Wind turbine gearboxes are all fixed ratio, as far as I can tell. The blade pitch is adjusted to maintain a constant speed in synchronous machines. Ones with AC-DC-AC converters don't need to do that. There's also something called a "doubly fed machine", which is a 3-phase generator where the field windings are actively driven to rotate the magnetic field to compensate for minor speed variations of the rotor.
Wind turbine gearboxes take a lot of pounding as the wind shifts. Wear is a big problem and not fully understood. The trend is toward gearless systems.
Transmission repair atop a wind turbine is not fun. Power semiconductors are good enough that it's easier to deal with this electrically.