Optimal shading coil cross-section for minimal ripple factor of AC electromagnet attracting force

For the sake of armature vibration reduction, the AC electromagnets are equipped with end of pole shading coils which split the magnetic flux in two phase-shifted fluxes. As result the magnet attracting force varies periodically between a minimum and maximum values. When the opposing force is about the minimal attracting force, the amplitude of vibration become proportional to the attracting force ripple factor, which consequently should be as low as possible. In the paper this minimal value of magnetic force ripple factor is determined as function of shading coil parameters. The given equations can be used for the determination of optimal shading coil cross-section. An example of application is given.