A wind power turbine electric generator, the electric generator having a tubular first supporting structure extending about an axis of rotation; a second supporting structure extending about the axis of rotation, substantially coaxial with the first supporting structure, and fitted to the first supporting structure to rotate about the axis of rotation; first active parts fitted to the first supporting structure; second active parts fitted to the second supporting structure, facing the first active parts, and separated from the first active parts by an annular gap; and a radial tensioning device configured to adjust the shape of the first supporting structure about the axis of rotation.