A Passive Inter Turn Short Circuit Fault Mitigation Technique for Electric Machines

This article proposes a passive inter turn short circuit current mitigation technique that adds differential mode chokes (DMCs) between the inverter and the phase pairs in a multiphase winding arrangement. The fault current manifests itself as a differential mode current between faulted phases, and this article shows that the DMCs can reduce the fault current, while the DMCs only slightly affect the common mode or healthy current. The amplitude of the fault current reduction depends on the DMC size. This study shows that a 200
$\mu$
H DMC can reduce the fault current by multiple orders of magnitude from 4586% (without DMCs) to 10% of the rated current for a simulated permanent magnet synchronous machine. With that level of fault current mitigation, the machine can continue operating almost normally. A setup based on transformers cores was built and tested. The experimental results show that, with a 65
$\mu$
H DMC, the fault current is reduced from 120% to less than 1% of the rated current. The good agreement between simulation and experimental results validates the model.