Motors and Drives Grow Up and Graduate

Motors and Drives Have Been Moving Up to Variable-Speed Control for Better Accuracy, but Now They're Also Increasing Power Density and Efficiency and Even Coordinating More Closely With PLCs and Intelligent Systems

By Jim Montague

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Explosion-Proof Pumping, Cooling
Figure 2: Petrobras is deploying 11 three-phase, explosion-proof induction motors on its centrifugal KSB pumps feeding water to the cooling towers at its Abreu e Lima refinery.
"These KSB pumps and equipment require motors that offer a high degree of reliability," says Marcelo Vedana, WEG's engineer. "To enhance their reliability, the motors are designed to be robust, and use the best quality bearings and ancillary components. The windings are precision made and balanced, while advanced thermal management ensures cool running."

Standards + Power Density = Efficiency

Beyond improved control from VFDs and VSDs, motors are also being pushed by government standards and user demands to achieve greater power density and efficiency, which is often achieved by integrating permanent magnets (PMs) made from rare earth materials.

"Increases in motor efficiency are driven mostly by government efficiency regulations, such as the Energy Policy Act (EPAct) and the Energy Independence and Security Act (EISA), and by end-user demands for reduced total cost of ownership," says Sam Harris, business manager for large drive technologies at Siemens Industry. "The recent introduction of die-cast copper rotors by Siemens and a few other motor manufacturers have yielded higher efficiencies than mandated by the present EISA."

Steve Evon, engineering manager for variable-speed and custom medium-AC motors at Baldor Electric Co., a member of ABB Group, reports that DoE is working on a follow-up to EISA that will require even more efficient motors, perhaps by 2015, and add frame sizes beyond the 200-hp and less motors it covers now, requiring builders to further optimize motor redesigns with finite analysis tools and better models to identify power losses more easily. "We're still using aluminum rotors with copper windings, but now we're using punched lamination stacks, such as our RPM AC line, which are thinner and easier to cool, and don't need the usual cast iron frame, so they allow more room for active components," says Evon.

"We've really reached the physical limit of how much wire we can get into our winding slots, which is why PM and synchronous reluctance motors are so popular. The key to the future is finding lower-cost magnetic materials."

Cooperating with Upper Levels

Drives and motors are also learning to communicate and better coordinate efforts with related programmable logic controllers (PLCs) and other supervisory systems. For instance, to provide balanced dewatering and remote monitoring and control in natural gas production, system integrator and machine designer Atfab LLC in West Branch, Tenn., recently worked with Schneider Electric (www.schneider-electric.com) to construct an automated, condition-based pump jack that combines Schneider's Altivar 312 VFD, Twido PLC and Megelis HMIs. Atfab and Schneider also developed software that calculates how long the pump jack should run based on site conditions, and shuts it down, instead of running for a set time that isn't always optimal.

"Some wells showed more than a 50% energy savings from not having to run in a time mode," explains Jeff Thornburg, Atfab's operations manager. "We also engineered this solution to allow the pump jacks to operate using three-phase motors instead of a single-phase mode, which garnered added energy savings and maintenance costs by eliminating the capacitive starts. The best part is that an algorithm in the PLC allows the pump jack to learn from itself, and make adjustments based on the unique characteristics of the well it's controlling."

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