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. 

When a customer requests a motor be rewound for a new set of conditions, that is typically what we in the service center industry provide them. However, there are occasions where the customer request may be fulfilled by reconnection; in some cases, this is done simply by revising the motor nameplate data. The purpose of this article is to identify and explain some of these scenarios.

Reconnections covered include:

• Part winding start (PWS)
• Single voltage 12 leads
• 2 wye and 1 delta
• 230/460-575 volts 380 volts 50 Hz and 460 volts 60 Hz
• 2300 and 4000 volts

For an additional reference, see "Variables to consider when making motor frequency changes between 50, 60 Hz" published November 2008.

EASA’s AC Motor Redesign manual explains how to make all possible changes in the ratings of AC electric motors, within design limitations. Besides mathematical formulas, it provides guidelines on the limitations for each type of redesign. These are useful in determining whether a desired new rating is possible before the motor is stripped. Terms are expressed in both English and metric units. Each chapter contains at least one example to guide you through your own redesigns.

This book is available as a FREE download (see link below) or printed copies can be purchased.                                                                                    

Chapters in this book include:

• Wire size change
• Voltage change
• Horsepower or kilowatt change
• Frequency change
• Phase change
• Circuit change
• Span or chord factor change
• Winding connection change
• The master formula
• Converting concentric windings to lap windings
• Converting lap windings to concentric windings
• Notes on pole changing
• Decreasing speed by increasing poles
• Increasing speed by decreasing poles
• Single-speed to two-speed, one winding
• Single-speed to two-speed, two winding
• Developing a winding for a bare core
• Strengthening or weakening a motor - short method
• Determining the proper connection
• Single-phase redesign
• Calculation of secondary voltage
• Determining three-phase coil grouping 

Mike Howell
EASA Technical Support Specialist

This technical paper from the 2014 EASA Convention focuses on AC motor redesigns involving speed changes. Service centers encounter scenarios such as the procurement of a single-speed motor that must be redesigned for two speeds or redesign of an existing two-speed motor for use on an adjustable-speed drive. Topics covered include:

• Single-speed, one-winding to two-speed, one-winding
• Single-speed, one-winding to two-speed, two-winding
• Two-speed, two-winding to single-speed, one-winding
• Two-speed, one-winding to single-speed, one winding

The redesign examples use EASA’s AC Motor Verification & Redesign program, including use of the integrated Motor Winding Database for locating comparative data. Examples include other changes such as voltage, frequency and horsepower.

EASA's AC Motor Verification & Redesign - Ver. 4 software has been further refined and now contains and is fully integrated with EASA's Motor Rewind Database. This makes it the perfect program to lookup motor data, to verify existing winding data, and to perform motor winding redesigns.

This valuable resource is available only to EASA Members.

The AC Motor Verification and Redesign software provides easy verification of either concentric or lap windings, as well as redesigns with changes in poles/speed, horsepower, frequency or voltage. The redesign report with original and new winding data is output as an Adobe Reader (PDF) file and can be printed or saved. The program also allows you to search EASA’s extensive motor winding database. Choose to use the included database containing more than 250,000 windings or connect to the live, ever-expanding online database. Once found, motors from the database can be automatically imported as a starting point for further redesign.

Key software features include:

• Improved redesign accuracy and database search options.
• Includes the EASA Motor Rewind Database with more than 250,000 reported AC and DC windings. Use static built-in rewind database, or choose to use the constantly-updated, online database.
• Allows multiple simultaneous input cases for comparison of different motors.
• Users can opt to exclude half-wire sizes from automatic calculations.
• Automatic conversion from AWG to metric wire and square/rectangular wire to round magnet wire.
• The user can limit redesigns to only those matching in-stock wire sizes.
• Standard "one line formula calculations" are available from the Reference menu.
• Help files provide context-sensitive help. Includes the full EASA AC Motor Redesign book. Spanish translation of Help reference materials is provided.
• Built-in reference tables for chord factor, coil grouping, distribution factors, flux densities, and more.

System requirements

• Windows® XP, Windows® Vista, Windows® 7, 8 or 10 (Note: To run on a Mac, you must run a supported Windows OS using virtual machine software such as Parallels or Fusion.) 
• CD-ROM or DVD drive
• Approximately 1.25 GB free space on hard drive
• Screen resolution of at least 1280x768 (with text size set at 100%)
• Java™ Virtual Machine 1.8 or higher (Version 1.8 included on CD-ROM)
• Adobe® Reader (for report output/printing; free download from https://get.adobe.com/reader/)
• Internet access for retrieving future software updates and optional online motor rewind database

By Mike Howell
EASA Technical Support Specialist

Manufacturers deploy various external connection schemes to produce three-phase induction motors for multiple voltages and/or starting methods. Be sure to follow the relevant connection diagram, which is usually affixed to the motor or contained in its manual. If the diagram is lost, damaged, or ignored, you could find yourself dealing with a costly rewind.

The tips in this article apply to connections commonly encountered on machines with one speed at power frequency. If the external connection information isn’t available, ask your local service center for assistance, especially if several lead tags are missing or there are multiple nameplate speed ratings at power frequency. The service center can also help with unconventional numbering or cross-referencing IEC and NEMA numbering.

READ THE FULL ARTICLE

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

When the number of coils per group is the same throughout a three-phase lap winding, the grouping sequence is simply that number of coils repeated three (since it is three-phase) times the number of poles. For example, a 48-slot 4-pole winding has 12 groups of 4 coils.

The formula used to determine the average number of coils per group is:
Coils per group = slots divided by groups.

We don’t advocate using full slot coils with a lap winding; thus, the total number of coils is equal to the number of slots. The number of groups in an alternating pole winding is equal to the number of phases times the number of poles. In many cases, there are windings that have unequal coils per group, such as a 36-slot 8-pole winding, which has 24 groups with an average of 1.5 (36/24) coils per group.

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.

Mike Howell
EASA Technical Support Specialist

The March 2013 Currents article titled “Stator I²R loss: considerations for rewinds and redesigns” describes the stator I²R loss, its calculation and how to control it during rewinds. This follow up will provide a brief review and then explore the additional stator copper losses mentioned in that article.

Carlos Ramirez
Especialista de Soporte Técnico de EASA

En este webinario explicaremos como los diferentes cambios efectuados en el bobinado impactan en el desempeño del motor. Si no es realizado de forma correcta, cualquier cambio en el bobinado podría llegar a tener consecuencias negativas. El torque de arranque, la potencia nominal y la eficiencia en general podrían verse afectadas. 

El webinario incluye:  

• Efectos de realizar conexiones Delta o Estrella incorrectas 
• Consecuencias de un error al contar las vueltas (espiras)  
• La fórmula maestra  
• Efectos al usar los dientes abarcados (Span) envés del paso (Pitch) 
• Limitaciones en la secuencia de agrupamiento  
• Conversión de bobinados concéntricos a excéntricos (imbricados)  

 Este webinario está dirigido a bobinadores, supervisores y técnicos de pruebas.   

By Chuck Yung
EASA Senior Technical Support Specialist

Existen beneficios e inconvenientes al usar circuitos en paralelo en un bobinado trifásico. Sea que estemos hablando de un bobinado de alambre redondo o de pletina (solera), algunas de las consideraciones se comparten. Comencemos con lo básico: Entre más alta la potencia y/o más bajo el voltaje nominal, menos vueltas por bobina se utilizan. Debido a que un devanado trifásico tiene grupos por fase y por polo que alternan ABC, ABC, ABC, etc., los puentes entre grupos podrían ser 1-4, 1-7, 1-10, 1-13, etc., o cualquier combinación de ellos, siempre y cuando se conserve la polaridad alternada de los grupos y que las fases no se crucen entre sí.

Presented by Chuck Yung
EASA Senior Technical Support Specialist

This webinar recording discusses the equalized connections found in an increasing number of factory windings, explains why they are used, and addresses whether or not they are needed when converting a concentric winding to a lap winding. Alternatives, such as changing the number of circuits, or the special extra-long jumpers, are also compared.

