I have face a new vibration problem in 1600 kW AC motor which is associated with fan. in this equipment vibration is high in vertical & Axial direction in motor Drive End & Non Drive end vibration is more than 3.5 mm/sec in axial direction whereas horizontal vibration is 0.85 mm/sec.

Motor has 8 pole , and that time running rpm is 337.5.

Wondering is that we found a peak in vibration signature at 30337.5 cpm and amplitude value is 3.20 mm/sec . also find side band of 6.25Hz (337.5 cpm) around this peak.

fan side vibration is less than 0.7 mm/sec. 

and Time Wave form is modulation pattern.

I dont know what is the problem. can any one help me

Original Post

If my calculations are correct this time,  the high amplitude is at a high frequency: 90x.


The sourse of vibration might be related to rotor bars or stator slots. Can you check these specifications from your books?

Have you done a shutdown test to observe the effect of cutting the electric power on the vibration? 

I guess the input from the forum members would more if you can post some vibration plots and more motor details.


Regards- Ali M. Al-Shurafa 

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