David Sattler
L&S Electric, Inc.

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.

Aunque los clientes rara vez notan la merma del rendimiento, nuestro objetivo durante la reparación de los motores es siempre llevar a cabo rebobinados de la más alta calidad posible. Por lo tanto, hemos diseñado e implementado el uso de discos (platos) retenedores para mantener los dientes del estator en su lugar mientras se saca el alambre magneto de las ranuras. Los discos que se ven en las fotografías nos han ayudado a evitar y garantizar dañar los dientes del estator al sacar el alambre del estator.

Presented by Chuck Yung
EASA Senior Technical Support Specialist

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. Topics covered include:

• Slot liner, separators and phase insulation
• Managing voltage stresses
• Making the connection: solder, crimp fittings or silphos
• Lacing tips
• Testing the completed winding

This webinar is intended for experienced and prospective winders, and those who supervise winders.

Chuck Yung
EASA Senior Technical Support Specialist

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.

Tom Bishop, PE
EASA Senior Technical Support Specialist

One of the most frequent member requests to our technical support group is for conversion of a 3 phase winding from concentric to lap. An excellent alternative to requesting the conversion is to use the EASA AC Motor Verification and Redesign (ACR) program to calculate the changes. In fact, many members have purchased the redesign program and have called us to confirm their conversions as they develop their proficiency and “comfort level” with the program. However, our emphasis here is not to convince you to purchase the ACR program but to cover the important details for a proper concentric to lap winding conversion.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA 

Al rebobinar un motor, el centro de servicio a menudo se siente limitado al diseño original y en ocasiones, nos encontramos con un diseño que desearíamos que nunca se hubiera llevado a cabo. El diseño del motor de 2300 voltios con bobinas de alambre redondo entra en esa categoría. La mayoría preferiríamos máquinas de media tensión (2300-4160 voltios) construidas exclusivamente con bobinas de alambre rectangular (solera o pletina). Este bobinado preformado (Figura 1) garantiza voltios/espira uniformes y sella los bobinados de forma confiable contra entornos hostiles.

Desde la perspectiva del fabricante, un motor de 2300 voltios con bobinas de alambre redondo representa una reducción sustancial en el costo de fabricación. Para el centro de servicio, el reto es rebobinarlos correctamente y, al mismo tiempo, ofrecer una reparación confiable.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

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.

Chuck Yung
EASA Senior Technical Support Specialist

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.

Tom Bishop, PE
Especialista Sénior de Soporte Técnico de EASA

Una de las solicitudes más frecuentes a nuestro grupo de soporte técnico es la conversión de un devanado trifásico de concéntrico a imbricado (excéntrico). Una excelente alternativa para dicha conversión es utilizar el programa EASA AC Motor Verification and Redesign (ACR). De hecho, muchos miembros compraron el programa de rediseño y nos han llamado para confirmar sus rediseños a medida que desarrollan su competencia y su "nivel de comodidad" con el programa. Sin embargo, nuestro énfasis aquí no es convencerlo de que compre el programa ACR, sino cubrir los detalles importantes para rediseñar el devanado concéntrico a imbricado.

David Sattler
L&S Electric, Inc.

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. Studies¹ show that motor efficiency may be reduced by splaying end teeth. Even if that reduction in efficiency is slight, any reduction in efficiency results in higher costs and wasted energy.

Even though these performance reductions are seldom noticed by customers, our goal in motor repair is always to produce the highest quality rewind possible. 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.

Tom Bishop, PE
Especialista Sénior de Soporte Técnico de EASA 

Con la llegada de los variadores de frecuencia electrónicos (VFD) de estado sólido a fines de la década de 1980, se descubrió que los bobinados de los motores que funcionaban con VFDs fallaban con más frecuencia que al estar alimentados con la energía convencional (onda sinusoidal). A principios de siglo, los fabricantes de motores habían comprendido mejor cómo los VFD afectaban los devanados del motor, y al igual que los proveedores de materiales electro aislantes habían desarrollado materiales y métodos para mejorar la confiabilidad de los devanados de los motores alimentados con VFDs. El término general para los devanados es "inverter duty (a prueba de inversor)". En este artículo, describiremos los materiales y métodos asociados con los devanados inverter duty. 

