Modified motor designs save energy

Modified motor designs save energy

by Greg Paula, Associate Editor

Reconfigured components such as rotors and fan blades plus a new generation of superconducting materials are resulting in more-energy-efficient motors

The 1992 Energy Policy Act takes effect this October, covering all general-purpose polyphase induction motors between 1 and 200 horsepower. It requires progressively higher efficiencies for higher horsepowers- -about 85 percent for a 5-horsepower motor, about 95 percent for 100 horsepower.

Baldor engineers are creating new motor designs relatively quickly using custom-designed software that can closely simulate operating conditions

To bring their motors into compliance, manufacturers have been modifying key portions of their standard designs, such as rotors and stators. Traditionally, manufacturers have had several standard configurations, with the other components of the motor modified as necessary for different horsepower ratings and speeds. That approach is now changing. Baldor Electric Co. in Fort Smith, Ark., for example, is switching to a larger number of configurations, with each satisfying fewer applications.

Another consideration is the cooling fan. Smaller fans cannot move as much air, but as more specific configurations produce lower losses, there is less heat to be dissipated. Smaller fans also use less energy. Further, a higher grade of electrical steel inside the motor and a more uniform grain structure and finish can produce lower magnetic losses.

A more radical departure from traditional design uses superconductive materials. A superconducting motor yields virtually no losses. Although energy is required to cool the superconductor, there is still a net energy saving. Superconducting motors are not yet available commercially, but several prototypes have been built and tested, some with better-than-expected results.

The first commercial superconducting applications will be in large industrial motors of 1,000 hp and higher. Superconductors, however, will eventually make their way into smaller motors such as electric-vehicle drives. Large superconductor motors are expected to be introduced for commercial use around 2000.

Superconducting motors would have high capital costs, personnel would have to be trained, and the long- term behavior of superconducting materials is little known. Still, early results indicate that these hurdles are not significant enough to forestall the potential benefits.

The above was adapted from an article by Greg Paula, Associate Editor. The full text may be found in the January 1997 issue of Mechanical Engineering magazine. © 1997 ASME International.© To obtain a copy of this issue, click here.