7.2 GW, 1.6 MV DC Pole-Pole 2,000 km Transmission Line

Multiple announcements are appearing (Siemens, T&D, ABB) for the world's first fully-operational 1600kV pole-pole long-distance transmission line (one pole operating at plus 800kV and the other at minus 800kV). This is 33% higher than the Itaipu ±600 kV line in Brazil, the world's previous highest HVDC transmission voltage rating.

"The ±800 kV Xiangjiaba-Shanghai UHV DC link, with a rated power of 6,400 MW, has the capacity to transmit up to 7,200 MW of power from the Xiangjiaba hydropower plant, located in the southwest of the country, to Shanghai, China's leading industrial and commercial center, approximately 2,000 kilometers away."

The Fulong converter station is pictured.

"At a transmission capacity of 5000 MW losses are as low as around two percent per 1000 kilometers, plus less than 1.5 percent losses for both converter stations at the sending and receiving end of the transmission line." I wonder, 2% and 1.5%, how does that compare with transmission lines and transformers our readers are familiar with?

Let's see, 2% of 5GW is 100MW, or 100kW per km, or 100W per meter. It'd be nice to know more details about the actual wire, towers, wire sag, etc. Here's ABB's illustration of a two-pole DC system vs the multi-line AC equivalent. Older lower-voltage lines used single poles, e.g., this DC line in the US southwest. ABB also specializes in "invisible power transmission" with underground cables.

It'd also be nice to learn more details about the design of the 525kV AC to 800kV DC converters. ABB has a brochure for this project, in which they say the 800kV voltage is formed by "two 400kV series-connected 12-pulse converters," using new 8.5kV thyristors with 6-inch diameters, "operating at a direct current of 4000 A."

I couldn't find datasheets for such parts on their website, instead having to content myself with 6.8-inch 6.5kV 1.6kA parts (pictured). These are bidirectional, using two thyristors integrated into one wafer, and feature "interdigitated amplifying gates." That sounds good, e.g., I see the 5STB 13N6500 part has a 400mA trigger gate current. Once on, they say the r_T slope is 0.6 mΩ. That's only 0.78V at the rated 1.3kA. Wow, and that's at T_vj = 125 °C, not 25 °C. (As an electronic, rather than electrical engineer, that's the kind of stuff that interests me.)

Hmm, I had thought they were using IGBTs. but maybe they can't compete with such efficient specs.