Alambre magneto
Antes de que se desarrollara el alambre “spike-resistant (resistente a picos)” a finales de la década de los 90s, una práctica común para bobinar los motores que funcionaban con VFDs consistía en utilizar alambre con un aislamiento más grueso a base de poliéster y algunos de ellos utilizaban películas de aislamiento triples o cuádruples. Estos alambres son muy efectivos cuando se les somete a voltajes de onda sinusoidal o voltajes transitorios intermitentes. Los alambres con aislamiento para trabajo pesado (heavy duty) son efectivos contra el efecto corona (Figura 1) porque la distancia entre los conductores reales es mayor con el aislamiento agregado. Esta mayor separación entre los conductores individuales obliga a que cualquier voltaje que se presente entre los conductores sea menor. Sin embargo, cuando la forma de onda del VFD somete a esfuerzos los alambres, la rigidez dieléctrica de los alambres con aislamiento para trabajo pesado, no es tan efectiva. Los alambres magneto modernos utilizados para motores con inversores tienen mayor capacidad dieléctrica con una vida útil más significativa (Figura 2). También pueden soportar picos de voltaje mejor que el alambre con aislamiento para trabajo pesado, pero con la misma estructura que el alambre magneto estándar. La Figura 3 ilustra el impacto en la vida útil del alambre magneto a medida que aumenta la frecuencia de conmutación de un variador. La vida del alambre con aislamiento de trabajo pesado se ve muy afectada, mientras que la del alambre inverter duty no se acorta por la frecuencia de conmutación. 

Usar alambres con mayor diámetro aumentará el voltaje donde comienza a producirse el efecto corona. Por eso, al rebobinar motores inverter duty puede ser importante utilizar la menor cantidad de alambres más gruesos disponibles. Al contrario, los alambres más delgados tienen menos pérdidas por efecto superficial a frecuencias más altas, como la frecuencia portadora de un variador. El efecto superficial hace que la corriente en un conductor redondo esté cerca de la superficie, y la frecuencia portadora es la velocidad a la que el voltaje de CC se "corta" en segmentos para simular la potencia de una onda sinusoidal. Si la frecuencia portadora es alta, por ejemplo, 12 kHz o más, utilice alambres con diámetros más pequeños si es posible; de lo contrario, considere utilizar alambres más gruesos. 

Llenado de ranura y sistema de aislamiento
Incluso el mejor sistema de aislamiento eventualmente comenzará a fallar, especialmente con el uso de un VFD. Para mayor resistencia eléctrica y mecánica, un diseño típico inverter duty maximizará el llenado de la ranura. Esto aumenta la eficiencia y permite que el motor funcione más frío, y también ayuda a evitar el movimiento de las bobinas que puede romper el aislamiento. Es una buena práctica utilizar amarres en al menos cada 3.ª o 4.ª cabezas de bobina, en el lado conexión y lado opuesto conexión para sujetar aún más el devanado.

Como lo ilustra la Figura 4, el fallo más común de los devanados que funcionan con VFDs ocurre en las primera(s) vuelta(s) conectada(s) al cable de salida, por lo que como protección eléctrica adicional algunos bobinados la primera vuelta de las bobina(s) conectada(s) al cable de salida pueden estar aislada(spaguetti). El aislamiento entre fases está diseñado para separar las bobinas de las diferentes fases. La mayor parte de la magnitud de los picos de voltaje vistos por el devanado se concentra en las bobinas conectadas a los cables de salida. Las vueltas inicial y final de una bobina de alambre redondo pueden estar en contacto y se puede presentar un pico de voltaje entre esos dos alambres adyacentes, así como a través de las bobinas. Debido a que los picos de voltaje pueden alcanzar los 2000 voltios o más, también se debe usar aislamiento de ranura adicional para el voltaje más alto, siempre que no sea necesario reducir la sección del alambre para poder insertar el bobinado en las ranuras. Maximice el aislamiento y utilice separadores en las ranuras y vueltas finales. Un motor que funciona con un VFD normalmente se calienta más que el mismo motor alimentado con una onda sinusoidal. Si la temperatura del devanado es 10°C más alta, la vida térmica útil del aislamiento se reduce a la mitad. El aislamiento Clase H (180 °C) tiene una clasificación de temperatura más alta que los devanados Clase B o F (130 °C o 155 °C), por lo que se puede extender la vida útil del devanado. Cuando el motor funciona a una velocidad inferior a la nominal o base, la disminución del flujo de aire hará que el devanado del motor se caliente más. Por esta razón, es ventajoso un sistema de aislamiento Clase H (180°C). 

