Deflection of 2 Pole Alternators Under Load

[RottenRobert]

We are running a 2-pole 90 kWe alternator @ 3600 rpm (driven by a Ford V-10) As load is applied we are experiencing shaft deflection, which somewhere
between 40-50 kW results in interference between the rotor and the stator. The alternator manufacture says they are developing a new larger alternator with a stiffer shaft. I would like to get an understanding of the electro/mechanical forces that cause this deflection.

 

[TheBlacksmith]

Some designers I know have likened a two pole alternator rotor to a 2x4. That is, depending upon it's construction, it may be stiff in one axis (where the pole pieces are) and weak 90 mechanical degress apart (where the windings are) and the shaft develops a "whip", like a jump rope. This may not be much of an affect on a small machine, unless it is marginal to begin with. Since they are developing a larger machine with a stiffer shaft... The stator also deflects under the magnetic forces, maybe you have loose windings or just no enough air gap to account for movement.

Blacksmith