What’s next for motor efficiency?
What has changed with motor efficiency and what will happen to future “motor payback” as energy costs decline?
Previous discussions (CE, April 2016, “U.S. motor-driven system energy savings”) looked at a potential change in energy metrics for motor-driven systems. This change will move from measuring efficiency to measuring power use. Adding a variable frequency drive to the motor-driven system can regulate speed [load] and reduce overall energy use by a far greater amount than reducing motor losses.
The current motor regulations, implemented on June 1, 2016 (the NEMA table 12-12 level), were agreed to and established to maximize motor efficiency while maintaining the performance and physical motor size that would provide the best results and still allow users a direct replacement for a failed motor. Members of the National Electrical Manufacturers Association (NEMA) motor generator section fully support this regulation.
Both IEC 61800-9-1 and 61800-9-2 have passed the ballot and are now published. There has been no significant deviation with regards to the levels or how to use the standard from EN 50598. EN 50598, the source for the new IEC standard, previously published in Europe multiple years ago, established this methodology that has been used successfully for many years.
Easier for system integrators
Manufacturers are beginning to publish efficiency levels at the eight load points as discussed in the previous article and repeated below in Figure 1. Working group (WG) 18 has begun work on the new version of 61800-9-2 to address needs discovered in the past few years with the intent of improving accuracy and making it easier to follow by system integrators.
The WG also will look at improving the interpolation method between load points, and will attempt to increase the accuracy of the testing portion of the standard.
System view: Drives, pumps
There has been a discussion on whether it is necessary to add multiple International Efficiency (EI) classifications. While both the before-mentioned standards establish energy classes for the drives (previously not defined), it was decided to primarily focus on system efficiency classes due to the higher potential. Because drives typically have higher than 97% efficiency, increasing their efficiency only has a potential to decrease total energy by 3% if drives are 100% efficient. Of course this is impossible; even after extensive effort probably only a small percentage of that could be achieved. Drive efficiency can be increased with faster switching frequencies, which may damage a motor unless filters are used to control the transients. Such filters would add system losses that would be overlooked when only looking at individual components, but inefficiency of filters in this example would be addressed in the system approach. This is another good reason for focusing on the system.
Compare this to a pump application that only requires 50% flow. In this example, using a drive could reduce the energy consumption by 85% as compared to a 20% reduction by throttling the load, as shown in Figure 2. It is clear that the energy savings potential is much greater taking the system approach.
It’s been reported that power utilities fear a downturn in business because of power generated from renewables and low-cost natural gas coupled with a reduction in demand. In this environment, evaluation shows how the payback for motor component efficiency has changed.
First the cost of power has come down from an average of $.08/kWh to $.07 or less. Predictions for solar- and wind-powered generation rates are dropping very quickly. NEMA has issued a “super Premium” efficiency table [Download MG10 free at www.NEMA.org]. Calculating the additional efficiency or delta between NEMA Premium and (future) Super Premium using 1-200 hp four-pole motors, it is 0.9% for 17 of the 19 ratings and no change for the 100 hp and 200 hp motors. By using an average run time of 2,500 hours per year and 7 cents/kWh, the average payback comes out to approximately 14 years. The DOE “rule” is more or less two years, although that has been modified in the past when the social cost of carbon is included.
Better power management
With such examples, the conclusion is that the most effective way to save energy when using a motor-driven device would be to add a variable frequency drive and use a more effective method of managing the system and power consumption. Many applications [variable flow], as demonstrated above, achieve a savings ranging from 30% to as much as 90% when using variable frequency drives. This far exceeds a 0.9% efficiency gain from the motor (when tested at 100% load under laboratory conditions with very specific power quality and environmental conditions).
It’s time to “get real” and reduce operating costs through better power management. There may be some potential remaining to use more efficient pumps, fans, or compressions, but even in those cases with savings due to use of a motor and drive to control the process, the effectively managed system will achieve much greater energy savings.
Understand system savings
It would be best to focus on helping the end-user understand how to establish energy conservation through the use of a motor and drive system and to provide the tools to be able to calculate and predict the energy savings. In the present scenario, there isn’t a significant opportunity to reduce energy consumption by going to higher efficiency motor or drive components; these approaches will not give a decent return on investment (ROI) with energy costs of today or those anticipated in the future.
Regulators seem to be going in the same direction in the European Union (EU) and in the U.S., focusing more on the system approach and less on raising the efficiencies of individual components. The drive continues towards ensuring that products being used today meet expected energy consumption levels, and that WGs also will focus on providing accurate methods to determine energy consumption. This will be even more interesting and difficult when trying to combine energy consumption of complete systems.
Future methods to establish energy consumption will use analytical models to combine losses of system components and alternate efficiency determination methods (AEDM) to calculate individual component efficiency. It has proven to be too costly to test all variations of individual components and impossible to test complete systems, therefore other methods will be required, but they must be proven reliable.
Globally the standards organizations are on the same page. They have harmonized motor efficiencies. They have developed a joint system efficiency standard and are in agreement on the path forward. Recently the U.S. has requested the U.S. Dept. of Energy (DOE) to recognize the IEC 60034-2-1 on testing motor efficiency, which has been proven to be equivalent to the U.S. IEEE 112 standard on motor testing. These efforts are expected to continue, with other methods, over time.
NEMA Motor Generator Section member representatives authors are: Rob Boteler of Nidec Motor Corp. (chairman NEMA Energy Management Committee), Bill Finley of Siemens (chair of the Technical Advisory Group for IEC TC2), and Tim Schumann of SEW Eurodrive (chair of the NEMA MG1 Technical Committee).
Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, email@example.com.