quote:

Originally posted by OLI:

It was found as endbell is aluminium cast etc., bearing that would have axial movement by sliding in the endbell for temp. expansion was stuck.

Olov,

How did you physically verify that bearing was stuck? After all, one can expect just 3-5 mil of axial movement due to temp. expansion.
Thanks,
David

David,

I didn´t, the original manufacturer that happened to be situated cross town did. Guess he if anybody could tell the difference, it sure made a difference whatever he did. Olov

Hi Olov and all others!

Finally, downloaded the last reading of another motor into my program, so i could take a look at it.
This was a new motor tested, not the other ones mentioned earlier.The test was run unloaded, meaning the motor was not coupled with the pump.

And guess what... the readings where almost replica of the other motor.
The peaks came exactly at the same places.
1X first with 3 or 4 harmonics, and a dominant peak close to 3X.
This means that we have 3 motors with these same symptoms. Only one of them where realtive high, with the other ones with just a little smaller peaks?!
One thing is almost for certain;The dominant peak is created by the motor.
So this tells me what...?
I havent figured it out yet. But the dominant peak is non synchronous, and that should rule out several things like poles, cooling fans, unbalance...
Again, the motor runs fine for 5-10 minutes, but then suddenly started to create a dominant 3x. This should normally also rule out a resonance problem.
I feel like we are closing in on something.

Hi Svein,

Looking at the spectra, the Motor/s may be experiencing mild speed oscillation perhaps due to improper magnetic centre setting. Its odd though you say all 3 Motor dispaly similar characteristics. I've seen 3X being affected by Motor Cooling fan condition/resonance. On the Motor with high 3X amplitude check Fan looseness, cracks,etc.

Regards....Rajan

Hi Rajan.

If the the speed oscillates, wouldn't you see a difference in the 1x peak.I mean , shouldn't it shift upwards or downwards.
Fan looseness was one of my initial toughts.I figured that if the fan was loose, it might shift back and forth in the axial direction.
But i can't see how it produces this certain frequence on all motors.(Just above 3x)

What we are seeing on the profile you posted and you referred to as modulation/beat, seem to be it. Almost every peak on the plot has another one close to it.
I agree with you that all 3 Motors having the same issue is an odd ball but then you did say these were new Motors and if they are from the same manufacturer/batch it could indicate an assembly oversight/boo-boo.
I've seen/learnt crazy things in my past tenures that has taught me not to discount any possibilities!

Cheers...Rajan

Well i guess it should be easy to check with a tachometer if the speed is changing.


I'll take that on with me.Thx.

Svein
Just happened to notice on youranswer about the equipment being to far away to be considered. Be very careful on this issue as there is noted caes of things being farther away than that and still cause catasrophic failure in equipment.Art crawford has a video tape with a good example of this and I was surprised by this as welll but he has proved this to be true so do not rule out anything until it is proven to not be the cause.Resonance is a strange bird and a small piece of equipment can cause issues on equipment that is many times it's own size.

I totally agree lee.But this plant is not up and running yet, so we are currently only testing equipment one by one.
So machines interfering with eachother...not likely at all.
Resonance is another matter. This is complex, and as you say, many things can be sources of resonance. We are trying to take bump tests where there are issues that can be explained by resonance.
We had 5 2800kw motors running submerged pumps.
Because of access, there where mounted cratings and scaffolding on top and on the side of the motor. These were in many cases not isolated between the joints, meaning that the scaffolding where put dircectly on the motor housing.
Man you should have seen those readings...puuuhh.
Case still unsolved, as i told i would not take any more readings until ALL scaffolding and cratings where removed.
Readings had ALOT of noise looking like haystacks between 100 and 200 hz.
I did a bump test of the scaffolding, and they all had resonance between 100 and 200 hz.
So my guess is that the scaffolding where indeed interfering in the readings.

Anyhow...back to the motor case i have now.
Look at attachment. And the last motor, i found this peak at 617 hz, with sidebands.
running speed is around 3000 rpm.
It looks like the spacing is 1,4 on each side, but i am not able to conlude on what creates this spacing, or the peak for that matter.

22-pa_2.doc (97 Kb, 26 downloads)

Ok. Couldn't post 2 attachments, so here is the other one.

22-pa.doc (94 Kb, 19 downloads)

I see BPFO at ~3.1x rpm very frequently on rebuilt motors. Usually is not a problem unless it gets worse... sometimes it does, and sometimes it just stays the same.

Nice to now rusty. Im standing as the stupid guy here, because this might be 1 out of 10 readings i have done in total. I see this 3,1x dominant on 3 of them.
I have no clue whether it is normal or not. Neither if is normal that this peak is dominant.

That's why i posted here in the first place
Im trying to build up some knowledge on this, but as they say;Knowledge comes with experience, and you cant read yourself an experiance in this.
So i hope you are not sitting there thinking what a jerk, should know this. But instead tell me so
I figured too, because we have 3 of the same, it might be normal. If we find 4-5 with the same, well either the vendor has a huge problem with their motors, there have been some serious installation faults or...its normal

In that case also found on different motors peaks at appr. 620 hz on one and 1300 on the other, containing sidebands with 1,4 hz spacing.
If anyone has a wise clue to give me here, i will be glad.
Only thing i can find in this spacing is the pole pass freq. But then, what is the peak?

Can anyone tell me if a sideband can only be on one side of the primary peak?
I saw that David earlier on mentioned it in a post above.
Is this a possibility and in that case, what causes it to only be on one side?

