Unbalanced magnetic pull
Unbalanced magnetic pull produced by an eccentricity between the rotor and stator magnetic centers of a permanent magnet synchronous generator.
How can the unbalanced magnetic pull caused by rotor eccentricity be found?
Build a plane-parallel DC Magnetics problem for the eccentric rotor and evaluate the unbalanced magnetic pull from the computed field results.
- Synchronous motor rotors
- Eccentric rotor systems
- Generator air-gap systems
Simulation Problem
- Problem Type
- Plane-parallel DC Magnetics
- Geometry
- Permanent magnet synchronous generator, rotor outer diameter Ø264 mm, inner diameter Ø185 mm, axial length 130 mm, rotor material steel.
- Given
- Permanent magnet coercivity 955 kA/m, relative permeability 1.2
- Air gap length 2 mm, static eccentricity ε equal to 50% of the air gap length
- The B-H curve for steel is given
- Task
- Compute the force acting on the rotor.
- Solution
The stator windings carry no current, so only the magnetic pull caused by eccentricity remains.
The rotor is shifted radially by half the air gap, i.e. 2 mm × 50% = 1 mm.
- Results
The unbalanced magnetic pull is 706 N. The field plot clearly shows the asymmetric flux density distribution in the air gap.
Reference: This reproduces a real test condition, with the generator assembled, the rotor stationary and no current in the stator windings.
