Copper Rotor Motors
Motor: Copper Rotor vs. Aluminum Rotor
Motors up to 20 horsepower with lower resistance losses in their copper rotor conductor bars, resulting in higher efficiency.
Item ID: 432
Commercial, Industrial, Agricultural
Motors & Drives--Motors
Copper rotor motors are 1 to 20 horsepower, basic alternating current induction motors with a reduced-loss copper rotor. Resistance losses in the rotor conductor bars account for about 25% of total motor losses, and copper rotors have 66% fewer losses compared to induction motors with conventional die cast aluminum rotors. Reduced electrical losses translate to less heat rejected into the motor enclosure. As a result, a smaller cooling fan can be employed, which reduces friction and windage losses and improves motor full- and part-load efficiency.
Energy savings depend on the horsepower rating and synchronous speed of the motor, efficiency class of an existing operating motor, motor oversizing, loading imposed on the motor by the rotating equipment, and annual operating hours. Replacement with a Premium Efficiency copper rotor motor should occur when the operating motor fails or if an existing standard efficiency motor operates more than 2,000 hours a year. It is often cheaper to purchase a new Premium Efficiency copper rotor motor than to repair a failed motor. Savings are greatest when motors operate for extended periods of time. Copper rotor motors come in NEMA and IEC frames, so they can be drop-in replacements for conventional motors.
Copper rotor motors generally exceed the Premium minimum full-load efficiency standards by 0.6 to 2 percentage points. General purpose copper rotor motor costs are about 11% to 17% higher than conventional Premium Efficiency motors, so simple paybacks are attractive when annual operating hours exceed 4000. Expected life and O&M costs are also very similar. Efficiency curves are flatter, so they have added benefits when operated with adjustable speed drives and when loads are frequently light.
Baseline Description: New Purchase of Premium Efficiency Motor
Baseline Energy Use: 7127 kWh per year per hp
Based on continuous operation of a 100% loaded, 10 hp Premium Efficiency 1800 RPM motor with a full-load efficiency of 91.7%. That gives energy usage of 71,265 kWh/yr. To get the value per horsepower, divide by 10 to get 7127 kWh/hp/yr. Annual energy use and savings would be much greater if we were examining the replacement of an old, standard efficiency or energy efficient motor.
Manufacturer's Energy Savings Claims:
"Typical" Savings: 1%
Savings Range: From 1% to 2%
Rotor losses typically account for about 25% of total motor losses, and copper rotor motors offer improved efficiency. Resistance or I2R losses in the rotor conductor bars decrease because copper has a volumetric electrical conductivity about 66% higher than aluminum. Reduced electrical losses translate into a reduction in the amount of thermal energy rejected into the motor enclosure. A lower temperature means that a smaller cooling fan can be employed, resulting in reduced friction and windage losses. Stray load losses are also exceedingly low for copper rotor motors.
Tests made using the IEEE/ANSI 112-1996 (Institute of Electrical and Electronics Engineers/American National Standards Institute) efficiency testing protocol show that copper rotor motors generally exceed the Premium minimum full-load efficiency standards by 0.6 to 2 percentage points. Typical test results are shown below:
|HP Rating ||3600 RPM ||3600 RPM ||1800 RPM ||1800 RPM |
| ||Premium Efficiency, % |
|Cast Copper Rotor Motor Efficiency (note 2), % ||Premium Efficiency, % ||Cast Copper Rotor Motor Efficiency (note 2), % |
|1 ||77.0 ||88.5 ||85.5 ||86.5 |
|2 ||86.5 ||88.5 ||86.5 ||87.5 |
|5 ||88.5 ||90.2 ||89.5 ||90.2 |
|10 ||90.2 ||91.7 ||91.7 ||92.4 |
|20 ||91.0 ||92.4 ||93.0 ||93.6 |
1. Courtesy of the Copper Development Association
2.TEFC, 2-pole (3600 RPM) and 4-pole (1800 RPM) motors. Nominal efficiency at full-load per manufacturer's catalog.
Assuming 8,760 hours per year operation for an HVAC fan (typical of a hospital application) with 100% loading, the expected energy savings due to installing and operating a copper rotor motor are 1185 kWh/year for a 3600 RPM, 10 hp motor and 540 kWh/year for an 1800 RPM motor. A 20 hp, 3600 RPM motor would yield savings of 1,088 kWh/year, while an 1800 RPM, 20 hp motor is expected to save about 900 kWh annually. While the savings are small on a per-motor basis, large facilities may operate many small HVAC motors.
