As with most industries, electric-motor repair has good and bad actors. I remember part of my training with Dreisilker Electric back in the early 1990s. If we lost a repair job to a lower-cost service company, we would take a current reading at a specific load and then show the customer the increase in operating current. Later I would use a wattmeter, infrared camera, and other tools to show the difference between a good-versus-bad repair. That difference would be obvious, especially when lower-cost shops were using liquid weld, reduced wire size, peening, extreme burnout temperatures, and other methods that would keep cost and reliability down.
Poorly repaired motors coming out of such shops would sometimes make it just through their warranty periods, or, when they failed, made it easy for end-users to void warranties. The customer’s concern, though, was typically more about cost than reliability. Unfortunately, that mindset continues in many companies today.
A number of Canadian studies on electric-motor repair were conducted in the early 1990s (1992 – 1995). Two of these were “blind” studies, where motors up to 50-hp in size were damaged and sent for repair. The units were then tested to CSA 390 (equivalent to IEEE Standard 112 Method B Efficiency Testing) and losses were isolated. The three most cited studies were Hydro Ontario and BC Hydro, with a controlled study by Hydro Quebec.
In all of those studies, machining and mechanical conditions (such as bearing replacement, including types used) had the greatest impact. The most significant impact was a reduction in efficiency of more than 3% (due to replacement of shielded bearings with full-contact-sealed bearings). From the standpoint of rewinding, the average efficiency decrease was 1%. This decrease was primarily due to changes in wire size (using a smaller standard wire versus metric wire) and winding changes that were basically for the convenience of the winder. Speed, after all, is important.
How real are potential issues associated with poor repair? Very. And are they unusual? No, they’re not. Over the years, I have evaluated many motor-repair operations for clients. Going through the evaluation process, such shops, might, for example, tout their respective temperature-controlled burnout ovens. When I examined them, though, I might find that water piping to an oven’s misting system wasn’t connected. In some cases, I inspected post-burned-out stators and discovered laminations falling apart. And in still other cases, I would find insulation materials and wire covered in dirt, soot, and oil. One of the worst situations surfaced was when I was helping evaluate a repair shop serving major manufacturing operation. The shop’s only stripping method was a rosebud torch; it used pour-through varnish for varnishing; and it had no test panel.
So, the question is this: Is it possible to do a quality repair in which the efficiency and length of life improves?
One of the most disturbing things I’ve ever heard from an end-user customer is the term “half-life of repair.” This customer had become so accustomed to poor repair practices that it determined a repaired motor repair would only last half as long as a new one. Is this really what motor users should expect?
Absolutely not. One of the keys behind any quality repair practice is the individual focus on the motor, or generator. In mass-production motor manufacturing, certain tolerances are allowed. In the repair process, the ability to meet tighter tolerances is quite real, as is the ability to provide modifications to meet the application. In the end, the opportunity to extend the life of a machine beyond the expectations of its original manufacture is not just possible: It should be expected.
Canadian and U.S. Department of Energy (USDOE, energy.gov) studies into electric-motor repair have proved something very important: It is not only possible, but easier to produce a good-quality repair than work as hard to do a cheaper repair. In a rough comparison, the warranty rates of a good repair shop will be less than 0.1%, while the warranty claims against a poor repair shop will exceed 5%. Although a short-cut savings concept should have brought a reasonable profit to low-quality shops, they usually suffered the costs associated with rework and the profits were lost.
At a high-quality repair shop, when a warranty claim comes in, it can be seen as an opportunity to explore why the motor failed, usually from an installation or operation standpoint. (On a sidenote, while turning a repair shop around, if an in-shop or customer warranty occurred, I would always ask, “Who tried to save us money.”)
How do you safeguard against poor repair practices? The number one way is to ensure that you reference a specification. For smaller electric motors, this is straightforward, given the fact industry specifications such as the ANSI/EASA AR100 (easa.com) or IEEE Standard 1068 (standards.ieee.org) provide excellent guidance. The Electrical Apparatus Service Association (EASA, easa.com) also provides some superb resources related to proper practice, and they’re available for download on the Association’s website and/or through your repair facility.
For end-user operations that don’t have in-house personnel experienced in motor repair, seeking out EASA-certified facilities is a step in the right direction. Additional information on motor-repair practices can be found through USDOE at this link, Motor Systems | Department of Energy, which cites industry-developed best practices for everything from repair or replace, to selecting new motors, among other things. While much of this information was developed in the 1990s, it is just as valid now as it was then.
CONCLUSION
An organization can take several additional steps to help ensure it gets top-notch motor repairs. The first is to evaluate the repair shop you are working with. This can be accomplished using the evaluation forms in the back of IEEE Standard 1068 and during an actual shop tour. Be ary of any repair shop that will not allow that access. The next step is to reference a repair specification or, for larger machines, provide a repair spec that includes stopping points and reporting. Pictures of defects and causes for repair are crucial. With so many good, reasonably priced cameras in today’s marketplace and the low cost of memory, there’s no excuse for not having quality photographic documentation. Finally, and particularly with critical motors, be sure to visit your chosen facility at key points during the repair process. And ask questions.
Note: Except for a poorly applied machine, an electric motor that has undergone a good-quality repair should last longer than a comparable new motor. And it also should have lower operating costs when good tolerances are met. (The Standards cited in this article include those tolerances.)TRR
ABOUT THE AUTHOR
Howard Penrose, Ph.D., CMRP, is Founder and President of Motor Doc LLC, Lombard, IL and, among other things, a Past Chair of the Society for Maintenance and Reliability Professionals, Atlanta (smrp.org). Email him at [email protected], or [email protected], and/or visit motordoc.com.
Tags: reliability, availability, maintenance, RAM, energy efficiency, pumps, electric motors, steam systems, compressed air systems, process-heat systems, greenhouse gas emissions, environmental sustainability, vibration, Electrical Signature Analysis, ESA, SMRP, Electrical Apparatus Association, EASA, OSHA, U.S. Dept. of Energy, National Institute of Standards and Technologies, NIST, General Motors
