Effect of Stator Fault Currents on Rotor Permanent Magnets for a SPM-type BLDC Motor

In this study, the effect of stator fault currents on the rotor Permanent Magnets (PMs) of the Surface Mounted PM (SPM)-type Brushless Direct Current (BLDC) motor is investigated. The steady state analysis of the machine is performed under the Stator Inter-turn Faults (SITF) conditions which give rise to stator phase currents. The consequent effect of high rise in stator currents has an adverse effect on the surface mounted rotor PMs of grade N35SH having a non-linearity characteristic depending upon the operating temperatures. The change in temperature (Delta T) is function of stator phase currents which alters (delta Is) and increases drastically under SITF conditions. Consequently, the rotor PMs demagnetizes, and the Partial Demagnetization (PD) condition commences. The Finite Element modeling of possible demagnetization fault cases under different current intensity (to imitate SITF) are studied. The adverse effect on the motor back-EMF (E-B) and magnetic flux (B-M) signatures are investigated which are used as fault indicators. The proposed study has the ability to determine the partial demagnetization state at its incipient stage post the SITF conditions.