FOCUS ON POWER AND ENERGY

nationalizing the Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/132/12/37/6383865/me-2010-dec3.pdf by guest on 28 September 2021 grid

Long broken into separate interconnections, the U.S. electrical system will be united when the Tres Amigas project is completed. By Phillip G. Harris and Jack McCall

he U.S. is blessed with abundant renewable Energy Regulatory Commission recently approved a energy, from wind in west to sunlight in project designed to break this longstanding transmis- the western deserts. And the nation is rapidly sion bottleneck and create a power-marketing hub that putting that clean energy to work. Although will provide developers of renewable—and convention- most forecasts project annual load growth al—generation with expanded regional and national of only 1 percent for the foreseeable future, markets in which to sell their power. This project, renewable power’s share of net generation is projected called the Tres Amigas SuperStation, will be located in to double by 2035. Clovis, N.M., close to large amounts of established and But this power cannot be put to work unless it can potential renewable generation, and in its first phase, be economically transmitted to load centers. At pres- slated to begin construction in 2012, will support the ent, a key deficiency inhibiting the development of our 5,000 megawatts of power transfer capacity. renewable energy sector is America’s balkanized power What’s more, the Tres Amigas project will be a tech- grid: the largely isolated Eastern, Western, and Texas nological wonder. The project will employ ultra-effi- interconnections. Only relatively small, bilateral dc links currently exist between any two interconnections—a mere 2,000 megawatts of combined power transfer. And Phillip G. Harris is chairman and chief executive officer of the three interconnections have never been integrated. Tres Amigas, LLC, in Sante Fe, N.M. Jack McCall is director of Uniting these interconnections has been a goal for high temperature superconductor transmission and distribu- some in the power industry for decades. But the Federal tion systems for American Superconductor in Devens, Mass.

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tresamigas.indd 37 5/9/12 10:43 AM superior returns on investment. In addition to elimi- nating energy losses in transmission, superconductor cables are compact, lightweight, and emit no heat or electromagnetic fields, and they are particularly easy to install, even in close proximity to other underground infrastructure. The right of way needed to move 5,000 megawatts using a superconducting electricity pipeline is significantly smaller than that of conventional 765 kV transmission lines. Power cables employing superconductor wires are

Tres Amigas available from several commercial producers and have Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/132/12/37/6383865/me-2010-dec3.pdf by guest on 28 September 2021 Clovis, NM demonstrated their reliability and performance in in-grid sites around the world. Such cables have been installed in New York City, Long Island, and Albany, cient, high-capacity dc superconductor cables coupled N.Y.; Columbus, Ohio; Detroit; Tokyo, and South with voltage-source converters in what will be, in Korea. While all installations to date have been for ac essence, a superconductive electricity pipeline. applications, applying this established technology to dc transmission is straightforward. High temperature superconductors used in In dc applications in particular, modern power power transmission are perfect direct current electronics have paved the way for superconducting conductors. Wires made from superconductor materi- electricity pipelines to become a significant operational als are over 100 times more powerful than copper or solution for transmission operators around the world. aluminum wires of the same size and they can transmit The technology can be used for such diverse applica- power with zero energy loss when carrying direct cur- tions as collecting wind turbine output from onshore rent. The lack of resistance makes it possible, indeed and offshore wind farms; collecting renewable energy practical, to construct dc superconductor cables with from solar and geothermal rich areas; enabling the virtually any desired power transmission capability. delivery of renewable power to distant major popula- The power density and efficiency advantages drive tion centers, including regions that have less produc- system economics, and they are fundamental to the tive renewable resources; and transferring power from reason that underground superconductor cables can achieve cost parity with overhead alternating current t Compared to traditional high voltage power lines, supercon- power lines over long distances while also delivering ducting cables are much more compact.

5 GW, 765 kV overhead power lines /// 600-foot wide ROW

130’

