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electricpete

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Reply with quote  #31 

Hi Jim.  I agree, we are looking at it the same way about the 2*LF.

Barry - what is RGFA? 

Barry

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Reply with quote  #32 
Should have been RCFA. Sorry for the confusion
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Curran919

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Reply with quote  #33 
Quote:
Originally Posted by Barry
I saw a lot more problems created or extended with the RCFA and the answer was always “we must have had bad data”. The leader always charted data until he got what he wanted.


Agreed, RCFA is almost always a waste of time, especially if a solution can be found another way. Often times, root causes once the problem is solved is just there to fulfill the interest of the analyst or engineer. That often has a bad effect on the project.

Of course, when it comes to the forum, this is exactly the sort of stuff we should be talking about, IMHO. It lets me quench my analyst thirst without hampering a project.
Curran919

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Reply with quote  #34 
Quote:
Originally Posted by electricpete

 

The motor is NEMA frame 449TZ.  This suggests stanrdard horizontal mounting. The Z indicates custom shaft dimensions (often to accomodate direct mounting of a fan to the motor shaft). Y would be used to indicate custom mounting.   

The photo shows a bird's eye view looking down at the top of the horizontal motor (you can see the shaft extension at the top of the photo).   It is a TEAO motor (totally enclosed air over). The long threaded rods shown at the location where endbells bolt to frame are a little bit odd. Some are removed.  It may be in a partially-disassembled / maintenance state. I have seen this style motor  used inside a vent duct (vane axial fan) and the endbell bolts are inserted through loops at the end of radial tie rods which help support or stabilize the motor within the duct.   However the article describes foot tightening with no mention of tie rods so it seems reasonable to assume simple horizontal mounting during the test. 



Thats what I had understood by looking up the frame, but I am convinced from the picture and objects in the background that the motor is actually foot-mounted vertically. Otherwise, why wouldn't he just rotate the images? I applaud him in his brevity in this article, but there is a lot of info he leaves out unfortunately.
RustyCas

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Reply with quote  #35 
Data is a funny thing sometimes. I was involved in two situations with the power company where the “data” was pointing to an “obvious” root cause. What the “team members” lacked however was firsthand observation of what was “physically” going on. You don’t get that sitting in the office. I was fortunate in that when I started to work my brother was an operations supervisor and gave me the wise advise of “spend a lot of time in the control room, especially during start-ups and trips.” I would camp out in the control room during start-ups and anytime I heard a turbine trip offline I would make a beeline to the control room. That’s how I learned that instrumentation “lies” - a lot, in ways big and small.

Another thing I learned from another old timer was to take a morning walk through the plant and talk to anyone that appeared to be fighting a problem, volunteer to help by “looking into” stuff they didn’t have time to or which wasn’t their job.

You can - and we do - see a lot of things “the data” misses, or misrepresents. Don’t dismiss your firsthand observations simply because what you are seeing “doesn’t make sense.”

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electricpete

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Reply with quote  #36 
Quote:
Thats what I had understood by looking up the frame, but I am convinced from the picture and objects in the background that the motor is actually foot-mounted vertically. Otherwise, why wouldn't he just rotate the images?

I'll email Jan K  and see if he wants to join the forum (he would be a great addition, especially for motors) or at least answer a few questions by email about the test setup. 

I'm also struggling to figure out how you would do this test on this particular motor (enclosed) since there is no access to measure the airgap without removing the endbell. 

  
MarkL

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Reply with quote  #37 
I know this is an old topic But came across this interesting video today.



Curran919

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Reply with quote  #38 
"The bolt is resonating on that foot"

That seems like a meaningless statement. That video has me even more convinced that this is a conflated diagnosis. How is this not just softfoot?
fburgos

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Reply with quote  #39 
That machine looks misaligned, alignment and softfoot check and re run test
Curran919

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Reply with quote  #40 
Quote:
Originally Posted by fburgos
That machine looks misaligned, alignment and softfoot check and re run test


I also saw the severe misalignment, but I think that is just distortion from the wide-angle lens. Unless the table is also really that bent.
electricpete

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Reply with quote  #41 
Quote:
I think that is just distortion from the wide-angle lens

I don't see any evidence of wide angle lens, including when the guy's arm comes into the picture and moves around in front of the camera (undistorted). 
Quote:
Unless the table is also really that bent.

I think you're right... the table is also bent. 
It looks like a small flimsy table clamped down on top of a large sturdy table using an adjustable C-clamp.
The C-clamp appears to be bending the small flimsy table in a manner that induces the misalignment. 
fburgos

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Reply with quote  #42 
look at the fft and the 2x, 3x, 4x,

a peak 2x is 0.2G also the 4x is 0.35G, if this is not misalignmet, what is?
Danny Harvey

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Reply with quote  #43 
I question the comparison of soft foot in a motor with 10 ga stamped steel feet to soft foot in a motor with 1" thick cast iron feet that gets additional structural integrity from the rest of the frame. 
electricpete

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Reply with quote  #44 

Quote:
if this is not misalignmet, what is?

Haha, yeah probably so.  In general harmonics would would suggest either misalignment or looseness, but given that we can see the misalignment with our eyes [eek],  misalignment seems like a pretty good bet to show up in the spectrum. 

And the frequency of the 1 g peak that he examines (at 4:27 in the video) is 91.3hz on a 30hz machine ?!?
Either that's a monster bearing defect, or his analyser isn't displaying frequency correctly, or the motor speed isn't really  30 hz (on a vfd, or slip due to friction loading) and this is really 3x. 
It doesn't seem to phase him on bit that the highest peak in his spectrum (see 3:54) is in the vicinity of 3x rather than 1x or 2*LF.

And why do you need software to help you do this check to begin with? 
It's good for a laugh, anyway. 

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