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More Motor Muscle PUBLIC ACCESS

Material and Design Improvements Convert More Electrical Energy into Mechanical Power.

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Mechanical Engineering 123(10), 56-59 (Oct 01, 2001) (4 pages) doi:10.1115/1.2001-OCT-2

This article reviews that material and design improvements convert more electrical energy into mechanical power. According to the Department of Energy, electric motors account for two-thirds of the energy consumed by US industries, including chemicals, general manufacturing, mining, and utilities. More than 1.2 million integral electrical motors are sold each year, 10–15% of them high-efficiency motors, according to the National Electrical Manufacturers Association (NEMA), based in Rosslyn, VA. Greenville Tube Corp., based in Greenville, PA, is a subsidiary of Chart Industries Inc. in Cleveland. Greenville Tube’s 100,000-square-foot plant in Clarksville, AR, made a name for itself by quickly producing stainless steel tubing of specific size and type to reduce costly downtime caused by equipment failure. The Clarksville plant cold draws approximately one million feet of stainless steel tubing each month for use in automotive, aerospace, food processing, and medical equipment, pharmaceutical and petrochemical applications.

The Tight Electrical generating capacity that stretched California’s energy supplies during the early summer underscored the importance of building sufficient generating capacity to meet demand—and making the most efficient use of available electricity. One strategy for reducing the strain on the power grid is to use more efficient electric motors, the workhorse of virtually all industrial processes.

According to the Department of Energy, electric motors account for two-thirds of the energy consumed by U.S. industries, including chemicals, general manufacturing, mining, and utilities. More than 1.2 million integral electrical motors are sold each year, 10 to 15 percent of them high-efficiency motors, according to the National Electrical Manufacturers Association, or NEMA, based in Rosslyn, Va.

Although they typically cost 25 to 30 percent more than standard electrical motors, this does not reflect high-efficiency motors’ overall cost effectiveness, because the purchase price of any electric motor accounts for only about 2 percent of the lifetime cost of the motor, which works for eight to 10 years. The electricity it consumes accounts for most of the remaining cost.

Thus, a typical 50-horsepower industrial motor converts 90 percent of its electrical input into mechanical power, and costs $25,000 to operate during the course of one year. A high-efficiency unit, capable of converting 93 to 94.5 percent of electricity into mechanical muscle, can save more than $1,000 per year in energy bills and pay back the higher price of the motor.

Energy consumed during the performance life of an electric motor dwarfs its purchase price, making costly high-efficiency motors more economical.

Grahic Jump LocationEnergy consumed during the performance life of an electric motor dwarfs its purchase price, making costly high-efficiency motors more economical.

A leading high-efficiency motor is the Super-E series designed by Baldor Motors and Drives in Fort Smith, Ark. These motors owe their high efficiency to material and design considerations that enable them to run cooler, longer, and more dependably than standard electrical motors.

For example, the Super-Es are equipped with 5 to 10 percent more copper windings than standard industrial electric motors. The pure copper windings are coated with insulation developed and patented by Phelps Dodge, made of 14 or 15 different varnishes and metals. This insulation is 100 times more resistant to inverter spikes than standard winding insulation. Inverter spikes can cause insulation to break down and thereby cause motor failure through overheating. The high-performance insulation also means that the motor generates less heat.

Baldor dynamically balanced the Super-E’s high-pressure die-cast aluminum rotor to half of the NEMA allowable vibration Emits to further minimize vibration. The rotor is coated with polymer to protect it from corrosion. There are proprietary Lube-Lok retainer grease seals on both ends of the rotor to keep the grease inside the cavity without leaking into the motor.

Baldor uses Exxon’s Polyrex EM Grease to lubricate the motor bearings. Polyrex is formulated to last longer, provide greater shear stability, and be more resistant to corrosion, rust, and washing out. The bearings are locked to reduce endplay, or unwanted movement, during operation.

Engineers intentionally oversized the Super-E’s cast-iron conduit box, exceeding National Electrical Code standards, to facilitate connections with the external power supply. The conduit box is sealed watertight by neoprene rubber gaskets.

