Rotor Faults Condition Monitoring in Direct on Line Start Permanent Magnet Motors

Direct on-line permanent magnet motors have been gaining attention in pumping and other applications due to their improved efficiency and smaller size-to-power ratio, while facilitating the acceleration of the motor. Being an induction motor and a permanent magnet synchronous motor at the same time, this machine's stress analysis and condition monitoring poses tremendous interest and little work has been accomplished so far. This paper sheds some light on this area by primarily studying the frequency spectra of the stator current under healthy conditions. Then two different rotor faults are studied: the demagnetization and a broken bar. The analysis concerns both the starting transient and the steady state. The results are based on extensive simulations with Finite Element Analysis of a model verified by experimental testing.