The actual savings in a particular application will depend on the hours of operation, motor loading, whether or not a variable frequency drive (VFD) is used, and baseline efficiency. Savings estimates will be much higher if compared to a standard efficiency motor, which is still by far the most common industrial motor in the field.
Best Estimate of Energy Savings:
"Typical" Savings: 1%
Low and High Energy Savings: 1% to 2%
Energy Savings Reliability: 4 - Extensive Assessment
Energy savings are dependent upon the horsepower rating and synchronous speed of the motor, efficiency class of an existing operating motor, motor oversizing, the loading imposed on the motor by the rotating equipment, and annual operating hours. Generally, motors should operate more than 2,000 hours a year to justify an immediate change-out with a Premium Efficiency or Premium Efficiency copper rotor motor. The simple payback for installation of a "greater than Premium efficiency" copper rotor motor instead of a conventional premium efficiency motor is attractive for applications that exceed over 2,000 annual operating hours. Copper rotor motor upgrades are most attractive when an operating standard efficiency motor fails and requires repair. For motors that are 20 hp and below, it is often cheaper to purchase a new Premium Efficiency copper rotor motor than to repair the old motor. Savings are greatest when motors are operated for extended periods of time.
Energy Use of Emerging Technology:
7,055.7 kWh per hp per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Based on use of a continuously operating 100% loaded 10 hp 1800 RPM copper rotor motor with a full-load efficiency of 92.4%.
Potential number of units replaced by this technology:
In this analysis, we only include industrial motors, and only those between 1 and 20 hp, since those are the sizes of copper rotor motors that are available. Trying to estimate or find the number of horsepower in service in the Northwest is challenging. What we can estimate, though, is the total energy usage of industrial motors, and divide that by the energy usage per horsepower calculated in the Baseline Energy Use field to get a number of hp that would give us that estimated total regional energy usage. According to the Northwest Power and Conservation Council's Sixth Power Plan estimates, industrial energy usage in the Northwest in 2014 is estimated to be approximately 4000 aMW, or 35,040 billion kWh/yr. (NWPCC, 2010 Pg 3-6) The U.S. Department of Energy (US DOE) estimates that 70% of industrial energy usage is motors, or 24,500 billion kWh/yr. Of this, approximately 24% of the energy usage is between 1 and 20 hp, based on typical horsepower distribution estimated by the US DOE (XENERGY Inc., 2002 App B). That gives us approximately 7.3 million hp of industrial motors in the Northwest between 1 and 20 hp.
Regional Technical Potential:
0.06 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: hp
Emerging Technology Unit Cost (Equipment Only): $674.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $497.00
Copper rotor motor costs are 11% to about 17% greater than those for conventional, aluminum squirrel-cage, NEMA Premium Efficiency motors of equal or lower efficiency. (Note: motor costs are constantly changing, due to changes in the commodity prices for copper, aluminum, and core iron.) Motor costs may vary from 20% to 60% off list price, with discount rates based on customer purchase history and suppliers' policies. Following is a Table showing general purpose, 1800 RPM Premium Efficiency copper rotor motor and convention aluminum rotor motor list prices and full-load efficiency values. Note that most industries receive a 50% discount off of list price. Prices and performance are for Siemens Premium Efficiency general purpose and copper rotor motors.
Prices are extracted from the "Low Voltage AC Motors: Selection and Pricing Guide", Catalog D81.2--2013, USA Edition, Siemens Energy and Automation.
Cast Iron Frame, Aluminum Rotor Copper Rotor Motor
Hp Rating List Price Full-Load Efficiency, % List Price Full-Load Efficiency, %
1 454 85.5 505 86.5
2 542 86.5 604 87.5
3 623 89.5 695 90.2
5 709 89.5 791 90.2
10 1,209 91.7 1,348 92.4
15 1,542 92.4 1,804 93
20 1,857 93 2,172 93.6
Simple payback, new construction (years): 27.6
Simple payback, retrofit (years): 105.1
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
For new motor purchases, the simple payback for this technology can be immediate because the price of the copper rotor motor may well be less than the price of a NEMA Premium Efficiency squirrel cage induction motor. In 2013, copper rotor motors had an 11% to 17% price premium when compared with a new Premium Efficiency iron frame aluminum rotor motor. When replacing existing motors at their time of failure, the simple payback depends on many variables, including new motor list price discount (which can vary by customer, changing the simple payback by a factor of 2 to 6), repair costs for the failed motor (if a motor repair versus replace analysis is being done), annual operating hours, motor load or load profile, utility rates for both energy and demand charges, and the availability of utility incentives.
