Finite Element Analysis and Experimental Study of the Near-Magnetic Field for Detection of Rotor Faults in Induction Motors

This paper deals with the finite element analysis and experimental study concerning the influence of the one broken bar and rotor dynamic eccentricity faults on the magnetic field outside a squirrel-cage induction motor. The spatial distribution of the magnetic field, the time variation of the magnetic flux density in a point outside the machine and the time variation of the output electromotive force delivered by a coil sensor are evaluated based on the finite element models of the healthy and faulty states of the motor. The increase of amplitude from the healthy to the faulty states of some low frequency harmonics measured in the nearmagnetic field is emphasized. For the one broken bar fault, the increase of the amplitudes of specific harmonics of the coil sensor electromotive force, with frequency lower than 25 Hz, is experimentally confirmed.