9MW motor that failed electically, can these patterns be from vibrations from bad coupling as owner suggest? Olov

9MW_motor_011 (474 Kb, 121 downloads) pic2

Next picture.

9MW_motor_010 (515 Kb, 94 downloads) pic1

The main thing we see in the pictures is sleeve bearing with circumferential streaks, right? Is there anything else we're supposed to see?

What type coupling was it and what was found wrong with the coupling? Any vibration or oil analysis or bearing temperature or other history we should know about? What does this motor drive?

If the problem is misalignment, the wear pattern should be distinctive for example more wear on one set of diagonal corners of the bearing than the other. What you're showing looks to me like particle contaminants got dragged thru the bearing (just a guess).

I do see some angular striations but there are many uniform striations so that I assume they have something to do with a process used to finish the babbit. I wouldn't expect multiple stripes from misalignment... just one stripe. Again, just guesses.

This message has been edited. Last edited by: electricpete,

Epete,
Motor is at the repairshop now, and yes the discussion is about the bearing surface. I will try to get some more details. Dirty oil also was a idea I had when I saw it. Olov

electrical discharge??

Is this a synchronous motor? Vertical or horizontal shaft?

Most likely horisontal.
I would expect more black marks from
electrical problems but since it failed
electrically it could be the case. I will
get back with more info when I get it. Olov

Olov,

The circumferential marks with babbit grooving are very visible as mentioned. I am more concerned with the diagonal light-dark lines. Never seen this before. Could they be from electrical dischage across the oil film like EDM in rolling element bearings?

Walt

Static discharge
I have seen this once on a 300 rpm synchronous Motor driving a recip. We used a cheap gauss meter that had a needle and would move plus or negative as you moved it around the bearing. The lines etched in the bearing matched the direction of the magnetic field. We also had the same dull finish with thousands of small pin hole marks that is seen on you bearing near the edges.

The bearing OD should have insulation plates and the housing hold down bolts should have insulated washers.

Olov,

If your question is also about a general effect vibration may have on electrical failure in a motor refer to:http://maintenanceforums.com/eve/forums/a/tpc/f/3751089011/m/9441054303

Looks like chatter marks from machining the babbit. Vertical boring machines like leaving thes marks when the tool preasure is light, has to do with gear meash on the table drive.

Lakeman - I don't know as much about the boring machine pattern as you do, but I also had the same opinion that
these were from machining process. (I was beginning to feel lonely in that opinion.)

I have a hard time imagining electrical discharge causing that very uniform pattern in a sleeve bearing where we expect the oil film thickness to vary around the bearing.

Attached is a portion of Kingsbury presentation on sleeve bearing failures.
(The full document is available here http://rapidshare.com/files/23128454/KingsburyFailures.ppt.html )

Slides 1 - 11 are electrical pitting... I don't see anything remotely resembling the diamond pattern.

Slides 12 and 13 are abrasion patterns for info... pretty obvious although the source of what got in there (foreign material as a cause or as a result of something else going on ) is always a question.

In any case, there doesn't appear anything in the bearing that is causing a big problem yet... we still don't know the big picture of what was the problem discussed with the coupling.

Sleeve1.ppt (2,494 Kb, 36 downloads)

Oli,
I've seen worse. I wouldn't be able to tell if there were electrical problems from the bearing, although I agree with the above comments that the diagonals look like machining marks. ( Does no one scrape bearings. This would have shown up on installation of the bearing if they had been scraped, however, this was the subject of an earlier thread.)
Regards,
Joe Mc Cormack

I have poured,machined and scraped thousands of babbit bearings in my life. I poured over 1 ton in a month once...another time. Chatter marks could be looked at as oil pockets if your mind was inclined to make excusses for bad work. Yes, some of us still scrape bearings. Others just change parts. I have seen elect. flutting on babbit, this does not look like it.

Some more info.

Motor drive 2 compressors via a gbx. Lufkin NF81.56C, compressors are Carrier 17DA86 and 17DA71. Eg. a large heatpump.
Bearing temp 60-66 DEG C.
Previous coupling used 48 rubber elements now swapped to metal lamell coupling.
Oil analysis is performed with nothing to report, system is filtered etc.

Supect is the fine diagonal lines, they was not there before when it was opened when swapping coupling.
Coupling design was swapped due to rubber elements got worn, stuck and created vibrations.
Marks are only on the lower half of the driveside bearing.

So one question is if this can have connection with the swapping of the coupling type.
On the other hand it may support the electrostatic theory as the new coupling gave a pathway for electrons as the previous rubber thingy didn´t. Olov

Well, it sure is tough for me to imagine that something happened during machine operation producing that nice pretty criss-cross pattern uniformly around the bearing. Also we are to believe that the non-uniform oil film thickness leads to a uniform electrical discharge pattern? One would think the discharge occurs at the point of minimum film thickness near the bottom of the bearing. And let's not forget the Kingsbury pictures... none of which looked anything like this. I guess those Kingsbury pictures were some different variety of EDM.

But if they say it wasn't there before, who am I to argue. I have been wrong many times before.

If this is EDM, it is more of a problem than just the coupling. You said it was the outboard (drive end) bearing. That bearing should always be insulated. The inboard bearing is sometimes insulated also.

Thank´s Pete,
I have two ideas.
1. Since the couplng before was rubber and isolating there may be electrons trickling by when swapping to a metal coupling, where do they come from? No idea, do large heatpump compressors or gbx generate static charge? Not that I know of?
2. Swapping from a relative axially "free" coupling type with the rubber inserts to in my view more fixed metal shim pack may give a axial not self adjusting offset for the rotor giving the famous mechanical axial oscillator syndrome, seen it ones in a device with a rewound motor but that was very impressive, this case may be more subtle and not noticed.
So question is, if you have a small axial movement going in to a fishbone gbx. What will the shaft movement be? I asked them to check if the pattern have the same angle as the fishbone gear just to know. They have monitoring so I asked them to look at the data but I am not sure there is a axial point around there.
It is the only thing I can see so far that may be locked and generate a so nicely pitched and accurate pattern. Olov