Twice the Capacity on the Same Towers

March 1, 2011
Brazil uprates an environmentally sensitive river crossing with ACCR.

Brazil is already South America's largest consumer of electric power, but over the next 10 years, the nation's demand for electricity is projected to increase by 50%, according to Energy Minister Edison Lobão. Accommodating that demand will require the addition of some 51,000 MW in generating capacity. Although it is possible current global financial problems might alter this projection downward to some extent, meeting any target even close to that figure poses an enormous challenge for Brazil's utility industry.

Having abundant river resources, Brazil currently relies on hydroelectric power to satisfy approximately 85% of its electricity consumption. However, much of those resources are situated a considerable distance from where the power is needed most, in the rapidly growing southeastern portion of the country, which includes the heavily populated states of São Paulo, Minas Gerais and Rio de Janeiro.

To meet the challenge of keeping pace with Brazil's growing demand for electricity, it will be necessary not only to add a great deal of generating capacity, but also to make distribution and transmission as efficient as possible. Hundreds of new power lines and substations nationwide are planned for the coming years, many of which are already under construction, and existing lines will be improved to remove or minimize bottlenecks.

Rio Paraná Crossing

As Brazil's largest non-government-owned transmission utility, Companhia de Transmissão de Energia Elétrica Paulista (ISA CTEEP) transports almost all of the electricity consumed in São Paulo and about 30% of the electrical power used nationwide. The effort to upgrade the power-delivery system includes a search for new technologies and approaches that enable achieving the greatest efficiency and reliability, while minimizing costs and adverse environmental impacts within the required time frames.

No project better illustrates that complex objective than the recent upgrade of a segment of the Jupiá-Três Irmãos line that crosses the Rio Paraná — South America's second-largest river system, after the Amazon — in an especially environmentally sensitive area where the river forms the border separating the states of São Paulo and Mato Grosso do Sul.

ISA CTEEP's engineering department studied many technical options for line upgrades on the Jupiá system. Initially designed to connect two hydro generators, the system's transmission capacity overloaded when the new Três Lagoas Thermoeletric Power Plant was connected to the system.

The purpose of this project was to more than double the capacity of the Jupiá-Três Irmãos line. To achieve that goal, it was determined the line should be rebuilt with a Grosbeak 636-kcmil aluminum conductor steel-reinforced (ACSR) 0.99-inch (25.2-mm)-diameter conductor, in place of the existing Oriole 336-kcmil ACSR 0.741-inch (18.8-mm)-diameter conductor.

However, a complication had to be taken into account. The 1.1-mile (1.8-km) Rio Paraná crossing has three towers that sit over special concrete foundations rising out of the water. Upgrading the line across the river with the larger ACSR conductor would have required construction of substantially larger towers in the river bed, creating difficult problems. The high cost of such an undertaking was one factor, but environmental considerations posed even greater obstacles. The river and its flood plains are home to a huge variety of fish and birds and, not surprisingly, are the subject of intense environmental scrutiny.

A Conductor Alternative

New construction of any kind in the river flood plain would have been unwelcome, but exacerbating the problem is the fact that not only the towers would have to be replaced, but also new foundations would have been required. The permitting process for such a disruptive procedure might have taken over a year or more; in fact, it was entirely possible a permit might never have been granted.

ISA CTEEP sought a reliable solution that would have mechanical properties similar to the existing Oriole ACSR conductor yet also the electrical current capacity similar to that of the Grosbeak conductor. After searching on the local and international markets and evaluating a limited set of options for the river crossing, the solution of choice was the 3M aluminum conductor composite-reinforced (ACCR) conductor.

One of the best benefits of this alternative is that the needed capacity could be achieved without having to replace or enlarge the towers. The solution, which more than doubles line capacity, is a 300-kcmil ACCR. This new conductor is not only much lighter than the original conductor, the diameter is smaller at 0.677 inches (17.2 mm). This means the same conductor that increased line capacity by more than 100% also reduced the wind loading on the existing structures by about 9%. It allowed the issue of river construction to be avoided entirely.

