This post is to answer many of the questions that have been asked since the original post. Thank you very much for your interest and suggestions in this matter. I apologize for being so long in answering the questions. Further insights, questions, and comments are welcome.
Q: How many "arms" or "legs" are used in the rotor?
A: There are not discrete "arms" or "legs". There are two 1/4" steel rings around the stator iron which are welded to a support box housing with a continuous steel support rails running down each side of and the length of the box parallel to the length of the stator iron.
Q: Who is manufacturer?
A: Sorry but I am not at liberty to yield that information.
Q: What is cooling method?
A: Fan cooled.
Q: I am curious to know if these higher Vib. levels are being measured with Online instrumentation such as Phasor Probes (Eg. B Nevada)or is it a Portable Vibration Analyzer?
A: There are two measurement systems that have provided the vibration data and each agrees with the other. One system includes an X direction prox probe mounted to look at the shaft vibration at both the outboard and inboard sides of the motor. Also included is a key phasor on the motor shaft. These probes feed a Bently-Nevada 3500 rack which in turn feeds the information to the facility's DCS. The other system used the aforementioned probes but with Y direction prox probes added at the outboard and inboard sides. All these probes provided input to a Bently-Nevada "Audre" analyzer.
Q: Also check for distortion of stator frame due to soft foot.
A: This test was performed as a running soft foot test and it was determined that soft foot was not an issue.
Q: Try applying voltage with motor uncoupled... if vibration remains you can rule out misalignment.
A: The motor was uncoupled and alignment was not an issue. Note, however, that whenever we do couple the motor to the load, the motor vibration usually drops by 50% or so.
Q: How could the rotor spin when there is no power supply ?
Do you mean coasting down phenomenon ?
A: Yes, I was referring to the difference in vibration between the powered spinning motor and the coast down. The vibration levels reduce by about a factor of 5 once the power is removed and the motor is allowed to coast.
Q: Have you check the power supply quality?
A: Yes, it is very good.
Q: How old is the machine?
A: The machine is brand new.
Q: What kind of load is driven?
A: The load is a fan. But note that the worst vibration occurs in the uncoupled state.
Q: What is the starting arrangement?
A: Starting is a full voltage, across the line start.
Q: Is there a speed control?
A: The only speed control is done through the use of the PAM motor windings. A speed switch is used to switch from low to high speed. This switch merely reconnects the motor's single winding to achieve the speed change.
Q: Pls verify what are the dominant vibration frequencies (measured on supplied motor).
You mentioned that “The freq of the vibration was primarily at 1x of running speed 515 RPM, hence, 515 Hz” – but for the 12/14-pole motor at 60 Hz the rotation frequency is respectively 10 Hz (speed 600 rpm) and 8.6 Hz (speed 515 rpm).
A: At low speed the dominant vibration frequency is 515Hz which equals the low speed running speed (515 RPM). At high speed the dominant vibration frequency is 600Hz which equals the high speed running speed (600RPM). There is very little 2x or above components.