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Composites May Have the Potential to Change the Landscape of Electricity Distribution.

[+] Author Notes

Alan S. Brown is a freelance technical writer based in Dayton, N.J.

Mechanical Engineering 121(06), 58-61 (Jun 01, 1999) (4 pages) doi:10.1115/1.1999-JUN-4

Composite Power Corp., Las Vegas, plans to use composites as a key material in a wind turbine a quarter-mile across that will turn on air or magnetic bearings in breezes as mild as 3 mph. Composite towers cost more than steel, however, are cheaper to transport and easier to assemble on-site, making them cost-competitive, especially in remote areas. Since composite towers have small footprints, they can share rights of way with railroad tracks. The system is designed so even if a car jumps the track and takes out up to three towers, the fiber-reinforced cable will remain intact. Beginning with inexpensive coal fuel, the proposed Montana-Wisconsin line will deliver power for an estimated 3 cents a kilowatt, compared with the 4 to 9 cents a kilowatt it costs other state utilities. The heart of the technology consists of cables made of aluminum strengthened by a composite wrapping. Although aluminum has a generous current-carrying capacity, its poor mechanical strength has curbed its role in power transmission lines.

Utilities usually generate electricity near their customers because running power lines over vast distances is costly and complicated.

However, that may be about to change, according to a small company in Las Vegas. Composite Power Corp. has developed an ambitious plan to build two privately owned, 850-mile-long transmission lines. One of them will stretch from a Montana coal mine to Wisconsin.

The other, nicknamed the " Green Line," will weave Columbia River hydroelectric generators, Washington wind turbines, and Neva da solar panels into the Las Vegas-Los Angeles power grid.

The technology that makes transmission lines economical is not some late breakthrough. Rather, the secret lies in the material used to make the transmission towers and reinforce the electrical cables: the same everyday glass-reinforced plastic composites that designers have used for decades to make hammer handles, ladders, and boat hulls.

"Everything we're doing has all been done before," said Composite Power's founder and chairman, Roger McCombs. "We're just re-engineering and rethinking it."

In addition to its transmission line, the company plans to use composites as a key material in a wind turbine a quarter-mile across that will turn on air or magnetic bearings in breezes as mild as 3 mph.

Composites are usually thought of as high-priced materials more often associated with aircraft than construction. A pound of composite costs many times more than the steel, wood, or concrete used in transmission line structures. Yet by taking advantage of composites' properties, McCombs believes his company has developed a solution to many of the economic, environmental, and safety problems that have bedeviled utilities for decades.

That's vital, McCombs said, because the United States may be heading for a power generation crisis. "Lots of people are building small, gas-fired 400- to 500-MW units scattered around the country," he explained. "But no one is building larger coal, nuclear, and hydroelectric systems."

Even utilities that want to build large coal-fired plants meet resistance. Environmentalists oppose railroading Western coal. Large shipments can close down intersections for more than an hour, cutting towns in half while blanketing them. with dust.

"The Dakota, Minnesota & Eastern Railroad has been trying for years to take 600 cars east," said McCombs.

"The reality of new coal production in Wyoming and Montana is that it is stranded."

The solution, said Composite Power's president, Bill Arrington, is to generate power near coal deposits. " It doesn't make sense to move coal; it makes sense to move electrons," he says.

Composite towers cost more than steel, but are cheaper to transport and easier to assemble on-site, making them cost-competitive, especially in remote areas.

Grahic Jump LocationComposite towers cost more than steel, but are cheaper to transport and easier to assemble on-site, making them cost-competitive, especially in remote areas.

Taking advantage of right of ways is harder than it sounds. In the past, infrastructure costs have proved prohibitive, especially when work had to be done in remote regions where there are few right of ways. It is not uncommon for utilities to spend more on building and relandscaping roads and right of ways than on the transmission hardware itself, McCombs said.

Even where right of ways exist, they are not always usable. Many of them already carry as much power as their steel towers can handle. To add towers, with their 10- to 30-foot footprints , utilities would have to clear entirely new paths.

Nor can new utilities use nonelectrical right of ways. Operators of underground natural gas pipelines, for example, never allow electrical lines to run overhead because their magnetic fields cause pipeline corrosion.

Composites resolve many of these problems. "Because they are insulating, we can use our composite towers on existing right of ways over gas pipelines or railroad tracks without fear of corrosion," McCombs said. With only a 30-inch base, more transmission towers can fit within a narrow path, and their composite-reinforced cables carry more current than conventional electrical cables.

According to Arrington, Composite Power's towers and cable can carry vastly more power than a conventional right of way because the nonconductive structure allows closer configuration.

