Gearboxes out of fashion in China -- Sino-Japanese joint venture

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Direct drive wind turbines are taking a growing share of the market in China. Most recently, Hara XEMC Windpower, a joint venture between two wind turbine makers, China's XEMC and Japan's Harakosan, commissioned the third stage of a 101.6 MW wind farm in central Hunan Province using 2 MW turbines, which it says are the largest wind converters without gearboxes in the country. In a direct drive turbine the rotor is connected directly to a slow-speed generator, a relatively unusual configuration compared with the use of standard high-speed generators and a gearbox to step up the speed of the rotor to that of the generator input shaft.

The first two stages of the Datang Zhangzhou Liu'ao Wind Farm use standard technology: 36 Gamesa 850 kW turbines and 36 Suzlon 1.25 MW turbines with gearboxes and standard generators, while the third stage uses 13 Hara XEMC 2 MW direct drive units with permanent magnet generators. The turbine, built under licence, is Harakosan technology that evolved out of the former Lagerwey/Zephyros stable in the Netherlands. The first Harokosan units, with 50% Finnish technology, went up in Finland nearly two years ago (Windpower Monthly, November 2007).

Hara XEMC cites high efficiency, reliable operation, simple maintenance and low noise as reasons for the interest in the direct drive/permanent magnet generator concept in China. Hara XEMC has received 480 orders in the domestic market for its turbines.

The company is not alone in China in favouring direct drive technology, though the economics of the concept are debatable (Windpower Monthly, November 2008). Chinese component supplier Zhuzhou CSR Electric and Chinese turbine manufacturer Goldwind say a prototype of their 3.2 MW direct drive turbine has passed testing in Zhuzhou, in central Hunan Province. CSR Electric says production of the machine, which it calls the world's largest powered by a permanent magnet generator, will begin in August. The company claims that compared with traditional wind turbines using double-fed asynchronous generators and gearboxes, its permanent magnet direct drive units will suffer fewer mechanical failures, reduce maintenance costs and produce wind power more efficiently.

CSR Electric and Goldwind in 2003 established a strategic cooperation partnership to jointly develop advanced, yet affordable wind turbines. Until now, they have developed turbines with rated capacities of 800 kW and 750 kW and a 1.5 MW model with a permanent magnet generator.

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