Art of Electric Motor Repair Part 4b

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The Impact of Motor Repair on Energy Efficiency

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I’ve covered this topic extensively since 1994 and many have tried to tackle it as an issue since the Energy Policy Act of 1992 and as a significant topic of discussion since 1973. Legislators and policymakers have attempted to include electric motor repair efficiency as a topic with energy policy all this time and it was again tackled in the industry and government partnerships that had progressed with the Motor Challenge programs under the US Department of Energy in the early 1990s. It was lost in the noise when the Challenge programs were blended together, but was brought up during meetings I had with legislators (Congressional and Senate) when I was meeting with energy policymakers in Washington, DC, this past February, 2016, as part of the SMRP Government Affairs Committee.

The topic relates to how do you know if you have maintained or improved the energy efficiency through the motor repair process. You cannot perform a before and after efficiency on each repair as the motor is damaged, and you cannot economically perform a before and after efficiency test. In fact, you cannot rely upon the nameplate efficiency as it is often the ‘nominal efficiency’ or average efficiency and may be a calculated value. To make matters more challenging, depending on the country of origin, the efficiency calculation may be very different from the IEEE 112 Method B, which is the legislated method for evaluating efficiency.

Unfortunately, most do not know that there is an impact on the efficiency of their motor until they receive it back and it is consuming far more energy than it did before it failed. There are several papers on this in the http://motordoc.com archives, but the most telling is that if a motor is drawing a single amp more in the same conditions, there is a significant impact on the efficiency of the motor, and by direct extension, the reliability of the machine.

What we do know is that a process can be followed that will maintain efficiency based upon best practices through repair. This was proven in both the Canadian Electrical Association studies and the EASA/AEMT study. There are a few things that must be considered:

  • Wire Size – with the growing number of metric machines, and how tight conductors are packed into slots, a change in wire size to adjust for thicker insulation systems will have a direct impact on the I2R losses resulting in decreased efficiency and higher operating temperatures. With most motors manufactured over the past two decades, regardless of size, manufacturers’ insulation systems are getting thinner and slots are getting smaller while the repair industry has not adjusted significantly.
  • Winding Configuration – changing the winding from concentric to lap or otherwise will have an impact on efficiency. This is done almost routinely by many repair shops and must be performed with care and knowledge. This will have the same, or more significant, impact as with wire size. In fact, in some cases, because of the slot fits, a winding design may be changed in order to make sure that the cross-section is correct to handle the current, but the impact on the air-gap or back iron may still have a negative impact.
  • Mechanical Fits – bearing fits, in particular, but also coupling fits and rabbet fits, all have a direct impact on efficiency. Bearing fits can have a significant impact on increasing the friction and windage in a machine and the resulting heat will reduce the life of the bearing. Surfaces must be smooth and not punched, gouged or otherwise blemished as the inner and outer races of the bearing emulate the surface they are on. This can have a measureable effect on the efficiency of a motor.
  • Bearings – changing the type of bearing can have one of the largest impacts on the efficiency of a motor, in particular if a bearing is changed from shielded to sealed. As shown in previous studies, this change, alone, can reduce the efficiency of a motor by 3 percentage points, or more.
  • Stripping Process – an area of interest for over 50 years of study on efficiency and reliability. The temperature settings and times in an oven have a direct impact on the losses within the core of an electric motor, in addition to failure damage and cleaning of the stator core. The ability to verify the impact of the repair process on the core is measureable in that a before and after core loss test can be performed in order to determine if there are damaged spots (hot spots) or increases in the core losses. Another area that is impacted by this area is the mechanical fits of the components that go into the oven. In 1997, I was involved in a study in which we looked at different temperatures and the impact on airgap and soft foot. When maintaining the proper stripping temperature this becomes less of an issue. It is equally important to understand that stripping temperatures are based upon the core temperature, not the oven setting temperature, and the concept is that a temperature sensor is placed upon each stator in an oven (usually one or two). What does happen, especially in smaller shops, is groups of motors are placed in an oven and some of them ignite causing temperature differences throughout the oven, causing problems with the motor cores and even cores ‘falling apart’ through the process, or warping of cores. The IEEE 1068-2015 allows for a 20% increase in core losses for each repair activity on a motor and many companies have a limit to three rewinds before disposing of a motor due to impacts in this area.

