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Copper Development Association Inc. (CDA) and Siemens Energy & Automation, Inc. (SEA), an operating unit of Siemens AG, are leaders in the development and commercialization, respectively, of ultra-efficient, general purpose, AC induction electric motors containing die-cast copper rotors.
The U.S. DOE estimates that some 40 million electric motors are used in U.S. manufacturing operations and that motor-driven systems account for nearly 70% of all electricity used in industry and 23% of all electricity consumed in the USA. Thus, even modest increases in motor efficiencies will measurably reduce national energy consumption as well as greenhouse gas emissions.
The Challenge: Between 16% and 29% of electrical losses (and correspondingly reduced efficiencies) in AC induction motors stem from resistance offered by the die-cast aluminum conductor bars and end rings, or “squirrel cages,” in the motors’ rotors. For that reason, conductor bars in fabricated motors are made from copper, taking advantage of the metal’s 63% lower (by volume) electrical resistivity. Unfortunately, copper’s high melting point makes the metal difficult, and, until now, uneconomical to use in the die-cast cages found in most motors today. The problem is that high thermal fatigue stresses during casting cause dies to fail after a few hundred “shots,” thus prohibiting reasonable amortization of the dies’ high cost.
The Resolution: Recognizing this as an opportunity, CDA, the trade organization for the U.S. copper industry, initiated research to solve the die-life problem and thus make die-cast copper motor rotors commercially viable. In 1997, CDA organized and subsequently led an international consortium of motor manufacturers, die casters, and private and government scientists and engineers. Success came in 2003, when it was found that using a common superalloy in critical portions of the die and maintaining the entire die assembly at a temperature of at least 600 C avoided the onset of thermal fatigue damage. In 2004, CDA was granted U.S. Patent No. 6,786,272 B2 for this breakthrough.
The Realization: In 2006, SEA, a member of the CDA-led consortium, announced that its own R&D, based on the consortium’s findings, enabled the company to bring to market a line of ultra-efficient motors fitted with die-cast copper rotors. Their efficiencies surpass even those of NEMA Premium-rated motors. By carefully redesigning the entire motor to take full advantage of the electromagnetic advantages made possible by copper, and by instituting the stringent manufacturing quality requirements needed to exploit those advantages fully, SEA became the first ― and to date, the only ― world-class industrial/commercial motor manufacturer to offer ultra-efficient, general-purpose, die-cast copper-rotor motors to the global market. Moreover, the new motors are cost-competitive with comparable premium-efficiency models, making them economically attractive even in those developing countries where energy conservation and its environmental benefits are especially needed.
The Impact: U.S.A. ― Motors consume 674 TWh per year in the manufacturing and mining industries. Since copper-rotor motors realize an average three-percentage-point increase in efficiency over the spectrum of all motors currently in service, the potential energy savings offered by copper motors is 20.2 TWh per year. Some 250,000 copper-rotor SEA motors are already in use, and it is reasonable to assume that copper motors will rapidly gain the 20% market share currently enjoyed by premium-efficiency motors. When that goal is attained, the actual annual savings in the USA. will be 4 TWh, resulting in nearly three million metric tons of carbon dioxide removed from the atmosphere.
The Impact: Global ― Annual global electricity consumption is 15,000 TWh. If 23% of this total (3,450 TWh) can also be assigned to industrial-use motors, a 20% market share penetration by copper-rotor motors would reduce consumption by 21 TWh per year. Carbon dioxide emissions would be reduced by more than 15 million metric tons.
The Future: When die-cast copper rotor technology is extended to the much larger number of motors in commercial and consumer applications (appliances, air conditioning, etc.), the potential energy savings will more than double based on estimates of electricity usage by motors overall that range up to 70% of all electricity produced, a figure far greater than the 23% assigned to industrial motors alone.
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