The webinar recording covers

• Explanation of why machine-wound concentric windings use equalizers
• Effect of unbalanced voltage
• Role of air gap in causing circulating currents
• Labor involved and risk of failures due to increased complexity
• How to properly locate the equalizers

This webinar is useful for engineers, service center managers, mechanics and sales representatives.

Chuck Yung
EASA Senior Technical Support Specialist 

My purpose in writing this article is to explain in layman’s terms what electromechanical professionals refer to as circulating currents, why they exist in three-phase electric motors and to offer practical solutions.

Chuck Yung
EASA Technical Support Specialist

One of the most misunderstood winding connections is the part-winding start. Many customers (and some members) tend to blur the differences between the part-winding-start (PWS) connection and wye-start, delta-run connections.

Let’s review the Wye-Delta first before looking more closely at the part-winding-start connection. The wye-start, delta-run connection is designed to reduce starting current, heating of the windings and rotor, and starting torque. It does this by temporarily connecting the motor for a voltage higher than line voltage.

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
EASA Senior Technical Support Specialist

While manufacturers use concentric windings due to their ability to wind the coils directly into a core, many repairers convert them to lap windings to take advantage of the superior MMF (magneto-motive force) curve.

Although the former Tech Note 12 (see page 2-187 of the EASA Technical Manual), and the AC Motor Verification and Redesign Program, Version 4 allow us to convert a concentric winding to a comparable lap winding, there are still some winders using “shortcuts” they have learned over the years.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Mientras los fabricantes usan devanados concéntricos por su capacidad para bobinarlos directamente dentro del núcleo, muchos reparadores los convierten en bobinados excéntricos para aprovechar su curva FMM (fuerza magnetomotriz) superior.

Aunque la antigua Tech Note 12 (vea la página 2-187 del Manual Técnico de EASA), y la versión 4 del AC Motor Verification and Redesign Program, permiten convertir un bobinado concéntrico en un bobinado excéntrico comparable, aún existen algunos bobinadores empleando “atajos” que han aprendido con el tiempo.

Presentado por Carlos Ramirez, EASA Technical Support Specialist

La conexión incorrecta de los motores eléctricos es una causa frecuente de fallo y es más común de lo que parece. La falta de información y la mala interpretación de los datos de placa son algunas de sus causas. En este webinario se explican los diferentes tipos de conexiones para los motores eléctricos trifásicos de una o varias velocidades con al menos 6 cables de salida y se comparan las equivalencias NEMA e IEC para el marcado de cables. La información proporcionada también será de gran utilidad para evitar el conexionado incorrecto en los diferentes voltajes. También incluye las conexiones por devanado partido (Part Winding) y como interpretar la información de la conexión de la placa de datos.

El webinar incluye:

• Conexiones Estrella y Delta (“Triángulo”)
• Conexiones para motores de una sola velocidad con al menos 6 cables de salida
• Conexiones para motores de dos velocidades con al menos 6 cables de salida
• Conexiones para Devanado Partido (Part winding)
• Equivalencias NEMA e IEC para el marcado de cables  
• Interpretación de la información de la conexión de la placa de datos

Este webinario es útil para supervisores, personal encargado de realizar pruebas y responsables del centro de servicio.

Jim Bryan (deceased)
Technical Support Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO

The paper "Connections for Winding & Starting" by Jim Bryan, presented at the EASA Convention 2015, provides a comprehensive overview of the various methods used to design and implement motor winding connections. The paper emphasizes the importance of understanding the nuances of winding design and connection to ensure efficient and reliable motor operation. It primarily focuses on NEMA designations, although IEC standards are briefly mentioned.

Bryan begins by explaining the significance of the sine wave in three-phase electrical power, highlighting the role of the square root of three (√3) in power calculations. He compares single-phase and three-phase power, demonstrating the efficiency advantages of three-phase motors. The paper then delves into the numbering conventions for motor coil ends, providing detailed diagrams for wye and delta connections.

The discussion moves to the relationship between coil, phase, and line voltage, emphasizing the importance of √3 in determining voltage and current values for wye and delta connections. Bryan provides clear illustrations to show how these connections are made and the resulting voltage and current relationships.

The paper covers various external connections and ladder diagrams, starting with the simplest form of single voltage wye and delta connections. Bryan explains dual voltage motors, which use nine leads to configure the winding in series or parallel for different voltage levels. He provides detailed diagrams for dual voltage wye and delta connections, highlighting the importance of correct connections to avoid motor failure.

Bryan discusses across the line (ACL) starting, reduced voltage starters, and part winding start (PWS) motors. He explains the NEMA MG1 standards for part winding starting, noting the potential issues with insufficient torque and the importance of incremental starting current. The paper includes ladder diagrams for PWS motors and various starting methods, such as wye start-delta run and double delta or extended delta part winding start.

The paper also covers motors designed for multiple speeds, including two distinct speeds with two windings and one winding with high and low speed configurations. Bryan explains constant horsepower, constant torque, and variable torque connections, providing detailed diagrams for each.

Parallel circuits are discussed as a means to accommodate different applications and voltages. Bryan provides examples of parallel circuit configurations and the impact on motor performance. He also addresses odd connections, such as tri-voltage and single voltage wye-delta or part winding start motors.

The paper concludes with a discussion on jumper selection, explaining the difference between adjacent-pole (1-4) and skip-pole (1-7) jumpers. Bryan emphasizes the importance of correct jumper selection to avoid circulating currents and ensure balanced magnetic forces.

Key Points Covered:

• Importance of sine wave and √3 in three-phase power
• Numbering conventions for motor coil ends
• Relationship between coil, phase, and line voltage
• External connections and ladder diagrams for various starting methods
• Dual voltage motors and correct connection practices
• Part winding start (PWS) motors and NEMA MG1 standards
• Multiple speed motors and their configurations
• Parallel circuits and their impact on motor performance
• Odd connections and their applications
• Jumper selection and its importance

Key Takeaways:

• Understanding winding design and connection is crucial for efficient and reliable motor operation.
• Correct connections are essential to avoid motor failure and ensure proper voltage and current relationships.
• Various starting methods and configurations can be used to accommodate different applications and voltages.
• Parallel circuits offer flexibility but require careful consideration to avoid excessive voltage between coils.
• Jumper selection is important to ensure balanced magnetic forces and avoid circulating currents.

Anthony Sieracki
Spina Electric Co.

In all aspects of electric motor repair specifications and instructions, we should refer to industry standards, government standards, electrical codes, manufacturing recommendations and of course EASA's Recommended Practice for the Repair of Rotating Electrical Apparatus (ANSI/EASA AR100-2010). All are written to help us perform and accomplish the best repairs possible. This article covers a topic that is often times taken for granted, yet it is key to making sure your repaired motor does not fail prematurely. We will cover the proper methods for making connections on AC electric motors under 600 volts. The most common methods are crimped terminals, multiple bolt connector points and split bolts connectors.

Mike Howell
EASA Technical Support Specialist

Most AC stator windings installed by EASA service centers are balanced, three-phase, two-layer, lap windings. But, what does it mean for such a winding to be balanced? If balanced, the voltages generated in each phase are equal in magnitude and displaced from each other by the same angle (See Figure 1 Balanced). If there is any difference in magnitude or angle displacement, the winding is unbalanced (See Figure 1 Unbalanced). It is well established that unbalanced windings can cause undesirable vibration, electromagnetic noise, and additional conductor heating due to circulating currents.

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.

Mike Howell
Especialista de Soporte Técnico de EASA

El artículo publicado en marzo del 2013 en la revista Currents de EASA titulado “Stator I²R loss: considerations for rewinds and redesigns” describe las pérdidas I²R del estator, su cálculo y cómo controlarlas durante el rebobinado. Esta continuación, proporcionará una breve revisión y luego explorará las pérdidas adicionales en el cobre del estator mencionadas en ese artículo.