Because the Super-E’s winding insulation reduces overheating, Baldor was able to design smaller fans with blades shaped to optimize airflow and cooling, yet reduce noise of operation.

Greenville Tube Corp., based in Greenville, Pa., is a subsidiary of Chart Industries Inc. in Cleveland. Greenville Tube’s 100,000-square-foot plant in Clarksville, Ark., made a name for itself by quickly producing stainless steel tubing of specific size and type to reduce costly downtime caused by equipment failure. The Clarksville plant cold draws approximately one million feet of stainless steel tubing each month for use in automotive, aerospace, food processing, medical equipment, pharmaceutical, and petrochemical applications.

The manufacturing process at Clarksville involves using electric motors to draw lengths of stainless steel tubing through dies mounted on benches to reduce the tubing’s diameter and wall thickness. Typically, each steel tube undergoes several “breaking” draws that form the tube close to its specified dimensions before a few finishing draws achieve the final tube size.

The breaking draws are performed on the No. 6 workbench, which does about 400 draws per shift, and works three eight-hour shifts per day, five days a week. The drawbench originally used a 150-hp electric motor coupled to a gearbox through an eddy current clutch to draw tubing. The motor consumed more than 439,000 kilowatt-hours per year.

In addition, the No. 6 motor and drive experienced frequent overload shutdowns that interrupted production. Plant engineers investigated this bottleneck, and found that the 150-hp motor, which was rated for 250 amps, would receive as many as 900 amps, causing the unit to overheat. The tube maker decided to reduce the thermal load on No. 6’s motor to prevent trips.

Baldor engineers equip their Super-E motors with more copper windings, coated with an insulation made of multiple varnishes and metals, making them more resistant to inverter spikes than standard windings.

Greenville Tubing also wanted to increase the torque of the draw bench, improve its drive efficiency, reduce its energy consumption, and enhance the operator’s control of the motor at low speeds. The company addressed these goals through its participation in the DOE’s Motor Challenge program.

This program, recently redesignated BestPractices, encourages the use of efficient motor systems by bringing together energy-intensive industries and specialists from energy service companies, electric motor system suppliers, and academic research programs. Earlier efficiency-improvement efforts under the program were the subject of an article in Mechanical Engineering in October 1999.

Baldor provided the high-efficiency electric motor, its controls, and vector drive control for upgrading the draw bench. Evans Electric Inc., the local Baldor distributor, designed the upgrade and, once the equipment was installed, started it up. The DOE assembled an independent performance validation team that analyzed the results of the high-efficiency motor and drive, and provided the technical assistance to validate its energy savings.

The Baldor engineers replaced the existing 150-hp, 1,770-rpm motor with their 200-hp Super-E high-efficiency motor, rated at 1,180 rpm. They also replaced the magnetic starter and eddy current clutch with a Baldor vector controller and line reactor, both encased in a NEMA 12 enclosure with an air conditioner to prevent overheating.

The vector drive controller at Greenville Tube monitors the current, voltage, and position of the ac induction motor. Algorithms enable the controller to regulate motor torque, speed, and position to optimize energy use and motor performance.

The improved efficiency means that the No. 6 draw-bench uses less than half the energy to draw steel tubing. A job that required 190 hp of the old, eddy current drive requires only 87 hp from the more efficient vector drive. The greater available horsepower has cut the number of breaking draws needed to work steel tubing, cutting No. 6’s annual operating time by 623 hours, and freeing the drawbench to do work previously performed by other, less efficient drawbenches.

The independent performance validation team calculated that the upgraded drawbench uses 290,218 kilowatt-hours per year, a 34 percent decrease in annual electrical costs.

The efficient motor and drive also improved the drawing process itself, according to Greenville Tube, by eliminating one draw for 50 percent of the tubes worked at No. 6. This cuts the time needed to break the tubes, and to degrease, cut off, swage, and anneal them, correlating to 2,762 man-hours of labor per year, or $23,473 at $8.50 per hour. In addition, the smaller number of draws has trimmed the Clarksville plant’s stainless steel bill by $41,322, because fewer draws means that fewer swaged ends need to be cut off after each draw.

