The original targets identified by the ICA/CDA research team, for the die-cast copper motor rotors were threefold, as outlined below:
- Achieve a 10-15% further reduction in overall losses compared to today's energy efficient motors, or:
- Achieve the same efficiency as an aluminum rotor while reducing the total manufactured cost of the motor, or:
- Or reduce the overall weight of the motor while still achieving the same efficiency as a motor utilizing an aluminum rotor.
- View the reduction in losses achievable for motors utilizing copper rotors
- View reduction in total manufacturing costs
- View the weight reductions achievable
1.2.1 Reduction in Overall Losses
Due to the excellent electrical conductivity of copper, replacing the aluminum in a rotor's conductor bars with die-cast copper can produce a significant improvement in the efficiency of an electrical motor. Typically, however, an even greater improvement in efficiency can be achieved when the substitution of the aluminum by copper is accompanied by a redesign of the motor, to account for the improved properties of the copper conductor bars.
For example, Table 1.2.1.1 lists reports from the technical literature showing the magnitude of efficiency improvement that can be achieved when an aluminum rotor is simply replaced with one die-cast from copper. Other than the changes in the squirrel cage material, no other design changes were made to these rotors.
| Motor Power (HP) | Motor Frequency (Hz) | Efficiency | Improvement in Efficiency (percentage points) | Percentage Reduction in Rotor Losses | Ref | |
|---|---|---|---|---|---|---|
| Aluminum Rotor | Copper Rotor | |||||
| 2 | 50 | 78.0% | 80.3% | 2.3 | 53% | 5 |
| 2 | 50 | 81.1% | 82.5% | 1.4 | -- | 4 |
| 3 | 50 | 83.6% | 85.9% | 2.3 | -- | 4 |
| 4 | 60 | 83.2% | 86.4% | 3.2 | 58% | 1, 2 |
| 4 | 50 | 82.0% | 84.1% | 2.1 | 46% | 6 |
| 4 | 50 | 81.8% | 84.3% | 2.5 | 53% | 5 |
| 5 | 50 | 84.0% | 87.1% | 3.1 | -- | 4 |
| 5 | 50 | 83.0% | 86.0% | 3.0 | -- | 4 |
| 5 | 50 | -- | -- | -- | 38% | 1, 2 |
| 7.4 | 50 | 83.4% | 84.3% | 0.9 | -- | 3 |
| 7.4 | 50 | 83.0% | 84.3% | 1.3 | -- | 7, 8 |
| 7.5† | 50 | 74.0% | 79.0% | 5.0 | -- | 9 |
| 10 | 50 | 84.2% | 87.4% | 3.2 | 50% | 6 |
| 10 | 50 | 86.1% | 88.0% | 1.9 | 52% | 5 |
| 10 | 60 | 85.0% | 86.5% | 1.5 | -- | 10 |
| 20 | 50 | 90.1% | 91.0% | 0.9 | 40% | 11 |
| 40† | -- | 88.8% | 90.1% | 1.3 | -- | 1, 2 |
| 120† | -- | 91.4% | 92.8% | 1.4 | -- | 1, 2 |
| 270† | 50 | 92.0% | 93.0% | 1.0 | -- | 9 |
| † Calculations rather than experimental measurements | ||||||
Table 1.2.1.2 (below) lists the larger efficiency improvements that can be achieved when, not only are the aluminum rotor conductor bars replaced with copper, but the motor is also redesigned to account for the improved properties of the copper.
