Unusual 60 Hz Vibration on Motor. Let's try again... 1

[CRS1]

The highest peak observed on a large 6-pole motor running a direct drive axial fan in cleanroom service is .122 at exactly 3600 cpm/60 Hz. The motor rotational rate is 1195 rpm. The data was collected when the motor was being driven by a VFD, operating at full speed, (60 Hz.) When the motor is operated directly from line voltage (with the VFD in bypass), the 60 Hz peak drops to .001 ips. and there are no other changes in the spectrum. The motor picks up a couple of rpm in bypass.

The carrier frequency was varied between 2 kHz and 6 kHz with no appreciable effect, however an "auto-tune" procedure was performed by a factory rep. and a number or loose connections were tightened. This reduced the level of the 60 Hz peak to .06 ips, but it is still present. Any suggestions about what could be causing the problem or further testing would be greatly appreciated. I apologize for the confusion and misinformation in my previous post.

Regards,
Tim Wechsler

 

[electricpete]

Just a guess with limited knowledge of vfd’s:

I would say likely you have a problem (for example) in one of your six diodes in your full wave rectifier. That would give a dip in your dc once every 17 msec and would also result in a disturbance of the output ac voltage once every 17 msec.

Can you check the internal dc voltage waveform with scope?


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[CESSNA1]

CRS1:

Always be wary of 60 Hz stuff. You never really know if it is from the equipment as a real level or from some other place, like ground loops, electrical fields, and the like. I assume you are talking about vibration levels. 1195 rpm corresponds to about 20 Hz, and you have a 60 Hz peak. This indicates an outside source of noise. Just the fact that the level was reduced from .122 in/sec to .06 in/sec by some minor work is significant. You did not say whether or not the .122 and .06 were RMS or peak. .122 in/sec at 60 Hz corresponds to about .105G This level is on the upper end of what is considered "okay" operation. The .06 in/sec corresponds to about .055G. This is considered to be in about the middle of the "okay" operational range. What are the specs for the equipment?

Regards
Dave

 

[rob768]

In't the net frequency in your country 60 Hz? It may just be intereference.