Assuming a 50% list price discount factor, installation of a copper rotor motor instead of a Premium Efficiency motor that just exceeds the mandatory federal minimum value produces an annual energy savings of 345 kWh (assuming a 70% load on a 10 hp motor that operates for 8,000 hours per year). The assumed efficiency of the copper rotor motor is 92.4% versus 91.7% for the conventional Premium Efficiency motor. The price premium is $69.50 when a 50% list price discount factor is assumed (this is a typical discount for industry). At $0.09/kWh, this yields a simple payback of 2.24 years. These motors are suitable for materials handling, pumps, fans, compressors, and other industrial applications.
Copper rotor motors are basic motors with a reduced-loss copper rotor. Resistance losses in the aluminum rotor conductor bars of conventional induction motor designs account for about 25% of total motor losses. Copper rotor motors offer improved efficiency as rotor losses are greatly decreased because copper has a volumetric electrical conductivity about 66% higher than aluminum. Reduced electrical losses translate into a reduction in heat rejected into the motor enclosure, meaning a smaller cooling fan can be employed, which reduces friction and windage losses and improves copper rotor motor full- and part-load efficiency.
Copper rotor motors are sometimes called "Beyond NEMA Premium" motors. Dynamometer testing indicates their full-load efficiency exceeds the Premium Efficiency motor standards. Siemens Energy and Automation – the only manufacturer in the U.S. currently licensed to provide copper rotor motors – has introduced a line of die cast copper rotor motors in North America for general purpose, totally enclosed, fan-cooled TEFC, and IEEE 841 (severe-duty) configurations in ratings from 1 hp to 20 hp.
Standard practice is the continued operation of old standard or energy-efficient motors or replacement through purchase, installation and operation of conventional NEMA Premium Efficiency squirrel-cage induction motors. Premium efficiency motors (copper rotor or conventional) are often 2% to 8% more efficient than old standard efficiency motor models.
Motor efficiency standards are constantly evolving, so standard practice evolves as well. In 2012, the U.S. Department of Energy (US DOE) adopted energy efficiency standards for fractional horsepower polyphase and single phase motors. These standards cover motors operating at 3600, 1800 and 1200 revolutions per minute (RPM), and include capacitor-start/induction run and capacitor-start/capacitor run open motors rated between 0.25 hp and 3 hp. These small motor standards are applicable in March of 2015.
The National Electrical Manufacturers Association (NEMA), whose members manufacture electric motors and several other groups, filed a petition with the US DOE recommending both new and more robust energy efficiency standards for the larger types of electric motors used in commercial and industrial applications, such as pumps, conveyors and fans.
Petitioners include the American Council for an Energy Efficient Economy (ACEEE), the Appliance Standards Awareness Project (ASAP), Earthjustice, Natural Resources Defense Council (NRDC), Alliance to Save Energy (ASE), Northwest Energy Efficiency Alliance (NEEA), Northeast Energy Efficiency Partnerships, and Northwest Power and Conservation Council.
In 1995, the Copper Development Association undertook a project to substitute copper for aluminum in the “squirrel cage” structure of the motor rotor. The goal was to increase motor efficiency.
A short mold life was the limiting factor in achieving a cost-effective copper rotor die casting operation. Copper has a higher melting temperature than aluminum (1,083°C versus 660°C). Die life was extended through materials selection (use of nickel-based superalloys) and by preheating the die assemblies to approximately 650°C. Preheating minimizes expansion- and contraction-induced thermal fatigue that leads to premature die cracking. Additional problems that were ultimately resolved included porosity, die checking and variations in electrical conductivity.
Copper rotor motors were developed, tested, and have been shown to operate with efficiencies above the current (2012) NEMA Premium efficiency levels. They are now available in the U.S. market at ratings up to 20 hp. Siemens Industry Inc., under license with the Copper Development Association, has introduced a line of “Ultra-Efficient” die cast copper rotor motors. These motors are available in North America for general purpose totally enclosed, fan cooled (TEFC) and IEEE 841 (severe-duty) configurations in 1200, 1800 and 3600 RPM ratings up to 20 hp.