Because the Super-E’s winding insulation reduces overheating, Baldor was able to design smaller fans with blades that optimize the airflow and cooling of the motor.

Grahic Jump LocationBecause the Super-E’s winding insulation reduces overheating, Baldor was able to design smaller fans with blades that optimize the airflow and cooling of the motor.

The IPV team calculated that, based on annual savings of $77,266, the Baldor equipment installation was paid back in five months.

The World Trade Center in Portland, Ore., has been providing office space to international companies from Yakima, Wash., to Yokohama, Japan, for the past 24 years. Heating, ventilating, and air conditioning this space is an energy-intensive process that the centers owner, Portland General Electric, wanted to improve in September 1999. That’s when it contacted the local branch of Consolidated Electrical Distributors Inc. to help rein in HVAC costs by using more efficient electrical equipment.

“We used Allen Bradley energy evaluation software to study the performance of the supply and return air fans on the World Trade Center, and found that using high-efficiency motors and variable-frequency drives would improve their electrical efficiency,” said Gene Kirkendoll, an electrical engineer and senior drives applications engineer at CED in Portland, which is also the local distributor of Baldor motors.

 Setting a Premium Standard

In June, the national electrical manufacturers association, or NEMA, launched its Premium efficient electric motor program, to promote and encourage the installation of higher-efficiency motors. “The program was conceived and launched by electric motor manufacturers, including Emerson Electric in St. Louis; Rockwell Automation/Reliance Electric in Greenville, S.C.; GE Motors in Fort Wayne, Ind., and Toshiba International in Houston, among others,” said Kyle Pitsor, industry director at NEMA.

Pitsor explained that the new program represents a needed consensus on premium efficiency motors, because each motor manufacturer had its own definition of premium efficiency. So did different utilities that offer rebates to manufacturers, processors, and building owners to install high-efficiency motors. “We based the program specifications— which will be added to the NEMA MG-1 standard—on the type of motor and its output. For example, a 10-hp, six-pole ODP motor would have to convert 91.7 percent or more of its electrical input into mechanical power,” said Pitsor.

In general, Premium motors are 1 to 4 percent more efficient than today’s “energy-efficient” electric motors. The NEMA Premium designation certifies that the motor meets or exceeds the association’s specification, said Pitsor.

According to DOE estimates cited by NEMA, the program has the potential of saving more than 5,800 gigawatt-hours of electricity, while preventing the generation of 80 million metric tons of carbon into the atmosphere, over the next 10 years. This is approximately the equivalent of keeping 16 million cars off the road.

As chairman of NEMA’s Energy Management Task Force, Robert Boteler, director of marketing technology products and services at Emerson Electric, was intimately involved with developing the NEMA Premium standard now available on his company’s 1- to 500-hp motors. The actual design of Emerson’s premium motors predates the logo launch last June.

“We used our own finite element analysis program to redesign our standard motors to deliver premium energy efficiency. Basically, this included adding special laminations to the rotor and stator, and adding more copper in the wire windings, and more aluminum in the rotor, which made the motors longer and larger," explained Boteler.

As a result of the design changes, Emerson’s premium motors run cooler, enabling engineers to reduce the size of their cooling fans. This reduced the windage losses that cut motor efficiency. “Also, we reworked our motor bearings and the machining of our rotor surfaces, to increase efficiency," said Boteler.

About 90 percent of Emerson’s premium, three-phase, industrial motors produce 50 hp or less for the company's traditional markets—namely, oil refineries, chemical processors, and pulp and paper plants. About 60 percent of those motors are used to power pumps; the remainder power fans and compressors.

While it is too early for Emerson and other manufacturers to have case studies of their NEMA Premium motors, Boteler recently analyzed the energy usage and needs of a local water utility whose pumps were powered by standard electric motors ranging from 40 to 400 hp.

“These motors are about 30 years old, having been rewound several times,” said Boteler. “We estimate the cost of replacing them with NEMA Premium motors to be $48,000. The new motors would save $26,900 per year, giving a payback of about one and three-quarter years."

