Motion efficiency is bolstered with newer technologies: Motor Summit 2014
Three-phase, squirrel-cage asynchronous (or induction) motors have led the way to dramatic energy-efficiency improvements over the past 20 years. The gains were enabled by improved designs—such as use of more electrically active materials and motor circuit advancements—coupled with standardized testing and enactment of mandatory minimum energy performance standards (MEPS). Highly efficient advanced motor designs were among discussions at this 5th Motor Summit, hosted by European and international energy associations and co-hosted by the National Electric Manufacturers Association (NEMA) of the U.S. The event drew 180 participants to Zurich, Switzerland, during Oct. 7-9, 2014 (Figure 1).
It was no accident that ac induction motors were targeted for efficiency improvements as they represent a huge installed base of units worldwide. Rugged, relatively simple construction, and low production cost through large sales volume has made induction machines the industrial "workhorse" of electric motors. Energy requirements of motor-driven systems represent about 46% of total electric power generated globally.
One concise view of electric motor efficiency comes from the IE-class designation, defined in International Electrotechnical Commission (IEC) standard 60034-30 "International Efficiency (IE) Classes." The standard defines increasingly higher efficiency classes IE1 (standard) to IE4 (super premium) along with required nominal efficiency values for 0.12- to 1,000 kW motor sizes. Provision is made for an IE5-class (ultra premium). IE5-class motors are not yet rigorously defined, but proposed as able to reduce motor losses by 20% compared to IE4 class.
So far MEPS have become mandatory only in a select number of countries and only to the IE3 level. The U.S. has led the MEPS effort, with IE3 as the required efficiency level for new installations for some time. Canada and Mexico, among others, have followed, and other nations are heading toward adoption. The European Union has implemented the second of three stages toward IE3 parity as of Jan. 1, 2015, but will not reach full compliance for the all motor sizes until January 2017 (Ref. 1). Motors covered under U.S. regulations currently include virtually all categories of polyphase continuous-duty motors from 1 to 500 hp (0.75
to 375 kW).
As a reference point, an IE3-class motor translates approximately to NEMA Premium efficiency level as applied in the U.S. For example, a 200 hp (150 kW), 4-pole 60 Hz NEMA Premium motor has a required nominal efficiency of 96.2% at full load. A comparable 160 kW, 4-pole 50 Hz IEC motor must provide 95.8% nominal efficiency to be IE3 class.
It should be noted that as IE3 motors become mandatory in more countries, lower efficiency motors cannot legally enter the marketplace. Yet the overall transition has been slow; older, less efficient motors in use still comprise large numbers worldwide (see more at Ref. 1).
Motor manufacturers have kept ahead of mandatory efficiency standards, and today’s induction motor designs can meet requirements up to IE4. However, it can be a stretch for some smaller motor sizes and IEC frame sizes. One interesting development for meeting IE4 requirements is the die-cast copper rotor design used in select motor models from SEW Eurodrive and Siemens, among others. The various approaches used to bring induction motors to IE4 efficiency level raise their initial cost as well.
IE5 and beyond
IE4-class induction motors have demonstrated very high efficiencies, especially in larger power sizes. Still, motor developers and manufacturers continue to look ahead to further efficiency gains, even in the face of diminishing returns beyond existing levels. This is where topologies other than the venerable induction motor come into play.
Prime alternative topologies include synchronous reluctance (SynR) and permanent magnet (PM) ac motor types. "Alternative" topology—with the latest design refinements applied—rather than "new" topology is the proper perspective, because most electric motor types have historic origins. Alternative motor designs seek to eliminate the substantial rotor I²R heating losses inherent to the induction motor. Instead, the SynR design uses a rotor with multiple salient poles to optimize magnetic flux direction and produce variable reluctance as the rotor turns. And as the name implies, the PM rotor design incorporates permanent magnets either on its outer surface or internally. Both the SynR and PM motors have a stator structure similar to an induction machine.
