See Inside November 2007

Rotor in Motor

Replacing aluminum with copper in electric motors saves energy

Afew percentage points of improvement in energy efficiency are rarely noteworthy, but those digits add up fast when the technology involved annually consumes several hundred billion kilowatt-hours of electricity worldwide. About two thirds of the juice used by American industry, for example, drives the countless electric motors running pumps, compressors, fans, conveyors and other devices in factories and plants nationwide, according to the U.S. Department of Energy. After a decade-long R&D effort, engineers have succeeded in wresting a bit more efficiency from these motors. And industry has just begun to take notice.

Small versions of so-called three-phase AC induction motors, which generate from one to 20 horsepower, can convert as much as 90 percent of the power they draw into rotary mechanical force. Today’s standard designs feature rotors—rotating electromagnetic armatures—composed of die-cast aluminum, but motor engineers have long known that copper rotors would save energy, says metallurgist Dale Peters. “Copper has substantially higher electrical conductivity than aluminum, which significantly cuts the resistive losses in rotors,” he explains. “But copper melts at 1,083 degrees Celsius, significantly hotter than aluminum’s melting point, which poses big problems for die casters.”

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