Friendly Transmission

“Tres Amigas” means “three friends” in Spanish, and developers of a major transmission hub bearing that amicable moniker hope their efforts to join North America’s three largest transmission interconnections proceed in an equally friendly fashion. Sited in Clovis, N.M., near the Texas border, the project would provide Eastern U.S. customers access to the vast renewable-energy resources of the West and Southwest and give producers in those regions access to half-a-continent’s worth of new customers.

Electricity in the United States is transmitted over three major interconnections—the Eastern Interconnection, Western Interconnection and the Electric Reliability Council of Texas (ERCOT), an independent system for the state of Texas. While numerous systems are incorporated within these interconnections, the networks themselves remain, essentially, isolated from each other. This disconnect is why only Westerners have access to California’s solar-generating capacity and why vast Texas wind farms may not be used to their fullest potential.

“There is more renewable energy in the American Southwest than in Alaska’s Prudhoe Bay, if you translate everything into Btus,” said Phil Harris, the project’s founder and president of Tres Amigas LLC. When you are able to move such power from low-cost areas to high-cost areas, he said, “all citizens win.”

The wind industry also sees promise in the project. Transmission expansion is a priority for wind developers, who see improving access to more wind resources as a way to balance regional wind-supply differences at any given time.

“In general, building new transmission capacity is critical to getting more wind power onto the grid,” said Michael Goggin, manager of transmission policy for the American Wind Energy Association. “As you get better power flows from region to region, you’re helping wind.”

A major technical challenge any electrical union between these three transmission networks faces is the fact that each operates using alternating current (AC) at frequencies slightly asynchronous to the other two systems. A connection requires converting that AC power to direct current (DC) at some midpoint, and then reconverting the DC to AC at the receiving end’s frequency. Such a process using conventional equipment entails large efficiency losses.

To solve this problem, Harris and his engineers are planning what will be the largest public installation of high-temperature superconducting cable to date. The design now calls for 6 miles of two parallel cable lines, in three 2-mile legs, to be supplied by Devens, Mass.-based American Superconductor, which has become an investor in the project. This cable, when cooled to –360°F, poses no resistance to electricity transmission, meaning no energy is lost in the process.

To visualize the system, think of a typical traffic rotary or roundabout, with three points of entry for traffic. Transmission lines take the place of roadways in this design, with overhead lines entering and leaving the project area at each of those three connection points. Voltage source converters will be installed at those three points to convert incoming power from AC to DC and reverse that conversion for outgoing electricity.
Minimizing the footprint of this transmission roundabout is almost as critical to the plan’s design as maximizing its efficiency. From the start, engineers have been determined to bury lines within the project to protect facility operations from both the area’s sometimes-volatile weather conditions and potential terrorist attack. Meeting the anticipated 5 gigawatts of capacity requirements, with traditional conductors would have required much larger cable lines and would have generated enormous amount of heat.

“It would have been a massive quagmire of cabling,” Harris said. “We looked at alternatives, and [superconductors] made all sorts of sense.”
Two superconducting cables—one traveling in each direction—will fit in a single 3-foot-diameter pipe, according to Jason Fredette, American Superconductor’s director of investor and media relations. He added that the current system can be scaled up to carry up to 10 gigawatts in the same 3-foot sleeve. Superconducting cable currently is serving short-run transmission needs in several other installations, but the 12 miles this project requires marks a significant industry milestone.

“The project has gotten a lot of attention nationally,” Fredette said. “Superconductors, as a business, are starting to turn a corner.”
Technology isn’t the only hurdle Harris’ plans have to jump before groundbreaking can take place. Bringing together three independent interconnections also poses significant bureaucratic challenges. In March, the Federal Energy Regulatory Commission (FERC), which oversees the Eastern and Western Interconnections, granted Tres Amigas the authority to negotiate rates for transmission services, a necessary precursor to any signing any agreements with potential transmission customers. Negotiations with several companies covered by this decision now are moving forward, Harris said.

But FERC did not grant the blanket exemption sought by Tres Amigas to waive required case-by-case reviews of connections with ERCOT-overseen companies. These lines will have to gain individual waivers from FERC to connect to the new superstation.

ROSS is a freelance writer located in Brewster, Mass. He can be reached at

About the Author

Chuck Ross

Freelance Writer
Chuck Ross is a freelance writer and editor who has covered building and energy technologies for a range of industry publications and websites for more than 25 years. He specializes in building and energy technologies, along with electric-utility bus...

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