I guess this is more of a lesson learned... However, I thought I would share.

SUBJ: 2pole, 2000HP , WP2, sleeve brg. job

We sent this motor to our local repair shop to be balanced due to its poor performance in the field. (Higher 1x's than what we'd like to see) Well, the repair shop received the motor went through mechanical fits and electrical test, wash and dry rotor and stator then balance(The basic recondition mode). When it came time to test run the motor for shipment the motor would not pass the acceptable vibration limits and also exhibits a noise that the only way I can describe here is "rattled the air-vent hood assembly". Vibration data pointed to the rotor still being "Out-of-balance"! Then I was called to come watch the motor get dis-assembled and verify that the balance in the spin-stand was "OK"...well... it was'nt. This rotor had higher amplitudes than what was about to be printed on the recondition report. It moved approx. 1/2 a mil. out of specs. The next step was to re-balance and move back to acceptable tolorances...we did so with great success. HOWEVER!!!

Now comes the intresting stuff...

I got to looking at the rotor a little closer and noticed the rotor bars didnt appear to be full in the iron slots and the swedging didnt appear to be sufficient for this rotor. So, we began to hit the rotor bars (listening, feeling for change in tone or movement) and there was a very noticeable change in both. After doing so we ran the rotor back up to balance speed in the spin-stand and found phase and amplitudes to just go crazy! To bring this story to close and shorten it up a bit... After "re-swedging" the rotor and performing another balance job. This motor runs really nice on the shop floor and meets acceptable tolorance for shipment.

In short of it all... This cage "APPEARED" to be moving in the Iron of the rotor...

There's alot more to this story...but Im sleepy and going to bed!!!

P.S. I still like this new message board format... and still being patient on the speed issue.

Wow -- I have seen a lot of odd stuff from two pole motors, but this is a first. If I understand, you think the cage/rotor bar assembly is/was moving relative to the lamination stack......

Could you provide details of the rotor construction --- welded, cast, copper, aluminum, etc......???

Darned interesting...and thanks for the post....interesting case.

The rotor is a Westinghouse rotor... Copper Bars welded to the endrings... and in this particular frame and "year make" at the endrings and where the bars mate, had banding material around them. Made me think at first the rotor had seen damage before. But, I learned that W.H. did this to force air flow back to the center of the rotor so that it didnt just escape to the outter rings and be useless air-flow. Also... for the longest time I thought that the air-ducts were always supposed to line-up between the rotor and stator for proper cooling. Now, I'm learning that in some designs the air ducts are offset to allow air to travel down the iron of both rotor and stator for better cooling. (More surface area I guess) Anyway, I had the repair shop cut this banding material off so we could see if there where any cracks or bars moving where they meet the end-rings and nothing was found.

There was only two areas that movement could have taken place in my mind. That was the Lamination Core to the shaft or the copper bar cage to the lamination. I failed to tell you also... I had them dip and bake this rotor two times not for insulation purposes but more so to use the varnish as a filler!

I will try and post an image of this rotor here soon.

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I posted my rotor pics in an album... but it's in a new post...Im unsure of how to post the images to the discussion I started. Any help? I see the icon asking for "url" but unsure of how to use this.

Sorry I can't help you with posting images... still trying to figure it out.

One comment about vent ducts on rotor and stator - a big reason for not aligning them is to minimize the rotor axial magnetic centering force. If rotor and stator vent ducts were spaced the same as each other the centering force would be much bigger than in actual motors with staggered vent ducts.

You are definitely right about the two possible areas for movement. edison on the old board posted an example of rotor core movement on the shaft. Also I understand movement of bars within the rotor slots is pretty common due to variety of factors including differential expansion between copper and iron. Not only does the copper get hotter but it has higher coefficient of thermal expansion.

We have had a motor 1970's vintage. OEM S****** rhymes with demons. OEM tells us bad bar swedging design. It started vibrating at 1x beyond our ability to troubleshoot. We called in OEM who unsuccessfully tried to field balance it. He pulled the whole motor back to his shop for extensive testing and told us the bars were moving in the slots and this particular style of motor was not suitable for re-swedging. With a new rotor we had no problems. The weird thing is the vibration had been extremely temperature dependent. My theory is through repeated cycles the bars had ratcheted unevenly within the rotor slots and grabbed at a new position. Now when rotor heats up there is not uniform tension on all bars and rotor bends

By the way, thanks for sharing your experience Scott.

That's a tough one to troubleshoot.

Pete,

Thanks for your post and good info. I've seen only one other motor with bar movement like this but, seems to me it had "tappered-wedges" to lock the bars in place. The wedges were backing out...


I made reference to dipping this rotor two times earlier in this post... Do you see any adverse effects of this...or maybe problems we might run into for trying to help prevent bar movement?

Also... Could you post your webpage? I had it from the old board and cant seem to locate it now. Thanks!

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