Online Stator Turn Fault Detection for Inverter-Fed Electric Machines Using Neutral Point Voltages Difference

This paper proposes a stator turn-to-turn fault detection for inverter-fed electric machines using the voltage difference between two neutral points (NP's). By designing machine Y-connected windings with a secondary NP, a voltage difference between two NP's appears once a turn fault occurs. Because this fault signal is induced by the voltage difference between two independent windings, only the turn fault reflected signal is resultant. It leads to an important improvement on the fault detection of electric machines since NP voltages difference is immune to the influence of saliency and flux saturation. In addition, the load and speed affect the signal level and frequency, but not the detection accuracy. It is possible to monitor a small turn fault during the machine real-time operation. A 1-kw permanent magnet machine and a 200-W induction machine with proposed two independent Y-connected windings are tested for the experimental evaluation.