There are other areas, of course, but these cover the main areas that have the more significant impacts.

The CEA and US DOE originally noted that there is an average of 1.1% reduction in efficiency through the repair process, based upon the studies. Due to discussions between the US DOE and EASA, programs such as MotorMaster Plus only accounted for a 0.5% decrease in repair, once and not compounded.

Starting the next part of the series we will be discussing the development of motor repair practices and specifications that will help you avoid losses in your machines.

For more information or assistance, please feel free to contact info@motordoc.com

Art of Electric Motor Repair Part 4a

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Electric Motor Repair Certification

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As mentioned at the beginning of the series, this topic is an update to a blog series I had produced in 2002. At the time there were no attempts at certifying motor repair shops outside of ISO 9000 and the EASA-Q, which was the Electrical Apparatus Service Association’s work to assist repair shops in achieving a version of ISO 9000 status.

In about 1997-9, there were the beginnings of organizations within the USA (I am not sure about outside of the USA, I will investigate that for a future topic) on certification for motor repair shops. There are several programs that started with commercial interests in mind, and good intentions, of course, a few independent programs and, more recently, trade association programs. Following are a few of the more well-known programs:

  • SKF Certification – primarily a commercial program with a focus on bearings. Provides training for repair shop personnel and third party review of repair shop capabilities. It does focus on whether a repair shop is using SKF equipment and bearings, of course, but that is not really a down-side as the products are top-of-the-line.
  • IEMD – The Institute of Electrical Motor Diagnostics, which closed its doors in 2009, was focused on the development of certifications for motor diagnostic technologies and was also working on an independent, end-user driven, motor repair certification. Progress stopped when a majority of the 200+ members were impacted by the economic downturn of 2009/10. There are presently discussions about re-starting IEMD or rolling its work into one of several organizations.
  • Advanced Energy – Closest to independent as IEMD’s work, Advanced Energy’s program focus’ on the evaluation of a repair shops ability to maintain an electric motor’s efficiency through the repair process. At the present time, it is one of the more intense programs which includes proving that a repair shop is capable of maintaining efficiency by performing before and after efficiency tests on a repaired electric motor. It does include a site visit and review of the repair facility to EASA standards.
  • EASA Repair Certification – Released within the past 12 months, this program is EASA’s first real attempt to verify that members are meeting the best practices reviewed and recommended as a result of the EASA/AEMT Repair Study. A growing number of repair shops are joining in.

The development of certification for motor repair is still in its infancy. Primarily because the days of a company witness testing or performing their own in-process inspections of their repairs has all but ended. What this does mean, at this time, is that while a repair shop can meet or pass these certifications, they do not generally follow the practices that are required. While the certification programs that have been developed, or are being developed, have been implemented, and repair shops have passed the certification process, I have been in a few that do not actually follow what they are supposed to do in the normal course of business.

What does this mean? It means that you still have to be very attentive to whether or not you are getting what you think you should be getting from a repair shop. The important thing is that the above mentioned certifications say that the repair shop that holds that certification is capable of meeting industry standard. However, it does not mean that they would meet your repair specification nor that they normally perform to industry standard. In most cases, they do. However, it is still incumbent upon the end user to verify, especially critical machines, through in-process and final inspections and witness testing.

At the present time, in the USA at least, there are no recognized certification programs for individual motor repair technicians. With the high turnover of motor repair specialists, there are some training programs that are available through EASA, but most new technicians are trained OJT, which means they may know what they are doing, but not necessarily why, which is a bad combination.

MotorDoc LLC provides repair shop inspections as well as in process and final witness testing. Contact us at info@motordoc.com for more information.

Art of Electric Motor Repair Part 4

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Selecting the Right Motor Repair Shop for You

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If performed properly, a successful motor management program has partnered with a motor repair vendor. When this is not the case, you will be in a position to have to expect the standards and quality of the shop you send your equipment to. Unfortunately, this may also mean that you are focusing on price versus quality and, perhaps worse, you may be expecting an extremely fast turnaround.