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.

Chuck Yung
Especiaslista Sénior de Soporte Técnico de EASA 

Mi propósito al escribir este artículo es explicar en términos sencillos a qué se refieren los profesionales de la electromecánica como corrientes circulantes, por qué existen en los motores eléctricos trifásicos y ofrecer soluciones prácticas.

Mike Howell, PE
Especialista de Soporte Técnico de EASA

Siempre que sea posible, EASA recomienda usar el cable de salida especificado por el fabricante original del equipo. Si no está disponible, la sección 6 del Manual técnico de EASA proporciona orientación al respecto y hay una calculadora en línea disponible en go.easa.com/calculators para determinar el tamaño mínimo recomendado según la clasificación de temperatura, la corriente esperada, la cantidad de cables y el tipo de conexión. Este artículo describirá la función de la calculadora. Es importante tener en cuenta que no existe una respuesta correcta en este proceso cuando se desconoce la información original. Al seleccionar un cable conductor, se deben considerar los siguientes aspectos

Chuck Yung & Cyndi Nyberg
Technical Support Specialists
Electrical Apparatus Service Association, Inc.
St. Louis, MO

The paper "Distribution Factor and Winding Conversion Issues" by Cyndi Nyberg and Chuck Yung, presented at the EASA Convention 2006, explores the complexities involved in modifying three-phase stator windings in electric motors. The authors begin by explaining the concept of the distribution factor (K_d), which is the ratio of the resultant voltage induced in a series-connected group of coils to the arithmetic sum of the magnitudes of the voltages induced in the coils. This factor is crucial in accounting for the asynchronous contribution of each coil to the overall torque of the motor.

Nyberg and Yung highlight the differences between concentrated and distributed windings. In a concentrated winding, such as a DC machine field coil, each coil is wound around a single pole, resulting in a distribution factor of 1.0. In contrast, a distributed winding, such as a lap winding in an AC motor, consists of multiple coils placed symmetrically in the slots of the stator core. The distribution factor for these windings is less than 1.0 due to the slight delay in the contribution of each coil to the torque.

The paper delves into the impact of different winding layouts on the distribution factor. For example, a standard salient pole winding with 12 groups of 3 coils has a different distribution factor compared to a consequent pole winding with 6 groups of 3 coils. The authors provide detailed calculations for determining the distribution factor based on the number of slots, poles, and the electrical angle between each slot.

Nyberg and Yung also address the challenges of converting windings from one type to another, such as from concentric to lap windings. They emphasize the importance of using the correct distribution factor in these conversions to avoid significant changes in motor performance. The paper includes several examples to illustrate the potential errors that can occur when the distribution factor is not correctly applied. For instance, converting a lap winding with 12 groups of 4 coils to a single-layer lap winding with 12 groups of 2 coils requires careful calculation to ensure the effective turns per coil remain consistent.

The authors explain that the selected winding pattern, whether sequential or skip-slot, affects the distribution factor and, consequently, the torque and flux densities of the motor. They provide formulas for converting concentric windings to lap windings and emphasize the need to consider the air gap density to maintain the same torque.

The paper concludes with practical examples of winding conversions, demonstrating the importance of accurate calculations to avoid unintended changes in motor performance. Nyberg and Yung stress that any winding change should be carefully considered, as errors in the new turns calculation can significantly impact the motor's torque and efficiency.

Key Points Covered:

• Definition and importance of the distribution factor (K_d)
• Differences between concentrated and distributed windings
• Impact of winding layouts on the distribution factor
• Challenges and calculations for converting windings
• Importance of using the correct distribution factor in conversions
• Practical examples of winding conversions

Key Takeaways:

• The distribution factor is crucial for accounting for the asynchronous contribution of each coil to the motor's torque.
• Concentrated windings have a distribution factor of 1.0, while distributed windings have a lower distribution factor.
• Different winding layouts affect the distribution factor and motor performance.
• Accurate calculations are essential when converting windings to avoid significant changes in torque and efficiency.
• Any winding change should be carefully considered to prevent errors in the new turns calculation.

Chuck Yung 
EASA Technical Support Specialist 

In the world of three-phase electric motors, one area which seems to cause great confusion is the use of electric motors which are rated for more than one voltage. Especially today, with so much international commerce, it is understandable that different meanings might be assumed for this simple term. 

Those readers in the U.S. are ac­customed to “dual-voltage” 230/460v ratings. The 1:2 ratio lends itself to 9-lead windings, with connection combinations such as 1- and 2-circuit wye, 2 and 4-delta, 3 and 6-wye, etc. The common factor is that the circuits and the possible operating voltages have the same 1:2 ratio.

Gene Vogel
EASA Pump & Vibration Specialist

The EASA AC Motor Verification & Redesign - Version 4 software (ACR-MotorDb) is a powerful tool for service centers providing the capability to meet their customer’s needs for AC stator and wound rotor redesigns. In most cases, the data from the existing winding is recorded when that winding is removed from the core. But occasions arise where that original data is not available; it may have been recorded incorrectly or a different service center may have stripped the core but not completed the repair. In those cases, the service center must come up with a new “bare core” winding design. ACR-MotorDb has some specific features to address this need.

LEARN MORE ABOUT THE SOFTWARE

HOW TO CALCULATE A WINDING FROM A BARE CORE

The MotorDb segment of the program is the EASA Winding Database compiled over decades from winding data submitted by EASA members. With over 300,000 winding records, it is likely that windings similar to the original winding are available in MotorDb. By simply searching the database for the core dimension criteria, a list of prospective matching windings is returned. A winding from the database does not have to match the original motor nameplate exactly to be used as basis for the bare core design. When a matching winding is selected, that data can be automatically transferred to the Redesign program where modifications needed to match the desired criteria can be adjusted. The process is smooth, effortless and accommodates most 3 phase induction motor windings.

The first step is to display a list of prospective windings that closely match the bare core dimension criteria. Enter the core length, bore diameter, number of slots and poles into the MotorDb search dialog box. As an example, we will search for a 12” core length, 14” bore diameter and 72 slots for a 125 HP, 6 pole Marathon motor. Initially enter only the core dimensions, number of slots and number of poles (Figure 1); the Get Count feature will quickly return the number of matching records. If the result is about 50 or fewer motors, click OK to retrieve those records into a spreadsheet format where the records can be sorted by columns and reviewed. If the Record Count is too large, enter additional criteria to narrow the search. For our example, 44 records were found, and the resulting spreadsheet is illustrated in Figure 2.

The spreadsheet can be sorted by columns to easily review the data. It is useful to sort by the AirDensity (AGD) and Power (Pwr) columns to assess if the bare core is a good candidate for the desired resulting winding. If there are several windings with the desired power rating and the AGD is within acceptable limits, there is assurance the redesign will be successful. For our example, there are 16 windings rated at 125 HP and 10 of them are Marathon motors. So, in this example, it is likely original factory data is available. Of course, that is not always the case. Suppose our bare core is a Siemens motor, which is not listed. We can still select a different manufacturer winding as the basis for our bare cored design. Select one of the windings from the spreadsheet that matches the desired nameplate data as closely as possible. The full winding data will be displayed in an editor (Figure 3).

This original data record was in the database so no redesign was necessary; the bare core can be wound directly from the database record. Such is not always the case, and the EASA software has a function in MotorDb to transfer data from a MotorDb winding record to ACR for redesign. The Send to ACR function in MotorDb creates a new record in ACR where all the ACR redesign functions are available. Taking our example motor, suppose the desired winding is 575 Volts. MotorDb records are only 230 or 460 Volts.

Figure 4 illustrates a MotorDb record sent to ACR and the Volts redesigned from 460 Volts to 575 Volts. The winding is redesigned for 575 Volts and the connection was changed from 6Y to 3Y to keep the Volts per Coil within acceptable limits (Figure 5).

