm/s in the X and Y axis and 1.0 mm/s in the axial position. Above 3050 rpm, the vibration reached 30 mm/s in the X and Y positions and 2,5 mm/s axially. It is important to note that new bearings were fitted to the motor.
According to the vibration expert, the rotor might need balancing. My opinion is that if the rotor was not balanced, the vibration would have been observed even below nominal speed.
Any opinion?
Thanks.
Guardiano
We are experiencing severe vibration problem with a 500 k W 2 pole 400 V 50 Hz squirrel cage electric motor. The motor is driven by a VSD. The motor was uncoupled from the drive and run at nominal speed, the vibration was 2-3 mm/s in the X and Y axis and 1.0 mm/s in the axial position. Above 3050 rpm, the vibration reached 30 mm/s in the X and Y positions and 2,5 mm/s axially. It is important to note that new bearings were fitted to the motor.
According to the vibration expert, the rotor might need balancing. My opinion is that if the rotor was not balanced, the vibration would have been observed even below nominal speed.
Any opinion?
Thanks.
Guardiano





RE: Vibration
Let's say your first resonant freq was far above that. Then you would see displacement approx proportional to speed^2 and velocity proportional to speed^3 as you vary speed far below resonance if the excitation was due to unbalance (unbalance generates speed^2 force)
Is this a vertical? I would be more inclined to believe both directions reach resonance at about the same speed on a vertical machine than on a horizontal machine.
The vib analyst may have other info at his disposal. Is the vib entirely 1x. And if so, phase change can also give a clue whether resonant behavior is occuring or not
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(2B)+(2B)' ?
RE: Vibration
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(2B)+(2B)' ?
RE: Vibration
You might want to double check the bearings. Make sure the right bearings were put in and installed correctly.
RE: Vibration
Another solution, much complicate is to drive motor by other motor (beter with variable speed capability) and check vibrations.
RE: Vibration
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