STABILITY OF THE ROTOR OF AN INDUCTION MOTOR IN THE MAGNETIC FIELD OF THE CURRENT WINDINGS

An increase in the level of vibration of the rotor of an electric motor or generator can be caused by the misalignment of the rotor and the stator. In the case of alignment the resultant of the electrodynamic forces is zero. The misalignment violates the balance offerees acting on the rotor and leads to a nonzero resultant. The influence of the magnetic stretch on the vibration of an electric motor with a ferromagnetic rotor was studied in [1, 2]. The results of the experiments of [3] show that in certain conditions, the central position of a rotor with a ferromagnetic core looses its stability and self-oscillations are excited. The authors explain this effect by the appearance of the tangential component of the electrodynamic force. In the present paper, we calculate the magnetic field in the air clearance of an induction motor and obtain explicit expressions for the electrodynamic forces acting on the eccentric rotor moving in the rotating magnetic field. By applying the averaging method to the Lagrange-Maxwell equations, we study small oscillations of a ferromagnetic rotor and determine steady-state modes of motion and the stability boundary for the central position of the rotor, depending on the system parameters.