5 GW, 200 kV superconductor electricity pipeline /// 3-foot diameter pipe

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tresamigas.indd 38 5/9/12 10:43 AM region to region to take advantage of seasonal and daily Interconnection), ERCOT and the WECC. Our studies, power generation and load profiles. during sample time intervals, showed that energy prices Direct current power transmission itself is not new: vary by more than $50 per MWh for over 2,000 hours it has been used for decades around the world to per year between CAISO and ERCOT, over 1,600 hours move large amounts of power from a single source per year between ERCOT and the Palo Verde hub, of power generation to one load center. While a few over 1,500 hours per year between SPP and the CAISO, multi-terminal systems using conventional cables have and over approximately 800 hours per year between been built, they were very difficult to implement. But ERCOT and the SPP. The key conclusion is that signifi- recently, multi-terminal technology based on new cant opportunities exist to bring lower cost power to power electronic designs incorporating voltage-source market by allowing more efficient producers access to

converters has become available. VSC technology pro- the market. Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/132/12/37/6383865/me-2010-dec3.pdf by guest on 28 September 2021 vides greater control and flexibility and, most impor- tant, enables dc lines to connect to multiple generation sources and multiple areas of electrical demand. Direct current terminals employing VSC technol- Pick Up and Drop Off ogy, however, are available only at mid-level voltages in the range of 100 to 300 kV. By comparison, ultra- uperconductor electricity pipeline systems have high voltages (around 800 kV) are used for conven- a broad scope of application. The superconductor tional point-to-point dc transmission. Thus, to be used dc cable functions as a virtual bus-bar that can in high power transmission, the lower voltage levels carry a set amount of power across its length. The VSC terminals are then able to inject power require the use of very high currents. But transmit- S onto the line, or pull power off the line in precisely con- ting high currents long distances through conventional trolled amounts. This operation would be akin to valves on aluminum or copper conductors results in considerable a gas pipeline or on- and off-ramps on a highway. resistive losses. One possible use of that capability is long-distance Superconductor power cables bypass that limita- tion by providing the ability to carry very high levels Wind Resources and Transmission Lines of current with zero electrical loss. The combina- tion of a VSC-based multi-terminal dc system and superconductor cables makes for a compelling new transmission option, uniquely suited to transmitting renewable energy over long distances with multiple collection and distribution points. In the target applications, superconductor dc cables have higher lifecycle returns on investment because of their effi- ciency and operational advantages.

The Tres Amigas SuperStation will employ

this technology toward an exciting goal. The Transmission Lines SuperStation will make it practical, and economi- Voltage (kV) 345-499 500-699 Superconductor Electricity Pipeline cal, to “firm up” intermittent and variable renewable 700-799 energy by taking advantage of geographical diversity 1000 (DC) AC/DC Converter Stations and energy storage, such as the onsite batteries at Tres Amigas or systems such as compressed air energy stor- power transmission. For instance, a superconductor elec- age. This capability greatly enhances the value of new tricity pipeline system could consist of several linked loops generation, creating additional economic incentives for of long-distance superconducting cable, each with discrete its development. points of connection to the ac grid. (Connecting such a pipe- Tres Amigas also will expand the geographic reach of line in loops increases reliability, since maintenance work or unavailability in one section would not prevent power markets, offering new opportunities to take advantage from flowing from one location to another.) Traditional of load and resource diversity, which will reduce costs. ac transmission would be utilized to collect power from For example, at present, marginal prices for energy geographically adjacent wind farms and provide a common in the three U.S. interconnections typically diverge point of connection to the pipeline at converter stations. For because these three markets operate in isolation. Studies example, 250 MW would be injected into a 5,000 MW super- that Tres Amigas submitted during FERC proceedings conductor dc cable at 20 locations as it passes through the showed that marginal energy prices do vary significant- wind-energy-rich upper Midwest, and 500 MW would be ly between the (in the Eastern delivered to each of ten cities on the East or West Coast.

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tresamigas.indd 39 5/9/12 10:44 AM Superconducting cables will enable the Tres Amigas SuperStation to move electric- ity among the three interconnected grids.

station with backup power and voltage-source converter technol- ogy that will provide substantial reactive power to the transmission system in each of the intercon- 5 GW dc VSC 22.5 sq. miles superconductor cable nections. s can rapidly control

Clovis, N.M. both active and reactive power Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/132/12/37/6383865/me-2010-dec3.pdf by guest on 28 September 2021 independently. The reactive power will be controlled separately at each synchronous interconnection inde- pendent of the voltage levels on the other synchronized systems. By using VSCs, Tres Amigas will not place restrictions on each ac network’s minimum short- Just as important is that the Tres Amigas SuperSta- circuit capacity. The self-commutation feature of VSC tion will enhance the value of transmission investments technology will permit the set of three different phase made in the region by allowing power to move freely voltages to be synthesized. Because VSC converters between the interconnections. Tres Amigas will permit themselves have no reactive demand, Tres Amigas will power to move to and from different markets, expand- be able to control reactive power for regulation in each ing the potential use of the existing transmission grid separate ac system. The real-time dynamic support of and future additions. Tres Amigas should also provide each ac system will be managed based on each system’s system planners new opportunities to improve the separate and individual needs, thus improving stability efficiency and reliability of the electric system at a lower and transfer capability, and most likely reducing losses overall cost. on each connecting ac system. Also, the reliability of the electric system in the area Finally, the VSC will provide black start capability around Tres Amigas will be improved. Tres Amigas to each interconnection separately. Tres Amigas will will connect the three asynchronous grids at a robust appear, electrically, to each interconnection as a large