The Installation

For the purpose of the upgrade, the 138-kV line required an increase in capacity from 335 A to 860 A. The ACCR line chosen can be operated up to 1,043 A for continuous operation at 210°C (410°F) and 1,113 A for emergency operation at 240°C (464°F). The ACCR conductor weighs 36% less than the Oriole ACSR that had been in place. Maximum sag and maximum horizontal tension would remain essentially the same.

ISA CTEEP's technical team worked with 3M's Brazil and U.S. teams to plan and prepare all the logistics for the installation in February 2009. The installation itself required only six days. The 3M technical team provided pre-construction training for both ISA CTEEP and contractor employees.

The process and equipment were similar to that used for installing an ACSR conductor. In fact, the existing ACSR conductor was used to pull the ACCR through the existing towers. Following manufacturer's recommendations for ACCR installation techniques, the stringing employed a 59-inch (1,499-mm) tensioner and 27-inch (686-mm)-diameter stringing blocks on suspension towers. Splice and dead-ended connectors were applied using a 100-ton (91-metric-ton) press. This installation process enabled the tension to remain constant throughout, avoiding any conductor contact with lower phases.

By using this lightweight, high-performance conductor for the Rio Paraná crossing, ISA CTEEP was able to avoid a potentially interminable delay, save costs, work with innovative technology on its transmission line and complete a vital project to help meet the power needs of a growing region. As ISA CTEEP and Brazil's entire utility industry move forward toward achieving the nation's ambitious expansion goals for generating and delivering electrical power, technological innovations such as the 3M ACCR will play an expanding problem-solving role.

Caetano Cezario Neto ([email protected]) is the engineering department manager for Companhia de Transmissão de Energia Elétrica Paulista (CTEEP), principally owned by Grupo Empresarial ISA (ISA Group), one of South America's largest electricity and telecommunications providers. He is a graduate of Faculdade de Engenharia de Barretos in Barretos, Brazil, with a degree in electrical engineering, and he has been an employee of CTEEP since 1984.

Genesis of ACCR

3M's aluminum conductor composite reinforced (ACCR) had a serendipitous genesis in the 1990s, when the company's engineers were experimenting with metal-based ceramic-reinforced composites for aeronautical applications. Working with a composite that demonstrated a strong ability to resist the effects of heat, it occurred to the engineers that such a quality could be useful to the electric utility industry by reducing heat-induced sag on overhead transmission lines.

The innovative product that emerged from that idea was a conductor composed of a ceramic fiber-reinforced aluminum core wrapped in aluminum-zirconium wires. Basic feasibility testing began in the late 1990s. Less heat-induced sag was only one of its potential benefits. The high conductivity of aluminum combined with the metal's relatively light weight suggested the experimental product could carry more power than conventional steel conductors while using the same infrastructure. For line upgrades, that would mean no tower construction, no additional easements and fewer environmental issues.

In 2000, 3M proposed a large-scale testing program to the U.S. Department of Energy (DOE) and several U.S. utilities. The following year, intrigued by the new conductor's promise, the DOE began a field test at its Oak Ridge National Laboratories, while similar test projects were inaugurated by Xcel Energy, Hawaiian Electric and Western Area Power Administration (WAPA) to gather experience in a wide range of climate conditions and weather extremes. In 2004, WAPA installed additional test sites in the Arizona desert, Salt River Project began a test installation just outside of Phoenix and the Bonneville Power Administration undertook field testing in Washington State.

Meanwhile, in August of that same year, Xcel Energy decided that four years of successful field testing had established the new conductor's dependability and committed to ACCR's first commercial application — a key 10-mile (16-km) line designed to accommodate peak power demand for the Twin Cities area. That line was energized in May 2005, and one month later, WAPA chose ACCR to upgrade a 20-mile (32-km) circuit line along the Colorado River supplying power to communities in Arizona, California and Nevada.

Today, ACCR is in use by more than two dozen U.S. utilities and in six other nations, including those with the world's three fastest-growing economies: Brazil, China and India.

Companies mentioned:

3M Bonneville Power Administration

Companhia de Transmissão de Energia Elétrica Paulista

Energy Minister Edison Lobão

Hawaiian Electric Co.

Oak Ridge National Laboratories

Salt River Project

U.S. Department of Energy

Western Area Power Administration

Xcel Energy

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