| Motor Power (HP) | Motor Frequency (Hz) | Design Change | Efficiency | Improvement in Efficiency (percentage points) | Percentage Reduction in Rotor Losses | Ref | |
|---|---|---|---|---|---|---|---|
| Aluminum Rotor | Copper Rotor | ||||||
| 1.5 | 50 | L | 75.7% | 82.8% | 7.1 | -- | 4 |
| 2 | 50 | L+ST | 78.0% | 83.5% | 5.5 | 58% | 5 |
| 4 | 50 | L | 82.0% | 84.5% | 2.5 | 46% | 6 |
| 4 | 50 | L + ST | 82.0% | 86.5% | 4.5 | 50% | 6 |
| 4 | 50 | L + ST | 81.8% | 88.2% | 6.4 | 63% | 5 |
| 7.4 | 50 | R | 84.1% | 88.4% | 4.3 | -- | 7 |
| 7.4 | 50 | R | 84.8% | 88.1% | 3.3 | -- | 4 |
| 10 | 50 | L | 84.2% | 88.1% | 3.9 | 50% | 6 |
| 10 | 50 | L + ST | 84.2% | 89.0% | 4.8 | 60% | 6 |
| 10 | 50 | L + ST | 86.1% | 90.7% | 4.6 | 59% | 5 |
| 15 | 60 | F | 89.5% | 90.7% | 1.2 | 40% | 1, 2 |
| 20 | 50 | L | 90.1% | 91.9% | 1.8 | 48% | 11 |
| 25 | 60 | Slot | 90.9% | 92.5% | 1.6 | 40% | 1, 2 |
| The key to the design changes are as follows: L = improved quality of lamination steel only; L + ST = improved quality of lamination steel & increased the stack length; F = Fan removed; Slot = slot redesigned for copper; R = complete redesign |
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1.2.1 References
- E.F. Brush, J.G. Cowie, D.T Peters & D.J. Van Son, "Die-Cast Copper Motor Rotors; Motor Test Results, Copper Compared to Aluminum", Energy Efficiency in Motor Driven Systems, Eds: F. Parasiliti & P. Bertoldi, Published by Springer, 2003, p 136 to 143
- D.T. Peters, J.G. Cowie, E.F. Brush, Jr. & D.J. Van Son, "Copper in the Squirrel Cage for Improved Motor Performance", The International Electric Machines and Drives Conference, June, 2003, Madison, WI
- Christophe Paris and Olivier Walti, "A New Technology to Make Rotors with Copper as Magnetic Conductor", Energy Efficiency in Motor Driven Systems, Ed. F. Parasiliti & P. Bertoldi, Springer, 2003, pp 152 to 161)
- E.F. Brush, Jr., D.T. Peters, J.G. Cowie, M. Doppelbauer & R. Kimmich, "Recent advances in Development of the Die-Cast Copper Rotor Motor", 2004
- Francesco Parasiliti & Marco Villani, "Design and High Efficiency Induction Motors with Die-Casting Copper Rotors", get reference
- E. Chiricozzi, F. Parasiliti & M. Villani, "New Materials and Innovative Technologies to Improve the Efficiency of Three Phase Induction Motors – A Case Study", ICEM 2004 Conference Proceedings, Lodz, Poland, Eds: S. Wiak, M. Dems & K. Komeza, 2004
- L. Doffe and O. Walti, "New Industrial Process to Make Squirrel Cage Copper Rotors and to Optimize Induction Machine Performance", Presented at PCIM, Nurnberg, May 27, 2004
- Favi Copper Info Rotor sheet #7, "Energy Report on Asynchronous Machine With Al or C97 Conductor Rotor"
- M. Poloujadoff, J.C. Mipo & M. Nurdin, "Some Economical Comparisons Between Aluminum and Copper Squirrel Cages", IEEE Trans. Energy Convers., Vol. 10, no. 3, 1995, September, p 415-418
- Sian Lie and Carlo Di Pietro, "Copper Die-Cast Rotor Efficiency Improvement and Economic Consideration", IEEE Transactions on Energy Conversion, Vol. 10, no.3, Sept 1995, p 419
- F. Parasiliti, M. Villani, C. Paris, O. Walti, G. Songini, A. Novello & T. Rossi, "Three Phase Induction Motor Efficiency Improvements With Die-Cast Copper Rotor Cage and Premium Steel", Proceedings of SPEEDAM '04 Symposium, Capri, Italy 16-18th June, 2004
1.2.2 Reducing Total Manufacturing Cost
Although the cost of die-casting a copper rotor is higher than that of die-casting an aluminum rotor, the overall cost of the motor utilizing the copper rotor can be lower. Due to the higher efficiency of the copper rotor, the overall length of the rotor (and motor) can be decreased, while still matching the performance of a motor utilizing an aluminum rotor. Shortening the motor eliminates some of the rotor and stator laminations, decreases the amount of stator windings, and reduces the length of the shaft, reducing cost in each case. As demonstrated in Tables 1.2.2.1 and 1.2.2.2 for 11 kW and 5.5 kW motors respectively, the increased cost of copper rotor is more than off-set by the cost savings elsewhere in the motor, and an overall cost decrease of about 14-18% is predicted.
