Motor repair and replace by the numbers

05/09/2013


The calculator

The simplest way to make a preliminary repair/replace decision is to use the calculator shown in Figure 2. Here is how it works. First determine the following:

  • Annual running hours for the motor application (HA)
  • Local energy cost, in $/kWh (E)
  • Efficiency change, in % (FNEW – FREPAIR)
  • Cost of repair, in $ (CR)
  • Cost of a new motor, in $ (CN)
  • and insert the values in the following equation: 
  • Decision coefficient = HA • E • (FNEW – FREPAIR) • CR/CN 

The Replace/Repair Calculator is an empirical index to enable motor users to estimate whether to replace or repair an existing motor that has failed or is about to fail. Courtesy: Integrated Power ServicesFor example, assume that a 100 hp, 3,000 hr energy-efficient motor is showing signs of failure. Energy cost is $0.09 from the local utility. Also, conservatively estimate that if the motor is rewound, it will lose 1% efficiency, from 95.5% for the new one to 94.5%. Cost of rewinding is $2,600, and a new replacement costs $8,800. Should it be rewound or replaced? 

Decision coefficient = 3,000 • 0.09 • 1 • 2,600 /8,800 = 79.77 

On the calculator, this figure falls well within the “repair” region. On the other hand, had the motor run another 1,500 hours and been located in an area where energy costs are $0.13, then the answer would have been right at the breakpoint. 

This equation shows the overriding importance of efficiency. By simply changing the efficiency shift from 1 to 2, the coefficient doubles. Also, the equation is conservative in that it does not include an escalator factor for increases in power costs—which, like death and taxes, are a certainty. Thus, if the calculator indicates that the repair/replace decision is near the breakpoint, the wise choice would be to replace the motor to take advantage of the new motor’s greater efficiency as power costs increase. 

Decisions on dc motors

Not all motors show such graphic evidence of failure, but when the time comes to repair or replace a motor, making a cost-efficient choice can provide the best long-term solution. Courtesy: Integrated Power ServicesThe dc machine is, as the saying goes, a different animal. Except for bearings, its wear points are different than those of ac machines and it’s much more expensive to build—by a factor of 2 to 4, depending on its design. Likewise, dc machines are somewhat more expensive to repair than ac units, but not by a factor of 4 unless the commutator and armature are completely destroyed.

Large dc machines cling to those specialized applications where extremely precise control of speed is paramount, or where it is possible to use a regenerative drive to recapture a portion of the energy already invested in the rotating mechanism. Other than that, dc technology has been shouldered aside by ac, and large dc motors have become relegated to those applications where nothing else can be controlled as precisely.

Repair/replace decisions for dc are usually simpler than those for ac because there is no premium efficiency line manufactured. Also, because the motors are more expensive to manufacture, users tend to hold onto them longer. For dc machines, the repair/replace breakpoint tends to be higher than that for ac, about 65% the price of a new unit.


<< First < Previous 1 2 Next > Last >>

FUJI , KS, United States, 06/06/13 11:55 AM:

This is a very good artical for plant team to learn. Fuji Wu.
VILLALAN , Non-US/Not Applicable, Malaysia, 06/06/13 09:38 PM:

Very informative. Dr.Villa
BILL , VA, United States, 06/07/13 08:16 AM:

thanks for the insight
GEORGE , TX, United States, 07/18/13 12:52 PM:

Good article.
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Hannover Messe 2016: Taking hold of the future - Partner Country status spotlights U.S. manufacturing; Honoring manufacturing excellence: The 2015 Product of the Year Winners
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
Improving flowmeter calibration; Selecting flowmeters for natural gas; Case study: Streamlining assembly systems using PC-based control; CLPM: Improving process efficiency, throughput
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Warehouse winter comfort: The HTHV solution; Cooling with natural gas; Plastics industry booming

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me