Winding turn-to-turn faults in permanent magnet synchronous machine drives

This paper examines the effect of different numbers of shorted turns in one coil of the stator winding upon the operation of vector-controlled permanent magnet synchronous machine drives. A simple thermal model of the coil is used to examine the duration the fault can be allowed to exist before there is further degradation of the insulation. Simulation results by DMRM incorporate saturation and slotting effects. Short circuit current is difficult to limit due to the uncontrolled permanent magnet produced field. Permanent magnets are also prone to demagnetization due to the compound effect of the demagnetising MMF produced by the high short circuit current together with the armature reaction MMF. Shorting small numbers of turns gives very little time before further failures could occur. Shorts of large numbers of turns change machine flux levels, saturation and torque constant. Part functionality following a winding fault might aid controlled, drive shutdown or keep up operation in intermittent, short duration, load cycles.