stator coils being loose in the slots 2

[elecfrance]

Hello
Recently a motor1 1600 kW 1500 tr/min was examined because of a suspect sound : the stator coils were losen.(that's what my collegue said). It was replaced by a new one motor2.

I have to look another 1600kW 1500 tr/min motor3 (exactely the same year of installation than motor1) which may have stator coils being loose in the slots : a sound is suspect too on this motor.
I'm not on the site but will go in a few days.
Must I verify vibrations? 100 Hz? 1*RPM?
Can someone notify a vibration collector (3000 euros or dollars) with FFT good resolution?

Thanks for your help
pierre

 

[elecfrance]

i agree with electripete, i hope that the first motor still exist or photos...
i think it's endwinding blocking material too

 

[testtech]

Highspeed and electricpete:

Concerning the software--It sells for $1,000, according to the website. I use an older software version. I use it generally when I am on a job but do not have vibration test equipment with me. Periodically, I will be approached by someone saying that a machine is making a strange noise. I simply set the computer next to the machine and look at the the sound spectrum. Also, because it is so simple to record real time data to disk and then do post-processing, it is useful for analyzing start-up sounds from machines. I generally use it with the built in PC microphone (believe it or not). I have also used it with a B&K microphone with a preamplifier. It is all uncalibrated data. I am simply looking for frequency patterns to reveal a sound source.

I have not used the software with an accelerometer. It would work, of course, but I have dedicated spectrum analyzers that have the added benefit of actually being calibrated.

Regarding my comment about finding bearings by using only the PC microphone and the software--that did not imply that this case had anything to do with bearings. However, with VPI coils, it seems like other sources of the sound need to be considered.

It certainly begs the question, why someone has concluded that this is an electrical sound. We have not discussed the types of bearings used here. If anti-friction bearings are used and their fault frequency harmonics are close to electrical field frequency harmonics, they can certainly sound like an electrical fault. If journal bearings are present, then we need not be concerned that they are the source of the sound.

How about the tried and true test to distinguish between electrical and mechanical vibration (or noise). If the noise is electrical it will end the instant the motor is de-energized. If it is mechanical, the noise will continue during coastdown once power is removed.

 

[edison123]

electricpete & elecfrance,

With global impregnation, the entire core+winding assembly is impregnated. So, movement of end winding or its support blocks is moot.

 

[electricpete]

Certainly vpi makes it easier to secure the end turns. But I have heard of movement in endwinding of vpi machines. It was common in early designs of Westinghouse reactor coolant pump motors (vpi like all other W motors). They fixed it with some kind of improvement to their method of tieing and blocking.

 

[Highspeed]

Elecfrance,
I am using the MTM/1800 (1000 mV/g)serie with an home made amplifier (Instrumentation amplifier with adjustable gains)
Our application beeing in the µm/s range.
Calibration :
We have a "calibration motor" with a well known unbalanced level that is used for calibration( in fact it is a fully balanced motor with a calibrated weight)
The software that we use is an "home made" labview based application.
Bonne chance !