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Squirrel Cage Induction Motor vibration

Squirrel Cage Induction Motor vibration

Squirrel Cage Induction Motor vibration

(OP)
Hi!
Any one please explain me the cause of the induction motor vibration with the following data:
Motor specs:75kW, 2987rpm,415V,3-ph, 50hz
Vibration details: Decoupled condition (load is pump),
DE: Horizantal:4.2mm/sec, Vertical:0.9mm/sec & axial: Nil
NDE: Horizantal:4.1mm/sec, Vertical: 1.0mm/sec & Axial: Nil
The above readings noticed at 5985rpm in the spectrum.
I am grateful to your reply.

RE: Squirrel Cage Induction Motor vibration

I would say likely the horizontal vibration is being amplified by resonance.

With runnning speed 2987rpm, and vibration at 5985rpm, you need to sort out whether the exact frequency is
A - 2*line frequency
B - 2*running speed - extremely close to 2*LF when uncoupled
C - neither of the above (non-sync) (related to bearings)

Do you know the frequency bin width of the measurement? (what was Fmax and how many frequency lines)?.  Also did you use a peak label feature to determine the frequency (can get much more accurate than the bin width).  If the bin width is 4cpm or above I would recommend to re-take with higher resolution to see if you can rule out C.

If you can rule out C based on frequency, you could do a power-down to try to check between A and C.  Even without power-down test for 2-pole motor I would suspect 2*LF vibration. First thing to check is the hold-down bolts.  Carefully loosen 1 at a time and retigten while monitoring for vib. If you see vib going away you have a soft foot condition which needs to be corrected.

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