2400 cpm on motor...still

I have no more understanding today than I did in 2002 of WTF is going on with 2400cpm tied to motor “phasing problems” on the infamous chart. I gather from one reference it's supposed to be lose connection. I've never seen that frequency and can't really come up with a reason it would exist (*). But that doesn't mean it's not true... presumably someone saw something at some time that led to that chart entry.

Coincidentally, there is another guy troubleshooting 2400cpm on a motor right now as described here:
http://www.eng-tips.com/viewthread.cfm?qid=374242

If either one of you guys figure it out, post back and it might help the other one.

* Edit - The words "phasing problem" leads me to wonder about reversal of the line/neutral connections on one phase of a wye- connected 6-lead motor. That results in oddball behavior, I'd have to think some more about possible frequencies.

Pete,

Happy to say, mine is not so complex and on a much smaller scale.

I'll let you know if I find anything and I'll let Robbie know if I learn anything that might be of help to him. It sounds like he's really under the gun.

Good stab at the clutch. I was going to post the same if I didn't see it. I have rebuilt many and 12 didn't sound like enough for one of that size but it was still a pretty good guess for an electrical guy

Can you post HVA data at all bearing locations using multiple point plot, display an fmax of 24000cpm. I believe the motor to be 1800 and fan speed is 757, correct?
The base of the 2400cpm peak appears to indicate a resonance. Can you also provide a high resolution spectrum of M2A.
Do not discount the fact of external excitation. Had a 250HP 3600rpm multistage pump vibrate over .5 ips @ 1200 cpm, the culprit was loose/worn indexed fits on mating flanges and a 1200 rpm vacuum pump about 100 feet away, transmitting thru piping.
It is quite apparent there is a large rise in the axial direction, have you done any bump tests on the motor? Can you provide a pictures from several angles of the actual machine installation?
Dave

I am Robbie and have been searching for the mystery 2400 CPM on a 5,500KW 200 RPM Synchronous motor
I would appreciate any feed back

I'm returning to the site either Friday or early next week.

I'll get the extra data as requested but unless this motor does something other than vibrate at 2400 cpm, I'm afraid that nothing will happen.

Robbie,

I'll let you know if I learn anything new but we are talking about very different scenarios.

My motor is a plain-jane AC induction, 4-pole, NEMA B motor of about 100-150 hp operated on 480/60/3.

Dave,

Yes, you are correct on the speeds.

I don't discount external sources but I don't recall being able to detect this in the duct work. I'll check again.

They may have an IR camera on site. If they do, I'll get them to take a look.