The combination of the EASA Winding Database and the Verification and Redesign program is an easy-to-use solution when presented with bare core winding challenges. For complete step-by-step instructions on bare core redesign, view the tutorial video How to calculate a winding from a bare core available at go.easa.com/wbc.

Kent Henry 
EASA Technical Support Specialist 

When taking winding data, equal­izer connections can be mistaken for wye points. You may wonder what purpose equalizer connections serve and whether they can just be elimi­nated to simplify the repair process. Before discussing equalizers, we will explore the factors that lead to a need for equalizers. 

A magnetic unbalance within a motor or generator can be a very seri­ous problem. The magnetic balance Stator relies on a marriage of electrical and mechanical elements. When either of these electro-mechani­cal elements changes, it may create a magnetic unbalance. 

Tom Bishop, P.E.
Especialista Sénior de Soporte Técnico de EASA

Cuando el número de bobinas por grupo es el mismo a lo largo de un devanado trifásico excéntrico (imbricado), la secuencia de agrupación es simplemente ese número de bobinas repetido tres veces multiplicado por el número de polos (ya que es trifásico). Por ejemplo, un devanado de 4 polos y 48 ranuras tiene 12 grupos de 4 bobinas.

La fórmula utilizada para determinar el número promedio de bobinas por grupo es: Bobinas por grupo = Ranuras divididas por grupos. Ya que no recomendamos el uso de bobinas a ranura llena en bobinados imbricados, el número de bobinas es igual al número de ranuras. El número de grupos en un devanado de polos alternos es igual al número de fases multiplicado por el número de polos. En muchos casos, existen devanados que tienen bobinas por grupo desiguales, como un bobinado de 8 polos de 36 ranuras, que tiene 24 grupos con un promedio de 1,5 (36/24) bobinas por grupo.

Mike Howell
EASA Technical Support Specialist

Los bobinados fraccionarios concentrados, en inglés Fractional-Slot Concentrated Windings (FSCW), han sido empleados durante décadas, principalmente en máquinas pequeñas. Sin embargo, el avance continuo en la electrónica de potencia junto con la necesidad de tener máquinas más eficientes y con mayor densidad de potencia está aumentando el uso de este tipo de bobinados en máquinas de diferentes tipos y tamaños.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA 

Todos nosotros tenemos ese cliente ocasional que compró “una ganga” en una subasta, como un compresor, un torno o una máquina para trabajar madera y que solo descubre al comenzar a instalarlo que ese equipo tenía un motor trifásico y que él dispone únicamente de energía monofásica. Posiblemente sea su vecino o un amigo de la iglesia. En cualquier caso, usted está a punto de ser contactado para “convertir” esa parte del equipo y probablemente piensa que eso le va a costar más de lo que el puede gastar.

Mike Howell
EASA Technical Support Specialist

Fractional-slot concentrated windings (FSCW) have been used for decades, primarily in small machines. But continued technological advancement in power electronics along with the need for more efficient and power-dense machines is increasing use of FSCW in a variety of machine types and sizes.

Cyndi Nyberg 
Former EASA Technical Support Specialist 

“I have rewound a two-speed, two-winding motor. The high speed runs fine — the no-load current seems right. But when I test the low speed, the amps are far too high at rated voltage. It draws significantly above the rated current, at no-load! I know that the winding data is correct. What could be wrong?” 

This is one of the most common problems we encounter at the EASA office.  The solution is almost always the same. There are three questions we ask in return.

1. What are the two speeds?
2. What are the number of circuits in each winding?
3. What jumpers are used to connect each winding? 

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

Presented by Tom Bishop, P.E.
EASA Senior Technical Support Specialist

This webinar recording focuses on the effect of three-phase stator winding changes on efficiency and reliability.

Specific changes addressed will include:

• Connection
• Circuits
• Turns
• Span/pitch
• Grouping sequence
• Concentric to lap, and vice versa
• Wire area per turn and per slot

Target audience: Service center technicians and supervisors.

By Tom Bishop, P.E.
Senior Technical Support Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO

The paper "How Winding Changes Affect Motor Performance" by Tom Bishop, presented at the EASA Convention 2016, explores the intended and unintended consequences of various winding changes in three-phase stator motors. The paper delves into common and less common winding modifications, examining their potential impacts on motor efficiency and reliability. One of the primary considerations is the connection type, with wye (star) and delta being the two options. Delta connections require more turns and less wire area per turn compared to wye connections, which can lead to higher volts per coil and potential electrical stress.

Bishop emphasizes the importance of ensuring that changes in winding connections, such as switching from wye to delta, do not result in excessive volts per coil. He provides formulas and examples to illustrate the calculations needed to determine volts per coil and the necessity of additional insulation if the volts per coil exceed 80. The paper also discusses the consequences of misconnecting a motor, such as reduced torque capability and increased heating, which can significantly affect motor performance and reliability.

The number of circuits in a winding is another critical factor. Increasing the number of circuits can lead to unbalanced windings and circulating currents, reducing efficiency and reliability. The paper highlights the importance of equalizing connections to mitigate unbalanced magnetic pull and electrical noise. Bishop also addresses the impact of turns count errors, which can result in increased current, higher operating temperatures, and reduced efficiency.

The paper explores the effects of changing winding pitch, noting that reducing pitch increases magnetic flux densities and developed torque, while increasing pitch has the opposite effect. Incorrect coil grouping sequences can lead to unbalanced windings and circulating currents, emphasizing the need for accurate grouping sequences. Bishop provides examples and tables to illustrate the correct and incorrect grouping sequences for various winding configurations.

The conversion of concentric windings to lap windings is discussed, with lap windings generally offering better performance due to their more sinusoidal magnetomotive waveform. However, the conversion process must be carefully managed to avoid issues such as increased losses and noise. The paper also covers the importance of wire area per turn and slot fill, noting that increasing wire area per turn can improve efficiency and reliability, while reducing wire area can have detrimental effects.

Bishop concludes by emphasizing the need for careful consideration of winding changes to ensure that motor performance and reliability are not compromised. He provides practical advice and examples to guide service centers in making informed decisions about winding modifications.

Key Points Covered:

• Differences between wye and delta connections
• Importance of volts per coil and additional insulation
• Consequences of misconnecting motors
• Impact of the number of circuits on winding balance
• Effects of turns count errors
• Influence of winding pitch changes
• Correct and incorrect coil grouping sequences
• Conversion from concentric to lap windings
• Importance of wire area per turn and slot fill

Key Takeaways:

• Winding changes can significantly affect motor performance and reliability.
• Ensuring proper volts per coil and additional insulation is crucial.
• Misconnecting motors can lead to reduced torque and increased heating.
• Balanced windings are essential to avoid circulating currents and unbalanced magnetic pull.
• Accurate turns count and winding pitch are critical for optimal performance.
• Converting to lap windings can improve performance but must be managed carefully.
• Increasing wire area per turn can enhance efficiency and reliability.
• Careful consideration of winding changes is necessary to maintain motor performance and reliability.

Chuck Yung
Especialista Senior de Soporte Técnico de EASA

Un requerimiento frecuente al personal de soporte técnico de EASA es la solicitud de ayuda para la identificación de los cables de salida que no están marcados. Este artículo establece una serie de procedimientos para identificar los cables no marcados en motores con 1 ó 2 bobinados que tienen 6 cables de salida. Para identificar la mayoría de las conexiones, los únicos instrumentos necesarios son un óhmetro y un equipo de onda de choque. (surge tester)

Chuck Yung 
EASA Technical Support Specialist

One frequent request of EASA’s technical support staff is for help in identifying unmarked motor leads. This article introduces a set of proce­dures for identifying unmarked leads of 6-lead motors with 1 or 2 wind­ings. For most connections, the only tools required for these procedures are an ohmmeter and surge tester. 

An additional benefit is that these procedures can be used to identify the type of connection (Table 1); for example, when a motor is received without a nameplate. With 6 leads, the motor connection could be part-winding start, wye-delta, or a 2-speed design. 