Impregnación y barniz
Se debe utilizar un proceso de doble inmersión y horneado. Si está disponible, una mejor alternativa sería sumergir y hornear(dip & bake)seguido de impregnación por presión y vacío (VPI) y luego secar. Asegúrese de seguir las instrucciones del fabricante del barniz/resina en cuanto a la temperatura de precalentamiento del bobinado como támbién la temperatura y el tiempo de curado. Tenga en cuenta que el tiempo de curado no comienza hasta que el devanado se haya calentado a la temperatura mínima de curado recomendada para el barniz/resina. Precaución: La mayoría de los alambres magneto tienen una capa lubricante que se utiliza para facilitar su fabricación. El proceso de precalentamiento del devanado tiene dos propósitos: Primero, evaporar el lubricante del alambre, lo que luego permite que el barniz/resina se adhiera al conductor y el segundo es que ayude a aliviar las tensiones residuales en la película aislante del alambre para que este no se agriete (crazing). 

Técnica de bobinado inverter
Cuando se fabrica o rebobina un motor que funciona con un VFD, se debe tener mucho cuidado al insertar las bobinas en las ranuras para evitar que la película aislante del alambre no se raye ni se pele. Es una buena práctica utilizar papel mylar en las ranuras para ayudar a la inserción de las bobinas y protegerlas de daños. Algunos fabricantes utilizan una técnica de bobinado que hace que quede menos "aleatorio" al alinear el alambre en las ranuras empleando un espaciado más ordenado de las vueltas. La idea es mantener el principio y el final de las bobinas lo más alejados posible entre sí para reducir la magnitud del voltaje entre los conductores adyacentes. Las máquinas bobinadoras semiautomáticas utilizadas en los centros de servicio se acercan a este nivel de espaciado ordenado de las vueltas. 

Especificaciones para bobinados inverter duty
La siguiente es una especificación guía para un sistema inverter duty. 

General 

• Aislamiento Clase H o superior 

Alambre magneto 

• Inverter duty 

Sección del conductor 

• Conserve o aumente la sección transversal 
• Conserve o aumente el número de alambres (reduce las pérdidas por corrientes parásitas 

Aislamiento 

• Separadores entre fases 
• Como mínimo aislamiento a tierra de 0.015” (0.38 mm) 
• Arriba de 80 voltios por bobina instale separadores en la mitad de cada grupo 

Atado y soporte 

• Amarre al menos cada tercera o cuarta bobina 
• Encinte las cabezas con un mínimo de 3 medias capas de de vidrio virgen [1 pulgada (25 mm)] a partir de 1 pulgada (25 mm) del núcleo hasta 1 pulgada de las puntas 

Impregnación 

• Pre caliente el barníz de acuerdo con las instrucciones del fabricante 
• Sumerja y cure(dip & bake) dos veces 
• Cure durante el mayor tiempo recomendado por el fabricante 
• Note que el tiempo de curado no comienza hasta que el devanado se haya calentado a la temperatura de curado

This video shows one step in collecting motor winding data: how to measure magnet wire. A service center could use this data to:

• Duplicate an original winding
• Verify that a previous rewind was done correctly
• Serve as a basis for redesigning a winding
• Store recorded data for future reference

 

Helpful tools

• EASA's magnet wire table can be found in Section 6 of EASA's Technical Manual and can be downloaded for free by EASA members.
  
  DOWNLOAD FREE PDF BUY LAMINATED WIRE TABLE
   
• EASA's polyphase and single phase winding data cards are available for purchase in EASA's online store.
  
