|
|
|
A Motor Management Program Cuts Energy and Maintenance Costs With energy costs constantly rising, it is critical to identify opportunities to reduce energy use and cut costs. One aspect of this effort is establishing a motor management program that can ultimately reduce downtime, energy costs and motor costs. Product Manager Applied Industrial Technologies Cleveland, Ohio Motor Management
Motor Management is about managing motors as an asset, not as individual products. It involves planning ahead, making decisions before a motor fails and considering the true cost of operating motors to save energy, reduce downtime and increase profitability. This asset management approach can substantially reduce energy and maintenance costs by preparing plant and maintenance management to make the most cost-effective decision when a motor fails. Elements of the program include: - Evaluating the energy savings that accompany the purchase of a NEMA Premium Motor - A relatively small upfront investment will not only pay back quickly, it will also continue to pay dividends in energy savings for years and years to come.
- Repair vs. replacement policies – The decision to repair or replace a failed motor has a direct impact on operating costs and reliability. Evaluating motors and making repair vs. replace decisions in advance avoids reactive decisions that may be costly in the long run.
Other components of a Motor Management Program may include: - Critical spare motor inventory
- Purchase and repair polices
- Motor inventory analysis
- Motor surveys and tagging
- Data management
- Storage program
- Preventive and predictive maintenance
NEMA Premium Motors Until the 1970s, most general-purpose motors were designed to provide rated output and operating characteristics at reasonable cost. As energy prices began to rise during the energy crisis, manufacturers promoted improved motors they called "high-efficient" or “energy efficient.” Standard inefficient models remained popular, however, because they cost less than these new “energy efficient” models. This presented national energy implications and Congress eventually passed the Energy Policy Act of 1992 (EPAct), which set minimum efficiency standards for certain electric motors. EPAct required that select motors sold in the U.S. after October 1997 were required to have efficiency ratings equal to or better than ratings dictated by NEMA (National Electrical Manufacturers Association). Efficiencies of "EPAct motors" were one to four percentage points higher than the previous “standard efficient” motors. Manufacturers continued to improve motor design and, in many cases, exceeded EPAct standards. In June 2001, NEMA granted these "better-than-EPAct" motors special recognition by creating a designation called NEMA Premium™. In most cases, replacing an older, serviceable, standard-efficiency motor with an EPAct-minimum motor results in significant energy and cost savings, as well as payback periods of three years or less. A more rapid return can be gained by investing in a NEMA Premium model. Consider purchasing NEMA Premium™ efficiency motors:
- For new motor procurements
- When specifying motor-driven equipment
- When repairing or rewinding failed standard-efficiency motors
- As replacements for older, operable lower-efficiency motors, particularly when the existing motor has been rewound or is oversized and underloaded
Repair or Replace? Motors often fail without warning, and when they do the primary concern is getting the production line up and running as quickly as possible. The decision to repair or replace the motor, at this point, is a critical one for a number of reasons. First, the cost of unscheduled downtime can be significant in terms of lost production and maintenance costs. These costs can run into thousands of dollars per hour. Second, expediting motor repair can significantly increase repair costs. Finally, and most importantly, the repaired motor cost may actually be more than the cost of a new motor. In addition, the repaired motor generally is less efficient than a new, replacement motor. Operating cost is a primary consideration in making this decision because the cost of a motor is insignificant compared to the cost of the electricity required to operate it. In addition, the Department of Energy (DOE) estimates that almost 25% of all electrical energy is consumed by motor driven systems and that converting this energy to mechanical work through motors accounts for about 70% of most companies’ electric bill. Thus, managing electric motors makes a great deal of sense.
Plant and maintenance managers have little time to consider these issues when faced with a failed motor. Their objective is to get the plant running as soon as possible. A cost-effective approach is to establish a motor management program that tracks the condition of each motor in a plant and bases the repair/replace decision on clear cost guidelines.
Motor Management Decision Tree
Repair: In making the decision to repair a motor, the Standard Practice is to rush the repair because no backup motor is on hand. The main pitfall of this decision is that repaired motors are never as efficient as new motors, and continually repairing a motor continually degrades its efficiency. The efficiency loss can vary widely depending on the quality of the repair shop, so repairing a motor can significantly increase operating costs.
The Best Practice is to be prepared with replacement motors in stock so that the repair decision need not be rushed. Another aspect of Best Practices is to track the repair history of each motor in a facility, including how many times it has failed and the efficiency before and after each failure. Also, the capabilities of the motor repair facility should be carefully assessed to ensure they understand the motor’s history and purpose. The sidebar “Motor Repair Best Practice” outlines the elements of a motor repair policy.
