Characterization of Coil Faults in an Axial Flux Variable Reluctance PM Motor

In recent years, variable reluctance (VR) and switch reluctance (SR) motors have been proposed for use in applications requiring a degree of fault tolerance. A range of topologies of brushless SR and VR permanent magnet (PM) motors are not susceptible to some types of faults, such as phase-to-phase shorts, and can often continue to function in the presence of other faults. In particular, coil winding faults in a single stator coil may have relatively little effect on motor performance, but may affect overall motor reliability, availability, and longevity. It is important to distinguish between, and characterize, various winding faults for maintenance and diagnostic purposes. These fault characterization and analysis results are a necessary first step in the process of motor fault detection and diagnosis for this motor topology. This paper examines rotor velocity damping due to stator winding turn-to-turn short faults in a fault-tolerant axial flux variable reluctance PM motor. In this type of motor, turn-to-turn shorts due to insulation failures have similar I-V characteristics to coil faults resulting from other problems, such as faulty maintenance or damage due to impact. In order to investigate the effects of such coil faults, a prototype axial flux variable reluctance PM motor was constructed. The motor was equipped with experimental fault simulation stator windings capable of simulating these and other types of stator winding faults. This paper will focus on two common types of winding faults and their effects on rotor velocity in this type of motor.