Insulation failure detection in the stator windings of ASD-driven induction machines using standard deviation of line currents

This paper develops a straightforward, current-based scheme to detect stator turn faults that have occurred due to insulation failure in an ASD-driven, three-phase induction machine. The method employs simple statistical analysis to detect turn shorts in the stator of the machine. It is shown that the standard deviation of the calibrated, RMS line currents reveals a change in the machine´s electrical symmetry that can be caused by turn shorts. To account for inherent machine imbalance, calibration is performed with the machine in a known fault-free state; additionally, current normalization accounts for varying loads. The method is sensitive to source balance, and is thus proposed only for inverter-fed machines.