High-capacity Transmission Cable Comes of Age

By Steven M. Brown, Editor in Chief

Long-promised technology to improve the current-carrying capacity of transmission cable is now being demonstrated and is quickly becoming commercially available. As a bonus, much of the new technology fits in existing rights of way and, in the case of overhead cable technology, can be strung on existing towers.

New high-capacity overhead transmission cables from companies like Composite Technology Corp. and 3M use familiar conducting material—aluminum—but replace the steel core of traditional ACSR (aluminum conductor steel reinforced) transmission cable with lighter composite cores. As a result of the engineered core material, a number of advantages are realized:

  • Due to their overall lighter weight and their ability to operate at higher temperatures, composite core cables can carry more power while exhibiting less sag than steel core cable;
  • with the lighter core, a greater amount of aluminum (the conductive material) can be used in a composite core cable as compared with a traditional cable of the same weight, which results in greater current-carrying capacity;
  • composite core cables reportedly exhibit greater resistance to corrosion, which is important in coastal installations;
  • since they’re lighter and exhibit less sag than traditional steel core cables, composite core cables can be strung on shorter towers, or a lesser number of towers of traditional height, which can be important in areas where aesthetics are a concern.

Those are just a few of the benefits touted by both 3M, with its aluminum conductor composite reinforced (ACCR) cable, and CTC, with its aluminum conductor composite core (ACCC) cable. 3M says its conductor provides one-and-a-half to three times the capacity of traditional cable. CTC says its cable can cost more than five times less per mile than traditional cable. Both companies report that their technology is stronger than ACSR cable.

And, most importantly, both cables are commercially available in various sizes and are being demonstrated at utilities across the United States.

Making Progress Easier

While both 3M’s and CTC’s products have been commercially available for only about a year, one has to wonder what would hold utility companies back from investing in the new breed of overhead cables. The reported benefits are many—high capacity, low sag, low cost, high resistance to corrosion, etc. The main problem, as is the often the case with new power industry technology, is the very novelty of the technology.

“Typically, utilities are very conservative,” said Bill Arrington, CTC’s president and chief operating officer. “They like to be ‘first to be second.’ Bringing in a new technology to the utility industry takes a lot of time and energy.”

For that reason, both CTC and 3M are trying to make their cable and the hardware that accompanies it as close to standard sizes and shapes as possible.


Workers install 3M’s Aluminum Conductor Composite Reinforced (ACCR) cable at WAPA’S Liberty Substation near Phoenix. The cable can transmit two to three times more power than conventional cables of the same diameter, without increasing stress on existing towers.
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In late June, CTC announced that it had entered a joint development agreement with FCI for the manufacture and distribution of hardware and connections for CTC’s line of ACCC cable. While new splices and deadends were developed for use with the new ACCC product, CTC and FCI wanted all the hardware and tools to be familiar to those who would be working most closely with it.

“We’re trying to bring as many positive aspects together aswe can but, at thesame time, makethe cable and hardware as much like what the linemen are used to as possible,” Arrington said. “We’ve made everything so that the lineman already has all the tools on the truck he would need to put up our conductor.”

Doug Johnson, 3M’s product development specialist for the company’s ACCR cable, also noted the importance of delivering innovation, but in a form factor similar to that which utilities are accustomed.

“We’re trying to provide a high-performance product that can be a tool in the utility’s toolbox to increase capacity on existing lines without them having to change the supporting structures,” Johnson said. “At the same time, we provide a cost savings to them.”

A number of utilities are implementing 3M and CTC cable into their systems for demonstration purposes. It’s important to note that while the installations are referred to as “demonstrations,” they’re generally all actually working in the respective utilities’ transmission grids, carrying actual power to actual customers.

3M’s ACCR cable is being demonstrated at Hawaii Electric, Xcel Energy, Salt River Project, Bonneville Power and two installations with the Western Area Power Administration (WAPA)—one in Arizona, one in North Dakota.

CTC is also working to get its product out into the grid. The company is currently working with the City of Kingman, Kan., and Aquila Inc. to construct a 21-circuit-mile transmission line using CTC’s ACCC technology. CTC’s Arrington said the Kingman line should be finished by the end of 2004.

