Air Gap Tolerance in Electrical Motors

Electrically I do not see a problem with the rotor being neither concentric nor varying from being concentric with the stator field as long as a gap still exists between the rotor and stator cores. Theoretically there would be a small perturbations in the possible torque one can generate as this gap dimension varies, but I cannot think of any easy way to discern this difference from any of the other variations in loading that might happen. Similarly an axial drift of your rotor would uniformly vary the gap dimension, if it changed this parameter at all. The question then comes down to, how does the rotor magnetic field get generated? If your motor is an induction motor then there are no brushes that require proper alignment. If instead the motor is a brushed DC motor or a brushed synchronous motor, then a half inch drift in the rotor might disturb continuity to the windings.

Mechanically though your machine tolerances scare the hell out of me. +2000hp that can slap around 4 to 7 mm sounds more like a way to make a jack hammer that the sitcom character Tim Taylor would design.

Since this is a sleeve bearing motor, so I think 4 to 7 mm of axial play is given deliberately to avoid direct axial thrust of rotor on the sleeve bearing face, spatially if motor is not on horizontal surface, or if there is some external force that is pushing or pulling shaft during its operation like in the case air blowers.

There are a few field devices that will allow one to check the Eccentricity of the Rotor. .

PDMA or Baker sells some of these. There are also consultants who do this as well. Some motor shops have this equipment.

A Static Eccentricity is not something I sweat, because the rotor is simply off center and rotates in the same spot.

Dynamic Eccentricity I do sweat if excessive, simply because this means that the rotor may be warped and set up vibrations which lead to various things such as bearing damage over time...

Interesting! Educate me (please).

I never really thought about it, but I guess there could be both mechanical eccentricity and such at thing as an electrical / magnetic field eccentricity?

And, I guess there could be rotational eccentricity as well as axial eccentricity (where the magnetic widings / fields of the motor lead to some axial movement (presumably as the motor rotates)?

What do the terms static and dynamic eccentricity refer to? Is it all mechanical, or does one consider the possible electrical eccentricity?

Generally speaking a Mechanical Eccentricity of the Rotor can be measured electrically and thus effects the fields around it.

Some rotors by being Defective (Broken rotor bars, castings, etc.)

Some rotors by being out of position. (offset permanently to one point or another)

Some rotors by being bowed, warped or out-of-round. (This is evidenced generally by vibration as well.

These conditions can be picked up a variety of ways.

Rotor-influence Checks (Static, not running) is one way.

Another is by Dynamic Checks (viewing the waveforms and picking them apart)

Vibration analysis can also help correlate some of this...

Maybe someone can chime in here and speak of the different companies and technologies to determine these conditions....

Generally the subject is Predictive Maintenance or Relaibility when searching for some of this stuff