A further differentiator of the alternative motors is that they can’t run directly from the line. That is, they require electronic control. (Actually, a "line-start" variant of the PM motor exists, but this hybrid design is not covered here.) The need for an electronic drive poses a slight efficiency setback for a SynR or standard PM motor and drive "system," compared to an induction motor that can run directly on line. However, a similar drive efficiency factor applies to the growing number of induction motors controlled by variable-speed drives.
John Petro, consultant at California-based JPEAM LLC, included the above motor topologies in the presentation "Next horizon for efficiency in electric motors" (Ref. 2). He cited examples of commercial and prototype products with IE5 performance available from ABB, Hitachi, and NovaTorque.
ABB’s product, named the SynRM², is a synchronous reluctance motor offering energy losses reduced by 20% from the IE4 level. It was introduced in 2014 to target applications in the 1 to 15 kW power and 1,000 to 4,000 rpm speed ranges.
NovaTorque offers ferrite PM motors featuring innovative geometry that maximizes the surface area of the rotor and stator interface. The design enhances magnetic flux development across the interface and is said to obtain efficiency values exceeding the proposed IE5 level-even with the lower cost magnets.
Also in 2014, Hitachi developed an IE5 prototype motor with an amorphous metal core (stator). The 11 kW-rated motor reportedly obtains 96% energy efficiency at full load and reduces motor losses 30% below IE4 class (see Figure 2). Product commercialization is expected in 2015.
Importantly, all three of the above motor examples use ferrite magnets to obtain their high performance. Ferrite magnets are seeing renewed development effort to make the material more competitive with higher strength but much costlier rare-earth magnets.
"In addition, there is significant work being conducted in Japan, the U.S., Europe, and likely China, on making motors that meet or exceed the IE5 standard," Petro said. "Motors beyond IE5 are in development, with cost reduction being the ultimate goal." Moreover, Petro noted the need to define still higher IE6, IE7, and IE8 efficiency classes. "Having these levels gives manufacturers targets to aim for and allows leading manufacturers to differentiate their products in the marketplace," he added.
Figure 3 shows these extended IE levels. Note that an expected 20% loss reduction per each energy class beyond IE5 would require a further 49% cut in motor losses. That’s quite an ambitious forecast but a worthy target.
What’s the most significant change likely ahead for motor design and associated increase in efficiency? Petro believes it will be the use of soft magnets, such as amorphous and nano-crystalline lamination materials. "This has already started in Japan and other parts of Asia and is likely to spread to the industrial motor market," Petro said. The Hitachi motor previously mentioned is one example of this initiative.
Use of amorphous metal magnets as a way forward for further motor efficiency gains was also mentioned in the presentation "New ideas for advanced MEPS" by Anibal De Almeida, University of Coimbra, Portugal (Ref. 3). Other Motor Summit presenters also suggested the importance of amorphous metals and low-loss nano-crystalline materials for motor magnets in the years ahead. Still, the processing of these magnet materials is complex and substantial work remains to perfect the best manufacturing methods needed.
A recent European Commission study on energy efficiency has extended its scope to cover technologies other than three-phase induction motors, explained De Almeida. Again, the main candidates are synchronous reluctance and permanent magnet ac motors. De Almeida noted the recent IE5-caliber motors in the market from ABB, Hitachi, and NovaTorque (see above), and added another example from WEG SA. This PM ac motor introduced in 2014 is part of WEG’s W22 series and reportedly offers 96.6% efficiency at full load with losses lower than IE4.
High torque-to-size ratio has been a characteristic of PM ac motors. Earlier, rare-earth (RE) magnets had been the choice to deliver the highest performance. Over the past few years RE magnet materials have run into issues of very high cost and supply uncertainty. One alternative being explored is to reduce or eliminate the most costly elements in RE magnet compounds—such as neodymium and dysprosium. Research on other potential PM materials is also on the rise.
Meanwhile, ferrite (or ceramic) magnets provide another alternative. This lower-cost, plentiful magnet material has seen wide usage but carries the downside of about 3:1 lower power density compared to RE neodymium-iron-boron magnets.
Extensive research and development have gone into improving the power of ferrite magnets through higher grade compounds, design refinements, and innovative motor configurations. Recent introduction of new ferrite magnet motors speaks for the progress made to date. "Low-cost ferrite magnets are alive and well," De Almeida said.
