We’ve heard the bit that claims knowledge is equivalent to power. In our economic system and field of endeavor, one must learn as much as possible about the business, art and science of maintenance lest we see our favorite technical discipline degenerate into nothing more than another battered victim of rampant outsourcing.
It’s always been the philosophy of this publication that you can never get too much education. When things go wrong, if you don’t know the answer or can’t come up with a solution, there’s someone out there who can.
Because electric motors are ubiquitous in the manufacturing arena, they’re sometimes taken for granted. Getting them right the first time, though, is a worthwhile endeavor because, conservatively speaking, a motor’s lifetime operating cost can exceed its purchase price by an order of magnitude. The opportunity exists for you to keep the plant from spending any more than it needs to spend. It takes a little learning. That’s why, this month, we’re digging through the morass we call the Web in search of practical, zero-cost, noncommercial, registration-free resources that can help you become one of the most motor-conversant people in the building. Remember, we search the Web so you don't have to.
Read all about it
It appears that the good folks at SM Service & Technology, a distributor of electric and electronic hardware in Union, N.J., believe that an educated customer is the best customer. I draw this conclusion based on the fact that the company (a) sells motors and (b) posts free educational material about them on its Web site. You will find it at http://smservice.com/litlist.htm. This is the place to visit if you want to know about, for example, reducing power factor cost and optimizing your motor drive system. The total offering includes eight articles, of which you can access six without having to register your identity. This select group comes from the Bonneville Power Administration and each is tagged with the line “Download PDF File.”
From spark to twist
An AC induction motor is nothing more than a device that converts invisible electrical energy into torque, which, in turn, might be persuaded to do some useful work. But don’t think of a motor as a black box whose inner workings are mysterious beyond comprehension. Mankind has been building motors for more years than you can count and the general construction details behind the phenomenon are clearly presented in an article from Control Engineering at www.controleng.com/article/CA6427335.html?rssid=129. Scroll down to the part dated June 21, 2005, and wrap your mind around AC induction motor anatomy, the reasons synchronous and actual speeds differ, and the design and construction differences among several motor varieties.
The U.S. isn’t the only entity on this side of the Atlantic with an interest in motors. Our neighbors to the north have their Office of Energy Efficiency, which is part of Natural Resources Canada in Ottawa and is dedicated to making that country as energy efficient as possible. Part of the obligatory Web site addresses the topic for the month. Pay a visit to http://oee.nrcan.gc.ca and click the following links as pages load: “English,” “Industrial: Facilities and Equipment” and “Technical Information.” If you then select “Energy efficient equipment” and its subcategory, “Electric Motors,” you’re poised to begin a six-part motor article. Heed the warnings about speed and power factor differences between the old and new motor that are listed under purchasing tips. As an aside, select “Tools and Calculators” to take a look at the “Energy Use Calculator,” which tabulates all the energy you bring inside the building envelope or burn up in vehicles.
From the West coast
Southern California Edison, Rosemead, Calif., weighs in with its Web contribution to motor issues at www.sce.com [no hyphens]. The route to this site’s relevant content takes you through “Large Business” in the lower right followed by “Large Business Tips” found under “Tips, Tools & Training.” At that point, scroll down to “Motors” for a set of four articles. Of those, the two best are titled “Improving the Efficiency of Motors” and “Adjustable Speed Drives.” The first shows you how to calculate the dollar value of higher motor efficiency. This knowledge can be useful when you need to cost-justify your next motor purchase. The second offers four practical tips for keeping your drives operating at their best. The remaining articles are too short to be of much value for the purposes of this column.
Discussion group speaks
Research this month uncovered a series of 14 motor-related articles by Howard G. Murphy, P.E. He uses a modified Q&A format that includes a single question followed by answers that appear to have been provided by a discussion group. Topics include calculating motor acceleration, the effect of 50 Hertz on 60 Hertz motors, regenerative braking and motor performance at low speeds. All this is posted on the Web site operated by Rexel, Inc., an electrical parts distributor based in Dallas. Y’all just let your mouse mosey on down to www.rexelusa.com [no hyphens] and lead it to “News” to select “Archives” from the drop-down menu. Click on “Motors & Drives” at the far left and you’ll be rewarded with a good read. By the way, Murphy authored a two-part article about drive harmonics that was published in Plant Services in late spring of 1999.
New wires are good wires
There comes a time in the career of nearly every large electric motor when it needs a heart transplant that only your local rewind shop can provide. It’s primarily an industrial malady as most of the smaller motors found in residential or commercial applications are simply discarded when they sicken and die. If you trek to www.energyideas.org [no hyphens], you can find some information about motor repairs that is presented by EnergyIdeas Clearinghouse, a service that helps Pacific Northwest business, industry, government and utilities implement energy technologies and practices. The clearinghouse is operated and managed by the Washington State University Extension Energy Program in Olympia, Wash., and funded by the Northwest Energy Efficiency Alliance, Portland, Ore. So, if you click “Site map” near the bottom of the page, you can then scroll down to “Browse by Topics” and select “Motor Systems.”
