U.S. motor-driven system energy savings

Efficiency of motor-driven systems: Motor-driven system regulations are changing in the U.S. to improve efficiencies beyond individual motors. Considering the motion control system can deliver more than six times the power savings compared to motor efficiencies alone, according to NEMA committee members. Power electronics are helping.

By Rob Boteler, Bill Finley, and Tim Schumann April 11, 2016

Electric motor system efficiency and power electronics are impacting future energy saving opportunities as attention moves from motor efficiency to motor-driven system energy savings. In the U.S., the first move was to apply motor efficiency regulation. Next is addressing the system. Focusing on the motion control system can deliver more than six times the power savings compared to looking at motor efficiencies alone. 

Stage 1: motor as a component

U.S. motor efficiency regulation began in 1992. At this time, the motor already included efficiency data on each name plate. The U.S. Congress drafted legislative language that included definitions of products to be included as well as referencing test methods and efficiency levels. The motor community began a journey into federal regulation that continues today.

In 2001, motor manufacturers created a premium efficiency level that raised the efficiency levels above the federal requirement (NEMA Table 12-12). In 2010, this new level was added to a second round of regulation bringing the markets greater savings to a select category of motors know as Subtype 1, required to meet NEMA Table 12-12, and Subtype 2, required to meet table 12-11. These categories impacted approximately 40% of the units sold each year. In 2014, a third round of regulation was released that will take effect June 1, 2016. This latest round of regulation essentially covers all polyphase motors from 1 hp (0.75 kW) to 500 hp (375 kW). This latest round of regulation was carefully constructed to expand the scope of products to be covered while paying particular attention to unintended consequences that would defeat the energy saving goal of the rule. The motor community worked diligently with the energy advocates and the U.S. Dept. of Energy to create a regulation that took into account mechanical and electrical issues that would undermine the regulation if an efficiency level were to be increased to a point that triggered any or all of the following 10 consequences. 

Higher efficiency risks

There were 10 areas considered by the group as "potential consequences" or risks to raising efficiency levels beyond the NEMA Table 12-12 (IE3) levels in existing rules.

  1. Torque necessary to start loads may be compromised potentially requiring a jump to a higher motor horsepower rating.
  2. Power factors may diminish, forcing utility or plant modification to correct.
  3. Inrush currents may increase, requiring cable and switch gear replacement.
  4. Mechanical sizes may increase, eliminating retrofit ability.
  5. Repair of failed motors as an alternative may increase, placing previously unregulated product back in service for many more years.
  6. Motor supplier resources will be used to overcome design and application issues that are better applied to power management solutions.
  7. The remaining efficiency gains of the motor are extremely small when measured under controlled conditions. Under actual uses that include power quality and varying load conditions, the efficiency gain in industrial and commercial applications are questionable.
  8. Motor testing and lab variance may be outside their ability to accurately measure such small gains with necessary repeatability.
  9. The amount of active material such as copper, magnetic steel increases dramatically for an extremely small gain in efficiency (such as 11 kW motor needs about 60% to 70% more material to gain 1.3% efficiency increase).
  10. The investments needed to redesign and reconfigure production facilities would be better applied to the power drive system (motor + variable frequency drive) which delivers much greater energy savings than regulation in isolation of the motor as one component.

The Figure 1 graph from Michael Turner, Nidec U.K. Technology Center, provides a visual that helps explain motor energy loss (red) versus useful motor energy (blue). By continuing to peruse efficiency of the motor, the challenge would be to reduce losses, which in this example, are less than 5% the kW loss, exposing the motor user to one or more of the 10 issues discussed above. The greatest opportunity for energy saving (reduction in kWh) is achieved by adding the power converter to the motor-driven system to optimize the system and reduce the kW loss by 30%, 40%, 50%, or more. When seen in this perspective it becomes clear that the addition of the power converter to the motor-driven system has distinct advantages. 

Avoid dampers, throttling

In the past many motors ran without the benefit of electronic speed control devices. Therefore, the control of the output volume of the pump, fan, or compressor had to be throttled by closing the valve, dampers, or vanes. Though this will adequately control the flow, this is by no means an efficient method. There are significant losses generated in the throttling mechanism and the motor’s efficiency drops significantly at the lower operating speeds.

Next generation of savings, called Stage 2 here, for sake of discussion, will change the current metric from efficiency, expressed as a percentage, to energy savings (kWh) by employing power electronics within the power drive system to eliminate mechanical flow control devices. The European Union (EU) began looking at the system in EN 50598, which was published in December 2014. This was an excellent start in establishing a guideline for energy savings as it relates to the entire system.

This work is taking place today in an international standard Working Group (WG) 18 within the International Electrotechnical Commission (IEC). WG 18 is creating the international standard IEC 61800-9-1, 2, which establishes the needed methodology and necessary metrics. The work continues on establishing energy efficiency levels for entire systems. Figure 2 shows all the components that make up the system.

Learn more about stage 2 and see additional information about the authors.

Stage 2: power drive system

The second stage is to create standards that quantify energy saving delivered by a power drive system. It becomes clear that the motor is a critical part of this system, but it only makes up a small percentage of the losses in the Stage 2 energy saving opportunity.

Stage 2 will leverage the motor, inverter, and controls system referred to here as the power drive system (PDS). Also, in consideration are the starters, torque transmission devices, and of course the load (pump, fan, compressor) which is now referred to as the extended product. While moving forward on this topic, it was discovered that it was necessary for a metric to move to losses versus efficiency. The reduction in losses as a result of process control through the use of a PDS delivers the reduction in kWh.

