China has long depended on coal-burning power plants to fuel its explosive growth over the past three decades.

As pollutants such as PM2.5 and PM10 have risen to alarming levels in the central and eastern regions in recent years, policymakers are trying to shift the country's energy structure by using greener power and transporting more electricity from the western regions to the east.

The construction of UHV AC transmission lines, however, remains controversial, as some argue whether such lines are safe.

"The country has never operated a UHV AC line, we don't know what result it may bring," said Lin Boqiang, director of the China Center for Energy Economics Research at Xiamen University.

Lin expressed caution over the mass construction of UHV transmission lines the size planned by the SGCC, but said a trial is necessary.

"If we build such UHV AC lines one by one, it will be clear whether such technology is okay or not," he said.

UHV, defined as voltage of 1,000 kilovolts or above in alternating current and 800 kilovolts or above in direct current, is designed to deliver large quantities of power over long distances with less power loss than the most commonly used 500-kilovolt line.

A single UHV line can carry about 6 gigawatts of power but requires stable and reliable electricity generation at its starting point.

Cai Guoxiong, deputy chief engineer at SGCC, said relevant simulation tests by China Electric Power Research Institute and Tsinghua University on grid failure showed the technology of UHV AC lines is a positive and safety is not a problem.

UHV DC lines are frequently used in point-to-point power transmission, while UHV AC technology is preferred in massive grid transmission.

China currently has two UHV DC power transmission lines in operation, the Xiangjiaba-Shanghai and Jinping-Nanjing transmission lines, which were completed in 2010 and 2012, respectively.

A third 1,679.9-km UHV DC line, which starts in Sichuan Province and traverses Jiangxi, Hunan and Guizhou provinces, is due to be completed this year.

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