Mike Howell, PE
EASA Technical Support Specialist

The markings on the external leads of a motor sometimes become defaced or are removed, which makes it necessary to identify and mark them before the motor can be properly connected to the line. This presentation reviews procedures that explain how to identify unmarked leads of three-phase motors with one or two windings.

Topics include:

• IEC / NEMA numbering systems 
• Three-lead machines 
• Six-lead machines 
• Nine-lead machines
• Twelve-lead machines

This presentation is intended for all personnel who troubleshoot machines with unmarked leads.

Chuck Yung 
EASA Technical Support Specialist 

When a customer calls and orders a motor, he usually specifies only the Hp/kW rating, rpm, frame, enclosure and voltage rating. That leaves at least one critical area where the elec­trician can go wrong: The starting method and number of leads. 

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.

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. 

Jim Bryan
EASA Technical Support Specialist (retired)

En la edición de Febrero de nuestra revista Currents, Mike Parsons proporcionó excelentes consejos para contactar y formular preguntas al Departamento de Soporte Técnico de EASA. Mike hace parte de Hupp Electric Motors Co. en Marion, Iowa y es miembro del Comité de Educación Técnica y me gustaría resaltar una declaración que hizo: “¡Ustedes no son ninguna molestia!” De hecho, son nuestro sustento. 

Durante años, sus Juntas Directivas y Gerentes han asignado recursos para aumentar el número de especialistas de soporte técnico y en encuestas anteriores de evaluación de necesidades, los miembros han calificado al soporte técnico/ingeniería de EASA como el beneficio número uno de la membresía. Así que aprovechad esto por todos los medios. 

Para ayudarle a obtener el mayor beneficio, este artículo explicará la información requerida para llenar la Solicitud de Verificación de Datos & Rediseño. Puede completar y enviar su solicitud en línea en www. easa.com/resources/tech_support/ redesign_inquiry o descargarla en este link y enviarla por fax o correo electrónico. Ver Figura 1. En el caso que llene la solicitud a mano, asegúrese de escribir claramente. Por ejemplo, los números “1” o “7”, o “5” o “6”, se parecen cuando se escriben muy rápido.

Figura 1

Cuando esté llenando la solicitud impresa o en línea, verá que ciertos campos están marcados con un asterisco (*), esto implica que son obligatorios para poder completar la solicitud. Algunas veces toda esta información no está disponible por lo que se debe informar de esto en el campo apropiado. Entonces nosotros haremos lo posible para determinar lo que se debe hacer. 

Comenzando con la información de la empresa, los datos importantes son su número de identificación de EASA, su nombre y la información de contacto por si nos surgen algunas preguntas. Indique porque medio prefiere recibir su respuesta, proporcionando un número de fax, un correo electrónico o su número telefónico. Nosotros utilizamos los datos de placa y la información del fabricante para ingresarla en la base de datos de EASA. Aunque esta información será de ayuda para futuras consultas, en caso que falte, no impedirá que la solicitud sea procesada. 

Datos de placa 

*Hp o kW es la potencia de la placa de datos que determina la capacidad de carga de la máquina. Cuando existen opciones como esta, se debe encerrar dentro de un círculo la unidad correcta. Las rpm o el número de polos y la frecuencia determinan la velocidad de la máquina. La frecuencia, el voltaje y los amperios también son tomados de la placa de datos. Si existe más de un valor todos deberán ser reportados.

Datos y dimensiones del núcleo 

Uno de los puntos clave para evaluar o rediseñar un bobinado es verificar si las densidades de flujo magnético en el entre hierro y en el núcleo del estator son razonables. Estas se pueden expresar en miles de líneas de flujo por pulgada cuadrada (klíneas/ pul²) o Teslas (T) y se comparan con los valores máximos establecidos en el entre hierro (65 klíneas/pul² o 1 T), yugo (130 klíneas/pul² o 2 T) y diente (130 klíneas/pul² o 2 T). También son comparadas con motores de la base de datos de EASA con dimensiones y potencias similares. Podemos calcular el número de líneas de flujo por pulgada cuadrada utilizando el voltaje, la frecuencia, los datos del bobinado y las dimensiones del núcleo. Los cálculos requieren mediciones precisas de cada uno de los componentes así como también el número de ranuras del estator. La Figura 2 proporciona las directrices para tomar estas medidas.

Figura 2

El número de ranuras del rotor es opcional a no ser que se requiera un cambio de velocidad. Dependiendo del número de polos, ciertas combinaciones de ranuras rotor-estator producirán ruido, variación del torque a muy baja velocidad (cogging) o una reducción del torque cuando el motor comienza acelerar (cusp). Con el número de barras del rotor podemos verificar si esta combinación ocasionará problemas en su motor. Tenga en cuenta que si las ranuras del estator o del rotor son inclinadas, dicha combinación no deberá causar estos problemas. 

El largo del núcleo deberá ser la distancia total entre los dos extremos del núcleo. Si existen ductos de aire, el número y ancho de los mismos se deberán anotar en los campos provistos. Estos datos serán incluidos posteriormente en la evaluación. 

En los bobinados preformados (pletina) son necesarias las dimensiones de la ranura del estator. Las medidas exactas facilitarán el cálculo de los calibres o tamaños de alambre y del aislamiento, para que se ajusten adecuadamente en la ranura cuando se construyan las bobinas. 

Información del bobinado 

El número de grupos y bobinas se requiere para evaluar el bobinado. Aquí tenga cuidado con la matemática. Un ejemplo es un motor de 48 ranuras con 3 bobinas por grupo, en el cual el llenado de todas las ranuras es el mismo. Muchas veces este diseño se reporta como un bobinado concéntrico de 12 grupos y 4 bobinas por grupo con un total de 48 ranuras y tres pasos de bobina. Realmente existen 36 ranuras y la tercera bobina de cada grupo tiene el doble o casi el doble del número de espiras de las otras dos bobinas del grupo. En cada grupo de bobina, dos bobinas compartirán una ranura y la otra bobina llenará por completo una ranura. Esto puede causar confusión y muchas veces requiere de una llamada telefónica para aclarar lo que realmente hay ahí. 

La sección de los datos del alambre indica el número de alambres en paralelo y los calibres de cada bobina. Recuerde que el alambre redondo puede ser métrico o AWG. Si no está seguro, proporcione las medidas con micrómetro y nosotros tomaremos la decisión. Tenga en cuenta que si una máquina no está fabricada en Norte América, bien podría tener alambre métrico. Se debe evitar el uso de galgas ya que generalmente no cuentan con la suficiente precisión para poder determinar la diferencia entre los calibres medios o AWG versus los métricos. Incluso un alambre medio puede marcar la diferencia. Una mejor práctica consiste en medir el alambre con un micrómetro y utilizar la tabla de Alambres Redondos de EASA para identificar el calibre del alambre. 

Sin duda, la parte de este rompe cabezas que se reporta erróneamente con más frecuencia, es la conexión. Una buena regla a tener en cuenta es que si el motor tiene más de tres cables, existe más de una conexión. Una discusión acerca de esto y de cómo determinar la conexión, se encuentra en el artículo publicado en octubre de 2011 en la revista Currents titulado “Understanding three-phase motor connections.” 

Sera necesario contar las espiras en varios grupos de bobina ya que no es raro que exista un número de espiras diferentes en las bobinas de un mismo grupo o en grupos distintos. Algunas de estas pueden parecer impares, por lo que es bueno contar varios grupos de bobinas hasta que se identifique el patrón. El número de espiras será el número total de alambres dentro de la ranura dividido por los alambres en paralelo y el número de lados de bobina. Por ejemplo, en la ranura compartida de un bobinado excéntrico (imbricado) con 90 alambres dentro de la ranura y con 3#16, 2#17, el número de espiras es: 

90/2 = 9 espiras
( 3 + 2 ) 

El paso indica la ranura en la cual se aloja el primer lado de bobina y la ranura en la cual se inserta el lado opuesto. Ver Figura 3. Por lo que en un paso 1-8, el primer lado de bobina está insertado en la ranura 1 y el otro lado cae en la ranura 8. Un paso de bobina 1-8 abarca 7 dientes, por lo que la extensión de la bobina es igual a 7 (span). Todas las bobinas de ese grupo tendrán el mismo espacio entre ellas y a continuación comenzará la siguiente fase.