Beginning with inexpensive coal fuel, the proposed Montana-Wisconsin line will deliver power for an estimated 3 cents a kilowatt , compared with the 4 to 9 cents a kilowatt it costs other state utilities.

Arrington expects to spend $1.5 billion to build four 500-MW coal-fired power plants near Composite Power's Bear Creek, Mont., coal deposits . The 850-mile high-voltage transmission line will cost an additional $850 million. He said that several large companies have approached Composite Power to invest or become joint-venture partners in the project.

The heart of the technology consists of cables made of aluminum strengthened by a composite wrapping. Although aluminum has a generous current-carrying capacity, its poor mechanical strength has curbed its role in power transmission lines. Aluminum cables cannot maintain their stability as they loop from one transmission tower to the next. Switching to aluminum-steel provides the necessary strength, but only at the price of lower conductivity.

Composite Power worked with Brandt Goldsworthy, a pioneer in the field of composite materials, and together they came up with the idea of wrapping aluminum in a composite sheath. The outer material strengthens and stiffens the cable. The low thermal expansion coefficient of the composites constrains the temperature-related expansion and contraction of the aluminum. With conductivity approaching that of copper, composite-wrapped pure aluminum carries significantly more electrical current than conventional cables with the same mechanical stability.

According to McCombs, Composite Power's cables will do more than carry electricity. They will also sense trouble along the transmission line through it glass fiber optic wire running through their center. Optical fibers monitor the line continuously for hot spots and damage.

"Optical fibers have lots of capacity," said McCombs. He plans to use some of that capacity for a separate line of business by running telephone conversations through them. According to this part of the scheme, Composite Power will install antennas in every tenth transmission tower and run a supplemental cellular telephone network through them. Because the tower materials are transparent to cellular transmissions, the structures can house the antennas within their hollow hexagonal bodies.

McCombs speculates that his first customers could be railroad crews that want to use cellular phones in remote areas of the country.

Composite-also allow for more-flexibility in power line construction and configuration because of the material's mechanical properties and its ability to insulate electricity At 500 ksi composites exhibit tensile strength four times greater than the best steel. At 10.5 Msi tensile modulus their stiffens easily outperforms metals.

As a result, glass-reinforced composite towers can soar up to 120 feet tall, yet remain mechanically stable with only a 30-inch base. Their small footprint, McCombs said, allows utilities to run two or even three composite-based transmission lines on the same right-of-ways now occupied by one large steel structure.

Composites also weigh less than steel. A typical 40-foot Class 1 pole, the type used to carry moderate power loads, checks in at only 390 lbs. This is 60 percent less than steel, 80 percent less than wood, and 90 percent less than concrete.

Because of their light weight, composite towers are easier to transport. The same flatbed truck that carries three' concrete towers can haul 72 composite poles. McCombs says they can be lifted to remote sites by helicopter. Their light weight also makes them easier to manipulate and install.

The poles are completely field-modifiable. Fittings slip into vertical notches running the length of the pole. They then lock into place by tightening a molly-type bolt that squeezes them against the sides of the notch. The system can be used with conventional transmission line hardware of Composite Power's own configurations.

Once installed, composite poles resist corrosion and insect and fungal attack. Accelerated aging tests suggest lifespans of more than 50 years. Because they are insulating, they do not attract lightning, the most common cause of line outages.

Since composite towers have small footprints, they are able to share rights of way with railroad tracks. The system is designed so even if a car jumps the track and takes out up to three towers, the fiber-reinforced cable will remain intact.

Grahic Jump LocationSince composite towers have small footprints, they are able to share rights of way with railroad tracks. The system is designed so even if a car jumps the track and takes out up to three towers, the fiber-reinforced cable will remain intact.

Big foot, little foot: The towers in a conventional power transmission line require significantly more space than a line built of composite materials.

Grahic Jump LocationBig foot, little foot: The towers in a conventional power transmission line require significantly more space than a line built of composite materials.

While mechanical properties are important, the real breakthrough in composite towers lies in their outstanding electrical resistivity. Not only are wires highly insulated, but so are the towers. Composite Power takes advantage of this property to simplify transmission line design and improve safety while it fits more power cables into a smaller space.

Steel towers are grounded electrical conductors. Unless designers isolate power cables, electricity could arc from the cable to the tower. To prevent this, utilities suspend cables on 10- to 12-foot insulators hanging off large crossbeams at the top of the tower.

Hot cables also generate electromagnetic fields. "You can't let the fields get too close to a tower because they will magnetize the steel and create a much larger field," said McCombs. The fields disrupt radios, cell phones, and even electric engines on locomotives. They also cause corrosion of underground gas pipelines.