Here are a few secrets:

  1. In the world of motor repair, cheaper rarely means better as the backbone of motor repair is the craftsmen. Few motor repair shops are union shops; therefore, the wages are set by the employer. Lowest cost normally means lowest wages, which in turn may mean (but not always) lower quality workmanship. Also, parts may not be of the highest quality. The best motor repair shop that I worked for had one of the highest prices in the Chicago area and would, literally, turn away customers that would insist on discounts on their prices in the past. Their feeling was that if you wanted their level of quality, you would pay their level of pricing. The workers were well paid and the work environment conditioned and exceptionally clean. It was extremely rare to see a workmanship related warranty. I also had the unfortunate experience of working for a low cost repair shop for about two weeks in Virginia. They were the lowest cost, lowest quality that I had ever seen. I actually watched the shop manager glue a bearing into a housing because he forgot to check the housing on disassembly and they had not quoted machining. The final straw was when a part from a motor, that another technician was working on, sprung and stuck in the concrete inches from my head due to the company not purchasing required tools and the technicians not being paid enough to buy their own. One of the rewinders had even determined how much to reduce the wire size in order to get a particular high volume stator, from a large customer, to just make it through the warranty period. The burnout oven was often allowed to exceed 1,000 degrees F. (this was an EASA repair shop). They went out of business about a year after I left and I worked as General Manager for a competing motor repair shop.
  2. With only a few exceptions, proper motor rewind repair practice processes do not allow for a 24 hour turnaround. When this type of turnaround is required or the repair shop, shortcuts must be made, which reduce reliability. For the following examples we will use a 50 horsepower motor:
  • Standard motor repair: Disassembly and test – 2 hours; Wire removal (burnout oven at 650 degrees F) – 7 hours; Coil winding and insertion – 5 hours; 2-dips and bakes – 20 hours; Re-assembly – 4 hours. Estimated linear time for proper repair: 40 hours (we will be describing these steps in-depth).
  • Alternate motor repair: Disassembly and test – 2 hours; Wire removal (mechanical stripping at 410 degrees F) – 2.5 hours; Coil winding and insertion – 12 hours; Trickle system with full cure – 4 hours; Re-assembly – 4 hours. Estimated linear time for proper repair: 24.5 hours.

When selecting a motor repair shop, you must consider a number of facets:

  • Create a motor repair specification;
  • Certify the repair shop to your specification;
  • Include the repair vendor in your motor management program;
  • Periodically visit and audit the repair shop and witness tests; and,
  • Commission test all repairs.

There is a great checklist built in to the IEEE 1068-2015 “IEEE Standard for the Repair and Rewinding of AC Electric Motors in the Petroleum, Chemical and Process Industries,” which is a comprehensive repair document we will cover in future blogs. Note: the title relates to the IEEE standards group that developed it. The standard, itself, is valid for all industries.

I use the checklist from the standard as a guide and the ability to ‘grade’ the repair shop. However, understanding what you are looking at is just as important as obtaining the grade. For instance, I have been in shops that have temperature controlled burnoff ovens, only to find that the water lines are not hooked up or are even turned off. In other cases, all the wire exists and the winding area is segregated, but open to outside air so that dirt, dust and other contaminants coat the wire, insulation material and working surfaces. In one case, I was touring a repair shop and had noted a blackened area on the concrete pad in the shipping area and discovered that they used it to stack wood into stators in order to cause a bonfire to remove old windings.

Yes, there are repair shops that still use a version of flamethrowers, bonfires, torches and other uncontrolled temperature means to remove coils. These repair shops must be avoided at all costs from both a reliability and efficiency/environmental standpoint.

Starting in the next lecture (part 5), we will discuss how to create a motor repair specification. In the next parts (part 4a and b) we will discuss motor repair certification and efficiency.

Art of Electric Motor Repair Part 3

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The motor has failed, now what? This can be a failed electric motor or it has been found to be in a state of failure by the condition maintenance program. What is the next step?

Download a free paper on Repair Vs Replace decisions here.

If the motor is not critical, nor has any impact on production or safety, then just remove and replace it, right? No. You still have an investment, even if it is a few hundred dollars plus time. I have literally seen a company invest signficant man-hours over a bathroom fan! Even to the point where the plant manager was aware that there was difficulties with a motor in the bathroom and specialists were brought in to figure out the problem. As it turned out, the whole problem had to do with the mounting of a vibration transducer… on a bathroom fan? And, here it is, I specifically remember the incident over 20 years later. You get the idea.