| Motor Type | Steel Cost ($)† | Windings Cost ($) | Rotor Cost ($) | Shaft/Housing Assembly Cost* ($) | Total ($) | Cost Savings for Copper vs. Aluminum Rotor Motors | |
|---|---|---|---|---|---|---|---|
| Dollars | Percent | ||||||
| Copper Rotor Motor | 179.4 | 39.2 | 18.1 | 142 | 378.7 | $63.3 | 14.3% |
| Aluminum Rotor Motor** | 222.2 | 46.1 | 5.7 | 168 | 442 | -- | -- |
| † Figures are in US dollars *Includes burden for all components; selected direct portions of burden are also included within the columns for individual direct costs **Industry equivalent in EE (91.1%) and performance |
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| Motor Type | Steel Cost ($)† | Windings Cost ($) | Rotor Cost ($) | Shaft/Housing Assembly Cost* ($) | Total ($) | Cost Savings Copper vs. Aluminum Rotor Motors | |
|---|---|---|---|---|---|---|---|
| Dollars | Percent | ||||||
| Copper Rotor Motor | 122.9 | 19.9 | 11.4 | 117 | 271.2 | $59.3 | 17.9% |
| Aluminum Rotor Motor** | 155.7 | 32.8 | 4 | 128 | 330.5 | -- | -- |
| † Figures are in US dollars *Includes burden for all components; selected direct portions of burden are also included within the columns for individual direct costs **Industry equivalent in EE (91.1%) and performance |
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It should be noted that Tables 1.2.2.1 and 1.2.2.2 have been prepared on the basis of information from manufacturers, interviews, published references and assumptions based on standard methodologies. Because any forecast is subject to uncertainties, these projections are not represented as specific results that actually will be achieved.
1.2.3 Reduction in Overall Motor Weight
Although counterintuitive, the overall weight of a motor can also be reduced when replacing an aluminum rotor with one cast using copper. Again, the higher efficiency of the copper rotor allows the overall length of the rotor (and motor) to be decreased, while still matching the performance of a motor utilizing an aluminum rotor. Shortening the motor eliminates some of the rotor and stator laminations, decreases the amount of stator windings, and reduces the length of the shaft. As demonstrated in Tables 1.2.3.1 and 1.2.3.2 for 11 kW and 5.5 kW motors respectively, the increased weight of copper in the rotor is more than off-set by the weight savings elsewhere in the motor, and an overall weight reduction of about 20% is predicted.
| Motor Type | Rotor + Stator Weight (kg) | Weight of Windings (kg) | Weight of Rotor Conductor (kg) | Weight of Shaft + Housing, etc (kg) | Total Weight (kg) | Copper Rotor Motor Weight Reduction Vs Aluminum Rotor Motor | |
|---|---|---|---|---|---|---|---|
| Kg | Percent | ||||||
| Copper Rotor Motor | 43 | 8.7 | 5.9 | 18.1 | 75.7 | 17.1 | 18.4% |
| Aluminum Rotor Motor* | 54.6 | 10.2 | 3 | 25 | 92.8 | -- | -- |
| *Industry equivalent in EE (91.1%) and performance | |||||||
| Motor Type | Rotor + Stator Weight (kg) | Weight of Windings (kg) | Weight of Rotor Conductor (kg) | Weight of Shaft + Housing, etc (kg) | Total Weight (kg) | Copper Rotor Motor Weight Reduction Vs Aluminum Rotor Motor | |
|---|---|---|---|---|---|---|---|
| Kg | Percent | ||||||
| Copper Rotor Motor | 27 | 4.4 | 3.6 | 13.6 | 48.6 | 13.3 | 21.4% |
| Aluminum Rotor Motor* | 34.5 | 7.3 | 2 | 18.1 | 61.9 | -- | -- |
| *Industry equivalent in EE (91.1%) and performance | |||||||
It should be noted that Tables 1.2.3.1 and 1.2.3.2 have been prepared on the basis of information from manufacturers, interviews, published references and assumptions based on standard methodologies. Because any forecast is subject to uncertainties, these projections are not represented as specific results that actually will be achieved.