The 2.5-megawatt direct-drive permanent magnetic wind turbine, independently developed by Guangxi Yinhe Avantis Wind Power Co Ltd, recently passed a low-voltage ride-through test, said Lars Andreasen, general manager of the turbine maker in Beijing.

"This is so far the largest direct-drive permanent magnetic wind turbine in the world that has passed the test," Lars said.

The test measures the capacity of a turbine to continue operating when the voltage on the electrical grid dips.

In June 2009, the device became the first 2.5 MW wind turbine to be connected to China's national grid.

On March 5 this year, the turbine, which stands at a testing site in Beihai, South China's Guangxi Zhuang autonomous region, passed two-phase and three-phase low-voltage ride-through tests, carried out by the China Electric Power Research Institute.

And on March 7, the prototype again passed the test, which, this time, was conducted according to standards upheld by the International Electrotechnical Commission.

Few of the 1.5 MW wind turbines now popular in China have done so well.

In October 2010, a 5 MW direct-drive wind turbine rolled off the production line of the Xingtan Electric Manufacturing Corporation, a wind turbine maker in Central China's Hunan province.

The turbine is now the largest in the country, and the company is planning to develop 6 MW and 7.5 MW direct-drive wind turbines.

In March 2010, the National Energy Bureau announced it had established a special committee and charged it with drafting standards for the connection of wind-power devices to the power grid.

The committee's main proposals have already been prepared and submitted to the central government for examination.

"Compared with the current technical rules for connecting wind farms to the State grid, the national standard concerning the low-voltage ride-through test is stricter," said Amanda Yang, an engineer with Guangxi Yinhe Avantis Wind Power.

Operators of Chinese wind farms have been perplexed and disappointed with the quality of wind turbines.

According to Dai Huizhu, a professor with the China Electric Power Research Institute, 598 wind turbines in Jiuquan, Northwest China's Gansu province, were disconnected from the grid during voltage sags in February this year. Hundreds of turbines in Northeast China's Jilin province had the same troubles in January.

Xie Wenbo, with the wind power branch of the China Guangdong Nuclear Power Group, said: "The 1.5MW wind turbines could operate soundly only for three years. After that, they will begin to show problems in one way or another."

"As wind-farm operators, we are most concerned with the rate of return on investment," Xie said.

Liu Bin from China Wind Power, a leading developer of wind farms, said: "With wind turbines of this quality, China cannot realize its ambitious capacity objectives for 2020."

Bringing the thousands of wind turbines now in operations up to a better standard will require large expenditures, amounting to up to 1 percent of the value of the turbines themselves, industry officials say.

China aims to have the capacity to generate 290 gigawatts from new energy sources by 2020. Of that, 150 GW will come from wind power and 70 GW from nuclear power.