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Energy savings turn on better motors

Energy savings turn on better motors

We're all going to die.

No we're not.

This about sums up the level of public debate now raging over whether so-called "greenhouse gases" will alter the Earth's climate if emissions continue unabated. The United Nations environmental conference in Kyoto, Japan, this month probably will not produce the dramatic reductions in carbon dioxide envisioned at the Rio Summit earlier in the decade.

The issue also is focusing attention on what engineers can do to reduce air pollution. Energy use is viewed by many as the most significant contributor to carbon dioxide emissions. ACEEE estimates electric motors operating in the U.S. account for more than half of the electricity consumed in the country. Therefore, the adoption of energy-efficient motors has become an important factor in reducing emissions.

Engineers are being encouraged not only to come up with more energy-efficient designs, but to specify existing designs that consume less power to get the job done. Increasingly, such encouragement has the force of law behind it.

For example, the terms of the Energy Policy Act declare that most general-purpose motors sold after October 1997 must meet standards of energy efficiency as defined by the National Electric Manufacturers Association (NEMA). Certain high-torque and low-horsepower motors are exempt, and some vendors are encouraging customers to consider these motors as alternatives to expensive upgrades.

Most applications will be affected, however, and in all likelihood there is an energy-efficient motor in your future. Fortunately, most major motor manufacturers produce both standard motors and high-efficiency motors. According to NEMA, energy-efficient motors, also called premium- or high-efficiency motors, are 2-8% more efficient than standard motors.

The cost of clean. Efficiency comes with many other benefits, NEMA adds. The organization reports:

"Energy-efficient motors owe their higher performance to key design improvements and more accurate manufacturing tolerances. Lengthening the core and using lower-electrical-loss steel, thinner stator laminations, and more copper in the windings reduce electrical losses. Improved bearings and a smaller, more aerodynamic cooling fan further increase efficiency. Energy-efficient motors generally have longer insulation and bearing lives, lower heat output, and less vibration.

According to Jerry Peerbolte, vice president of marketing at Baldor Electric Co. (Ft. Smith, AR), the new standards offer customers an opportunity to select better performing motors. "The energy-efficient motors run cooler and with less vibration," Peerbolte says. "This means less stress and longer life."

All is not wine and roses, however. The initial cost of energy-efficient motors can be 15-30% higher than for a comparable standard motor, and payback is affected by motor size, energy rates, and operating hours per year. "Although energy-efficient motors cost more than the standard line, they are usually justified on a payback basis, since they consume less energy per horsepower," points out an Allen-Bradley white paper entitled "A Comprehensive Guide to Understanding Motor Fundamentals."

Michael Offik, manager of product marketing for Reliance Electric in Atlanta, GA, notes the life-cycle costs for energy-efficient motors are better than for previous standard-efficient motors. "The economics of energy-efficient designs are attractive in the long run," Offik says.

For those companies that must convert, the U.S. Department of Energy (DoE) sponsors the Motor Challenge program. The industry/government partnership encourages companies to select efficient motors, pumps, fans, and other motor-driven equipment. By encouraging the most appropriate matching and integration of these system components, the DoE expects to help manufacturers realize 2 billion kW-hr per year of electricity savings by the year 2000.

Participants in the Motor Challenge program have reported successes. Minnesota Mining and Manufacturing (3M, St. Paul) formed a Motor Challenge team that evaluated approximately 1,000 electric motor systems in 29 buildings at the 3M Center to identify feasible projects. In one of the first facilities evaluated as part of the project, four key motor upgrades reduced electricity use by 41% and resulted in cost savings of $77,554 per year. 3M estimates the company's savings for all surveyed facilities at 10,821 MW-hr.

Lockheed Martin Armament Systems was looking for a way to improve the performance of the ventilation system at its industrial plating plant in Burlington, VT, where electrical costs are highest of any Lockheed Martin plant in the country. A variety of small and large machined metal parts are plated, anodized, finished, and cleaned at the facility.

In all, the plant consists of nine plating production lines with 64 tanks handling 19 different plating processes. The constant volume ventilation system provides exhaust for lateral hoods over the plating dip tanks, and prevents toxic fumes from escaping from the tanks into the workers' area. The system has 10 motors ranging in size from 5 to 100 hp.

The best solution proved to be the addition of variable frequency drives (VFDs), which permit variable-speed control of the motors driving the ventilation fans. This allows the ventilation supplied by the fans to be matched to needed levels at any given time automatically. The new variable-output ventilation system includes nine electronic VFDs, which reduce airflow to 55-65% of full speed during idle times.

