Ct-fan/motor
motor rpm 1485 (110 kw)
fan rpm 127
vibration data on motor inboard/outboard shows high vibration peaks at 25 hz & 50 hz both.
In horizontal plane 50 hz is high, In vertical plane 25 hz is high.

overall vibration is 14 mm/sec (pk).

i am very new in this field so is it imbalance or misalignment.
need help.
zee khan

Okay..It seems you are getting 1X and 2X vibrations at the Motor..It depicts that you have combination Misalignment problems or a bent shaft... Did you have any maintenance work on the machine recently?

Misalignment between a drive motor shaft and fan shaft also typically results in a 1X and 2X harmonic component of vibration... In available oppurtunity, Just dis couple the motor from the Fan and run it alone and see the vibration behavior...

If you can post some more details (Motor poles, , Foundation condition, spectrum etc)..It will be helpful to diagnose the main reason...

This message has been edited. Last edited by: Khalid Khattak,

Pl. attach spectrum or/and waveform of the vibration signature.
Regards
Akhtar

Dear Khalid bhai and Akhtar bhai,
Thanks for ur sharing!
Please find the attached Spectrums and last month overall vibration readings on the subject motor.

Can we have the standards for the type of this machine or the set limits?

recently we didn't perform any maintenance work on the motor, except only greasing. discouple test means that we surely need to do the alignment again but before doing this we would like to get on some conclusion.
we have 12 nos. of same machines in all and most of them are running from 5mm/sec to 9 mm/sec but this one is at higher level now.
hope to listen from you soon.
Regards,
Zee khan
Tech Services Engr.

CT-FAN_E.xls (186 KB, 60 downloads) overall readings and spectrums

Need Suggestion!

Dear Zee-Kahn

Though it is very difficult to analyze a machine we have so little information on I will try. The vibration occurring at 50 hz is most likely a worn coupling if it is indeed two times motor rotational speed. Often when no repairs have been performed on a machine and two times suddenly increases it is due to a worn coupling. However we have very little information on this equipment, what type of couppling does it have? what does the higher frequncy vibration data look like? what does the waveform look like?

Anyway check the coupling.

In the 0 to 200HZ range, there are too many peaks. The peaks are non synchronous. There may be severe rubbing or bearing wear. Misalignment is ruled out since only 1x is high.
Some more data is required. What is the speed reduction means, belt of gear.
Regards

Sorry Zee-Khan , I couldn't replied you back as i was a bit busy with my home made CNC machine... After a bird eye view on the spectrums you provided, I will ask you to give us more details...

I will print the spectrums tommorrow and will study in details... I think you are getting the vibrations from hand held probe so i will not ask you to provide the orbit and polar plots (hmmm.. difficult i think)... This i am asking because if you are getting phase change or not?.. If the phase is also changes then there must be misalignment and rub probably crack in coupling or shaft...May be the you have a stuck coupling that causes the misalignment...

I am not heading toward direct conclusion but we need more information...

I will check the data in detail tomorrow and will post my opinion here...


PS:

1- What was the condition of vibrations before greasing?... Did you pressure fill the grease?... Is that grease is recommended by OEM?...

2- Can you measure the temperature at bearing locations?.. Compare the temperatures with other similar machine and please post here...

3- Forget the Orbit/Polar plot , I think you have the roller bearing installed not the general bearing

This message has been edited. Last edited by: Khalid Khattak,

Hi...

What is the arrangement of the motor/fan drive?

Is this a fairly large cooling tower where the horizontal shaft motor is located outside the CT cell, coupled to a long drive shaft, coupled to a right angle reduction gearbox whose slow speed vertical shaft accomodated the "propeller" blade style fan? Also, the long drive shaft couplings are probably a disk type rather than gear or grid style, right?

If this is the case, I would suspect you can certainly disconnect the coupling (marking the halves so you can get them rotationally back in the same spot) at the motor and run the motor solo without need to realign after reassembly.

An arrangement like this probably also means that the motor is on top of a torque tube which extends out to the gearbox base... Make a few measures around on the motor base to see if you see many differences to the motor H and V themselves...

Back to your collected spectra... I agree you have LOTS of activity in that 200 Hz and lower range, but you dont have nearly the frequency resolution to see where its coming from. You really need to bump up your number of lines, reduce your Fmax, or both. Additionally, you may want to make sure your High Pass Filter stting in your collector/acqusition system is not set to a value where you are throwing away valuable data...

Looking at the big "peaks" you have and comparing them to the overalls you are seeing, your bigger concern is all that other stuff that is not just 1xMtr or 2xMtr...

Would appreciate spectra with better frequency resolution...

Brian :-)

Can you please post whats the outcome?

zee-khan.

I am thinking of the same arrangement as Brian has described. In this case the drive shaft from motor to gearbox can be up to 4+ metres long and could be slightly bent or developing a whip if attached to a 4 pole motor.
By the way i noticed in you spectrums the motor speed was N/A
It might also be possible that the disc coupling may be bored slightly eccentric.

The described cooling tower arrangement that I'm familiar with is also of timber construction and lack of rigidity might also be exaggerating the 1 and 2 X