Wind turbine power transmission system

A power transmission system for increasing the rotational speed from a rotor of a wind turbine, comprising:

• a main shaft configured to be driven by the rotor about a main axis;
• a support structure including at least one bearing supporting the main shaft for rotation about the main axis and constraining other movements of the main shaft;
• and
• a gearbox having a gearbox housing arranged adjacent to the support structure in a direction of the main axis, the gearbox housing rigidly coupled to the support structure and a gearbox input member coupled to the main shaft, the gearbox housing supporting the gearbox input member for rotation about the main axis while constraining other movements of the gearbox input member, and the gearbox input member being coupled to the main shaft with a translational degree of freedom along the main axis and rotational degrees of freedom about axes perpendicular to the main axis,
• wherein the main shaft is coupled to the gearbox input member by a flexible coupling positioned at least partially within the main shaft.