BEIJING, May 13 -- China's largest grid operator said Tuesday that energy authorities might soon approve a plan to build 12 electricity transmission lines linking the coal production and hydropower centers in inland areas to the densely populated east.

With a total investment of more than 210 billion yuan (about 34 billion U.S. dollars), the 12 major projects include four ultra-high-voltage alternating current (UHV AC) power transmission lines, five UHV direct current (DC) lines and three conventional 500-kilovolt networks.

Zhang Zhengling, a planning official with the State Grid Corporation of China (SGCC), said the lines will send electric power from Inner Mongolia, Shanxi, Shaanxi and Yunnan to Beijing, Tianjin and Hebei, as well as to two delta economic hubs along the Yangtze and Pearl rivers.

"The projects, considered important investment measures to stabilize economic growth, aim to ease power shortage in the east and alleviate the worsening smog problems in central and eastern regions," Zhang said.

If the National Development and Reform Commission, the top economic planner, and the National Energy Administration agree with the plan, all the projects are expected to start construction this year.

The SGCC, which supplies electricity to 80 percent of China's population, will be responsible for building 11 electricity transmission lines, while the China Southern Power Grid will construct the line distributing power from Yunnan to Guangdong, Guangxi, Yunnan, Guizhou and Hainan, which are home to some 230 million users.

As part of China's action plan to control air pollution, the projects will help cut thermal coal consumption by 200 million tonnes a year and reduce the density of PM2.5 pollutant particles by 4 to 5 percent in the central and eastern regions, the SGCC estimated.

The heavy investment could add another 90 billion yuan in output value for electricity equipment manufacturers, while bringing 500 billion yuan of investment to the power generating sectors, according to the SGCC.

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.