Ultra HVDC Transmission System

General Information

Description
Benefits
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References

Throughout the world, the demand for power keeps growing at a scale and speed never imagined in the past. For various reasons we also witness a strong push for renewable energy sources (RES) with power generation becoming increasingly distributed and a growing number of generation facilities located far away from load centers. At the same time, demanding economic objectives as well as obligations to reduce greenhouse gases have to be met.

To meet all these demands precisely, Siemens has taken great efforts to overcome the hitherto limitations in the technology available for high-voltage direct current (HVDC) power transmission. Thanks to Siemens Ultra HVDC (UHV DC) long-distance power transmission at a voltage level of 800 kV providing power capacities of up to seven gigawatts and more has now become technically as well as economically feasible for the first time ever. The first 800 kV UHV DC system, ordered by the China Southern Power Grid Co. in Guangzhou, is scheduled to commence commercial service by mid-2010. It allows the country to tap more hydropower instead of adding new coal plants. The CO₂emissions offset amount to a whopping 33 million tons at the Yunnan-Guangdong project alone.

The most economic solution for long-distance bulk power transmission, due to lower losses, is transmission with High Voltage Direct Current (HVDC). A basic rule of thumb: for every 1,000 kilometres the DC line losses are less than 3% (e.g. for 5,000 MW at a voltage of 800 kV). Typically, DC line losses are 30–40% less than with AC lines, at the same voltage levels, and for long-distance cable transmission DC is the only solution, technically and economically.

Siemens UHV DC is a newly developed system that provides the key to increased performance and robustness of the transmission grid, to keeping pace with the steadily growing energy demand, and to a highly economical way of CO₂ emissions reduction:

single bipole power transmission capacity of more than 7 gigawatts at a voltage of ± 800 kV
60 % reduction in transmission losses and CO₂ emissions with UHV DC compared with standard ± 500 kV HVDC
significantly smaller footprint and lower OHL costs compared with 800 kV AC solutions
deally suited for bulk power transmission over very long distances of 2,000 km and more for infrastructure upratings
capable of interconnecting large grids and of stabilizing parallel AC systems
advanced high-speed system control with Win TDC

UHV DC – More than 50 % Reduction in Right-of-Way Requirements

Siemens UHV DC will be the bulk power energy highway and security backbone of the future power grids

UHV DC – A significant reduction in Transmission Losses

The next level of HVDC technology, Siemens UHV DC, is characterized by its innovative 800 kV voltage level, its transmission capacity of up to 7,200 Megawatts, and a substantial loss reduction. Thanks to thorough R&D efforts, Siemens is able to produce the entire range of components required for 800 kV DC power transmission itself and supply complete UHV DC systems from a single source. An example of the station Layout and the converter arrangement with two 400 kV systems in series in each pole for n-1 redundancy is given in the following figures.

Example of a Bipolar Station Layout with two 400 kV Converters in Series

A converter station links the DC transmission line at each end to the AC grids. It consists of a number of components which have reached a high degree of maturity. However, for UHV DC application, innovative solutions have been implemented to fully meet the extended requirements for ultra-high voltage bulk power transmission, ref. to the figures.

Siemens the innovation leader with the first UHV DC System worldwide in Guangzhou, China provides the optimal solution for today´s and future bulk power demands. In early projects our high standard technology has now the chance to prove its numerous benefits which at last make long-distance power transmission at a voltage level of 800 kV technically as well as economically feasible.

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