  BUY WINDING DATA CARDS

This EASA software is a valuable interactive training tool ideal for training your novice(s). Even experienced winders will learn from it. The CD teaches how to wind in a richly detailed, step-by-step approach. It includes narrative, animations and video clips, with tests to assess student comprehension. The training, which is divided into 13 lessons, covers data taking, core testing, coil cutoff, burnout, stripping, core preparation, coil making, stator insulation, coil insertion, internal connections, lacing and bracing, inspection and test of untreated and treated windings, and winding treatment. Features include "Pro Tips" and "Drill Downs" that enhance the learning experience and assure that even the most experienced technician will learn from this product. The course is delivered as an interactive Adobe PDF file containing text, audio, video, supporting documents and quizzes.

LEARN MORE

Mike Howell
Technical Support Specialist
Electrical Apparatus Service Association

Three-phase induction motors, which are fundamental to numerous industrial applications, feature either squirrel-cage rotors or wound-rotors. Squirrel-cage rotors are prevalent due to their robustness, reliability, and cost-effectiveness, while wound-rotor induction motors, though less common due to advances in power electronics and variable frequency drives, are still used in applications such as cranes, hoists, and mills. This paper explores the construction and operation of both types of rotor windings in three-phase induction motors.

The operation of induction motors is based on the interaction between a rotating magnetic field produced by the stator and the rotor windings. When the stator windings are energized by a three-phase voltage source, a rotating magnetic field is created, which induces a voltage in the rotor conductors. This induced voltage causes a current to flow, generating a magnetic field that interacts with the stator field to produce torque. The rotor speed lags the synchronous speed of the stator field, a difference known as slip, which is essential for torque production.

Squirrel-cage rotors consist of uninsulated bars shorted together by end rings, and can be either cast or fabricated. Cast rotors, typically made of aluminum or aluminum alloy, are common in smaller motors, while larger motors often use fabricated rotors made of copper or copper alloy. The rotor bars and end rings are designed to optimize electrical resistance and mechanical strength. The deep-bar effect, where current tends to flow on the outer surface of the rotor bars at high frequencies, affects the rotor's resistance and reactance, influencing the motor's starting and running characteristics.

Wound-rotor motors feature phase windings connected to slip rings, allowing external resistances to be added to the rotor circuit. This adjustability provides high starting torque and controlled acceleration. Wound-rotor motors are particularly useful in applications requiring variable speed and high starting torque. The rotor windings are typically wave-wound, with conductors arranged to maximize induced voltage and minimize losses. The construction of wound-rotor windings involves precise placement and connection of conductors, ensuring mechanical stability and electrical performance.

The paper also addresses issues such as rotor slot harmonics, which can cause noise and vibration, and the importance of skewing rotor bars to mitigate these effects. Additionally, the construction and maintenance of wound-rotor windings, including the use of slip rings and carbon brushes, are discussed. Proper insulation, bracing, and banding are critical to ensure the longevity and reliability of rotor windings.

In conclusion, the construction and operation of induction motor rotor windings are complex but essential for the efficient performance of three-phase induction motors. Understanding the principles and practices involved in rotor winding design and maintenance is crucial for service centers and engineers working with these motors.

Key Points Covered:

• Differences between squirrel-cage and wound-rotor windings
• Basic operation of three-phase induction motors
• Construction and materials used in squirrel-cage rotors
• Deep-bar effect and its impact on rotor performance
• Advantages and applications of wound-rotor motors
• Wave-wound rotor winding configuration
• Mitigation of rotor slot harmonics through skewing
• Importance of proper insulation, bracing, and banding in wound-rotor windings

Key Takeaways:

• Squirrel-cage rotors are robust and cost-effective, while wound-rotor motors offer high starting torque and variable speed control.
• The interaction between the stator's rotating magnetic field and the rotor windings is fundamental to induction motor operation.
• Proper design and maintenance of rotor windings are crucial for motor performance and longevity.
• Understanding the deep-bar effect and rotor slot harmonics is important for optimizing motor efficiency and reducing noise and vibration.
• Wound-rotor motors, though less common, are still valuable in specific industrial applications requiring adjustable speed and high torque.

