Monitoring of the evolution of a squirrel-cage bar breakage through harmonics of the magnetic field outside the induction motor

This paper deals with the non-invasive online monitoring of the evolution of a rotor bar breakage in a squirrel-cage induction motor. The investigation of the magnetic field outside the motor based on a dedicated finite element model takes into account the rms value and the amplitudes of particular harmonics of the output voltage of coil sensors. The early detection of the broken bar fault should be based on the exceeding of imposed limits in the change of the rms value or of the amplitude of selected harmonics of the output voltage.