Electric motor operation at less than full load and speed has become an important consideration with the increasing numbers of motors under control of a drive. However, published MEPS only prescribe full-load efficiency values. The need to define part-load efficiencies-particularly for pump and fan systems-was emphasized by Steve Dereyne, University of Ghent, Belgium, in the presentation "Total drive train optimization" (Ref. 4).
Dereyne further noted that IE4 to IE5 efficiency levels have taken induction motors almost to their technology limits. The synchronous reluctance motor was again mentioned as a promising alternative. In an industrial fan application test case, a SynR motor was evaluated as an alternative to a standard IE2 induction motor. Basic ratings of the machines were 11 kW and 1,500 rpm. The SynR motor gave promising efficiency results, for example, more than 5% higher efficiency at nominal load—and also maintained superior part-load efficiency compared to the induction motor.
Part-load motor operation was included in "Efficiency measurements of converters and motors," presented by Pierre Angers, Hydro Quebec, Canada (Ref. 5). Angers tested four types of 75 kW motors (induction, SynR, switched reluctance, and PM ac) driven by a variable-speed drive at torque and speed combinations from 100% to 10% (20 test points). The PM motor-drive system had the highest combined efficiencies at all speeds, according to Angers.
"Differences between the PM system efficiencies and others are minimal: from four percentage points at 100% speed up to eight to 10 percentage points at 25% speed," Angers said. "Test results tend to demonstrate a general efficiency advantage of PM technology compared to the others. The SynR is a net follower with slightly lower efficiency over the range of operation."
Future motor influences
Other new technologies are likely to impact the future design of electric motors. Ubiquitous 3D printing technology is one of those-although "additive layer manufacturing" (ALM) is a more fitting descriptor for that ongoing major development.
Alex Chausovsky—manager and senior analyst for industrial automation, at IHS Technology (USA)—concluded his presentation "Motor market update" with a section on the impact of 3D printing technology (Ref. 6). Chausovsky referred to ALM as a "transformative manufacturing process" that will have a bearing on motor technology. For example, he suggested the possibility of new rotor designs built without traditional laminations.
In the next several years, ALM will likely take on serious industrial manufacturing applications, working with types of metals and other industrial materials associated with electric motors. Chausovsky mentioned ALM’s ability to work with stainless steel, nickel and other alloys, and ceramics, among other materials.
Upcoming in a shorter time frame is another technology conference that addresses electric motor system efficiency and is associated with Motor Summit. This conference is EEMODS (Energy Efficiency in Motor Driven Systems), which has been held in alternate years between the staging of Summits. The next event, EEMODS ’15, is scheduled to run in Helsinki, Finland, during Sept. 15-17, 2015.
– Frank J. Bartos, PE, is a Control Engineering contributing content specialist. Reach him at email@example.com
- Alternative motor designs seek to eliminate I²R rotor heating losses inherent to the induction motor.
- Ferrite magnets compete with much costlier rare-earth magnets.
- Amorphous metal and nano-crystalline magnets may be the next breakthrough for motor design and efficiency increase.
Energy requirements of motor-driven systems represent about 46% of total electric power generated globally.
References cited from Motor Summit 2014 including part 1 of this story from Nov/Dec. 2014 for Control Engineering.
1. "Motor Summit 2014: energy efficiency focus is on total motor systems" http://www.controleng.com/single-article/motor-summit-2014-energy-efficiency-focus-is-on-total-motor-systems/802eb6f9fcd45502070d2a4aa87597c0.html
2. "Next horizon for efficiency in electric motors," John Petro, JPEAM LLC
3. "New ideas for advanced MEPS," Anibal De Almeida, ISR, University of Coimbra, Portugal
4. "Total drive train optimization of industrial fans and pumps considering VFD driven motor, transmission and load," Steve Dereyne, University of Ghent, Belgium
5. "Recent results of efficiency measurements of converters and motors," Pierre Angers, Hydro Quebec, Canada
6. "Motor market update," Alex Chausovsky, IHS Technology