Introduction Overheating of a motor due to an abnormal use shortens considerably the life time of its components and causes short-cuts. Overloads are tolerated only for a limited period of time. Concerning short-cuts, their effects are destructive and they must be quickly cut off. Fault types Internal Faults That type of internal faults generally appears when insulating components areageing. It is then preferable to release the protection as fast as possible. Those faults can be detected by comparing the ongoing and outgoing currents of the same phase. The protection is then provided by an percentage differential overcurrent relay connected to two sets of three current transformers placed on each input and output phases of the stator. Because of the imprecision linked to the TC, the fault current