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Modified clutch helps to halve wind turbine weights

22 March, 2008

A novel mechanical power transmission system for wind turbines has cut their weight by about 50%, as well as making them more efficient. The new system, based on a modified over-running sprag clutch and vee pulley assembly, was developed by Renold Clutches & Couplings of Cardiff for a wind turbine manufacturer outside the UK that wishes to remain anonymous.

The modified assembly is connected to a gearbox via a Renoldflex torsionally rigid coupling. This allows the gearbox to change the pitch angle of the turbineís rotors to suit different wind conditions.

Most wind turbines use fixed-speed rotors and in high winds they have to cope with large torque fluctuations that can cause variations in generator output power of up to 100%. The new design counters this problem by using a gearbox and clutch combination that allows the rotor speed to be adjusted by varying the pitch angle of the blades. This allows the generator output to be maintained at a constant level, regardless of fluctuations in wind speed. If an overspeed occurs, the rotor reaches a fully feathered position and cuts out, but the clutch allows the generator to continue running.

Conventional wind turbine transmissions require heavy, robust assemblies to cope with large fatigue loads in high wind conditions. The new design, incorporated in a wind turbine with a 33m swept blade diameter and a top speed of 50 rpm, is about half the weight of conventional designs. This improves the cost-to-weight ratio and reduces operating costs, because only 3% of the rated power is consumed by the components.

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