Composite electrical cable installed in Brazil eliminates tower cost

3M Aluminum Conductor Composite Reinforced (ACCR) electric-power transmission cable bridges a 968m/3,177-ft span without intermediate tower support.

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CPFL Energia SA’s (Sao Paulo, Brazil) power distribution unit, CPFL Paulista (Campinas, Brazil), has installed and put into service a 3M Aluminum Conductor Composite Reinforced (ACCR) electric-power transmission cable across the Tietê River as part of a new line to boost power to northwestern portions of the state of São Paulo. ACCR, developed by 3M (St. Paul, Minn.), features a conductive aluminum/aluminum metal-matrix composite load-bearing core instead of a steel core. The 3M cable was chosen for the project because it would bridge the 968m/3,177-ft span without intermediate tower support.

The project originally involved a conventional steel-cored cable that would have required a tower on a small island about midway across the river. However, the island in question is currently under water as a result of a long period of above-normal rainfall in September 2009, when the swollen river submerged the island, according to Paulo Ricardo Bombassaro, engineering and planning manager for CPFL Energia. The patented 3M ACCR solution eliminated the need for the island tower, enabling a single segment of the 138 kV line to make the full crossing with 23m (75.5 ft) of overhead clearance to accommodate river traffic.

The Tietê River crossing is the third application of 3M’s new conductor in Latin America and the second by CPFL, one of Brazil’s largest investor-owned electric utilities, which serves some 6.5 million customers in four states. In the prior application, lightweight ACCR enabled CPFL to upgrade a line passing through a densely populated suburb of the city of Varzea Paulista without having to build larger towers, which would have caused expensive and disruptive logistical problems.

The 3M ACCR reportedly has higher temperature- and sag-resistance than steel-cored cable, and it can carry more than twice the electricity of conventional steel conductors of the same diameter. Because 3M’s ACCR is based on aluminum, it is less susceptible to moisture or UV damage than traditional conductors, and it has better corrosion resistance. ACCR is now in use by some two dozen utilities in the U.S. and six other nations. For more about 3M’s ACCR cable, see “Composites on the line” (link at right).