Tom Bishop, PE
EAS A Senior Technical Support Specialist 

With the advent of solid-state electronic variable frequency drives (VFDs) in the late 1980s, it was found that the windings of motors used on VFDs failed more frequently than when powered by a utility (sine wave) supply. By the turn of the century, motor manufacturers had gained a better understanding of how VFDs affected motor windings, and motor manufacturers and suppliers of winding materials had developed materials and methods to improve the reliability of motor windings supplied from VFDs. The general term for the windings is “inverter duty.” In this article, we will describe the materials and methods associated with inverter duty windings.

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 recording explains why they are used, provides a balanced review of the benefits and negative issues associated with their use, and explains how to avoid the problems.

• Why some manufacturers use magnetic wedges
• Benefits of magnetic wedges
• Downside of magnetic wedges
• Fitting and installation to prevent them from falling out in service

Target audience: This will benefit service center technicians and supervisors.

Chuck Yung
EASA Technical Support Specialist

Note: This article was originally published October 2001 and was updated September 2021.

When rewinding a motor, the service center is restricted by the original design. Sometimes, we encounter a motor design we wish had never been developed. The random-wound, 2300-volt motor design falls into that category. Most of us would prefer to see medium voltage (2300-4160 volt) machines built exclusively using form coils. The form coil winding assures uniform volts/turn stresses, and reliably seals the windings against hostile environments.

From the manufacturer’s perspective, a random-wound, 2300-volt motor represents a substantial reduction in manufacturing cost. And competitive pricing is important if they want to sell motors. The great challenge to the service center is in successfully rewinding this design while maintaining profit.

Chuck Yung
EASA Senior Technical Support Specialist 

When rewinding a motor, the service center often feels restricted to the original design. Sometimes, we encounter a motor design we wish had never been developed. The random-wound, 2300-volt motor design falls into that category. Most of us would prefer to see medium voltage (2300-4160 volt) machines built exclusively using form coils. The form coil winding (Figure 1) assures uniform volts/turn stresses and reliably seals the windings against hostile environments.

From the manufacturer’s perspective, a random-wound, 2300 volt motor represents a substantial reduction in manufacturing cost. For the service center, the challenge is to successfully rewind them while providing a reliable repair.

Mike Howell
EASA Technical Support Specialist

Cuando sus procesos pueden facilitarlo y para rebajar costos de fabricación, los fabricantes casi siempre emplean en los estatores trifásicos de alambre redondo, bobinados concéntricos insertados con máquinas. Muchos centros de servicio también pueden rebobinar bobinados concéntricos, pero la práctica más común es la de utilizar bobinados excéntricos de doble capa. Para los estatores con bobinas pre-formadas, los fabricantes y los centros de servicio utilizan la mayoría de las veces, bobinados excéntricos de doble capa.

La finalidad de este artículo es proporcionar algunos consejos para trabajar con bobinados con espiras diferentes (impares) o con bobinados excéntricos de doble capa donde el número de espiras por ranura es un número impar (Ej. 3,5,7,9…n). En estos casos, los lados superior e inferior de la bobina deben tener un número de espiras diferente.

Teaches procedures for winding diamond and round-nosed coils. Includes determining coil dimensions from a bare core and winding multiple groups at one time.

This training film is archived here solely for historical purposes. The film was produced many years ago and does not meet EASA's current presentation standards. Some procedures may have also changed.

Mike Howell, PE
EASA Technical Support Specialist

The EASA Motor Rewind Database software has the ability to connect to a live, ever-expanding online database of more than 250,000 windings. This live database is monitored, updated and corrected as needed by EASA’s Technical Support Staff. Using the online database guarantees you’ll have the most up-to-date information available at all times. 

The database includes: 

• Three-phase, single-speed AC motors 
• Three-phase, multi-speed AC motors 
• Single-phase AC motors 
• DC motors & generators 

This webinar covers how to get the software, how to use the software, and several guided examples. It is intended for all personnel who need access to winding data. 

12 presentations

$60 for EASA members

 

A special discounted collection of 12 webinar recordings focusing on AC motor windings.

