Tulsa, OK -- An aging infrastructure and increasing demand for energy makes technology more important than ever in meeting and sustaining the power needs of the world. In its 2012 World Energy Outlook, the International Energy Agency said global energy dependency will grow by more than 30 percent between now and 2035. As the shift to more renewable sources catches on, questions are raised about how to make grids more flexible and better able to accommodate intermittent renewable generation. Alstom Grid believes high voltage, direct current (HVDC) technologies are part of the answer.
Alstom Grid recently opened its worldwide center of excellence for HVDC, as well as its large-scale transformer factory in Stafford, England, to more than a dozen journalists from around the world to talk about the future of HVDC. The company cited the benefits of HVDC and how the technology is helping connect mass amounts of renewable energy to the grid and transfer it long distances to load centers.
There are two types of HVDC technologies: Line commutated converters (LCC), which encourage energy trading and HVDC transmission; and, voltage source converters (VSC), which enables renewable energy by connecting variable energy resources and DC grids. LCC is ideal for major bulk power projects, while VSC is better suited for more compact projects, according to Alstom Grid.
“If a line is spanning a distance of more than 700 km (435 miles), it’s typically more cost efficient to go with HVDC rather than the AC solution,” said Claes Scheibe, Alstom Grid’s vice president of Power Electronics Applications.
Scheibe described other benefits of HVDC, such as increased energy efficiency to help operators meet growing electricity demand while reducing transmission losses and land use. It also is the ideal technology for connecting offshore energy sources to onshore grids, he said.
Another advantage of HVDC is that it allows operators to quickly change the direction of power flow, which makes it suitable for connecting wind, solar and other renewable sources beyond national borders, such as in Europe, or between North American Electric Reliability Regions in the U.S., Scheibe said.
HVDC also can connect AC grids to renewable sources while improving power quality, stability and reliability on those networks by reducing disturbances. The networks can be managed by control centers while operators keep the grid balanced by injecting the necessary power when there is a dip or peak in demand.
Like many countries around the world, the electricity grid in the U.S. is mostly comprised of HVAC transmission. Although HVAC has been the most commonly used form of energy transmission for over a century, the changing energy landscape has driven the need for the implementation of HVDC technology.
Utilities and companies like Alstom are looking to integrate more new HVDC networks into existing HVAC networks to create meshed grids, which would make the transmission system more efficient and flexible.
In the future, DC grids will mesh with the AC network to become more stable and more controllable. As grids evolve, direct current at high and medium voltage in transmission and distribution networks will be more commonplace, giving rise to a greater concentration of interconnected networks.
Alstom is involved in two projects in the U.S. where AC and DC technologies will be integrated. The first is the Tres Amigas Super Station, which would provide a first-ever connection between the three major U.S. transmission networks, the Eastern (Southwest Power Pool), Western (Western Electricity Coordinating Council) and Texas (Electric Reliability Council of Texas) networks. Tres Amigas would make it possible for clean renewable electricity generated on the West Coast to power homes on the Eastern Seaboard. The second project is the New Jersey Energy Link, which would serve as a backbone for connecting offshore wind farms to the state’s power grids.
Alstom is also working on projects in South America, Asia, Europe, North America and the Middle East. Its largest project, being constructed in Brazil, will be the world’s longest HVDC transmission line. The 2,375 km line will link 3,150 MW of power from the new hydro power plants in the Madeira River to the South-Eastern region of Brazil.