Figura 3

Los bobinados concéntricos siempre tendrán más de un paso, como 1-8, 10, 12. Éste es un grupo de tres bobinas que están concéntricamente anidadas como se ve en la Figura 4 a la derecha. No todas las potenciales combinaciones de paso permitirán una distribución equitativa de las bobinas y por consiguiente no se pueden utilizar. Por ejemplo, un motor de 4 polos con 48 ranuras y 36 bobinas no puede utilizar un paso 1-7, 9, 11 ya que la bobina a ranura llena caerá en la parte superior de la ranura de una bobina compartida y habrá ranuras vacías. 

Datos nuevos

Esta sección contiene las instrucciones de lo que usted desea obtener. Esto puede incluir cambios de potencia, velocidad, frecuencia o de voltaje. El motivo de la solicitud es muy importante ya que no necesitamos adivinar o suponer nada. Entre más detalles proporcione, especialmente en solicitudes complicadas, mejor serán los resultados. Si alguna información no está disponible, incluya una nota al respecto para que podamos hacer nuestro mejor esfuerzo para llenar los vacíos. 

Conclusión 

Entre más completa y exacta sea la información, recibirá una respuesta más rápida y precisa. Agradecemos mucho cuando nos envían al Departamento de Soporte Técnico de EASA sus solicitudes en línea o mediante los formatos que pueden descargar en la WEB. Al parecer cada centro de servicio tiene su propia forma de registrar esta información y esto es bueno. No obstante toma más tiempo encontrar la información cuando no estamos familiarizados con dichos formatos. Enviar la información en los formatos estandarizados por EASA acelera el proceso.

Jim Bryan
EASA Technical Support Specialist (retired)

In the February 2017 edition of Currents, Mike Parsons provided excellent advice on contacting EASA Technical Support with questions. Mike is with Hupp Electric Motors Co. in Marion, Iowa, and is a member of the Technical Education Committee. I would like to underline one statement he made: “You are not a bother!” In fact, you are our livelihood. 

Over the years, your Board of Directors has allocated resources to increase the number of technical support specialists. And in past Member Needs Assessment Surveys, members have consistently rated technical/engineering support as the number one benefit of membership. By all means, take advantage of it. 

To help you get the most from the benefit, this article will explain the information required to complete the Data Verification & Redesign Request form. You can complete and submit the request online or you may complete and fax or email the form that is available to download. See Figure 1. If the forms are filled out manually, be sure to write clearly. For example, numbers such as “1” or “7”, or “5” or “6”, can look the same if written too quickly.

Figure 1: EASA's Data Verification & Redesign Form

When completing both the printed and online forms, certain fields are marked with an asterisk (*) implying that they are required to complete your request. Sometimes all of this information is not available and should be noted so in the appropriate spot. We will then make every attempt to determine what should be done. 

Starting with the company information block, the important data are your company EASA identification number, a name and contact information in case we have questions. Let us know which medium you prefer to receive your response by filling in either the fax, email, or phone area. We use information in the manufacturer block to enter into the EASA database. While helpful for future reference, it will not impede the request if it is missing. 

Nameplate data 

*Hp or kW is the rating from the nameplate for the machine’s load capacity. When there are choices such as this, the correct unit should be circled. Entering rpm or poles and frequency determines the speed of the machine. Frequency, volts and amperes are also from the nameplate. If there is more than one of any of these values, all should be reported. 

Core data & dimensions 

One of the keys to evaluating or changing a design is to determine if the magnetic flux densities in the air gap and core iron are reasonable. This can be expressed in thousands of lines of flux per square inch (klines/in²) or Tesla (T). This is compared to the maximum values established for the air gap (65 klines/in² or 1T), core (130 klines/ in² or 2T) and tooth (130 klines/in² or 2T). They are also compared to motors with similar cores and ratings found in the EASA motor database. We can calculate the number of lines of flux per square inch using the voltage, frequency, winding data and core dimensions. The calculations require accurate measurements for each of the components as well as the number of stator slots. Figure 2 provides guidelines for these measurements.

Figure 2: Important information for taking measurements

The number of rotor bars is optional unless a speed change is requested. Depending on the number of poles, certain combinations of numbers of rotor bars compared to stator slots will produce noise, cogging or torque cusps. With the number of bars, we can check to see if the combination in your motor will be a problem. Note that if the rotor bars or stator slots are skewed, the combination should not cause these problems. 

The core length should be given as the overall distance from one end of the core to the other. If there are air ducts, the number and width of these can be reported in the spaces provided. They will then be included in the evaluation. 

For form coil windings, the stator slot dimensions are needed. Accurate measurements will facilitate designing the wire size and insulation to fit properly in the slot when the coil is made. 

Winding information 

The number of groups and coils is required for the winding evaluation. Be careful with the math here. An example is a motor with 48 slots with 12 groups of 3 coils, but all the slots are equally full. Many times this will be reported as 12 groups of 4 for 48 total coils with 3 pitches in the concentric winding. Actually, there are 36 total coils and the third coil in each group has twice or nearly twice the number of turns of the other two coils in the group. In each coil group, two coils will share a slot and one of the coils will fill the slot alone. It can be confusing and often require a phone call to clarify what is really there. 

The wire data section tells the number and size of the wires in hand for each turn. Remember the wire could be AWG or metric. If you are not sure, provide the micrometer readings for the wire sizes and we will make the determination. Note that if the machine is not made in North America, it well could be metric wire. Wire gauges should be avoided; they are generally not sufficiently accurate to determine the difference between half sizes or AWG versus metric sizes. Even a half wire size can make a difference. It is best practice to measure the wire with a micrometer and use the EASA Round Magnet Wire Data chart to identify the wire size. 

By far the most often misreported piece in this puzzle is the connection. A good rule to remember is that if the motor has more than three leads, there is more than one connection. A discussion of this and how to determine the connection is found in the October 2011 Currents article titled “Understanding three-phase motor connections.” 

Several examples should be taken to determine the number of turns in each coil; it is not uncommon for there to be different turns in the coils in the same group or for different groups. Some of these may seem odd, so it is good to count multiple coil groups until you recognize a pattern. The number of turns will equal the total number of strands (wires) in the slot divided by the number of wires in hand and the number of coil sides. For instance, in a shared slot lap winding with 90 total wires in the slot and 3#16, 2#17 the number of turns is: 

90/2 = 9 turns
(3+2) 

The pitch is the slot the first coil side falls in and the slot for the opposite side reached. See Figure 3. Such as in a pitch of 1-8, the first coil side is in slot 1 and the other side is in slot 8. A coil pitch of 1-8 spans 7 teeth, so the span = 7. All of the coils in that group will have the same space between them and then the next phase begins.

Figure 3: Coil pitch

Concentric windings will always have more than one pitch listed such as 1-8, 10, 12. This is a group of three coils that are concentrically nested as seen in Figure 4 at the right. Not all potential pitch combinations will allow the coils to be distributed evenly and therefore cannot be used. For instance, a 4-pole motor with 48 slots and 36 coils cannot use a pitch of 1-7, 9, 11; the full slot coil will fall on top of a shared slot coil and there will be empty slots. 

New rating 

This section contains the instructions for what you would like to accomplish. This may include changes in the horsepower, speed, frequency or voltage. The reason for the inquiry is very important so we do not need to guess. The more detail provided, especially for complicated requests, the better the results. If any of the information is not available, include a note to that effect so we can do our best to fill in the gaps. 