Even in non-critical equipment, you need to know the basic cause of failure. Was there excessive dirt in fan blades? The motor? Did it single phase? Did a single phase motor blow a capacitor? Was the motor installed correctly?   How long did it last? Is the protection right-sized? In effect, a basic review of the system will allow you to avoid having to spend time on the same piece of equipment overa and over again. It is less the importance of the cost of the motor and associated equipment and more the investment of valuable man-hours… yours.

On critical, production or safety related equipment (you never know, it might be that bathroom fan!), you will want to look a little deeper. First, you will want to determine the cause of the failure and how it effected its associated system. The information may be obtained through using troubleshooting tools, such as electrical motor diagnostic techniques (MCA and ESA), infrared, vibration, ultrasonics and other tools. This allows you to make a repair versus replace decision during the removal of the failed equipment. It also allows you to:

  • Verify the accuracy of your motor diagnostics program through confirmation in the repair facility;
  • Provide information to the repair facility;
  • Perform a more in-depth root-cause-failure-analysis (forensics) quickly in order to prevent the same type of failure, or to allow for earlier detection; and,
  • Help determine if there are additional monitoring requirements for this particular equipment.

At this point, the motor should be removed. The technician must note such things as:

  • The condition of the motor feet;
  • The condition of the base and any grouting;
  • Tightness of bolts;
  • Condition of the coupling, belts and/or sheave;
  • Condition of the conductors and connectors;
  • Condition of the starter or drive;
  • Condition of the driven equipment, including gear boxes, fans and pumps;
  • Condition of surroundings, such as contamination, water, steam, etc.; and,
  • Other obvious conditions that would affect the new or repaired motor that will be installed.

At this point, any corrections to the base, coupling, belts, sheaves, etc. should be addressed prior to the installation of the new, repaired or spare motor. This is one of the reasons why condition based monitoring is so important. If a motor fails during a production run, the motor is removed and replaced quickly with little regard for its operation conditions, or parts are swapped until the system works again. This is less effective and incredibly expensive.

However, using proper tools and planning, you can plan an outtage or address the problem with more leisure and the ability to address the root problem.

Remember the following:

  • The motor often acts as a fuse for the real problem;
  • Utilizing a proper program, you can expect a 20-year average life from your motors.

Do you get a 20 year life out of your motors? Or, are you replacing the same ones on a regular basis?

 

To have a custom electric machine system PdM program planned and implemented for your facility or for assistance with a long-term electric machine system problem, email us at info@motordoc.com.

Art of Electric Motor Repair Part 2

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Figure 4 UV Flashlight

There are three common reasons for motor repair. These are, simply:

  • Scheduled Maintenance: the ancient practice of periodically shutting down and removing equipment for a general inspection and overhaul regardless of condition. For example: every five years a power plant shuts down, removes all critical motors and has tehm overhauled. This, of course, is not limited to power plants, which have been moving away from this practice from a cost savings standpoint. I refer to this as an ancient method as it has been realized more and more that this method is far too expensive and programs such as RCM and predictive maintenance can reduce the amount of work. Removing and installing regardless of condition actually exposes the owner to infant mortality problems and the general reliability of machines may drop signficantly as a direct result of this practice.
  • Condition-Based Maintenance: the modern art of identifying critical operations equipment, and monitoring them effectively, to determine the point where a motor is no longer performing its function, as defined by the operation and owner. For instance, the detection of bearing failure, winding contamination, early stage winding shorts, phase impedance unbalances and other conditions that are possibly corrective in nature. The key to this approach is that the owner can decide how soon the remove the motor on schedule, reducing unplanned downtime and can make an informed repair versus replace decision, bringing equipment back online much faster.
  • Motor Failure: in critical operations this can be looked at as both an ancient and modern practice of allowing the motor to run to failure. Why both? If the equipment is critical and no monitoring is being performed, or the wrong monitoring, then this is the ancient art of allowing equipment to fail, opening operations to extremely high mainteance costs. The reactive approach to maintenance results in patchwork, low grade repair, and more issues, that result in reduced system reliability. However, when part of a planned process, there may be equipment that has little to no effect on the mission of the company, such as production, safety, etc. In this case, it makes very little sense to invest manpower and equipment for testing.

We will return to these three reasons as we progress through the series.