Unless great care is taken, pulling magnet wire from a motor stator often bends or splays the lamination’s end teeth. Bent teeth, or teeth that have been splayed outward at the ends of the core stack, will likely compromise the quality of the repair job. Therefore, we have designed and implemented the use of disc clamps to hold the stator tooth tips in place while pulling magnet wire from the slots. The clamping fixtures described in the photos have helped ensure that we avoid damaging the stator teeth during the stripping process.

A no ser que se tenga mucho cuidado, tirar del alambre magneto al desmantelar el estator de un motor a menudo deforma o dobla los dientes de las laminaciones. Estos dientes deformados comprometerán la calidad de la reparación y hay estudios que demuestran que este problema puede reducir la eficiencia del motor. Sin embargo, aunque esta reducción puede ser pequeña, genera altos costos y desperdicio de energía.

This video shows one step in collecting motor winding data: how to measure magnet wire.

The goal of vacuum pressure impregnation is complete saturation of a winding with insulating resin. As resin penetrates the insulating materials, it causes them to darken. If some insulation is a lighter shade, the coil or jumper is not fully saturated. The winding is not properly protected, and if the problem is not addressed, it is likely to cause premature failure of the unit. This could result in costly warranty work, or at a minimum, will be a failure to provide your customers with the quality they expect and deserve.

El objetivo de la impregnación por vacío y presión (VPI) es saturar completamente un devanado con resina aislante. A medida que la resina penetra en los materiales aislantes, los oscurece y al drenar la resina VPI del devanado, todo el aislamiento de las cabezas queda oscuro en un tono uniforme. El aislamiento de la conexión también debe quedar oscuro de forma pareja. Si algún aislamiento muestra un tono más claro, la bobina o el puente no han quedado completamente saturados y el devanado no está debidamente protegido. Si no se soluciona el problema, es probable que esto provoque un fallo prematuro en el equipo. Esto podría generar una garantía costosa o, como mínimo, la reparación no brindará a sus clientes la calidad que esperan y merecen.

This webinar recording shares some of the “best practice” rewind methods used by (and learned from) EASA service centers around the world: connection recognition, best insulating materials, wire choices and tips to save time and effort.

This handy form provides fields to record all of the details needed to document and/or order replacement coils for an AC form-wound machine. The form also includes detailed descriptions/definitions of the data to be recorded in each field. 

This webinar recording looks at several aspects of winding design to prevent increased temperature rise and decreased efficiency.

With a steady increase in random wound AC motor sizes and the obvious superiority of the form coil winding, one area where we can help improve customers' motor reliability is by redesigning those large random wound motors to accept form coils. Most repairers would agree that machines rated larger than 600 hp (450 kW) should be designed as form coil machines. Likewise, those rated over 2 kV will be much more reliable as form coil machines.

No one wants to rewind a motor using 60 #14 AWG (62- 1.6 mm) wires in hand. With an abundance of niche suppliers of stator laminations, the cost and practicality of converting a random wound motor to form coil are available to nearly all service centers. Replacement laminations can be punched, laser-cut or water-cut, and supplied with very reasonable delivery times.

Con el aumento continuo de los tamaños de los motores CA y la obvia superioridad de los devanados con bobinas preformadas (pletina o solera), un área en la que podemos ayudar a mejorar la confiabilidad de los motores de nuestros clientes es rediseñando estos motores grandes de alambre redondo para que acepten bobinas preformadas. La mayoría de los reparadores estarían de acuerdo en que las máquinas de alambre redondo por arriba de 600 hp (450 kW) deberían rediseñarse con bobinas preformadas. Así mismo, aquellas con tensiones nominales superiores a 2 kV serían más confiables con bobinas de pletina.

Nadie quiere rebobinar un motor con 60 #14 AWG (62- 1.6 mm). Con la abundancia de proveedores especializados en laminaciones de estatores, el costo y la practicidad para convertir motores de alambre redondo a pletina está al alcance de casi todos los centros de servicio. Las laminaciones para reemplazar el núcleo pueden ser troqueladas o cortadas con láser o agua y entregadas en tiempos muy razonables.

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.

This presentation covers induction motor basics for squirrel-cage and wound rotor motors

This presentation covers:

• The importance of the stator core test 
• Simple theory to share with technicians and customers 
• Practical approach for testing small stators demonstrated 
• Eliminating pen + paper; loop test calculations for any device 
• Assessing the results

When an electric motor is expected to be stored for an appreciable time before it is placed into service, certain steps should be taken to ensure that it will be suitable for operation when it is needed. The practical limitation we need to recognize is that much of what we do when putting a motor into long-term storage has to be undone when the same motor is moved into operation. This article addresses common recommendations for stored motors.

The October 2012 Currents article titled "How to properly test AC stator and wound rotor windings" provides a thorough explanation on the proper application of insulation resistance, winding resistance, surge testing and high potential testing for stators and wound rotors. The article emphasizes that NEMA MG 1-2011 specifies AC and DC high potential (hi-pot) test levels for new windings and does not recommend repeated application of the high potential test. This is reinforced in EASA's Recommended Practice for the Repair of Rotating Electrical Apparatus (ANSI/EASA AR100-2010) which calls for reduced voltage levels for repeated tests should they be required. This article is intended to provide additional information on the high potential test performed on new windings. Specifically, it addresses the advantages of AC high potential testing for new, form coil stator windings. Topics discussed include: A real-world example Destructive test? Sizing the AC test set Example calculation Bibliographic references to additional reference materials

There are times when a winding cannot be processed through the burnout oven, so it must be removed "cold." The bond strength of most resins is approximately 8-10 psi (55-70 kPa), which means that a fairly large coil might have nearly 3,000 pounds (1350 kg) of bonding force with the slot. In those cases, there are some useful tips that can be used to reduce the difficulty in removing the coils. Many of the techniques in this article can be adapted for open-slot, wound rotors and armatures.

When rewinding motors rated 6 kV and above, there are certain steps beyond the normal rewind procedures used for 2.3 kV/4 kV machines. Whether a machine is to be VPI processed makes a difference in how the winding should be treated.

It is very important to take accurate data when you rewind a form-wound motor or generator, especially if the coils will be made by an outside coil manufacturer. There are a couple of variations to the standard coil design that are not common, but that you may come across from time to time.

Describes the procedures for inserting a formed coil into a stator. Shows proper tools and various wedging methods. Includes connecting the coils and insulating the connections.

Teaches how to determine type of connection, number of parallel circuits, turns per coil, wire size, span and groups. Shows step-by-step way to properly record all information.

Shows how to determine loop dimensions, winding the loop, insulating it and spreading the coils, along with determining the dimensions of the spread coil.