A segmented inner stator comprises a stator core and a stator winding. The stator core includes a plurality of core segments which are retained together in a circular arrangement by at least one retaining ring and are mated with each other. At least some of the core segments are provided with slots on the radial side surfaces. The at least one retaining ring comprises a radial extension portion extending along the axial side surface of the core segment. A plurality of corresponding axial projections are provided on the radial extension portion of the at least one retaining ring along the circumferential direction to be inserted into the slot on one of the core segments so that the core segments are not free to move axially and radially relative to each other or relative to the retaining rings.