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Danny Harvey

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I looked at a newly rebuilt AC induction motor today and among other issues, I found a copper colored reflective powder coating areas around the motor vents.

Are there coatings used in the rewind process that would be considered normal or is this copper from the windings?
HuskerTim

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Reply with quote  #2 
Danny,

I'm guessing this is a open drip proof motor that you can see in to?

When a motor blows to ground it will spread copper BBs all over, but usually shot size and smaller.

What HP is this motor?
Danny Harvey

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Reply with quote  #3 
Tim,

Yes, it is a dpg motor which I think is GE lingo for ODP. It's 700 hp, 1770 rpm, 4000V. I'm told that it is on a VFD but it was running at 1669 rpm so unless it is, that's too much slip.

This was fine powder, no bb's. I'm not certain that it was copper but it was shiny like metal and copper colored. My guess would be that it was from some sort of rub rather than a short to ground explosion which is what I think you are describing.  Basically that's a pile of copper welding slag, isn't it?

There were what was probably pole pass frequency sidebands around 3 x running speed but not on the other harmonics.  They may be there with a log scale or in current analysis, though.

There are what appears to be grounding brushes attached to the outside of the drive end bearing housing. The guy didn't know for sure what they were. It has 110BC03 bearings on both ends.
HuskerTim

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Reply with quote  #4 
Danny,

Is this in the lower vents or the upper vents?  Or on the end bracket vents?  Some GE ODPs have all three!

do the brushes appear to be black carbon (soft) brushes or are they more grey/yellow brass in color(harder)?

Somebody at the motor shop could have gotten carried away with the Big Red/Red Glyptal which most shops LOVE to spray all over the iron  and rotor surfaces... but this would look like overspray not dust...

Do you happen to know if any machine work was completed during the rewind?  Sleeving a damaged exit surface with brass is not uncommon and if rubbed could appear like copper without picking up the dust and giving it a good look...
Danny Harvey

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Reply with quote  #5 
Tim,

This is on the upper and lower vents on both sides but not on the end vents.  That tells me that it's coming from inside the enclosure.

The brushes appear to be carbon.

There was machine work done and it may not have been done correctly.  I'm pretty sure that the motor shop told the client that they had a hard time getting the bearings positioned axially I'm not sure why they would tell the client that if it hadn't been corrected, though.

This is not brass colored, it's copper colored. It almost looks like a kind of pipe dope I used to use-if it were a powder instead of a liquid.
Ron Brook

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Reply with quote  #6 
Danny,
Copper bars are used in the rotor and the end rings as well. Bad rub would cause this. Let us know when you get her apart.
Danny Harvey

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Reply with quote  #7 
Yeah. I don't think the shop is going to be shocked to see this one come back.  I'm not sure why they would have let it go out in the first place.

It has some kind of vibration switch that shut it down a couple of times before I was called in. I guess it was right that time.
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