Finally, click on “Motor Repair” for access to the 10 relevant items currently on the site. The list includes a couple of articles, several Q&A bits and a fact sheet.
The machinery stopped when the drive motor ceased driving. With downtime being so universally odious (and obvious to management), no doubt you’ve got a spare unit that gets things moving again. But what do you do with that broken prime mover? If nothing else, be selective about which motors you send to be rewound. The payoff, you see, will be much greater if you simply replace the defective motor, even if the purchase cost exceeds that of a rewind. Introducing the cost issue as a deciding factor implies you can justify the approach you use in getting that machine shaft turning again. Deciding which motors should be scrapped is easy, says the Central Iowa Power Cooperative, which generates and transmits electric power to 13 electric cooperatives in the state. You can use the algorithm they post at http://cipco.apogee.net/mnd/merrovr.asp to guide you through the math. While you’re there, be sure to click on “Index” at the bottom of the page. Those folks in the Hawkeye State seem to know something about motors.
It’s one thing to rewind a motor when you’re standing on good ol’ terra firma, but it’s quite another to do it from inside the bowels of a ship at sea. You can, I’m sure, imagine the difficulties involved. It might hearten you to know that our U.S. Navy rewinds motors of all sorts while out on the briny blue. It’s definitely a team effort, as you’ll read when you float your mouse over to www.navy.mil and enter the numeral 9744 in the search box. “Rewind Shop Shows Fine Motor Skills,” an article by Journalist 3rd Class Fletcher Gibson, USS Enterprise Public Affairs, reveals some of the challenges that sailors must overcome to keep our vessels ship shape.
Your tax money at work
The U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) has a Web site full of information that you might find useful. Some of it even applies to motors and associated systems. For example, it wasn’t hard to uncover a page about motors and energy, where EERE posts its output. The motor tips sheets, seven in number, address voltage imbalance, nuisance tripping and extending a motor’s useful life. What I thought was most interesting was the tip sheet about estimating motor efficiency in the field, which highlights four ways to measure the five major losses associated with reduced motor efficiency. There also are links to case studies and at least five of the 11 shown involve motors. The 14 technical publications from several sources are predominately about motors. Finally, there are links to material about four motor software packages. This trove is yours for the asking. Simply go to www1.eere.energy.gov/industry and click on “Best Practices” in the middle column. When the page loads, aim for “Motors, Pumps, and Fans” found under the “Energy System Links” heading. There’s a lot here, so you might want to return when you need information about something other than motors.
Is motor RCM worthwhile?
Applying reliability-centered maintenance to everything in the plant might not be the best use of your collective time, writes Idcon, Inc., a consulting firm in Raleigh, N.C., that focuses on maintenance and operations practices. There are classes of assets for which it makes sense to spend the time and money that a proper RCM program requires, and motors might not be in that number. You can get the company’s take on the matter in a brief piece you’ll find at www.idcon.com, where you’re going to select “Reliability Tips” from the drop-down menu that appears under “Resources.” Select the tip dated October 2006. It’s a short article, but the real takeaway is the four-page preventive maintenance standard “Condition Monitoring Standard - AC Motor” that is highlighted in the last paragraph.
I’d guess that most of the motors in your plant are either single-phase or three-phase AC units. Being so common, one can almost become familiar with this class of machine through osmosis. But, industry also uses DC motors in a variety of configurations for specific applications. That’s why I point out “Electric Motors 101,” an element of the Electric Motors Reference Center, which comes to you from a trade magazine called Machine Design. In addition to material about AC motors, this is where you can learn about DC motors of all types: brushless, permanent magnet, coreless and linear. You might not become an instant expert, but you’ll get a good grounding in the fundamentals of this class of prime movers. The section about selecting a DC motor walks you through the basic calculations you’ll need to get it right the first time. All you need do is plug that mouse into www.electricmotors.machinedesign.com.
Speaking of DC motors, they don’t need to be nearly as complex as you might think they ought to be, according to Kinetic MicroScience, Los Gatos, Calif. The company offers you step-by-step instructions for building a functional DC motor using items you probably have in your maintenance shop. I’m not going to belabor the point because its simplicity is self-evident if you tool over to http://scitoys.com and click on “An electric motor in 10 minutes.”
E-mail Executive Editor Russ Kratowicz, P.E., CMRP, at [email protected].