The two-bladed design, from Windflow Technology Ltd, lets the turbine rotor teeter on a hinge. This teetering motion is linked to an asymmetric pitching mechanism of the turbine blades. Uneven wind gusts are passively absorbed, says the New Zealand-based company, thus reducing fatigue loads throughout the turbine. This reduces turbine weight and cost and increases reliability.
With active pitch control, the turbine blades and hub deliver a nearly constant rotation speed to the gearbox from the low-speed shaft. The high-speed shaft from the gearbox drives a synchronous generator that requires a constant rotation speed. Small variations in hub speed (caused by potentially damaging wind gusts) are absorbed by a hydraulic pump on a second output from the gearbox. The torque-limiting gearbox is patented in several countries.
The 500-kW turbine competes with three-bladed multi-mega watt designs. On a per megawatt installed basis, the smaller, 500 kW turbine allows for easier transportation, more straight-forward installation, says the company, along with reduced environmental and visual impact. These advantages are accentuated in typical New Zealand conditions where the wind resource is extreme, access is often limited, and sites can be ecologically sensitive.
With constant input from the torque limiting gearbox, Windflow turbines uses a generator synchronised directly with the grid and without the aid of costly and unreliable power electronics. As well as reducing costs and increasing reliability, this feature allows for easier connection to the grid. The table tells a bit more about the Windflow 500.
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