Conclusion 

The more complete and accurate the information provided, the more quickly and accurately the answer will be received. We very much appreciate when you submit your requests to EASA Technical Support online or using one of the downloadable forms. It seems that every facility has its own way to record this information and that is good. It does take extra time to find the information if you are not familiar with the format; submitting on standardized EASA forms expedites the process.

Chuck Yung
EASA Technical Support Specialist

Member Question: We recently received an 800 hp, 2-pole 460- volt motor for repair. It had a 4-Delta connection, and the windings show severe thermal stress. The customer confirmed that the motor was recently installed, drew high current, and failed quickly.

Published: August 2006 & Revised: September 2024

EASA members can download a PDF of Internal Connection Diagrams for FREE. Use the link below for the free PDF.

This edition of EASA Internal Connection Diagrams contains significantly more connections and winding diagrams than the previous version (1982), as well as improved templates for drawing connection diagrams. It provides internal connection diagrams for three-phase windings. It can be used with either concentric or lap windings. It also covers all possible parallels; wye and delta, 2 - 48 poles; part windings; two-speed windings; wye-delta and consequent-pole connections, 2 - 48 poles. It includes PAM connections, as well as triple- and quadruple-rated connections.

In terms of the number of connections, this edition covers more poles than before. It also now contains some less-common connections. These include the European pole amplitude modulation (PAM) design; multi-torque ratings; and part-salient, part-consequent pole connections that permit pole/slot combinations that otherwise would be unattainable.

Although the “by-the-numbers” method of drawing connections remains basically unchanged in this edition, the winding connection templates have been greatly improved. New templates for skip-pole and adjacent-pole diagrams also have been added to simplify drawing these connections. The jumpers are shown in gray with different line patterns for each phase. 

The book also includes templates for 2-pole through 30-pole, adjacent (1-4 jumpers) and skip pole (1-7) connections.

A printed version of this book is available for purchase in the online store.

Presented by Mike Howell
EASA Technical Support Specialist

Choosing an appropriate lead wire for a new stator winding is an important task. The manufacturer’s information is not always available, or the number of circuits or external connection may have been changed, requiring a redesign of the lead wire.  This webinar reviews: 

• Commonly available materials 
• Lead wire insulation classes 
• Lead wire voltage classes 
• General sizing procedures 

This webinar is intended for repair technicians and anyone who needs to select lead wire.  

Mike Howell, PE
EASA Technical Support Specialist

EASA recommends using the lead wire specified by the original equipment manufacturer (OEM) whenever possible. If not available, some guidance is provided in section 6 of the EASA Technical Manual and an online calculator is available at easa.com/calculators to determine a minimum recommended size based on temperature rating, expected current, number of leads and type of connection. This article will describe the calculator’s function. It’s important to note that there is no one right answer in this process when the original information is unknown. When selecting a lead wire, the following topics should be considered.

Gene Vogel
Especialista de Bombas y Vibraciones de EASA

Las nuevas funciones del programa AC Motor Verification and Redesign – Version 4 (ACRewind) de EASA mejoran la capacidad de los miembros de EASA para enviar datos originales de forma electrónica e incluirlos en la base de datos Motor Rewind Data – Version 4 (MotorDB). Pase directamente a la sección “mejoras” si ya está familiarizado con los programas y cómo funcionan.

El software de la Version 4 es un conjunto de herramientas poderosas que sirve para que los miembros de EASA validen los datos de un bobinado, rediseñen devanados concéntricos a imbricados y efectúen cambios en los parámetros de un motor. Una característica clave de esta última versión del programa es la integración de la base de datos MotorDB con el programa ACRewind. La disponibilidad de ambas funciones del programa dentro de una interfaz de usuario común no es por simple conveniencia. La capacidad de los programas para compartir las fuentes de datos crea nuevas capacidades que la versión de cada programa independiente no podría.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

One of the main objectives in rewinding is to maintain the original performance characteristics of the machine. Our focus with this article will be on three-phase motor stator windings. If it is known that the winding in the motor was original and there is certainty that the as-found data is correct, the original winding can be duplicated with confidence by using the as-found data. However, in some cases there is uncertainty that the as-found winding had original factory data. In those cases, extra steps need to be taken as described here.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

Uno de los principales objetivos del rebobinado es poder conservar las características de funcionamiento originales de la máquina. Nuestro artículo estará enfocado en los bobinados de los estatores de motores trifásicos. Si se sabe que el devanado del motor era original y estamos seguros que los datos que hemos tomado son correctos, el bobinado original se puede duplicar con confianza utilizando estos datos. Sin embargo, en ciertas ocasiones, no existe la certeza que los datos que hemos tomado correspondan al bobinado original de fábrica. En estos casos, es necesario tomar medidas adicionales como las aquí descritas.

By Mike Howell
EASA Technical Support Specialist

Manufacturers deploy various external connection schemes to produce three-phase induction motors for multiple voltages and/or starting methods, so successful installation depends on using the relevant connection diagram. If this information is lost, damaged, or ignored, a connection mistake could lead to a costly rewind.

The following tips apply to common connections on machines with one speed at power frequency. If the manufacturer's external connection diagram isn't available, ask a service center for assistance, especially if there are several missing lead tags, multiple speed ratings at power frequency, unconventional numbering, or NEMA-IEC cross-references.

READ THE FULL ARTICLE

This valuable resource is available only to EASA Members.

Active and Allied members can download this software for FREE!

This version of the EASA Motor Rewind Database software takes a large leap forward with the data that it provides members. Most notably, it now has the ability to connect to a live, ever-expanding online database of more than 250,000 windings. This live database will be continuously 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. If your computer does not have an Internet connection, the software will automatically switch to the static, local database that was included and loaded during installation. (Note: The local database does not receive updates.)

The database includes:

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

Chuck Yung
EASA Senior Technical Support Specialist

We all have that occasional customer who got a “deal” at an auction: a compressor, or lathe, or wood-working equipment, only to discover when he started to install it that this equipment has a three-phase motor and only single-phase power is available. Maybe it’s your neighbor or a friend from church. In any case, you know that you are about to be called upon to “convert” that piece of equipment, and you probably realize that it’s going to cost you more than you can charge.

Chuck Yung
EASA Senior Technical Support Specialist

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. Let’s start with the basics:  The higher the power rating, and/or the lower the voltage rating, the fewer turns/coil used. Because a 3-phase winding has pole-phase groups alternating ABC, ABC, ABC, etc., the intra-phase jumpers could be 1-4, 1-7, 1-10, 1-13, etc., or any combination of these so long as the alternating polarity of the groups is maintained and the phases are not cross-connected.

Cyndi Nyberg 
Former EASA Technical Support Specialist 

There are many applications where it is necessary for a low-voltage, single-phase AC or DC power supply to be available for auxiliary equipment such as brakes, clutches, lamps, etc., used along with a three-phase motor. The single-phase voltage can be supplied by tapping the stator winding at the correct place. DC voltage can be produced by tapping the single-phase or three-phase voltage from the three-phase winding and rectifying it to DC. Determining where to tap the winding is fairly straightforward. 

A three-phase stator winding, when energized, will have a certain number of volts per turn. That is, if you know the number of turns in each phase, and you know the phase voltage, you can determine the volts per turn. Knowing the number of volts per turn, and the required voltage supply for the auxiliary equipment, you can calculate pre­cisely where to tap the winding. 

Durante los últimos años, el rediseño de los motores eléctricos es un servicio que ha aumentado de popularidad en las compañías que reparan motores eléctricos. Al variar  uno o más datos del diseño, los centros de servicio muchas veces pueden adaptar motores para que cumplan con nuevos requisitos de forma más rápida y económica  que al comprar motores nuevos.
El manual de Rediseño de Motores de CA de EASA explica  la forma de realizar todos los cambios posibles en los valores nominales de los motores eléctricos de CA dentro de sus limitaciones de diseño. Además de fórmulas matemáticas, este manual proporciona directrices relacionadas con las limitaciones propias de cada tipo de rediseño, que  le ayudarán a determinar  si es posible obtener un nuevo valor nominal antes de retirar el bobinado. Los términos se expresan en Español y en unidades métricas y cada capítulo contiene al menos un ejemplo para guiarlo durante sus propios rediseños.