The Oregon utility decided to concentrate on the return fans, which send air that has passed throughout the building back to the air conditioner. Like most buildings, the Portland World Trade Center ran the return fan motors at full power and used dampers to regulate airflow as needed.

Portland’s World Trade Center reined in its HVAC costs by using 460-volt Super-E motors with variable-frequency drives to power its return fans.

Grahic Jump LocationPortland’s World Trade Center reined in its HVAC costs by using 460-volt Super-E motors with variable-frequency drives to power its return fans.

“This is like keeping your accelerator to the floor when driving your car, while using the brake to stay within the speed limit; you are using more energy than you need,” said Kirkendoll, who recommended replacing the existing return fan motors and air dampers with 30- and 40-hp Baldor Super-E motors, rated at 460 volts, with variable-frequency drives, in September 2000.

CED installed four high-efficiency motors and variable-frequency drives in one World Trade Center building to cool 280,000 square feet of office space, and another two motor/drive systems at another building to cool 120,000 square feet.

The variable-frequency drives are programmed to use the optimum amount of electricity to drive the motors. “Because the amount of airflow is three times the electrical energy needed to move the fan, this translates into 30 to 40 percent electrical savings,” explained Kirkendoll.

The CED engineers learned to deal with built-in anomalies while upgrading the Portland trade center. “For example, after we installed the Baldor equipment at the World Trade Center, we discovered that the supply fans would turn our return fans. This caused the VFDs to go into overspeed mode, default, then stop, so we disabled this fault on the drives,” Kirkendoll said.

Super-E motors are working in hospitals, military bases, schools, prisons, and quick-serve restaurants as part of the Power Soak pot washing systems designed by Met-craft Inc. of Kansas City, Mo. These continuous washing systems are basically made of three large stainless steel sinks, each one devoted to washing, rinsing, or sanitizing pots and pans. The wash sink holds 60 to 100 gallons of water that is electrically heated to 116°F.

Kitchen staff load the washing sink with dirty cookware as they walk by it. A low-pressure, high-volume centrifugal pump powered by an electric motor sends heated, soapy water through four or five jets mounted on the back wall of the wash sink. The kinetic energy in the water jets traveling 10 to 12 feet per second tumbles the pots so their entire surfaces are exposed to the spray, which removes food particles in a few minutes. Kitchen workers inspect the pots, and either dip or spray-rinse them before placing them in the sanitizer tank for 60 to 90 seconds, where they are cleansed by quaternary or chlorine-based water.

The Power Soak systems typically run 16 to 20 hours per day. The long hours of service combine with high humidity and temperature, and Power Soak motors don’t receive much maintenance from busy kitchen crews, so conditions sometimes caused the motors’ cooling fans to literally clog with grease. As a result, the motors ran hot and failed, along with their bearings. Including labor, it cost Metcraft three times the purchase cost of the electric motor to replace one after failure.

“We tried other pump and motor combinations to prevent this and realized we needed a motor as bulletproof as the cast-iron Ingersoll pump we use. We found it in the 2-hp, single-phase Baldor Super-E,” said Dave Stockdale, a mechanical engineer and engineering manager at Metcraft.

Metcraft improves the performance of its Power Soak pot washing systems 7 percent by equipping them with a 2-hp Super-E motor.

Grahic Jump LocationMetcraft improves the performance of its Power Soak pot washing systems 7 percent by equipping them with a 2-hp Super-E motor.

Stockdale said that incorporating the Super-E has cut motor failures of the Power Soak systems by two-thirds. “It also improved performance 7 percent over the standard motor we used, meaning that our customers will see payback of the extra cost of the motor in three months,” Stockdale said.

Metcraft also chose the Super-E because its three-year warranty complemented Metcraft’s own warranty for the Power Soak itself. The washer maker works closely with Baldor to refine the motors’ design, according to Stockdale. “Over six months, we tracked a number of rear bearing failures and informed Baldor. They are building me a motor with a larger rear bearing for evaluation,” he said.

Copyright © 2001 by ASME
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