In addition to the project in Kingman, CTC is working on three projects—one in the northeastern United States, two in the southwestern United States—that could actually come to completion prior to the Kansas project. CTC is also scheduled to take part in a demonstration project with WAPA in Phoenix this fall.

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    Composite Technology Corp.’s ACCC cable (left) and traditional ACSR cable (right). Note the difference in core material (CTC’s composite core material vs. traditional steel core) and the shape of conducting material (CTC’s trapezoidal aluminum vs. traditional wire shape). The trapezoidal shape results in a tight configuration, and thus a greater amount of aluminum—28.8 percent more per foot—than traditional cable, which translates into increased capacity and reduced line loss.

High-capacity Goes Underground, Too

Innovation in power cable technology isn’t all “up in the air.” Two high-profile projects in the northeastern United States, demonstrate that the same type of technological advancement is occurring underground as well—at both transmission and distribution voltages.

In late June, the construction phase of a high-temperature superconducting (HTS) underground cable project was launched at Niagara Mohawk, a National Grid Company. SuperPower Inc. (a subsidiary of Intermagnetics General Corp. and manager of the project) is working with Sumitomo Electric Industries (a developer and manufacturer of power cables) and the BOC Group (which develops the cryogenic refrigeration system that will cool the superconducting cable) on the 350-meter distribution voltage cable that will run between two Niagara Mohawk substations in Albany, N.Y.

The four-year project, with a projected $26 million cost, consists of a cable to be installed between the Niagara Mohawk Riverside and Menands substations, directly below an interstate highway. The project is intended to demonstrate the increased efficiency, reliability and safety of HTS power cables compared to conventional copper cables. The New York State Energy Research and Development Authority (NYSERDA) and the U.S. Department of Energy (DOE) are helping to fund the project.

Sumitomo Electric Industries is fabricating the 350-meter, 34.5-kV cable. The cable will be installed underground on the Niagara Mohawk distribution system with a joint, or “splice,” 30 meters from one end. Later in the project, the 30-meter section initially produced with first-generation HTS wire, will be replaced with an identical length using second-generation HTS wire to be manufactured by SuperPower.

Another underground HTS project in its early stages is expected to improve power quality and reliability in the Long Island Power Authority’s (LIPA’s) transmission system. Awarded in 2003, the project at LIPA involves American Superconductor as the HTS wire manufacturer and team lead, Nexans as the cable manufacturer, and Air Liquide as the refrigeration system provider. The team is currently focusing on the design of the cable, terminations and refrigeration system. The $30-million-plus project is being co-funded by the Department of Energy and the industrial partners involved in the project.

The nearly half-mile-long 138-kV cable will be installed in an existing right of way in East Garden City on Long Island. After an initial operational period followed by performance and economic reviews, LIPA plans to retain the superconductor cable as a permanent part of its grid. LIPA and American Superconductor are also working on plans to install more HTS cable elsewhere in the LIPA grid to address growing power demand on Long Island.

According to American Superconductor, HTS wire can conduct more than 140 times the power of copper or aluminum wires of the same dimensions. When HTS wire is cooled to minus-321 degrees F, it exhibits zero resistance, which translates to potentially loss-free power transmission. (When superconductor materials are cooled below a critical temperature, they can transmit power with 100 percent efficiency—no line loss due to resistive heating. This is why refrigeration is required in these HTS wire projects.)

“Siting new transmission lines has become a formidable challenge in congested areas such as Long Island,” said Michael Harvey, LIPA’s director of T&D, when the project was announced. “Superconductor cables can transmit substantially more power than conventional cables in the same right of way U This technology is a powerful new tool for relieving grid constraints reliably and unobtrusively.”

The project team expects the cable to be installed in the LIPA grid by the end of 2005.

Conclusion

Whether it’s overhead or underground, high-capacity transmission cable is becoming a commercial reality. As the technology matures and the costs—which are particularly high with some of the underground HTS technologies—decrease, these new lines may provide a feasible and reliable solution to the grid congestion and transmission line siting problems that have troubled power delivery for years.

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