High 1X vibrations in all 3 axes in decoupled motor 1

[edison123]

Have a 3000 RPM, 2 pole motor with following vibration spectra in decoupled condition. Both motor DE and NDE have high 1X vibrations in all H/V/A axes in decoupled state. The motor was running fine in coupled condition (a compressor) until it started showing high vibrations. Then the motor was decoupled and test run again with following vibrations. Any idea what could be the reason for these high 1X vibrations (and 2X in MDE - A)?

MNDE - H

MNDE - V

MNDE - A (2X)

MDE - H

MDE - V

MDE - A

Muthu

http://www.edison.co.in

 

[RedSnake]

The simplest answer is that a bearing is not okey.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[edison123]

Thanks, RedSnake.

Both sides are standard sealed ball bearings with C4 clearance. Why would a bearing issue produce 1X vibration?

Muthu

http://www.edison.co.in

 

[Parchie]

@muthu,
Try investigating if your motor has cracked or broken rotor bars or shorting rings. I am not sure but we had one that showed similar vibration signatures a long time ago.

 

[RedSnake]

I can't answer that, because when I was doing that kind of work I used a stethoscope.
If you where really good you could even hear on the sound which kind of fault the bearing, I was never that good, didn't need to be either, either the bearing sounded okey or it did not then you just had to change the motor before it broke down completely.
Sometimes I just used a screwdriver, hold it as close to the bearing as possible and listen at the end of the handel. ;-)

Another fault that can give vibration is the motor is detached is if it is running on 2 phases instead of 3 but it wouldn't run for long if that was the case before the fuses would go, I guess you have checked that the windings are ok.


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[edison123]

Thanks, Parchie. Will ask the client to check what is the vibration the moment power supply is cut off. If it vanishes immediately on power off, the rotor could be a problem as you say.

Muthu

http://www.edison.co.in

 

[spciesla]

Could it be unbalance associated with the manner in which the unit is uncoupled? An issue with the key/coupling in the uncoupled state? That would fit the characteristics of high radial 1X vibration. The 2X vibration in the axial direction could result from an overhung unbalance condition from the coupling as well.

 

[edison123]

The motor was tested for soft foot while running decoupled with one bolt at a time loosened on NDE. The vibration increased by 2 mm/sec on loosening the bolt and reduced to original high value on tightening. The vibration dropped off only gradually on power off confirming there are no electrical issues.

Muthu

http://www.edison.co.in

 

[BrianE22]

You're sure it is not an imbalance problem?

 

[edison123]

Thanks, Brian.

How does a well running motor with low vibrations suddenly develop an imbalance?

Muthu

http://www.edison.co.in

 

[wayne440]

How large is the motor? If it was balanced by the weight addition method, perhaps it has lost a weight or piece of balancing compound.
A bearing failure also might explain it, depending on the failure mode.

 

[edison123]

wayne - It's a 325 KW motor. Good point about balancing weight coming off though it's doubtful since they are fixed in V groove balancing disc.

Muthu

http://www.edison.co.in

 

[wayne440]

That is a much larger motor than I have experience with. Very interested to see what the eventual findings are.

 

[RedSnake]

I would think that if it was the balancing weights the imbalance wouldn't go away when it's rolling out without power.
How long has this motor been running?

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Gr8blu]

edison123 Two options.
1) Vibration falls IMMEDIATELY to zero on removal of electrical input (volt, amp) to stator winding. Cause: coil failure in stator winding OR broken rotor bar (or perhaps multiple bars in adjacent slots).
2) Vibration continues after removal of electrical power. Cause: mechanical unbalance (missing or loose balance weight, broken fan blade, bowed rotor shaft, etc.)

Converting energy to motion for more than half a century

 

[edison123]

The motor is coming to my shop. Will do detailed vib analysis on arrival.

Muthu

http://www.edison.co.in