Hi,
Just wanted to know your opinion on this case. I have detected what could might be a rotor bar issue on a newly installed vertical motor driving a pump. There are peaks and harmonics with sidebands around 2x LF in the spectrum we recently collected. I don't know the no. of bars but from textbook material I believed this is the rotor bar pass frequency. Should I worry? although the amplitude is very low and what are the telltale signs that it's really bad or not.
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One of the easiest and least invasive things to check when you have rotor bar pass frequency is verify you don't have a soft foot.
Thanks for the reply John, there might be some soft foot, from the velocity spectrum there are peaks <1 mm/sec and harmonics that indicates looseness and misalignment but I'm not sure if this can distort the motor frame enough since the motor sets on top of the pump frame. The 6x RPM from the spectrum I think is the 2x LF which is around 6000 CPM (airgap?) because this motor have 6 poles. I am from the Southern Hemisphere, so our line frequency is 50 Hz (3000 CPM).
I see quite a support stand for that motor. Usually those are fabricated by welding. I’ve often found them to not be properly stress relieved prior to machining the upper and lower flanges for concentricity and squareness. Unfortunately these dimensions aren’t easy to check in the field but if the stand is ever removed, it might be worthwhile to have the stand checked in a boring mill.
