Winding Failure
Winding Failure
(OP)
Dear All
We have to repair two wind generators, we found many grease(old grease) in contact with the winding, We think the the amount of grease on the windings over years (for 4-5 operation ) cause this failures.The questions are : How the grease week the insulation? Have someone good paper about this problem?Thanks for the inputs
Best Regards
Carlos
We have to repair two wind generators, we found many grease(old grease) in contact with the winding, We think the the amount of grease on the windings over years (for 4-5 operation ) cause this failures.The questions are : How the grease week the insulation? Have someone good paper about this problem?Thanks for the inputs
Best Regards
Carlos





RE: Winding Failure
I don't know about other adverse effects. I would think vpi winding would be relatively immune to other than thermal effects.
What votlage is the machine?
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(2B)+(2B)' ?
RE: Winding Failure
What kind of repair activities are required? Which components failed?
Wolf
www.hydropower-consult.com
RE: Winding Failure
1 - thermal failure (due to disruption in cooling airflow)
2 - chemical failure (interaction of grease chemicals)
3 - mechanical failure (grease facilitates movement of windings in presence of other vibratory forces, by reducing usefeul restraining friction forces at locations of blocks and ties, and possibly in the slot... movement results in failure.)
I don't know of any paper. I found a very cursory mention of these items as discussed below.
Can you share any further details of the failures you have seen on these generators?
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(2B)+(2B)' ?
RE: Winding Failure
Pete good information, Attached you will find photos.
Regards
Carlos
RE: Winding Failure
RE: Winding Failure
RE: Winding Failure
Generator #1 looks like insulation failure due to grease. I would think that the failure most likely started phase-phase and then progressed to phase-ground in the slots. Keep in mind that there is another phase winding in the bottom of the slots that cannot be seen from the photos. The #1 generator will need new stator laminations plus a rewind.
RE: Winding Failure
1 - thermal failure (due to disruption in cooling airflow)
2 - chemical failure (interaction of grease chemicals)
3 - mechanical failure (grease facilitates movement of windings)
4 - electrical/conducting failure (grease forms conducting path between pre-existing "pin-hole" defects in magnet wire enamel insulation
This is based in part on the following:
I don't know to what extent grease can be conducting. I do know that some non-negligible current conduction occurs through extrremely thin films of grease in a bearings undergoing with electrohydrodynamic lubration in bearings.
With possibility for contaminants and decomposition products, I would suspect the conductivity of grease can vary.
Fwiw, I think the failures shown certainly could have begun as turn-to-turn faults. Turn to turn faults often result in significant amount of melted copper, and continue until they go phase-to-phase or phase-to-ground to finally cause a trip.
The windings look unfamiliar to me. Certainly not lap wound. I guess they are concentric wound? I didn't see anything resembling phase separator paper that I could pick up, although I'm not sure where to look. If no phase separator paper, then it certainly could begin directly as phase to phase fault because the phases are in intimate contact in the endwindings and see a higher voltage than the interturn voltages.
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(2B)+(2B)' ?
RE: Winding Failure
Although phase paper could be used on a concentric winding, is is not used here. Nice (lps) observation. This is why I suggest a phase-phase winding failure with the (not visible) winding that is in the bottom of the same slot.
This suggestion is because of the idea that any degradation of insulation will cause failure at the point of weakness. In this case, the highest voltage stress occurs phase-phase where the windings of different phases lay over top of (or under) each other in the three different layers of coil end turns.
I will add a suggestion for an alternate failure mode for #1 generator. If the failure is mostly confined to the one, top layer and is truly a turn-turn failure, then a voltage surge may be the cause. If this is the case, the failed coil group will be the lead pole group in the phase winding. Specifically, there will be a line lead attached to this beginning group. If this is the case, then a voltage surge is a possible cause for #1.
I stick with the idea that #2 is an overload and a separate type of failure than #1. The 'burned from the inside out' look cause by the various holes in the winding are the key indicators for me.
RE: Winding Failure
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(2B)+(2B)' ?
RE: Winding Failure
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(2B)+(2B)' ?
RE: Winding Failure
The grease is an entirely different issue.
Fix it, and get the thing running again!
Always enjoying this forum,
John
RE: Winding Failure
Thanks again for the answers, thsi failures are happening in wind generators, our investigations point to a winding failure due to grease degradation.
We have two scenarios: One with a earth fault ( "Hence, many turn-to-turn and ground failures are actuallycaused by winding movement over time which breaks downthe insulation system. This can occur in the slot, end turnsor connections. Winding movement can be controlled or lessened by theuse of coil bracing.....[note there is no mention specifically of grease, but imo common sense dictates that a lubricant can contribute to undesired movement, along with loose blocking, loose coils, excess forces etc "]
and two Insulation breakdown ("EASA Motor Failure Root Cause AnalysisChapter 3 – Winding Failures. Contamination can come from within the motor. Overgreasing has led to contamination of the windings which in turn created thermal problems. [photo included")]
The winding is not in 3 layers, if you take a look of photo you can see one winding on other, so its a two speed two windings.
Regards
Carlos