How motors & drives save energy—and money

 It’s a matter of using the latest technology.

Energy is like any other commodity. If you’re not thrifty with it, it will slip through your fingers, so to speak. And profits will suffer, as New Holland Tractor’s plant in Greater Noida, India, learned recently. The fixed-speed motor on its compressor line ran continuously. It didn’t matter whether the paint shop, assembly line, utility room, machine shop and other areas in the plant were using the air or not. The motors kept running, consuming energy and shaving more money from profit margins.

To recoup that wasted energy and add it to the bottom line, management called M/S Elcon System Pvt. Ltd., a local systems integrator partnered with Rockwell Automation Inc., in Milwaukee. The solution was to install sensors and an Allen-Bradley 125-horsepower variable-frequency drive supplied by Rockwell. By adjusting the motor’s speed automatically for the demand, the variable-speed drive reduced the compressor line’s energy consumption by 35 percent, and paid for itself in about 13 months. “The realization of savings by controlling our compressors has been a remarkable achievement,” says Pawan Uppai, assistant manager and plant engineer at New Holland India.

He is not the only one making this observation. A growing number of manufacturers have recognized that replacing the various old-style motors and drives still used in their facilities with modern technology can conserve a tremendous amount of energy—and money. According to the U.S. Department of Energy (DOE), industry could reduce its electrical energy consumption by as much as 18 percent if it replaced its motors with the latest high-efficiency motors and, where appropriate, variable-speed drives.

These savings more than pay for the higher price tags on these motors, which can be 10 percent to 30 percent more than those on conventional motors, depending on model and size. The reason is that electric motors are responsible for about 63 percent of a manufacturing company’s electric bills, according to John McFarland, chairman and chief executive officer of Baldor Electric Co., in Fort Smith, Ark. “Over 97 percent of the lifetime cost of a motor is its electricity consumption,” he says.

For this reason, McFarland urges manufacturers to consider specifying high-efficiency motors whenever they replace broken motors or buy new equipment. “The small premium you pay for a high-efficiency motor is often recovered in the first year, depending on the motor’s duty cycle and the cost of power,” he contends. “The savings in electricity will then continue year after year.” So the contribution to the bottom line can be substantial over the 15- to 20-year lifetime of the average motor. *

Detecting dividends As Uppai at New Holland learned, upgrading fixed-speed motors with variable-speed drives pays handsome dividends too. Most manufacturing facilities find that they reap the biggest benefits from them by focusing on the fans, centrifugal pumps, and compressors in their heating, ventilation and air conditioning (HVAC) units and processing equipment. “Historically, engineers would just put a fixed-speed motor on a fan, sizing it to meet peak demand,” says David Mantey, fan and pump drive manager, Drives Division, Rockwell Automation. Hence, the motor almost always uses more power than is necessary.

A motor fitted with a variable-speed drive, on the other hand, runs at the necessary speeds at the appropriate times, and so, consumes much less energy. According to the Affinity Law, a mathematical relationship for determining the operating points of a pump or fan, power consumption drops by the cube of the cut in the motor’s operating speed. So cutting its speed in half reduces power consumption to an eighth.

Because of this relationship, variable-speed drives can save users a lot of money on operating their fans. Consider what would happen to power consumption when airflow is reduced by 60 percent with the various control schemes commonly used today. For motors regulated by a damper at the outlet, the airflow reduction typically would cut the power draw to only 80 percent to 85 percent of the power being consumed at 100 percent. For those regulated by an inlet vane, the 60 percent reduction would reduce the power consumed to about 60 percent to 65 percent. A variable frequency drive, on the other hand, would use approximately 22 percent of the power.

The results are similar for pumps. Regulating flow rates with a variable-frequency drive is much more efficient than with a throttle. An example might be an application needing 100 gallons per minute. “If you were to reduce that by half with a throttling system, power consumption would decrease to about 60 percent to 70 percent of what it was,” says Mantey. “With a variable-speed drive, power consumption drops down to 12.5 percent.”

These efficiencies also conserve energy at startup. A case when that might be true is a line moving materials among the various processes by conveyor. “Without variable-speed drives, just starting the motors up across the line would demand a lot of current to start—sometimes as much as 400 percent to 500 percent more [than the motor’s full load rating],” notes Lou Lambruschi, product manager of Seco AC/DC drives and systems at Danaher Motion ESC, in Charlotte, N.C. “Using AC drives on those motors would effectively reduce that to somewhere in the neighborhood of 150 percent.” Not only do these drives limit peak demand (especially important in places where industry pays a premium for peak-demand power), but they also offer smoother starts.

