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Creating a New Market: Testing and Promoting the Copper Motor Rotor
(continued) The level of consistency from copper rotor to rotor throughout the tests was incredibly high and not seen in aluminum die casting methods to date. The efficiency of the motors with copper rotors averaged 90.7 percent; all were within a range of 90.6 to 90.8. The process variables, such as fill rate and quenching media, had no effect on the final results. Due to the high quality of the casting with very little porosity, no balancing weights were required. If this practice could be brought to the production level, the costly balancing procedure would be eliminated. Because aluminum rotors have more variability in porosity, they are typically longer than needed to compensate for quality. Consequently, high-quality copper rotors could be reduced in stack length and provide the same efficiency at reduced material cost. Motors Designed Around a Copper Rotor Subsequent to the above tests, another set of tests was conducted on a series of rotors optimized for use of copper. The stator winding and iron core laminations were modified from standard motor design to gain the best possible results for the copper rotor. The results were even better than those from the previous set of tests. On average, copper rotor losses were 40 percent lower than those of an equivalent aluminum motor rotor. Total losses decreased 23 percent using the copper rotor. The operating temperature of the motor decreased even further than in previous tests. And, efficiency increased an impressive 1.6 percentage points from 90.9 to 92.5 percent. As motors have become more efficient over the past two decades, the industry is approaching a point of diminishing returns. After the adoption of cast copper rotors, only two known technologies are left to explore that could improve motor efficiency – amorphous steel laminations and superconducting stator windings – both presently extremely expensive. Further Developments Testing has continued since the CDA June meeting. Independent tests were performed by a motor company that replaced their existing motor rotors with copper. The motor sizes were 3kW, or 4 hp. The efficiency test results show a reduction in overall loss exceeding 20 percent, without even measuring stray load losses. Measurements by two previous motor companies show significant improvements to stray load losses using copper rotors. Therefore, the test results for the third motor company are conservative. Reductions in losses should be greater than 20 percent using this rotor. |
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