vfd waveform and vibration signiture

We have anilyzed a few motors that are powered by variable frequncy drives, that the spectra apears to be bearing faults. In one case however we were told by our customers electriction that the vfd was not set correctly.

After setting the vfd, the noise went away.

I am looking for information on vibration that vfds produce or can produce when not properly adjusted.

 

[VibrationSpecialist]

In general, you have some at fixed frequecy excitation forces such as 2 line frequency component and the rest are as the normal motor vibration response.

 

[butelja]

VFD's will also impose a high frequency "ringing" at their switching frequency.  This switching frequency is typically in the 1,000's to 10,000's hz.  Since bearing faults are also high frequency, this may be what you are seeing.  The manufacturer of the VFD should be able to tell you what its switching frequency is.  Once this is known, you should disregard the peak on the spectrum at the switching frequency.  If it also happens to coincide with bearing fault frequencies, then you have an unfortunate situation that I don't know how to resolve.