Once purchased, all 12 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

The Basics: Taking Motor Data
Presented September 2016

This presentation covers:

• Photo documentation
• Paper documentation
• Measurements
• Winding data: turns, wire size, connection, core dimensions
• Keeping cause of failure questions in mind

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Taking Three-Phase Winding Data
Presented October 2012

This presentation stresses the importance of taking accurate winding data and explains and emphasizes the consequences of inaccurate data. Details are provided on how to take accurate electrical and mechanical data as well as how to verify the data is correct. It gives you and improved ability to "get it right the first time" so as to avoid the added cost and time of another rewind to correct errors.

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The Basics: Motor Connections
Presented November 2016

This webinar covers:

• Internal connections
• Connections in the outlet box
• Connections in the MCC Ladder diagrams

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Tips and Techniques for Winders
Presented August 2015

This webinar covers:

• Procedural tips for coil insertion
• Creating slot room where there is none
• Faster, easier separators
• Lacing technique to prevent phase paper pull-out
• Interspersed coil winding made simple
• Better braze joints

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Rewinding Tips for Premium Efficient Motors
Presented June 2016

This webinar recording covers: 

• Importance of core loss testing
• Methods to reduce core losses
• Slot fill improvement without reducing copper

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Windings & Connections
Presented December 2015

This webinar recording focuses on the internal connections of AC motors, including:

• Wye or delta?
• Parallel circuits
• Dual voltage - delta connected, wye connected and wye/delta connected
• Tri-voltage - 2D2Y1D and others

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Concentric or Lap? Considerations for the 2-Pole Stator Rewind
Presented September 2014

Two-pole motors present special rewind issues, especially when converting them from concentric to lap windings. The pitch is especially important as certain coil pitches will cause harmonics that have a negative impact on performance. Optimum pitches are often very difficult to wind and shorter pitches result in sacrificed conductor area.

This presentation explores sample redesigns and present some guidelines to assist in deciding between the concentric and lap winding.

Target audience: This webinar will be most useful for service center winders, engineers, supervisors and managers. The content will be beneficial for beginners through highly experienced persons.

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Stator Rewinds: When Things Get Tight
Presented June 2015

When preparing to rewind random or form wound stators, sometimes there just doesn’t seem to be enough room in the stator slot for the desired conductor area and insulation quantities. Common scenarios encountered are redesigns from concentric to lap, changes to higher voltages or aggressive designs from the OEM.

This webinar will look at balancing stator copper losses against insulation reliability.

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Ensuring Success With VPI
Presented June 2014

Global vacuum pressure impregnation is the most common insulation system processing method utilized for form wound stators today. A successful VPI depends on several variables including materials, methods and maintenance. This recording will provide information to assist the service center with ensuring success with form wound VPI projects.

Target audience: This recording will be most useful for service center winders, engineers, supervisors and managers. The content will be beneficial for beginners through highly-experienced persons.

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Induction Motor Rotor Windings: Squirrel-Cage and Wonld Rotor Basics
Presented January 2018

This presentation covers the following topics:

• Induction motor basics for operation
• Squirrel-cage
  • Conductor material
  • Deep-bar effect
  • Multiple-cage windings
  • Phase resistance
  • IEC/NEMA design letters
  • Speed-torque characteristics
• Wound-rotor
  • Winding construction
  • Wave-wound connections
  • Distribution factor and chord factor
  • Rotor phase voltage
  • Speed-torque characteristics

Target audience: This webinar will benefit service center technicians and supervisors. 

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2-Speed, 2-Winding Pole Group Connections
Presented September 2018

The topics covered included in this webinar recording:

• One circuit wye connection — Best, no parallel paths, turns per coil may prevent this
• Delta or multiple parallel circuits—Produces closed circuits, Circulating currents
• Open delta (4 wire connection)
• Permissible connections—Skip pole, adjacent pole
• Determined by speed combination

T​arget audience: This webinar recording will benefit service center technicians and supervisors.

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Minimizing Risk With High-Voltage Rewinds
Presented February 2014

This webinar presents a product quality planning process for industrial motor stator windings rated above 4 kV. Emphasis is placed on analyzing gaps between these projects and lower voltage rewinds as they relate to:

• Stator winding design
• Insulation system validation
• Process control

Target audience: This presentation is most useful for service center winders, engineers, supervisors and managers. The content targets beginners through highly experienced persons.

Mike Howell
EASA Technical Support Specialist

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).