Lockheed Martin reports the benefits of the new system include a 38% reduction in electric and natural gas utilities costs, fewer emissions, and improved system and emergency ventilation control. The VFDs are not only used to increase system energy efficiency, but also to improve process control, overall productivity, and product quality while reducing wear on equipment and lowering maintenance costs. The project cost approximately $99,400 to implement and has resulted in annual savings of more than $68,000, providing a simple payback of just under 1.5 years.

Not all motor selection projects need to be so large-scale in order to see benefits. Appropriately enough, the DoE has developed a software program, called MotorMaster+, that can be used to identify inefficient or oversized inventory motors and compute the energy and demand savings associated with selection of a replacement energy-efficient model. The software includes an annually updated internal database containing price and performance information for more than 10,000 currently available NEMA Design B motors. The latest 2.0 version of the software also includes data on NEMA Design C and D motors, in addition to a number of specialty types.

MotorMaster+ is a Microsoft Windows-based computer software application designed to support motor management functions at medium-sized and large industrial facilities. The program includes a motor inventory and field measurement storage repository capability and an energy conservation analysis function that can determine energy savings, dollar savings, simple payback, cash flows, and after-tax rate of return-on-investment.

All-in-all, there need not be such a conflict of interests between energy and economic efficiency.


What is an energy-efficient motor?

The energy-efficient motor differs from a standard motor in both design and manufacturing techniques. It employs larger stator conductors with higher conductivity. The rotor bars are larger as well, to reduce the overall copper (or aluminum) loss, which comprises 55-60% of total motor losses. The motor flux density and air gap are reduced to minimize the magnetizing current required. Stator and rotor laminations are thinner to increase resistance to the flow of eddy currents. More laminations are added to the core stacks as well, producing a longer stator and rotor for increased torque.

Hysteresis losses, which are normally 20-25% of the total motor losses, are reduced by using silicon steel instead of low-carbon steel for the laminations. As a result, the motor uses less current, has better power factor, and runs cooler. Since the energy-efficient motor runs cooler, ventilation requirements are reduced, allowing a smaller fan to be installed. Windage loss (typically 5-9% of total losses) decreases and the smaller fan runs quieter. These motors are less susceptible to damage from impaired ventilation and also operate well at higher altitudes. Cooler operation also increases motor life.

Insulation life is up to four times longer--an important fact, since insulation breakdown is the primary cause of motor failures. Bearing lubrication lasts longer too, doubling the interval between required lubrication. Cooler operation means that less burden is placed on air conditioning equipment. Energy-efficient motors can also operate in higher ambient temperatures without requiring extra cooling, which in the case of a standard motor, could add substantially to the purchase price of the motor.

Energy-efficient motors are also more rugged than standard motors, tolerating greater fluctuations in applied voltage, voltage imbalance, and overload. Some can even tolerate 30-40% overloads for prolonged periods. They are also capable of starting higher inertia loads than standard motors because of their increased thermal capacity.

Source: "A Comprehensive Guide to Understanding Motor Fundamentals," published by Allen-Bradley.


Using MotorMaster+

The MotorMaster+ software program enables users to find just the right energy-efficient motor for the right application. It also provides many supporting functions, including:

Motor inventory management

  • Maintenance log tracking

  • Conservation analysis

  • Savings evaluation

  • Energy accounting

  • Environmental reporting

MotorMaster+ 2.0 can be acquired through the DoE's Motor Challenge Website at: www.motor.doe.gov/mcssoft.asp


Applications for VSDs

Variable-speed drives are most suited to the following motor types:

dc brush-type servo motors

  • ac or dc permanent-magnet brushless servo motors

  • ac non-vector induction motors

  • ac vector induction motors

Source: The Mike Kilroy Corp., Dayton, OH

Comparisons Between Standard-efficiency (SE) and Energy-efficient (EE) Motors
Motor (hp) Purchase Cost ($) Efficiency (%) Annual Savings Payback (years)
SE EE SE EE kW-hr $
10(a) 614 795 86.5 91.6 2,103 210 0.86
25(a) 1,230 1,608 88.1 94.2 6,004 600 0.63
50(a) 2,487 3,207 90.6 95.0 8,352 835 0.86
100(a) 5,756 7,140 90.7 95.7 18,822 1,882 0.74
200(b) 11,572 13,369 94.6 96.1 10,782 1,078 1.67
300(b) 15,126 18,385 94.6 96.0 15,111 1,511 2.16
Note: Based on 16 hr/dy operation at 75% load and $0.10/kWh
(a) Reliance Standard-Efficiency and Premium-Efficiency motors
(b) G.E. Standard-Efficiency and EnergySaver motors
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