High-pressure oil-hydraulic transmissions have long been considered for wind-turbines but the part-load efficiencies of the available hydraulic pumps and motors have been too poor to make them attractive. Artemis WindTM believes that the prototype Digital Displacement® wind-turbine transmission that it is now building will radically change this perspective. The new transmission will be lighter than competing technologies and will have unprecedented levels of controllability and electrical power quaility. It will be suitable for retro-fitting to existing machines and also for use in the next generations of very-large turbines.
Benefits
The majority of large modern wind-turbines use mechanical gearboxes to couple the slow rotation of the blades to the high-speed of the generator. However gearboxes are heavy and prone to failure. In-situ replacement is very expensive. Other wind-turbine designs use low-speed electrical-generators that are directly coupled to the shaft of the wind-rotor. Though reliable these machines are costly, very heavy and need full-power electronic frequency and voltage converters to condition their power for supply to the electrical network.
A continuously variable transmission-ratio allows the rotor to be operated at the best speed for optimal power capture whilst the synchronous generator is driven at a much higher constant speed. The hydraulic transmission shares its load across many pumping-modules and so avoids the few highly stressed line-contacts that are inherent in gear boxes. The ability of hydraulics to limit pressure to a safe working value avoids potential over-stressing of the driveline. Short-term storage in accumulators can smooth out wind turbulence.