Replace:
Motors can be replaced either with standard EPAct or NEMA Premium® designs. EPAct motors generally are less expensive; however, they usually are less efficient, run hotter and have higher operating costs. They will, however, offer significant energy savings compared to pre-EPAct motors you are operating. NEMA Premium motors cost more initially; however, some utilities offer rebates to help offset the cost difference. The motors are 0.5 to 4% more efficient than standard motors. They also run cooler, require less maintenance, experience less downtime and are available with extended warranties. NEMA Premium motors can save thousands of dollars in annual energy costs, and payback time can be as short as six months. A simple online tool from Advanced Energy can help guide the decision to repair or replace a motor. Inputs include enclosure type, operating speed, motor list price, electricity cost, desired payback period and load factor. With this data, the tool then creates a graph showing the breakeven point for one of the following comparisons as a function of motor horsepower and annual operating time: - NEMA Premium compared to motor rewinding
- EPAct compared to motor rewinding
- NEMA Premium compared to EPAct
As an example, consider a motor operating at 3600 rpm at a 90% load factor. The cost of electricity is $0.05/kW-h and the desired payback period is two years. The graph below shows the breakeven hours for a NEMA Premium motor compared to rewinding a conventional motor.
If the intersection of motor horsepower and operating time falls blow the breakpoint line, the motor should be replaced rather than repaired. Even above the breakpoint line, it might be worth replacing rather than repairing if a rebate is available. Help Is Just a Click Away The idea of motor management is based on research performed by Washington State University for the DOE. This research led to the development of the Motor Decisions Matter(SM) campaign ( http://www.motorsmatter.org/). The MDM website contains information that helps companies develop a motor management plan to meet their specific needs. The information can also lead to partnerships with local sales and service centers, vendors, utilities or other energy-efficiency organization that may offer more support. The website makes available a number of resources developed by MDM sponsors to demonstrate the financial benefits of life cycle costing and to help companies develop an effective Motor Management Program, including software, motor selection guides, and evaluation and planning materials. The 1-2-3 Approach to Motor Management is a software tool that demonstrates how to reduce downtime and save energy by managing motors. It is a good starting point for small to medium-sized companies that might not have the resources to develop a Motor Management Program. It requires only a limited amount of input to calculate annual motor operating costs. It then presents financial data for future decisions based on life cycle costing. It allows a user to make decisions on the cost effectiveness of repairing a motor, replacing it immediately or replacing it on failure with an EPAct or NEMA Premium motor. It is available free from the Consortium for Energy Efficiency with a one-time registration. MotorMaster+ 4.0 was created by Washington State University through a grant from the DOE. It is a comprehensive program that allows users to create and manage a motor database. It also contains manufacturer’s information for more than 20,000 AC motors, including nameplate data, list price and repair costs. The software is free and can be downloaded from the US Department of Energy’s Best Practices website. Motor manufacturers and utility and state motor programs endorse a common specification and label for NEMA premium-efficiency motors. A list of participating manufacturers is available from NEMA. The Consortium for Energy Efficiency has issued Efficient Motors: Selection and Application Considerations, a brochure that provides a brief guide to understanding and selecting efficient motors. It contains several examples that help users determine when using a premium-efficiency motor is appropriate. Advanced Energy offers two helpful pieces of literature. The Horsepower Bulletin outlines a policy for cost-effective management of motor purchases and repairs. The information is based on feedback from industrial customers, electric utilities, motor suppliers and service centers as well as test results measuring the efficiency of more than 100 new and repaired motors. The Motor Survey How-To Guide provides a method to identify motors in a single facility or on a company-wide basis. It explains how to gather data, including motor load and nameplate information. A form for documenting this information is provided. Both documents are available online or by contacting Advanced Energy at 800-869-8001.
Finally, the DOE offers a series of two-page Tip Sheets on various motor management topics. They provide overviews of energy saving opportunities and guidelines for calculating potential savings. Topics include: - Eliminate Voltage Unbalance
- Replace V-Belts with Cogged or Synchronous Belt Drives
- Avoid Nuisance Tripping with Premium Efficiency Motors
- Estimating Motor Efficiency in the Field
- Extend Your Motor's Operating Life
- The Importance of Motor Shaft Alignment
- When to Purchase NEMA Premium Efficiency Motors
Conclusion
The annual operating cost of a motor is often many times its initial cost. Therefore, paying closer attention to and managing electric motors makes a great deal of sense. In addition, anticipating when a motor might fail can be important in reaching production goals. That's why developing a Motor Management Program to determine when, whether and how motors should be replaced and repaired is a wise investment.
Motor Repair Best Practice
Require repaired motors to “exactly duplicate” original motors in:
- Number of turns
- Winding design and coil configuration
- Wire cross sectional area
- Rolling bearing size, type and specification, including seals or shielding
Always replace bearings when rewinding. One-third to one-half of all motor failures are due to bearing failures.
Ask the repair facility to:
- Record core loss before and after stripping
- Repair or replace defective laminations
- Calibrate instruments at least annually
- Measure and record winding resistance
- Measure and report repaired motor efficiency
- Establish a quality assurance program
- Provide a new motor warranty for repaired motors
Ask the repair facility not to: - Heat stators above 650°F
- Sandblast the iron core
- Knurl, peen or paint bearing fits
- Use an open flame for stripping
- Grind the laminations or file the slots
- Increase the air gap
- Increase stator winding resistance
- Make mechanical modifications without approval
- Change winding design
Ask the repair facility to maintain records of repairs and make them available to help identify root causes of failures.
Avoid rush rewinds if at all possible. Speeding up certain processes such as stator burnout is an easy way to introduce damage.
Source: Electrical Apparatus Service Association (EASA) Technical Note 16, www.easa.com. |
|
|
|
|
