China Completes Ultra-High-Voltage Transmission Superhighway

The State Grid Corp. of China (SGCC) in July put into operation the world’s first ultra-high-voltage direct current (UHVDC) superhighway when it commissioned the Xiangjiaba-Shanghai link. The ±800 kV project, completed in 30 months—a year ahead of schedule—has the capacity to transmit up to 7,200 MW from the Xiangjiaba hydropower plant in southwest China to Shanghai, the country’s leading industrial and commercial center, about 2,000 kilometers (km) away.

The project’s primary technology provider, ABB, also reported that transmission losses on the new $440 million line are under 7%—considerably lower than on the existing 500 kV system (Figure 1). This means that the single overhead line link sets a new benchmark in terms of voltage levels and transmission capacity, ABB said, superseding the 600-kV Itaipú transmission line in Brazil, which the company also delivered.

1. Somewhere along the line. China, which in 2008 had already completed one 1,000-kV UHV AC circuit, in July put into operation the 2,000-km, 800-kV Xiangjiaba-Shanghai link. Two other 800-kV DC circuits are under construction. The Longquan high-voltage direct current converter station shown here is similar to those used at these massive hydropower transmission projects in China. Courtesy: ABB

The project is the among the first of many to come online as part of China’s ambitious plan to boost trans-regional power supply capacity. Defining anything over 800 kV as “ultra-high voltage,” the country has pledged 300 billion yuan ($44 billion) to build as many as eight long-distance high-voltage lines by 2015 and as many as 15 by 2020. The new lines allow for the transmission of more power with significantly reduced losses from areas rich in resources to regions of heavy power consumption. Nearly 80% of China’s hydropower resources are in the southwest, and two-thirds of its coal is in three northern provinces. Demand centers, meanwhile, are in coastal regions.

Before the Xiangjiaba-Shanghai link, the SGCC put into operation a 600-km 1,000-kV UHV AC circuit in late 2008. Meanwhile, work continues at two other 800-kV DC projects. The China Southern Power Grid in June said it put into operation the second pole of a 1,500-km UHVDC line that would bring hydropower from Yunnan province to Guangdong province (and its megacities Guangzhou and Shenzhen)—effectively doubling transmission capacity to 5,000 MW.

Siemens Energy put into operation in December 2009 the first pole for that project, which operated at a nominal power of 2,500 MW. “At a transmission capacity of 5,000 MW, losses are as low as around 2% per 1,000 km, plus less than 1.5% losses for both converter stations at the sending and receiving end of the transmission line,” the company said.