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Full Rewind Study Results Now AvailableTests prove proper repair/rewind practices maintain the efficiency/reliability of Premium Efficiency/IE3 motors.
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This webinar recording looks at several aspects of winding design to prevent increased temperature rise and decreased efficiency.
Most modern rotating electric machines operate on the same principles their predecessors have for 100+ years. However, improvements in materials technology over that time have allowed for increasingly greater power density in machine design.
An increasing number of manufacturers are using magnetic wedges in their form-wound machines. When a winder fails to replace magnetic wedges in kind, the winding temperature rise can increase by 20°C, and the magnetizing current can increase by 20% or more.
There are benefits and drawbacks to the use of multiple circuits in a 3-phase winding. Whether discussing a random winding or form coil winding, some of the considerations are shared. Topics covered include:
Manufacturers almost always utilize machine-inserted concentric windings for random-wound, three-phase stators when their processes can facilitate it due to lower manufacturing costs. Many service centers can produce concentric windings too, but the most common practice is to utilize the two-layer lap winding. For form-wound stators, the two-layer lap winding is almost always used by manufacturers and service centers alike. The purpose of this article is to provide some tips for working with odd-turn (unequal-turn) windings, or two-layer windings where the total number of turns per slot is an odd number (e.g., 3,5,7,9…n). In such cases, the top and bottom coil sides must have a different number of turns.
Electric motor efficiency can be maintained during repair and rewind by following defined good practices. This article builds on a previous discussion of PM and PdM for three-phase squirrel-cage motors ("PM and PdM for electric motors") by outlining some of the expectations and good practices for repairs of these types of motors.
Most plant engineers and maintenance staff can attest to the reliability of standard-efficiency motors that have been repaired or rewound using industry best practices. They also know repair can cost far less than replacement, especially when the motor has special features. Despite this, some of them hesitate to have failed energy-efficient motors (NEMA Premium models, in particular) repaired because they’ve heard it degrades efficiency.
So, what’s the right answer? Is the decision to repair, rewind or replace a failed energy-efficient motor as simple and straightforward as you may have heard?
One of the pleasures of helping EASA members is in discovering challenges or specific areas where we can improve on the original design of the motor manufacturer. The most recent of these, for me, has been a noticeable cluster of calls about motors with multiple windings. The call usually starts with something like this: "We wound this motor, and one speed was terribly burned." Another one I often hear is: "We rewound both speeds, and the surge test pattern for one speed indicates a winding problem." These are but a couple of examples of a design issue we are seeing with motors having more than one winding. While the use of variable-frequency drives (VFDs) is increasingly common, there are still applications using 2-speed, 2-winding motors. Cranes are a good example of one such application. When a core has more than one winding, the two windings behave as a transformer. Applying voltage to either winding induces voltage in the other winding because the two windings are inductively coupled. As long as both windings are connected 1 wye, and the leads of the second winding are left open, no magnetizing current is drawn by the second winding. When both windings are conventional and symmetrical, this arrangement works just fine. The problems start when either winding deviates from the symmetry that is so important to 3-phase motor performance.
Topics covered include:
Time is a precious commodity, so making the best use of it can help you provide the best possible service to your customers. Following are just a few topics covered:
One of the most significant changes to occur in our industry over the past several decades has been the shift from simply repairing equipment to solving the customer's problem. By that, we mean determining why it failed, and improving the suitability and reliability of the equipment for the application. Doing so requires knowledge about what the motor is doing, where it is operating, and under what conditions. Our customers appreciate results and are increasingly aware of the value a good service center adds above and beyond a simple repair.
This 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors.
This booklet covers topics such as:
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The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors
Tests prove Premium Efficiency/IE3 Motors can be rewound without degrading efficiency.
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Recommended Practice for the Repair of Rotating Electrical Apparatus
This is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.
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The EASA Technical Manual is the association's definitive and most complete publication. It's available FREE to members in an online format. Members can also download PDFs of the entire manual or individual sections.
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