Svein,
I have seen it taught that if you have sidebands mainly on the right, it suggests eccentricity. If you have sidebands mainly on the left, it suggests looseness. I don't have any proof to post to say that it is true or false. My experience has taught me that the tallest peak isn't always the primary peak. In most of the things I see that are related to electricity, the tallest peak is a sideband to the right of the primary peak. Are you sure that the small peaks to the left of the tall peaks aren't harmonics of line frequency and the tall peaks aren't sidebands?

David Eason

Hi Svein,

Having read your posting/reply to Lee above, I'm a little concern with what your situation is at site.
When you raised your concern about the 3X Motor vibration, you mentioned that this is a brand new Motor. Do you have this Motor, Blower & Piping all tied-down and verified, all is in order? When you collected the data was the system/blower loaded?
The reason I'm asking these questions is, I've been involved in Plant startup and if you take data with the system being not loaded or tied down as it should be and get excited over vibration frequencies/amplitudes that you see; you may find things are different when collecting data under loaded conditions; during acceptance tests. Just as you mentioned above with the case of scaffolding on the Vertical Pump/Motor.
In my opinion, two things would raise a flag when looking at vibration conditions/ spectra ...i) Ascending Trend & ii) Sudden appearance of frequencies with high amplitudes.
As you may have already realized, proper equipment installation, foundation, skid, etc. will determine how well a machine will function during steady state operation.
So do enlighten us with what the scenario is at your facility, particularly on the Motor with 3X vibration.
Thanks

Rajan

Rajsha, not certain what you mean but i will try;
This is a plant which is still in the buildup and commisioning phase. We do at the moment vibration measurements on the single solo run tests and loaded tests.
Meaning, uncoupled and coupled.
As this is the commisioning tests, normally the euipment should be ready for startup. Give and take som problems of course.
Prior to these tests, the equipment has only been tested at the vendors factory.(FAT tests)
Also prior to these tests, all alignment,tie down and so on is done.
Where there is a motor running a pump, the pump will be running in the correct liquid and set up to run with the plant specifications.

About the 5 big motors, as said, there where scaffolding set up all around them.
This was done because of access to the motor.(Its BIG)
However,because of time and plans, they never did remove these scaffoldings, or tried to do it otherwise.So all 5 where run with scaffolding on top.
But that is a special case i think...
Vendors and all that running around...

To be short about it;
I assume when i come to the motor, that alignment has been done, the foundation bolts have been correctly torqued and that all other mechanical work prior to running it has been done.
Of course, i did not do any of them above, so i cant confirm it.But thats a part of the commisioning phase and also what the guys in commisioning should have checked to be done.
Heck...if not, i could be running wild in the plant chasing motors with strange readings.

But it has to be said that most of the equipment here, has stood still for 1-2 years with uncertain preservation routines, so i guess there could be some equipment with bad bearings and so on.I have heard people seeing rusty water coming down the axel from the bearing house on some motors...that can't be good.

But we are in the situation that we do not know how these machines will behave at this plant with this foundation and this process in general.We will have to find out by i.e. doing vibration measurements.
We do not know if there is rust in bearings on those that has stood out for too long.
And we do not know if the guys assembling this plant has done a good job.
All we have to do is assume...
Because if we don't, we have alot of equipment we need to pull apart
All of it is brand new equipment, and we should assume that they are all working as it should. However, there may be faulty installations and wrong preservation routines, which then could lead to other problems. It's up to us to find them before they are handed over for operation.

And to answer the 2 flags you mentioned;¨
1.)We have no trends.We are starting them now
2.)Whats a sudden appearance, when you are running the motor for the first time on the plant

Did you get any clever, RajSha.
This is all i can say, without going way beyond my employee regulations

So we have some hills to climb, and we lack the experience.
That is my situation.
But i love the challenge!

This message has been edited. Last edited by: Svein Hansen,

Hi Svein,

Good info, I guessed as much but wanted confirmation,from you. Was not trying to be a smart Alec, one has to have the right background info before trying to diagnose machine condition, using vibration signatures. One can be easily misled by just looking at spectra from a remote location and not understanding machine installed/operating conditions.
And you are quite right to love to be challenged because this phase will teach one the lessons that would be not available when the Plant is operating on-stream.
Now back to your 3X dominant frequency..did you get a chance to see if at all there is any speed oscillation?

Hi again !
Used a tachometer to track to speed of it, but only 1-2 rpm variations.
So i guess its not it.
Did a rerun of the last motor.And i could see clearly that the 3,1X was going up and down.
Looking at the cooling fan, i could see that the fans where not evenly spaced, but more like in groups. I will have to recheck, but is this normal.

Hi guys!

Still trying to work out a solution here.
But did find a interesting thing i overlooked earlier on.
Set up sidebands for the 3,1x peak on the first motor.
I have attached the image so you can see.
But there seems to be both sidebands and harmonics of the 3,1x, and the sideband spacing is...running speed.
I can seeat least 2 sets of sidebands, with possibly 3.Judge yourself.
If there is anything here, it is a bpfo with 1x sidebands and harmonics.
BUT...bpfo should have sidebands of the cage freq, shouldn't it??

54-kf.doc (85 Kb, 18 downloads)

For those of you still interested in this topic.
Here is an update:

Check all the points measured both axial and vertical DE and NDE.
Tried to set up sidebands with 1X spacing, and i got a huge amount of peaks matching this.
Im still not certain of what this means,except for that if this is actual sidebands,1x is creating the spacing.
Take a look and see what you mean.
BTW so there is no confusion.
The 1X in the first picture is just setup to show the harmonic of the dominant peak.

54-KF-103.doc (244 Kb, 18 downloads)