The Jiuquan-Hunan UHV line links Jiuquan in western Gansu province to Xiangtan in central Hunan province. It is the longest line of its kind to be built in China, stretching 2,383 kilometres and involving a total investment of CNY 26.2 billion ($4 billion).
The Jinbei-Jiangsu UHV line connects a converter station in the northern part of Shanxi province with another station 1,119 kilometres away in Nanjing in eastern Jiangsu province. The investment in this project is estimated at around CNY 16.2 billion. Both lines are scheduled to be operating in 2017.
China's northern and western regions have good wind resources and a significant amount of wind-power capacity has been installed in the last decade. However, the regions are underdeveloped and power demand is limited. As a result, the wind projects suffer from severe curtailments, and further development is limited.
UHV lines transmit electricity over long distance, moving surplus electricity from one region to another region with insufficient supply - known in China specifically as "sending electricity from west to east, or from north to south". The UHV lines are considered to be one of the key solutions to wind curtailments.
First UHV line
The country's UHV era began in 2006 with the construction of the Jingdongnan-Nanyang-Jingmen 1000kV UHV alternating current (AC) power line. The 654-kilometre line, from south-east Shanxi province to Jingmen in Hunan province, was completed in early 2009.
The first DC UHV line was the 800kV Yunnan-Guangdong line, 1,373 kilometers long, constructed by Southern Power Grid. This links Chuxiong in south-western Yunan province to Guangzhou, and started operating in 2010.
The State Grid Corporation of China is the major driving force behind the UHV endeavours. The giant utility delivers electricity to more than 1.1 billion people living in approximately 88% of the Chinese territory. By the end of 2014, 87.9GW of wind installations were connected to its network - 91.2% of the national total.
Over the last ten years, State Grid had added three AC and four DC UHV lines to its network. Another DC and two AC lines were being built at the end of 2014.
Southern Power Grid, which delivers across five provinces in southern China, had previously developed extra-high-voltage (EHV) lines, typically around 500kV, but since constructing the Yunnan-Guangdong line, has added another UHV DC line, and plans to build more.
Wind curtailments peaked in 2012 with an average rate of 17.12% across the country.
The northern regions suffered the most, with eastern Inner Mongolia recording the worst, at 34.3%.
By 2013 the average curtailment rate had improved to 10.7%, and last year was recorded as 8%. While 2014 curtailment figures were improved through lower wind speeds, the UHV lines also contributed.
Zhu Ming, a deputy director in the renewable energy division of the National Energy Administration (NEA), said last year that the national targets would help resolve curtailment issues by 2015. While this has not yet been achieved, curtailment rates will drop further as more UHV lines are built.
UHV power line development has been controversial since the very beginning. The AC technology is particularly criticised for being unstable and putting the power grid at risk, as well as being uneconomical given the construction cost and energy losses.
In December 2014, the NEA reportedly organised and sponsored research programmes covering theory, development and results of UHV AC lines. The findings may alter the strategy of UHV development in the future.
Meanwhile, constructions of UHV lines continues. State Grid plans to start work on 14 new UHV lines this year — six ACs and eight DCs. Next year, three AC lines and one DC will be commissioned. And in 2017, one AC and four DC lines will follow.
In a white paper published in April, State Grid said northern China remains a focus for wind-power developments. By 2020, 40% of the wind-generated electricity produced in the three northern regions would be transmitted across the country to other regions, with the remaining 60% consumed locally, the company predicted.