Copper Shines in Motor Rotors

Use of rotors cast from copper brings efficiencies that let small motors handle big jobs. • Induction motors employing copper rotors can be smaller than equivalent versions with aluminum rotors. • Copper rotors exhibit lower losses than aluminum which lets them run cooler and be more efficient. Green technology: More efficient motors, Siemens Energy & Automation Inc., Today the NEMA Premium rating is the highest motor efficiency standard in the world. Spelled out in the Energy Independence and Security Act of 2007, it boosts mandated efficiency levels for motors covered under older legislation and applies standards to seven additional motor types. The stringent levels spelled out in NEMA Premium tables have fostered a lot of interest in motor architectures that can deliver high efficiency. One of those architectures uses a rotor cast from copper. Today three motor makers, , all make copper-rotor designs. FAVI doesn't sell in the U.S., but SEW and Siemens copper models first came on the U.S. market about three years ago. The motivation for a copper-rotor design stems not only from efficiency considerations but also from a desire to minimize the size of the motor. "When you make a motor more efficient, it typically gets longer," says Siemens Marketing Manager John Caroff. "We wanted to keep the footprint as close as possible to EPAct (Energy Policy Act of 2005) motors. Our technical group decided copper rotors would be a good way to accomplish this goal. Copper cuts down on the I2R losses though it is more costly and increases the weight of the rotor a bit." But all motor makers had to grapple with the fact that the losses, but also because the design eliminates cooling fins on the end of the motor as part of the short-circuit ring, so there are no windage losses. We further