BEIJING - China on Friday put into operation a project extending its ultra high voltage (UHV) system to boost electricity transmission capacity from the country's energy-rich northern regions to the power-short central provinces.

After the extension, the 640-km Jindongnan-Nanyang-Jingmen 1,000-kilovolt alternating grids will double the electricity transmission capacity and greatly relieve the power shortage when demand peaks in winter and summer under the Central China Grid, according to the State Grid Corporation of China (SGCC), which built the UHV lines.

A total of 120 million kWh of electricity -- equal to 60,000 tons of coal equivalent -- can be transmitted daily through the grids, which run between the city of Jingdongnan in northern Shanxi province and Nanyang, Henan province and Jingmen, Hubei province in central China.

As the first such grid designed and built by China, the UHV grid became operational in January 2009 and was upgraded this year.

In January this year, the SGCC said it planned to invest 500 billion yuan ($78.9 billion) to extend its UHV electricity transmission lines to six by 2015.

UHV, defined as voltage of 1,000 kilovolts or higher of alternating current and 800 kilovolts of direct current, is designed to deliver large quantities of power over long distances with less power losses than traditional lines.