It is necessary to use loss reduction versus efficiency when considering total system energy savings. Considering an extreme case where the application requires a period of operation within its duty cycle at or near zero speed where the efficiency is 0% it becomes a little clearer that efficiency is no longer a meaningful metric.

The work that is now ongoing in WG 18 (working group 18) is to establish the losses generated at various operation points and determine the savings in energy as a result of using a PDS, which includes the extended product. The system standard establishes a series of 8 points that can be used to evaluate the energy savings. These are shown in Figure 3.

These points have been developed to represent every possible application, but not all load points will be required for every application. For example, a variable torque application such as a centrifugal pump may only find three of the points relevant; PL (100,100), PL (100, 50), and PL (50, 25).

Reference losses of typical equipment in operation today are used as the basis for the loss reduction. These reference losses have been established for the complete drive module (CDM), motor, and PDS.

The CDM can now have IE levels established based on the loss reduction from a reference CDM, which is defined in the standard. The motors already have IE levels established in 60034-30-1. The IE3 level established in 60034-30-1 is in harmony with premium levels in NEMA MG1, Table 12-12, regulated in the U.S. With this standard it will be necessary that the motor and inverter manufacturer provide the losses at all the required load points as requested by the system integrator who will be combining the entire system. The standard also provides a methodology for calculating or testing for all the losses of the inverter and supporting CDM equipment. It has been determined that the motor losses at any load point can be extrapolated from 7 points that can be provided by the motor manufacturer.

This method for extrapolation will be covered in detail in IEC 61800-9-2 and in IEC 60034-30-2. Methods for testing or calculating the losses for the motor at these load points are covered in the motor standard 60034-2-3 still in progress.

Using the methodology covered in the future IEC standard 61800-9 series, the system integrator now has the tools to accurately predict losses of the system. If the losses are equal to the losses of the reference PDS then the system is an IE 1, but if the losses are 20% lower than the reference losses of the PDS then it is an IE2 PDS. Even more important, the system integrator can now look at the extended product and compare the losses of the extended product versus the losses that would have occurred without a CDM by just throttling the load. The system integrator can then accurately establish the energy saving of the entire system. Considerably more energy savings can be achieved when evaluating the entire system rather than just the individual components. Incorporating the PDS advantage in stage 2 can increase the power saved by over six times the amount that could be saved by relying solely on the motor component efficiency.

NEMA Motor Generator Section member representatives authors are: Rob Boteler of Nidec Motor Corp. (chairman NEMA Energy Management Committee), Bill Finley of Siemens, and Tim Schumann of SEW Eurodrive. Edited by Mark T. Hoske, content manager, Control Engineering, CFE Media, mhoske@cfemedia.com.


Key concepts

U.S. regulation is moving from motor to motor-driven system.

A third round of motor efficiency regulation starts June 1.

The European Union (EU) began looking at the motor system in EN 50598, published in December 2014.

Consider this

Would six times the power savings be attractive in motor systems?


Related news: $25 million in funding for motor efficiency advances

The U.S. Dept. of Energy (DOE) announced, on March 11, up to $25 million in available funding aimed at advancing technologies for energy-efficient electric motors through applied R&D. It is part of the Obama Administration’s Mission Innovation effort to double clean energy research and development (R&D) investments over the next 5 years. The effort will fund innovative technologies that will significantly increase the efficiency of electric motors, which use approximately 70% of the electricity consumed by U.S. manufacturers and nearly a quarter of all electricity consumed nationally, according to the statement from DOE Office of Energy Efficiency and Renewable Energy. Link to more information, below.

Edited by CFE Media from DOE EERE information. 

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Author biographies

Rob Boteler is chairman NEMA Energy Management Committee and government relations consultant with Nidec Motor Corp., St. Louis, Mo., since 2011. He was director of marketing for U.S. Motor Division of Emerson Electric 1987 to 2011. Boteler was one of two motor manufacturer representatives to address the U.S. Congress as part of Epact 92, serving also as industry spokesperson in the drafting of the Energy Act of 1992 along with The American Council for an Energy Efficient Economy (ACEEE).

Boteler has been chairman of the NEMA motor section energy committee, previously the energy management task force since 1992. In this role he has lead the NEMA efforts in the Energy Independence and Security Act amendment to the original Epact motor regulation and most recently a second amendment taking effect June 1, 2016. He was the primary NEMA representative for drafting small motor regulations covering ¼ to 3 hp single and polyphase electric motors implemented in 2015. Boteler is currently drafting a proposal to amend the current small motor regulation that will add more products to be covered and establish a timeline of 5 years for implementation allowing end users and OEMs the time necessary to fully adopt changes.

Boteler has participated in DOE rule-making and ASRAC committees establishing regulations for pumps, fans, and compressors. He also serves as a visiting fellow to ACEEE in the development of power drive system labels identifying high performance extended product systems that will greatly reduce kWh in commercial and industrial motor-driven systems.

William Finley is the senior director of technology and innovation for Siemens Industry Inc., Large Drives USA. He has published more than 30 technical papers and holds multiple patents. He is chairman of multiple NEMA sub-committees, IEC maintenance teams, as well as the Technical Advisory Group Administrator in the U.S. for motor standards within IEC TC2. He is the U.S. expert on many motor-related performance and test international standards and working groups and the U.S. expert on IEC TC 22, SC 22G for system efficiency regarding drives and motors.

Tim Schumann is the senior electronic, motor, and NEC code support engineer working in the Corporate Engineering group for the U.S. operations for SEW-Eurodrive Inc. He is chairman of the NEMA Motor and Generator Technical Committee, Convener of IEC TC22/22G Working Group 18 responsible for IEC 61800-9 series for Power Drive Systems, and involved in several other committees within NEMA and IEC. He has been with SEW-Eurodrive for more than 27 years.