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Improving end-to-end system efficiency with variable speed drives and magnet-assisted synchronous reluctance motor technology (Part 1)

A large percentage of motors at work have been in service for a long time. It is estimated that more than 60 percent of motors in U.S. industry are at least 10 years old. While many motors are still in good working condition, these older designs are less efficient than modern motors, which impacts operating costs and energy consumption. Updating to newer, more efficient, motor systems can lead to significant gains from energy and cost savings. In this two-part blog post, we will focus on two proven methods of improving motor system efficiency: Adding a variable speed drive to control an existing motor and replacing an older motor with an IE5 efficiency integrated motor-drive.

Incentives to improve energy efficiency 

Motor age and efficiency are increasingly of interest because many countries and states have set targets to reduce energy use and emissions. To achieve these targets, government organizations enact tighter regulations and more stringent requirements, which put pressure on industry to improve efficiency. However, the higher price of new motors is often an impediment to investment in more efficient options. On the other side of the equation, financial incentives can be used to entice companies to invest in newer motors. 

Systems that use older motors are less efficient 

About 70 percent of the electricity used in industry is consumed by electric motor systems. Many of these motor systems are installed in facilities that typically have long equipment life cycles and long periods between investments and upgrades. Therefore, the motors in use are often many years old. For example, in the U.S., most of the electricity used by industrial motor systems is consumed in the plastic/rubber, paper and primary metal industries. In these industries, and most others, the motors in use are likely to be obsolete, with an IE3 - or even IE2 - efficiency rating. One of the reasons that these older motors are less efficient is that they have higher losses than more modern designs. 

The cost of this inefficiency over the years can be significant. On average, electricity costs account for about 96 percent of the total life-cycle cost of a motor, while the purchase price accounts for only three percent. As a result, there are significant potential financial benefits to improving motor system efficiency long before the end of the equipment life cycle – the long-term savings far outweigh the initial costs.

IE5 motors offer ultra-premium efficiency 

The most common type of electric motor is the induction motor. There are five international efficiency classes for motors specified by the International Electrotechnical Commission (IEC), ranging from IE1 to IE5, with IE1 being the least efficient and IE5 the most efficient. Each class of efficiency equates to 20 percent lower motors losses. For example, IE4 motors have 20 percent lower losses that IE3 motors, while IE5 motors have 40 percent lower losses than IE3 motors. It is estimated that if 80 percent of the world’s installed industrial motors were replaced with IE5-efficiency motors, 160 terawatt-hours of energy per year would be saved.

Variable speed drives for optimizing energy management 

Variable speed drives (VSDs) can help motor systems run more efficiently, and although they are required to operate synchronous reluctance motors, they can be used successfully with other motor systems, including older induction motors. VSDs offer great potential for improving the efficiency of many motor systems across different industries; however, in the U.S., only 16 percent of industrial motor systems use variable speed drives.

Direct speed control improves efficiency 

A VSD controls the frequency and voltage of the electricity fed to a motor, allowing for precise control of the torque and speed of the motor and the application it powers. Because the VSD can run the motor at the optimum speed for the application, no energy is wasted through mechanical speed controls like valves, gears, throttles or brakes. As a result, motor systems controlled by VSDs can operate more efficiently than motor systems without drives, especially systems that run at partial load. Adding a drive to a fixed-speed, across-the-line, system that uses mechanical throttling to control flow or pressure can result in system efficiency savings of as much as 25 percent.

VSDs match energy consumption to actual energy need 

In systems like HVAC, pumps and compressors, it is common to regulate speed or flow mechanically, which consumes more energy than the application requires and necessitates an oversized motor and power supply. In contrast, if the speed or flow is controlled by the motor directly using a VSD, the system only consumes the amount of energy required by the application. The motor and power supply can be “right-sized” rather than oversized, further reducing energy consumption. Another benefit of VSDs is that because they can precisely control the motor speed, they also enable better rpm tolerances and improved process stability.

In part two of this blog post, we will learn about reaching IE5 efficiency using magnet-assisted synchronous reluctance motors which include an integrated variable speed drive. Stay tuned!



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