Two-Pole induction-motor vibrations caused by homopolar alternating fluxes

Homopolar alternating fluxes of slip frequency will arise in a three-phase two-pole induction motor with a flexible shaft if the rotor is eccentrically placed in the stator bore. It is in fact the resulting eccentric air gap that creates the homopolar fluxes: these excite mechanical forces of double slip frequency, superposed on the double-frequency vibrations and on the force waves of the unbalanced magnetic pull. The latter rotates at the angular frequency of the rotor. The slowly changing force wave, whose amplitude can attain twice that of the fundamental force wave of the unbalanced pull, may cause intense vibration if no precautions are taken to suppress it. The origin of the alternating homopolar fluxes and the alternating homopolar fluxes created by them is analyzed.