SEW-EURODRIVE uses die cast copper rotor motors in their gear motor product lines. Conventional Premium efficiency motors are often longer and sometimes have an increased diameter than their Standard Efficiency counterparts. High power density copper rotor motors fit existing gearbox designs by providing the desired efficiency improvement with no change in motor dimensions. SEW-EURODRIVE also produces a line of energy efficient general purpose copper rotor motors up to 50 hp.
The efficiency curve for a copper rotor motor is very flat compared with that of a conventional squirrel-cage induction motor; even a 10 hp 1800 RPM copper rotor motor maintains a high efficiency down to the 25% load point (values are 92.7% at 100% load, 93.0% at 75% load, 92.5% at 50% load, and 89.1% at just 25% load). This performance curve is very useful for adjustable speed drive applications or for machines that operate for a portion of the time partially unloaded or at light loads (like an air compressor with load/unload controls). Copper rotor motors come in standardized NEMA frame designs, so a direct retrofit of an old, standard efficiency or energy efficient motor is possible (mounting bolts line up, and shaft height and diameter are the same).
End User Drawbacks:
Operations and Maintenance Costs:
O&M costs should be comparable to those of standard aluminum cage induction motors. Maintenance consists of periodic cleaning of motor cooling fins and inlet grills, and alignment testing.
There is no major difference in the life of a copper rotor versus a standard squirrel cage induction motor. Motor bearings and coupling should exhibit comparable lives to those of conventional motors. Tests have shown that the temperature rise of a copper-rotor motor is comfortably within Class B (40°C) limits. Because the windings are equipped with higher temperature-rated Class F insulation, a long winding insulation life is expected.
The U.S. Department of Energy performed a national impact analysis in support of their proposal to increase the energy efficiency standards for commercial and industrial motors ("Preliminary Technical Support Document: Energy Efficiency Program for Commercial Equipment: Energy Conservation Standards for Electric Motors," July 23, 2012). They assumed average motor operating lifetimes of 5 years for 1 to 20 hp motors used in industrial applications, with 14 to 15 years assumed given a commercial sector application. Motors in that size range used in agricultural applications were assumed to have average lifetime of 13 years. (Motor mechanical lifetimes of about 32,000 hours are assumed. Operating life is then determined by dividing the mechanical lifetime by the expected annual operating hours.)
Competing technologies include repair and return to service of failed standard or Premium Efficiency motors. If a replacement motor is specified, the end user may select a conventional, squirrel cage, NEMA Premium Efficiency induction motor (technology #230), a permanent magnet motor (technology #431), a switched reluctance motor (technology #433), or a line-start permanent magnet motor (technology #434). The permanent magnet and switched reluctance motors are more expensive and require a controller than gives them variable speed capability, which increases savings in applications where variable flow may be provided to meet process requirements. These motors come in standard NEMA frame sizes.
Recent research has focused on the combined efficiency of a Premium Efficiency copper rotor motor when controlled with a variable frequency drive contrasted with a Permanent magnet motor with controller (which also has variable speed capability). The target market is hybrid and plug-in electric vehicle traction drives. Permanent magnet motors often used for vehicle propulsion require rare earth metals while copper rotor induction motors do not. Copper rotor motors have comparable torque density and peak efficiency and do not have degraded performance under high speed, low torque conditions.
Reference and Citations:
Electrical: Energy Efficiency -- Performance information and case studies
Copper Development Association Inc.
Copper Motor Rotor Research
Copper Development Association Inc.
Tests Show Mass-Produced Copper-Rotor Motors More Efficient than Nameplate Claims
Copper Development Association Inc.
Copper Motor Rotor Commercialized
Copper Development Association Inc.
Copper Rotors Cast Vertically
Copper Development Association Inc.
Mineral Producer Installing 150 Copper-Rotor Motors: Rising Energy Costs Drive Upgrades, Rapid Payback Expected
Copper Applications, A Case Study
Materials and Modifications to Die Cast the Copper Conductors of the Induction Motor Rotor
Die Casting Engineer
Copper-Rotor Motors + Variable Frequency Drives Maximize Savings at a Brass Mill
Copper Development Association Inc.
Copper-Rotor Motors + Variable Frequency Drives Maximize Savings at Water Treatment Plant
Copper Development Association, Inc.