State Grid Corporation of China (SGCC), announced Thursday it will invest 4.3 billion yuan (648 million U.S. dollars) to extend its extra-high voltage (EHV) electricity transmission system this year.

The SGCC announcement came as it celebrated the second anniversary of the successful operation of the state-of-the-art 640-km EHV transmission lines stretching from Changzhi City in northern China's Shanxi Province to Jingmen City in central Hubei Province.

Upon completion, the extension project will double the EHV transmission system's capacity to 5 million kilowatts and enable the transmission of at least 25 billion kWh of electricity annually, according to SGCC.

Launched in January 2009, the EHV system has transmitted 20.9 billion kWh of electricity between north China and central China power grids.

According to SGCC, the EHV system has eased the coal transportation burden and cut the consumption of coal for electricity generation by 2.55 million tonnes over the past two years.