Patent ID: 7719285

Claim:
A ground fault detection arrangement for a synchronous three-phase electrical machine, which synchronous three-phase electrical machine has a neutral point connected to ground, wherein said ground fault detection arrangement comprises injection means arranged to inject an off-nominal frequency AC voltage (Ui) between said neutral point and said ground, characterized in that said ground fault detection arrangement comprises: a first measurement means arranged to measure a first current, resultant from said injected voltage, at a first position of said synchronous three-phase electrical machine, wherein said first position is between said neutral point and said ground; a second measurement means arranged to measure a second current, resultant from said injected voltage, at a second position of said synchronous three-phase electrical machine, wherein said second position is mounted on the phase windings of said synchronous three-phase electrical machine; a control means arranged to detect a ground fault in said synchronous three-phase electrical machine based on said first and second currents.