Overhead power lines look alike to the casual observer. The thick cables run in graceful shallow curves from pole to pole, so ordinarily the eye skips over them.
But on a day when electricity demand is peaking and the full load of current is moving through the lines, a keen watcher can see something amazing. As the cable gets hotter due to the increased flow of electricity, the steel-cored power lines gradually begin to sag into deeper curves between each support pole.
That sag can have far-reaching effects. A power line sagging into tree limbs set off the chain of events that led to the power outage in 2003 that blacked out several New England states and part of Canada.
General Cable of Highland Heights, Kentucky, and Composite Technology Corporation (CTC) of Irvine, California, offer a unique solution to the problem. In January 2005, they introduced a new cable with a non-metallic core.
Benton Wilcoxon, CTC chairman and CEO, says, “Instead of steel, the core of this new cable is a high-tech carbon and glass composite. This composite has greater strength than steel, and does not sag as it gets hotter.” This novel composite core is similar to the material used in the tail section of a Boeing 777 jet.
In the utility industry, the old-style cable is known as
ACSR, which stands for aluminum conductor steel reinforced. That design was introduced more than a century ago, in 1895, when Edison Electric ordered the first reels of cable with copper wrapped around steel. The steel core is simply the base; the electricity flows through the outer wrapping of copper wires. When copper became too expensive during wars in the first half of the 20th century, aluminum wires wrapped around the steel core became the industry standard.
The new cable is known as ACCC (aluminum conductor composite core) and goes by the trade name TransPowr.
“This new core material we invented is more compact than steel,” Wilcoxon explains. “That means the center of the cable weighs less and has a smaller diameter. This allows us to add more aluminum in the outer wrap, yet the entire ACCC cable still has the same external dimension as the old-style ACSR cable. What this means for utilities is that they can run up to two times as much power through this new kind of cable than was possible with comparably sized steel-cored cables.”
Having the same dimensions, gross weight per linear foot, and tension requirements also means that the new ACCC cable can be mounted on existing poles and towers without additional modifications.
Increasing capacity in existing power corridors is a key advantage to the new cable. In the past, as demand increased in a particular corridor of the grid, a utility would begin the lengthy process of arranging to build a new corridor. But with the new cable’s increased capacity, additional power can follow the same route, making it unnecessary to build a new section.
When a new corridor is needed to bring electricity to a new service area, the new cable offers yet another advantage: since ACCC cable doesn’t sag, support towers in a brand new corridor can be spaced further apart, thus saving on construction costs.
To find out more about composite core cable, visit CTC’s Web site at www.compositetechcorp.com.
Next month: Energy Awards