In for the Long Haul

uperconductor electricity pipe- transmitting up to 574 MW of electricity Amperium high-temperature supercon- lines can be the most efficient and powering 300,000 homes. The cabling ducting wire for fabrication into trans- option for long-haul transmis- for the LIPA installation was designed, mission cables. Just last year, AMSC re- sion, whether in ac or dc grids. manufactured, and installed by Nexans. ceived its first commercial order from LS In all applications, high- National Grid and American Electric Cable for approximately 80,000 meters of temperatureS superconductor cabling Power energized distribution-voltage its Amperium wire to manufacture a 22.9 cuts power losses by a factor of two or superconductor cable systems in their kV (distribution voltage) ac cable system three when compared with conventional commercial power grids in Albany, N.Y., that will be installed in a Korea Electric transmission options. This results in and Columbus, Ohio, respectively, in 2006. Power Corp. substation near Seoul. improved return on investment, and In the summer of 2010, Nexans com- Rated at 50 megawatts, that cable sys- reduced pollution and carbon emissions. pleted the first-ever successful demon- tem will be 0.5 kilometer long, making it These advantages underpin the stration of an HVDC high temperature the world’s longest distribution-voltage growing market for HTS cabling. For superconducting cable operating at 200 superconductor cable system. example, in the United States, the world’s kV. This prototype cable, together with LS Cable also is actively develop- first transmission-voltage cable system a newly designed termination, passed a ing a 154 kV (transmission voltage) ac has been operating successfully near series of tests based on CIGRE (Interna- superconductor cable system. KEPCO, New York City since April 2008. This 138 tional Council on Large Electric Sys- which is Korea’s only power grid opera- kV system is now a permanent part of tems) recommendations. tor, has forecasted the wide deployment Long Island Power Authority’s primary In October LS Cable Ltd. of South Ko- of superconductor power cables in the transmission corridor. At full capacity, rea announced the purchase of 3 million Korean grid starting in the 2012-2013 LIPA’s power cable system is capable of meters of American Superconductor’s time frame.

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tresamigas.indd 40 5/9/12 10:44 AM generator. The value of this to the long-distance ac ing platforms, and transmission system planning. Tres transmission lines planned for the region surrounding Amigas is in the final stages of selecting the vendors Tres Amigas is significant. Although specific engi- for the detailed engineering design and construction neering analysis of each line interconnecting to Tres services, as well as the supplier for the SuperStation’s Amigas will need to be carried out, intuitively we high-voltage dc technology. can predict that the technology that Tres Amigas is When completed, the power conversion technol- deploying will solve many voltage, reactive support, ogy at the Tres Amigas SuperStation will be a vast stability, and dynamic control improvement over the problems that long-distance equipment used at most of ac lines connected to large the existing ac/dc ties in

intermittent generation the United States. It will Downloaded from http://asmedigitalcollection.asme.org/memagazineselect/article-pdf/132/12/37/6383865/me-2010-dec3.pdf by guest on 28 September 2021 resources create. apply advanced and proven power grid technologies such as high-voltage direct It may sound futuristic, current superconductor s When chilled by liquid but the groundbreaking nitrogen, slender rib- power cables, voltage- for this project is actu- bons of superconducting source converters, and ally close at hand. With material can carry as energy storage systems. much electricity as thick the recent signing of vendor copper cables. Tres Amigas also will be contracts with CH2M Hill, the first high-capacity Xtreme Power, Burns & system to connect all three McDonnell, ZGlobal Inc., of America’s power grids, and Viridity Energy Inc., the design and build-out of transmitting gigawatts of power from region to region the Tres Amigas SuperStation is near fruition. The through the nation’s first renewable energy market hub. vendor agreements that Tres Amigas has completed It will be the first step toward a green—and conti- in recent months cover equipment, proprietary trad- nent-spanning—grid. n

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