Hydraulics topic starts at [0:25].
Youtube text: Mitsubishi Heavy Industries worked with Artemis Intelligent Power to build this prototype 7MW offshore wind-turbine which is now on test at Hunterston in Scotland. The video shows the rotor blades being made and the building and testing of the wind turbine’s Digital Displacement® hydraulic transmission at Yokohama.
Youtube text: Construction of the largest wind turbine in diameter in the world at 167m. The sea angel was designed by Mitsubishi Heavy Industries. Construction was in December 2014. Working with SSE, MHI Vestas, Artemis Intelligent Power, Innovate UK, and Department for Business Innovation and Skills to complete.
The Sea Angel Turbine is 7MW output and located within 1 mile of Hunterston Nuclear Power Station in Renfrewshire, West Scotland.
[windminds.com] – Mitsubishi 7MW Sea Angel Floating Turbine
[windpowerengineering.com] – Hello SeaAngel: Hydraulic drive train could provide 7 MW offshore turbine
[beta.machinedesign.com] – Hydraulic Wind Turbines?
P.S. in this design the generator is still located in the nacelle.