I have a recently reconditioned 2 pole, sleeve bearing, 1500 HP induction motor that has high axial vibration levels. Drive end axial is 0.42 in/sec and opposite drive end is 0.32 in/sec. Spectrum are nearly equivalent peaks at 1x and 2x. Horiz and vert readings are acceptable (0.12-0.14 in/sec). I have not performed any phase testing yet.
I don't believe it is coupling alignment. Motor was hot aligned (Rotalign). Also, during test run in shop (uncoupled), axial readings were a little high (0.16 in/sec). (Above axial numbers are with motor fully loaded.)
The axial readings in the shop did appear to respond to voltage. At half voltage, the axial vibration reduced to 0.09 in/sec.
Question 1. Is there an air gap problem. I thought that electrically induced problems with a motor (air gap, dynamic eccentricity, rotor bars etc.) show up as primarily radial vibration forces. Yet I did observe a direct repsonse to axial readings in the shop with voltage. How can varying the excitiation (voltage) affect axial readings??
Question 2. Do I have a bearing alignment problem in the motor? The bearings were repoured during the recent recondition. One housing was also built up 0.004 in.
In the field, we found by removing shims at a opposite drive end foot, we lowered the vibration levels. I don't know if I was inproving bearing alignment or improving air gap uniformity or both. But it did have quite an impact (down from 0.55 in/sec drive end).
As a final field observation, you can hear the sound surging 44 times per minute. I assume this is twicw slip frequency (3575 RPM full load). Motor load is constant. It's this surging noise that makes it hard to walk away from this one.
Any thoughts/opinions/experiences are welcome.
Thanks in advance.