Hydrostatic transmission technology for wind turbines: grid-forming, system service and maintenance capabilities

A Type 5 hydrostatic transmission-based wind turbine (HSWT) replaces the mechanical gearbox and power converter of conventional variable-speed wind turbines (VSWTs) with a robust variable displacement hydrostatic transmission (HST). As a result, HSWTs can drive a grid-connected synchronous generator, being able to deliver system services similar to conventional (thermal) generation, and can also operate in synchronous condenser mode (by using a clutch to disconnect the generator from the turbine rotor) to regulate reactive power and stabilise local voltage, thereby diversifying revenue streams. Integrating a hydraulic accumulator for short-term energy storage further enhances system capabilities and reduces maintenance needs. This paper qualitatively compares HSWTs with VSWTs in terms of design, efficiency, and maintenance. It also addresses maintenance implications related to hydraulic line configurations and the controllability of the accumulator. Finally, the paper evaluates the potential opportunities arising from future system services, highlighting the unique capabilities of Type 5 HSWTs in providing a broad range of services that are challenging for VSWTs to deliver.