By Ted Stearns, Applied Industrial Technologies
Motors often fail without warning and when they do the primary concern is getting the affected systems up and running as quickly as possible. If a replacement is readily available, the failed motor is usually replaced and sent out for repair. If no replacement is available, repair is often the only option.
This approach can be costly 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. Third, and most important, 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.
Plant and maintenance managers have little time to consider these issues when faced with a failed motor. Their objective is to do the required repair and get the plant running as soon as possible. A more 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 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.
A motor management program prepares plant and maintenance management to make the most cost-effective decision when a motor fails. Following the plan reduces downtime and energy costs and ensures the ready availability of replacement motors. Program elements include:
- Motor purchase and repair policiesThis involves developing new motor purchase and repair specifications that ensure the availability of high-quality, reliable motors.
- Repair vs. replacement policiesThe decision to repair or replace a failed motor has a direct affect 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.
- Spare motor inventory and replacement motor availability policiesEnsuring that the right motors are available in a timely manner so that the quickest resolution to a motor failure is also the most economical and reliable.
Other components of a motor management program might include:
- Motor inventory analysis
- Critical motor planning
- Motor surveys and tagging
- Data management
- Storage program
- Preventive and predictive maintenance
With a motor management program, plant and maintenance managers can work with suppliers to ensure that motors are available when needed. The decision tree shown in Figure 1 summarizes the decision-making process when a motor fails.
When an electric motor fails, the question is whether to repair it or replace it. Operating cost is a primary consideration 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 percent of all electrical energy is consumed by motor driven systems. Thus, managing electric motors makes a great deal of sense.
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. Continually repairing a motor 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 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.
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. NEMA Premium motors cost more initially. The motors are 0.5 percent to 4 percent 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.
Figure 2 NEMA Premium Efficiency Motor
A simple 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 3,600 rpm at a 90 percent load factor. The cost of electricity is $0.05/kWh and the desired payback period is two years. The graph in Figure 3 (page 34) 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.
A motor’s annual operating cost 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.
Author: Ted Stearns is product manager for Cleveland, Ohio-based Applied Industrial Technologies.
Motor 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 campaign (http://www.motorsmatter.org/). The 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 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, evaluation and planning materials.
“The 1-2-3 Approach to Motor Management” (http://www.motorsmatter.org/tools/123approach.html) is a software tool that demonstrates how to reduce downtime and save energy by managing motors. 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 ( http://www1.eere.energy.gov/industry/bestpractices/software.html) 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 U.S. Department of Energy’s Best Practices website listed above.
The Canadian Motor Selection Tool (CanMOST) (http://oee.nrcan.gc.ca/industrial/equipment/software/intro.cfm?attr=24). is the Canadian equivalent of MotorMaster. This program analyzes and compares the efficiency of three-phase electric motors.
A NEMA publication, “General Specification for Consultants, Industrial and Municipal: NEMA Premium Efficiency Electric Motors (600 Volts or Less)” outlines the minimum requirements for three-phase AC induction motors in municipal and industrial applications. It covers motors rated at 500 hp or less, operating voltages of 600 V or less, for more than 2,000 hours a year at more than 75 percent of full load.
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 (www.nema.org).
The Consortium for Energy Efficiency has issued “Efficient Motors: Selection and Application Considerations” (http://www.cee1.org/ind/motrs/motr-broch.pdf), 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 a helpful pieces of literature. The Horsepower Bulletin (http://www.motorsmatter.org/sponsors/industry/ae_hp.pdf) 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.
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:
- Eliminating voltage unbalance
- Replacing V-belts with cogged or synchronous belt drives
- Avoiding nuisance tripping with premium efficiency motors
- Estimating motor efficiency in the field
- Extending motor pperating life
- The importance of motor shaft alignment
- When to purchase NEMA Premium Efficiency Motors
These sheets are available at the “Motors, Pumps, and Fans Publications” (http://www1.eere.energy.gov/industry/
bestpractices/techpubs_motors.html) page of the EERE Best Practices website. TS