Variable-speed drives also can improve the energy efficiency of a process if the equipment is using old, inefficient motor-generator sets, eddy-current drives and mechanical variable-speed drives. Consider a metal fabricating line with ten motors being regulated by a motor-generator set and field control. “Even with the line idle, or with several motors off-line, the motor-generator set runs, consuming energy,” notes Lambruschi. “Retrofitting each existing motor on the machine with an AC motor and drive would ensure that energy is only used when that particular motor is in use. It also eliminates the losses associated with motor-generator sets.”

The same would hold for some of the older DC and eddy-current drives found on machine tools and other machinery. “Replacing that technology with a solid state unit would definitely save energy,” says Lambruschi. “It’s hard to find these opportunities, however, unless you have some really old equipment.”

Other old-style equipment that can benefit from variable-speed drives is continuous-web machinery fitted with drag brakes. An example is a continuous-form printing press. A friction brake maintains tension on the unwinding roll of blank forms. “The motors driving the press must overcome this friction, which is dissipated as heat,” says Lambruschi. “By using a regenerative AC drive instead of the brake, the energy returns to the power grid, increasing the overall efficiency of the press.”

Manufacturers buy in Even though the higher initial investment in modern motors and drives is still a barrier for many, a large and growing number of U.S. manufacturers are overlooking this cost and concentrating instead on lifecycle economics. Nearly a fifth of the motors sold in the United States are the modern, premium motors of the kind described by McFarland at Baldor and advocated by the government and conservation groups. Although too few manufacturers in the United States might be reaping these rewards to suit their tastes, the number exceeds that in Europe and Asia, despite higher energy costs there.

The greater interest is perhaps the work of various organizations promoting the concept. In 2001, for example, Boston-based Consortium for Energy Efficiency Inc. launched Motor Decisions Matter, a national campaign for educating industry about the energy savings that manufacturers can reap from motors and drives. The consortium undertook the campaign on behalf of a coalition of energy-efficiency organizations, motor manufacturers and service centers, electric utilities, trade associations, and governmental agencies.

Another reason for the greater interest in the United States is that various state governments and utilities are encouraging the installation of premium motors and variable-speed drives through rebates. California, for example, offers $300 million a year in rebates, and the New York State Energy Research and Development Authority, in Albany, grants a similar amount. “In some states, the rebate is in excess of what it costs to buy the product,” says John Malinowski, a product manager at Baldor. “In one, it’s almost a 50 percent premium over what it would cost you. So they are paying you to put it in.”

Their hope is to entice manufacturing facilities to consume less energy and lower their daily peak demand. If these governments and utilities are successful, they will get more from the existing infrastructure and not have to build more power plants.

The motor-and-drives industry supports the effort not only by promoting the rebates, but also by making various software analysis tools available. The DOE, for example, has developed a software tool called Motor Master, and various utilities and motor vendors offer their own analysis tools. Rockwell Automation has a software tool that calculates a return on a motor/drive investment based on a user’s 24-hour load profile and the local energy rates. Return on investment is the key parameter in determining whether replacing a fixed speed motor with a variable-speed drive makes sense, according to Mantey.

Rather than looking at the motors and drives per se, other organizations are concentrating instead on creating efficiencies among the devices that most commonly benefit from the switch. The Hydraulic Institute, of Parsippany, N.J., for example, worked with the DOE in the agency’s BestPractices Program to create software called PSAT, the Pumping System Assessment Tool. The software contains tools for helping users to specify the most efficient mix of pumps and pipes. “Maybe instead of one big pump, you really need to cascade two or three smaller ones,” says Malinoski, at Baldor.

Smart Motors and Drives Computer technology does more for the energy efficiency of modern motors and drives than just help users decide when and how to deploy them. Like many electronic devices these days, today’s drives are programmable, can log events in memory, and can receive and send information over a computer network.

In the case of an HVAC system, plant engineering can tie the drives into the building’s automatic controls. The controller can regulate the system automatically, adjusting blower and fan speeds based on temperature readings and the setpoint for the time of day and day of the week. “You don’t need to shut it off on weekends when nobody is going to be around,” says Mantey, at Rockwell. “It regulates itself.”

The drive can calculate how long the motor has been working and feed that information to a maintenance-scheduling program. Not only can the scheduler dispatch a technician to perform routine maintenance at the appropriate times, but it also can track the motor’s energy consumption. Because most mechanical equipment requires more energy as bearings and other mechanical components wear, this historical information also can warn the maintenance department of a developing problem so technicians can repair it before it becomes acute. Being proactive can prevent expensive failures.

Such is the case at New Holland India. Using RSPower32 software from Rockwell Automation, the plant collects data throughout the plant over its computer network and monitors power factors, harmonics and demand loads. Not only does it perform energy calculations automatically, but it also monitors events such as tripping, voltage dipping and power failures. Consequently, the company can follow trends, control costs and correlate power consumption to the appropriate places in production.

So electrical power at New Holland is like any other of its resources: It is under control and contributing to the bottom line.

For more information, search keywords “motors” and “energy” at www.automationworld.com.

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