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Stator leak root cause analysis

Stator leak root cause analysis

Stator leak root cause analysis

(OP)
Hello,

I am trying figure out the root cause of ATF fluid leaking into the stator rotor gap leading to horsepower loss and eventually motor failure.  The ATF is used to cool the motors by flowing through the windings and pulling heat out.  ATF is pumped through the gearbox and into the motor housing under pressure forcing it through the windings and out the other side of the motor.
 
The motor is made up of stator stack of laminations.  Attached to both ends are two powdercoated stainless steel plenums.  These plenums are bonded to the stator stack.  An encapsulate material is used on both sides of the stator to fill in gaps between the windings and around the plenum to keep ATF from leaking to the plenum/stator bond line and to keep ATF from reaching the stator laminations.

Over time ATF gets through/around this encapsulate material and under pressure leaks into the stator through the laminations and also through the plenum/stator bond line.

Upon physical inspection of the motors the plenum on the gearbox side is almost always detached from the stator.  It shows signs redish black tint material attached to the powdercoat.  Also often the powdercoat closest to the windings is gone and just the stainless is left.  Further up the plenum away from the stator powder coat is cracking and pulling away from the stainless.

With the evidence seen heat seems to be the main root cause of the leaks.  Sources of heat include electrical current through the windings and the rotor spinning in the stator.  I have also been told that eddy current/magnetic flux could be a source of heat.  (Don't understand eddy current or flux portion well as I do not have an electrical background)  Once the powdercoat fails on the plenum ATF can be pushed between the powdercoat and steel and behind the encapsulate material which is bonded to the powdercoat.

I was wondering if anyone has seen anything similar to what I have descibed or has any other ideas as to what could be causing increased heat.  As designed flow through windings should be suffencient.  Could eddy currents be a source of heat on the stainless steel plenums causing thermal expansion and cracking the powdercoat? Any help or additional avenues I could go down would be greatly appreciated.

Additional info:  250 HP 3 phase electric motor.  

Note:  Motor in photo missing plenum

RE: Stator leak root cause analysis

ATF = ?

Alcohol, Tobacco, & Fire Arms?

RE: Stator leak root cause analysis

(OP)
ATF = Automatic transmission fluid

RE: Stator leak root cause analysis

powder coating where cycles of heating and cooling is involved seems to be a bad idea to me. Also, you need insulation materials that are tested and found suitable for atf.

Muthu
www.edison.co.in

RE: Stator leak root cause analysis

(OP)
3M Scotchcast 5555 powder coat is being used.  I believe it is rated for use with oils.  However I do not know how it reacts with heating and cooling cycles and the thermal expansion of the stainless steel it is bonded too.  From others experiences do you find that powdercoats are usually not elastic enough to flex with the heating and cooling of the metal it is bonded to?

RE: Stator leak root cause analysis

As you said, the coated material is either gone or is separated from the bonded surface. So that might say something about the heating-cooling cycle.

What kinda winding failures are you seeing ? From your pics (very good btw), the winding appears to be healthy.

 

Muthu
www.edison.co.in

RE: Stator leak root cause analysis

(OP)
We haven't been seeing any winding issues.  They seem to be holding up.  They don't seem to be shorting either.  Most of the issues I believe are being caused by overheating of the plenum.  Once the powdercoat fails I believe the cooling fluid is getting around the encapsulate between the powdercoat and the stainless.  I believe due to thermal expansion of the stainless the powdercoat is being compromised.  Knowing that, now I am trying to find the root cause of this heat.  Sources I can think of are insufficient winding cooling or friction from rotor.  I am not seeing signs of wear or rubbing on the stator or rotor so I don't think it is friction related.  I was recommended to look into eddy current heating but I have a limited knowledge in that background.

Could eddy currents be causing increased heat on the plenum?

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