Motion System Design
Design by Objective: Replace motors, recoup dollars

Design by Objective: Replace motors, recoup dollars

With a little planning, initial efficiency-grade motor investments can pay off big time

These days, every chance you have to save money must be exhausted. An often overlooked opportunity: Many industrial motors are being repaired again and again when they actually should be replaced upon failure. Proper motor replacements are best planned in advance rather than hastily arranged during downtime. For that reason, it’s important to work with your distributor ahead of time to make sure the efficient model you need is available at the time of failure.

While the initial investment can be as much as 30% more for energyefficient motors, the acquisition cost of a motor is only a small portion of the lifetime ownership cost, including operation and maintenance. According to the Consortium for Energy Efficiency (CEE), the average standard efficiency motor can consume 40 to 60 times its initial purchase price in electricity during a typical 10-yr operating period.

The good news is that a little effort in motor system management can go a long way, reducing energy costs by almost 20 percent, according to the U.S. Dept. of Energy. Best of all, unlocking the savings through a motor replacement plan may be easier than you think.

Making plans

For every six motors that fail, one is replaced with a new motor, while five are either repaired or replaced with a rebuilt motor, according to Rob Boteler, director of marketing, Emerson Motor Technologies, St. Louis. The latter five represent opportunities for NEMA premium-efficiency motor replacement, points out Boteler, who chairs the Energy Management Task Force for the National Electrical Manufacturers Assn. (NEMA). Making the transition just takes a little forethought.

Anyone developing a motor plan will need the involvement of distributors and suppliers to make sure products are in stock when needed, either through purchase of a spare or arranging for a distributor to stock a replacement. Neal Elliot, spokesperson for the Motor Decisions matter campaign, emphasizes the importance of distributors. If a failed motor’s replacement does not arrive on time and your system is down, annual energy savings for an efficient motor could be wiped out in an hour of downtime.

Some plant engineers have an idea of what they’d do in a given motor failure situation, but if it’s not on paper, may just opt for the quickest solution during downtime.

Because energy consumption is such a large part of a motor’s total life cycle cost, one may wonder why every plant doesn’t already have a plan. Linda Raynes, EASA President and CEO, says there may be hesitation because a customer thinks a large asset management program is required, or there’s a need to do a complete motor inventory. Actually, in some cases, she says, merely making a decision on whether to replace or repair key motors once they fail helps immensely. And, many utility campaigns and other efficiency awareness efforts tend to overlook small and medium-size plants, where a basic spreadsheet is likely all that is needed to document a motor plan.

The Motor Decisions Matter campaign’s “Motor Planning Kit” suggests that the most comprehensive approach to planning motor decisions requires an inventory, or complete list of facility motors. A repair/replace decision should be documented for each motor along with a list of spares. This includes identifying critical motors and setting up inventory tracking. Your distributor may be able to help with this, but expect to pay for the assistance.

Motor manufacturers can help, too. For example, Emerson offers spreadsheet tools to help build an inventory of a facility, taking into consideration the particular energy costs, motor age, actual hours of operation, and so forth.

Sometimes, facility managers have a grasp of the opportunity for energy savings that a large-scale motor replacement investment would offer, but simply do not have the cash to implement a plan. To address this situation, Emerson just introduced an option letting companies pay for motors over time. With five-year operating leases, a company can install a 50-hp or larger motor and pay with their energy savings return over the term. After five years, they either buy or re-lease the motor. With an operating lease, the motors are not part of the user’s capital, so return on capital rises. Emerson also offers a capital lease for smaller motors. At the end of the term, the user owns the motor.

Understanding efficiency

Common sense says everyone should buy the most efficient motors available for the job. But, premiumefficiency motors do often carry a higher initial price tag than standardefficiency motors. It’s worth noting that aside from

lower energy costs, new energy-efficient and premium-efficiency motors have other benefits as well. According to “Efficient Motors: Selection and Application Considerations,” from the CEE:

• Many efficient motors run cooler and are more likely to withstand voltage variations and harmonics better than less efficient motors.
• Many efficient motors have a slightly higher power factor on average than their standard counterparts.
• Most efficient motors operate more quietly than standard motors.
• Manufacturers often provide extended warranties on efficient motors.

But, Raynes cautions that with motors it’s never a black-and-white decision. A premium-efficiency motor, for instance, doesn’t necessarily run cooler. Each application is different and needs to be treated as such.

EASA’s “Understanding Energy Efficient Motors” warns of several other common misconceptions regarding energy-efficient motors, and states that an oversized motor is not necessarily less efficient, and a more efficient motor does not always have a higher power factor. One thing that can offset the efficiencies of a premium motor is high in-rush current, which can translate to high peak demand charges, notes Boteler.

Sometimes repair is a more viable option than replacement, even in terms of efficiency. EASA is currently undertaking a study with its U.K. sister organization, the Assn. of Electrical and Mechanical Trades, to determine the impact of rewinding on large motor efficiency. A similar study was conducted previously on small motors and found that they can be rewound without compromising efficiency. The results of the large motor study are slated for release later this year.

In many cases the payback on purchasing an efficient motor is relatively short. Raynes says that in some instances people assume greater potential energy savings than is realistic. The whole application really needs to be examined because a premium motor coupled to an inefficient drive isn’t going to realize cost savings.

To determine potential energy savings of a premium-efficiency motor for a particular process, you need to compare the operating cost of an existing standard motor with an appropriately sized energy-efficient replacement. To do this, you’ll need to determine operating hours, efficiency improvement, values, and load. Keep in mind that most electric motors are designed to run at 50 to 100% of rated load, and maximum efficiency is near 75%. Resources are available from government agencies, trade associations, and motor manufacturers to walk both you and your customers through this process.

The Motor Challenge fact sheet “Determining Electric Motor Load and Efficiency” offers several load and efficiency calculation methods. It recommends surveying and testing all motors running more than 1,000 hr/yr and dividing into the following categories:

• Motors that are significantly over-sized and under loaded — replace with more efficient, properly sized models at the next opportunity, such as scheduled plant downtime.
• Motors that are moderately oversized and under loaded — replace with more efficient, properly sized motors when they fail.
• Motors that are properly sized but standard efficiency — replace most of these with energy-efficient models when they fail. The cost effectiveness of an energy-efficient motor depends on the number of hours the motor is used, electricity price, and the energy- efficient motor purchase price.

Several software calculation tools can help determine efficiency and suggest proper replacements. For example, MotorMaster+ software automatically determines motor load and efficiency values when measured values are entered into its motor inventory module. A built-in database provides new motor price and performance data and other energy management features, such as replacement analysis, maintenance logging, inventory control, energy savings, and life cycle cost analysis. This software is available from the Dept. of Energy (DOE) Office of Industrial Technologies.

Individual motor manufacturers also offer software tools based on their product lines. For instance, Baldor Electric Co., Fort Smith, Ark., recently introduced BE$T software, which calculates the annual electricity of an existing motor, based on nominal efficiency, compared to efficiency of standard and premiumefficiency motors. The complimentary software recommends by catalog number the best Baldor motor for the applications and notes the payback period in months for replacing the existing motor.

Horsepower breakpoint charts are another tool that can help with repair/ replace decisions. Outlined in the Industrial Electrotechnology Laboratory’s “Horsepower” bulletin, these charts use electricity prices, annual operating hours, motor enclosure type, and motor speed to determine a motor horsepower breakpoint. Motors above the breakpoint are repaired, and those below are replaced. Charts are available for totally enclosed, fan-cooled and open drip-proof motors at: 1,200, 1,800, and 3,600 rpm.

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