1500 HP Internal Cooling Fan Failure

[dArsonval]

Photos attached show what’s left of an Internal Cooling Fan on a 1500 HP gas compressor motor recently placed in service.
The relatively new Baldor/Reliance brand motor may have less than 500 hours on it.
Oil appeared very clean, and the sleeve bearings were not wiped out.
Internal fins connecting the “keyed” fan shaft hub to the outer fan blade(s) were completely ripped away
causing the fan to bang around inside the winding portion of the motor, hence a winding failure as well.
At this writing… I reluctantly admit I left the shop without looking at whether the motor is a two, or four
pole apparatus. (I’m thinking it’s a 4 pole unit but it may be a 2)
What kind of mechanical stress would cause such a failure? The light weight aluminum fan would seem to be
merely going for a ride affixed to the shaft. Yet it failed in the manor shown in the photos.
The end user appears to be pointing at the manufacturer as to the cause of fan failure.
Any additional ideas, opinions, questions would be helpful.

John

http://files.engineering.com/getfil...8672-4d53-908d-b69e93cc53e1&file=IMG_4880.JPG

http://files.engineering.com/getfil...ad41-4e16-a162-0b0572a95b1e&file=IMG_4881.JPG

http://files.engineering.com/getfil...df92-430a-bc89-7d910c832537&file=IMG_4882.JPG

http://files.engineering.com/getfil...783e-4072-b50a-92d0ae9af4ca&file=IMG_4883.JPG

http://files.engineering.com/getfil...0670-4d2a-92a2-5b3d0f6ba351&file=IMG_4884.JPG

 

[desertfox]

Have a look down page 12 of this link

http://www.greenheck.com/media/pdf/catalogs/VaneAxial_Application_Perf_Supplement.pdf

 

[electricpete]

I assume the reported hunting is while coupled.

For Mike's benefit - horizontal sleeve bearing motors have endplay as specified by NEMA. Typically 1/2" for motors in this size range. Any thrust bumpers are not designed to continuously carry thrust.

The coupling may be flexible or limited endfloat and should limit travel quite a bit less - typically 1/8".

When coupling, mechanical centering should be considered to avoid potential contact during operation. Traditional wisdom is also that a motor coupled off of magnetic center will cause hunting. I have never witnessed that personally. Ideally mechanical and magnetic center coincide and we can meet both.

When coupled, the position is established by the driven equipment thrust bearing which has very little endplay.

We have one family of sleeve bearing motors driving centrifugal pumps through shim pack coupling that experiences motor axial shaft hunting (approx 0.1" movement at approx 1hz rate) during certain flow conditions of the pump. Small movement within the pump bearing clearance can translate to larger movements of the motor shaft due to low axial stiffness of the coupling. This is particularly true if the driven equipment generates axial movement at a low or broadband frequency which can exite a natural frequency of the SDOF system comprised of axial coupling spring plus motor rotor mass.

Just trying to explore your thought process - how could axial hunting be related to reported problem:
1 - excess movement could allow contact of rotating to stationary parts.
2 - unusual contact between rotating/stationary parts or damaged fan could induce hunting


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(2B)+(2B)' ?

 

[waross]

A thought to share Pete;
If the hunting is caused by the fan, then the fan would be alternately pushing and pulling on the shaft. If there are fan stall issues already due to bad design, the fan may not be designed to withstand the stresses caused by hunting.
If the fan is stalling, it may be damaging itself by causing the hunting.

dArsonval: If I understood the link posted by DesertFox, it may be possible to check for fan stalling by restricting the air discharge openings on the motor. A restriction in the air discharge path will reduce the flow volume and may move the fan operating point down from the stall part of the curve. While the motor is hunting, plug the air discharge ports and see if the hunting ceases. Don't get any rags caught in the shaft while doing this.

Bill
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"Why not the best?"
Jimmy Carter