Isolating cables on crossbars minimizes the magnetic field problem, but does not eliminate it. Cables inevitably magnetize steel towers, said McCombs. "The field hits the steel structure and goes right down into the ground," he explained. "It causes corrosion in underground gas pipelines in the same way that car batteries corrode their cables."

Insulating composites cannot become grounded or magnetized. Because there is no danger of arcing, Composite Power can place its electrical cables closer together, preserving the tower's small footprint.

"When you bring cables closer together, their magnetic fields start canceling out one another," said McCombs. This makes it possible to run electrical towers over natural gas lines without worrying about corrosion, or alongside railroad tracks without disrupting electric motors used on locomotives.

Composite towers are also safer. Without a ground, linemen are in less danger of electrocution while working on hot wires. Composite Power has demonstrated this by installing one of its composite towers on an energized 138 kV power system.

Given the expected advantages of the materials, McCombs believes the economics are good enough that he will be able to plug renewable energy into the national grid at a profit. The company's 850-mile Green Line, which links Columbia River hydroelectric generators, Washington wind turbines, and Nevada solar panels, is the test case.

What if a small startup company could overturn some of the longstanding practices of the power business?

While developers of renewable energy have made enormous progress during the past decade, they still face logistics problems. They can only generate electricity cost-effectively under near-ideal conditions. Solar energy requires a cloudless desert ; windmills, continuous wind; hydroelectric power, fast- running water. Too often, these conditions occur far from the markets that need electricity. Like coal in Montana, alternate energy is stranded by expensive distribution.

Dams along the Columbia River, for example, supply regional utilities with virtually inexhaustible power. At night, when factories and stores close down, demand drops sharply. Although the energy costs virtually nothing to generate, local utilities do not have enough high-voltage transmission lines to move their power onto the national grid.

Composite Power hopes to change that with its Green Line. Low-cost distribution could open the door to wider use of alternate energy in locations where it is competitive. "We need about 1,200 MW to make the transmission line work," said McCombs. "The problem in the pas t is that no one thought big enough. One we're connected into the Las Vegas power market, we can move energy to Los Angeles, Phoenix, and other major metropolitan areas."

The company is also looking at a wind turbine originally developed by Goldsworthy for the Department of Energy in the 1970s. Most conventional wind generators mount turbines, gear, and rotors weighing 15 to 25 tons atop steel tubes that rise 200 feet or' more into the sky. To operate, they require a minimum wind between 7 and 9 mph, and they generate 600 to 800 kW It would take hundreds of windmills to equal the power generated by a single coal-fired plant.

Goldsworthy's design is different. It looks like a hamster wheel set on its side, and generates power in winds as slight as 3 mph. As Arrington likes to point out, 95 percent of the earth has a 3 mph wind 95 percent of the time. " It turns so slowly, birds can fly through it," he says.

Goldsworthy created a 30-foot-high demonstration system in the early 1980s for the Department of Energy. Now, Composite Power plans to build a full-scale generator. Located on the top of a ridge, its diameter will span a quarter-mile. Its circumference will house lightweight composite blades 12 feet wide and 80 feet high. If it works, it could generate as much as 250 MW at peak capacity.

"The reason it's so efficient is that the armature runs under the track," said McCombs. "The cage is suspended above the armature by magnetic or air bearings to reduce friction. It doesn't matter which way the wind is going. There's no gearbox and very few moving parts. If the wind grows too heavy, we can brake it using the magnetic bearings ."

In February, Composite Power struck a deal with Goldsworthy's company, Goldsworthy and Associates of Torrance, Calif., to build a 100,000- square-foot composite factory. A leading candidate for the site is Richland, Wash. According to McCombs, the plant will be vertically integrated to the point where it makes its own glass. The factory will supply the material for the power transmission lines.

McCombs's plans hinge on a combination of new and proven technologies. His composite transmission towers use proven technology, although no one has ever wrapped an electrical cable with composites before. According to McCombs, composites in power transmission lines so far largely involve replacements for wood poles , a use that is decades old , and a few towers built in California.

McCombs wants his Montana coal plant to use pollution control technologies developed by Pacific Northwest National Laboratory, but they've never been used commercially. While Goldsworthy has demonstrated a 30-foot-diameter model of his vertical axis windmill, a quarter-mile unit might pose a stiffer set of challenges.

As with any technical problems, some may prove difficult or expensive to surmount. Some may even prove impossible, at least given present technology. But if the stakes are high, so are the rewards. After all , what if a small startup company actually could overturn some of the longstanding practices of the power business?

Copyright © 1999 by ASME
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