We have a 4000 V, 3-phase, 366 A, 3575 rpm, 3000 HP induction motor that is making a modulated buzzing noise. The vibration in the horizontal planes of both bearing housings has increase from 0.1 IPS-PK to 0.3 IPS-PK over a one year period. My electrician suspects there maybe loose stator laminations, are there any field tests that can be employed to verify?
An indication of loose stator lamination would be vibration at precisely 2X line frequency and possibly harmonics of 2X line frequency. If the vibration ceases immediately when power is shut down, is absent with the motor coasting, that indicates loose stator laminations or some other electrical fault. It is probably not possible to verify in the field. If you search the internet you should be able to find additional information.