I am facing problem of high vibration in 148 kw vertical motor in no load condition. Repeated runs have resulted in further increase in vibration after running for 1 hour or more. th evibration frequency is 33 and 59 HZ. The machine is a 25HZ machine. During shutdown intermittent rattling sound is observed during coasting. The machine hand rotation is quite free and coasting down time is alos OK. Bearings have been checked in situ after opening bearing cover and found ok. I am unable to make out the meaning of high vibration with a frequency of 33 and 59 HZ. The vibration is highest at NDE bearing (7.8 mm/sec RMS).

It is expected that vibration would be highest at NDE end. 33 Hz is 1/3 of 100Hz which is 2x50Hz line frequency which shows up when you have one of the line phases failing on you. Presence of these frequencies after the motor works may be an indication of a thermal related whcih may be the result of the electrical problem. That 59 Hz can very well be a natural frequency evoked. However without seeing the actual spectra my statement above is pure coffee grind fortune telling! Give us some spectra and we will take it from there.

Regards
Ibrahim H Caglayan, PhD
Ankara Turkey

Dear Irshad,

Your quote : ''During shutdown intermittent rattling sound is observed during coasting.''

If this motor is driving a pump of some kind, the rattling sound you hear MAY BE caused by the anti-reverse rotation ratchet when the motor is decelerating.
Most, if not all, of these anti-reverse rotation devices are designed with a shat fitted disk that caries small pawls that fly outwards during acceleration. So, when the motor comes down in speed those spring loaded pawls return to their original position and come into contact with the indentations of the stationary disk. When completely stopped, then they engage into the stationary plate indentations; therefore preventing reverse rotation caused by the liquid wanting to flow back.

More info on frequencies, mounting, etc. would help us trying to figure this thing out. You can post a photo if you want on this site.

Regards,

MarkoLeo

I have recently posted another thread with lots of details about the possible perils of running certain vertical motors with no downward thrust load.

http://maintenanceforums.com/eve/forums/a/tpc/f/3751089011/m/4321071482

It may be that you have a vertical motor with a bearing configuration that doesn't provide enough preload for the thrust bearing in the uncoupled configuration. Can you describe hte bearing configuration?