Energy–Efficient Motors Energy–Efficient Motor Design – One Trend, Different Approaches
Energy efficiency was at the top of the list of issues which were communicated to visitors at Achema 2012. In the aftermath of the show, the industry continues to look for ways of exploiting the opportunities that exist to save energy in chemical production. The quest has been particularly rewarding in drive engineering. Learn more about different approaches to energy-efficient motor design.
Electric motors used to drive pumps, compressors, centrifuges, fans and linear axes account for roughly two-thirds of industrial energy consumption in Europe, making them a major cost factor. When you look at the cost breakdown, you find that the original procurement cost is actually the least expensive line item, contributing only 2.5% to total lifecycle cost. A gigantic 96% of the cost is incurred due to energy consumption. That is a classic case of “even free is too expensive”.
Energy Efficiency has Impact on Plant Design
This is now having an impact on the design of electric motors installed at chemical plants, which in many cases are (standard) asynchronous AC motors. Permanent-magnet synchronous motors are another option.
Compared to asynchronous motors, they have significantly higher power density and are massively more efficient, particularly under partial-load conditions. The rotor contains high power density (permanent) magnets.
Synchronous reluctance motors, such as the KSB Supreme, are another alternative. No magnets are needed with this new design which has won three awards (see text box on page 36). The SEW Line Start Permanent Magnet Motor is a hybrid solution (asynchronous start up with subsequent synchronous operation — see box).
High Performance, Low Energy Consumption
The efficiency scale for 2, 4 and 6 pole low-voltage electric motors is one key metric. Three energy efficiency categories have been defined, namely IE1, IE2 and IE3 (IE4 is on the way soon and there is already talk of IE5 motors). The motor regulation (EC640/2009) applies to nearly all motors rated between 0.75 kW and 375 kW as follows:
- Stage 1: as of June 16th 2011 all motors must be IE2-compliant.
- Stage 2: from January 1st 2015, all electric motors rated between 7.5 kW and 375 kW must be either IE3-compliant or IE2-compliant and have a frequency converter.
- Stage 3: from 2017, all electric motors rated between 0.75 kW and 375 kW must be either IE3-compliant or IE2-compliant and have a frequency converter.
This regulation applies only to the European market. However Australia, China, Brazil and Canada have introduced similar energy efficiency regulations. In the US, the NEMA Premium standard (equivalent to efficiency level IE3) has been in effect since the end of 2010.
Some Motors Already Exceed Standards
Ingo Landwehr from Grundfos reported that many manufacturers are skipping Stage 1 and are incorporating the 2015 standard into their designs: “IE3 motors or IE2 motors with frequency converters are already the standard at our company.” He highlighted the differences in functionality. “The frequency converter and the controller are built into our Blueflux MGE motors rated at up to 22 kW (IE3). This translates to lower cost for commissioning (cabling, matching the pump and the frequency converter) and operation, particularly in variable-load applications.” The list of optional features includes the capability to monitor bearing temperature and communicate with higher-level systems.
What About Motors That Are Already Installed?
The ErP and motor directive applies to new motors, but what about motors that are already installed? Frank Jüngst from Danfoss believes that there is significant business potential out there. “We see very substantial opportunities for retrofits in the chemical industry. Our estimates indicate that a frequency converter is fitted on only about 20% of the drives.”
This is the case because users have been reluctant to invest the time and money to modify the controller, replace cables, etc. Jüngst made the following observation: “Many people are probably not aware that a Danfoss frequency converter with sine filter can be operated in compliance with EMC regulations without a shielded cable.” The situation is much better on new installations. Jüngst estimates that 80% or more of the motors are equipped with frequency converters.
Are Energy Efficient Motors Worth the Investment?
Are a new motor and new frequency converter really worth the investment? Sebastian Schwarz from Siemens says that the answer is definitely yes. “For identical pumps, the up-front cost of state-of-the-art cascade topology is up to ten times higher per frequency converter compared to simple throttle control.
However, that has to be seen in context. About 1% of total lifecycle cost on a pump system is attributable to throttles. In the case of frequency converters, the figure is still only 2%–5%.” In either case, the cost of energy to drive the pumps is the dominant factor. Since the frequency converter alternative is much more energy efficient when operating conditions vary, Schwarz would argue that the investment is always justified.
Explosion Protection and Energy Efficiency
The motor regulation does not currently apply to motors designed for special applications such as explosion-protected motors. In the process industry where explosion-protected drives are often needed, the consequences of the exemption are generally adverse, as it tends to limit the number of suppliers. Nevertheless, several manufacturers had IE2 and even some IE3 explosion-protected motors on display at Achema (see text box).
Incidentally, if you look at the power/efficiency graph for IE1, IE2 and IE3 motors, you will see that the difference in motor efficiency is greatest in the lower end of the power range. At higher power, the efficiency figures are much more similar. This means that users who switch to a high-efficiency motor will see the biggest benefits in the lower end of the power range.
How to Save Costs and Energy With New Motors
IE3 and IE4 high-efficiency motors play an important role. They save significant amounts of energy and cost in a short space of time. For most users however, switching from a fixed-speed motor to, for example, a system with frequency converter control is the better solution, as is pointed out in the January 2012 issue of the VEM company newsletter.
“Process-based control using a frequency converter and a state-of-the-art IE2 motor is often significantly more effective than simply using an IE3 or IE4 motor.” The systems run in the optimal operating range. Reduced energy consumption is not the only benefit. The process is more stable and maintenance costs are lower.