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OLi

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Reply with quote  #1 

A rolling steel mill loaned out a rotating converter generators set to another mill 30 years ago after 20 years use. It so now back after refurb but the landscape changed. It is a setup of 2 motors running 2 gen and a 15+T flywheel all on the same shaft, 750 RPM a couple of MW in total.

Anyway they "forgot" to balance the gen's after refurb despite rewind and new collectors... So guess what my work was supposed to be?
Well they found that something changed so the gen stators were a bit high and bolt bound so they got uneven air gap in all directions so they didn't dare to start, maybe they grown a bit in 30 years, a wasted 4+4 hour drive anyway.
So they put the old ones back again to start the mill as the guys were waiting to run the mill.

If they had dared to start I would have had some vibration indicating air gap problems I guess as it was maybe 1+ mm of error out of 3-4 mm gap. Would that really been a problem in the short term? Like until they were able to fix that "adjustment"? I think it was a good decision to swap back if the old generators could run for some time and I don't know the status of those.
Electrical guys were afraid that they could not setup collector adjustment so the magnetizing would be proper but I doubt that not knowing that much about it. What do you think, would it be possible to run it some months w/o destroying it?


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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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Walt Strong

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Reply with quote  #2 
Olov,

As an old mechanical guy, that air gap would not bother me for doing a startup with an old machine design and running 750 rpm. Was the original air gap any better, or simply not measured before the rework? An old machine requires thinking like an old guy/gal. Can they bump-start so as not to reach full speed while you measure vibrations and assess unbalance? You know the story: pay me now or pay me MORE later!!

Walt
OLi

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Posts: 1,915
Reply with quote  #3 
They don't know the rotor weight anymore so even less about the latest operation or installation as it was at a another site. Yes it ramps up and you can stop at any speed and it will roll out so I tried to make a test run but they played safe to get it started. OEM gave them a % number of the air gap error to be accepted and it was by eye evaluation 2-3 times larger. The other set of generators are having a larger diameter and a larger air gap so that is a trouble to compare. So we will likely never know. They have no vibration measurement or used it on site so it can be a minor problem to inform on the possibilities in short time in a stressed case.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
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