Los miembros de EASA pueden descargar GRATIS este  libro  o pueden comprar copias impresas del mismo.                                                                         

Los capítulos del libro incluyen:

• Cambio del  tamaño del conductor
• Cambio de Voltaje 
• Cambio de Potencia
• Cambio de Frecuencia
• Cambio del Número de  Fases
• Cambio de los Circuitos en Paralelo
• Cambio de  Paso o del Factor de Cuerda
• Cambio en la conexión del bobinado
• La fórmula maestra
• Conversión de bobinados concéntricos en imbricados
• Conversión de bobinados imbricados en concéntricos
• Notas para el cambio del número de polos
• Disminución de la velocidad aumentando el número de polos
• Aumento de la velocidad disminuyendo el número de polos
• Una velocidad a dos velocidades con un solo devanado
• Una velocidad a dos velocidades con dos bobinados
• Cálculo de un bobinado para un núcleo sin datos
• Fortaleciendo o debilitando el motor- método corto
• Determinando la conexión apropiada
• Rediseño monofásico
• Cálculo del voltaje secundario
• Determinando el agrupamiento trifásico de las bobinas 

This webinar recording covers: 

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

Chuck Yung
EASA Senior Technical Support Specialist

One of the recurring questions asked of EASA technical support specialists is:  “Should I use 1-4 or 1-7 jumpers?” This article is a tutorial on jumper selection to help the reader recognize when it does – or does not – matter. 

Let’s start with a short review for the experienced winders and good fundamentals (Table 1) for the newer winders. First, three-phase windings are symmetrical. The connection is log­ical if we apply some basic rules. The groups are positioned symmetrically, in sequence of A-B-C-A-B-C, with an equal number of coil groups required in each phase.

Tom Bishop, PE
Senior Technical Support Specialist
EASA
St. Louis, MO

In his paper presented at the EASA Convention 2019, Tom Bishop explores various methods for starting three-phase squirrel cage induction motors, emphasizing the importance of understanding these methods for service centers involved in motor repair and sales. The paper covers traditional across-the-line starting and modern techniques such as variable frequency drives (VFDs), detailing the principles of operation, benefits, and potential drawbacks of each method.

Bishop begins by explaining the high current draw associated with induction motor startup, which can be five to eight times the rated current. This high current can cause voltage drops and other issues in the power supply, necessitating methods to reduce starting current. The paper categorizes these methods into reduced voltage, reduced current, and reduced voltage and frequency starting techniques.

Across-the-line (direct-on-line) starting is the simplest method, involving the application of full line voltage to the motor terminals. While this method provides the highest starting torque and shortest acceleration times, it also demands the most from the electrical power system and can cause transient torque loading on the driven equipment.

Reduced voltage starting methods include autotransformers and electronic soft starters. Autotransformers use voltage taps to control power to the motor, reducing starting current and torque. Soft starters use silicon controlled rectifiers (SCRs) to reduce the voltage supplied to the motor, allowing for smoother acceleration and the ability to set peak current limits.

Reduced current starting methods, such as reactors and resistors, directly reduce motor current by adding impedance or resistance to the motor circuit. Reactors limit current changes and provide closed transition to line voltage, while resistors offer smooth acceleration by gradually increasing voltage at the motor terminals.

Part winding (PWS) starting involves using only a portion of the motor winding, increasing impedance and reducing starting current. This method is beneficial for applications requiring utility supply voltage recovery and helps prevent excessive voltage dips.

Wye-delta (Y-D) starting changes the motor winding phase connections to reduce voltage during startup. This method is commonly used for high inertia loads and provides a smooth transition from wye to delta configuration, minimizing transient current and torque surges.

Variable frequency drive (VFD) starting offers the most advanced method, allowing for precise control of motor voltage and frequency. VFDs can maintain full load torque throughout the acceleration period while keeping motor current at or below rated full load current. This method provides smooth acceleration and deceleration, making it suitable for a wide range of applications.

In summary, Tom Bishop's paper provides a comprehensive overview of squirrel cage induction motor starting methods, highlighting the advantages and drawbacks of each technique. Understanding these methods is crucial for service centers to ensure successful motor operation and optimal performance.

Key Points Covered:

• High current draw during induction motor startup
• Across-the-line (direct-on-line) starting
• Reduced voltage starting methods: autotransformers and soft starters
• Reduced current starting methods: reactors and resistors
• Part winding (PWS) starting
• Wye-delta (Y-D) starting
• Variable frequency drive (VFD) starting

Key Takeaways:

• Various methods exist to reduce starting current and torque
• Across-the-line starting provides highest torque but demands most from power system
• Autotransformers and soft starters offer smoother acceleration and control
• Reactors and resistors directly reduce motor current
• Part winding starting helps prevent excessive voltage dips
• Wye-delta starting is suitable for high inertia loads
• VFDs provide precise control and smooth acceleration/deceleration

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

The most common method of start­ing squirrel cage three-phase motors is across the line (direct-on-line). Some applications require limiting the mo­tor starting current and/or torque to reduce the stress on the electrical and mechanical systems. 

Although there are other meth­ods such as autotransformer, reactor and using a variable frequency drive (VFD), the focus in this article will be on the reasons behind the selection of the three most common methods of achieving these objectives. Specifically, these methods are part winding, wye-delta, and electronic soft-starting. The windings in all three of these methods usually have 6 leads.

Cyndi Nyberg Esau
Former EASA Tenchincal Support Specialist

As we move into January, it's time to put into practice those New Year's resolutions we made. Many of us have the same ones every year. You know: eat less, exercise more, spend more time with the family, etc. However, rather than personal challenges, presented here are the"resolutions" for some of the more common calls we receive in the Technical Support Department at EASA Headquarters. A review of the basics is always a good idea to start the new year fresh!

Presented by Mike Howell, PE
EASA Technical Support Specialist

Note: This presentation is an update to the webinar originally presented June 2015.

When preparing to rewind random or form-wound status, 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
• Newer designs from the OEM

This presentation looks at balancing stator copper losses against insulation reliability and is intended for technicians and engineers working with stator rewinds. 

Chuck Yung
EASA Senior Technical Support Specialist
 
When taking winding data, the area most prone to error is in identifying the connection. This article includes a reference page (see Figure 1) that I encourage you to print and laminate for the winders to use.

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.

Presented by Tom Bishop, PE
EASA Senior Technical Support Specialist

This presentation stresses the importance of taking accurate winding data and explains and emphasizes the consequences of inaccurate data. One of the main benefits of this presentation is to improve ability to “get it right the first time” to avoid the added cost and time of another rewind to correct errors.

Primary topics are:

• How to take accurate electrical and mechanical data
• How to verify that the winding data is correct

This webinar is intended for winders, engineers, supervisors and managers. The content will be beneficial for beginners through highly experienced persons. 
 

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

We will begin this article by clarify­ing the terms “alternator” and “gen­erator.” Both terms refer to a machine that converts mechanical to electrical power. An alternator is a synchronous machine that converts mechanical to AC electrical power. A generator is a more general term and is a machine that converts mechanical to electrical power, either AC or DC. An alternator is always a generator, but not vice-versa. Our focus in this article will be on 3-phase alternators. However, much of the information provided also applies to single-phase alternators and single- or three-phase generators.

Editor's Note: This "encore" technical article first appeared in the September 2003 issue of Currents. It was written by former Technical Support Specialist Cyndi Nyberg Esau.

To make more efficient use of time and materials, winders may want to increase the number of parallel circuits when winding an AC stator (or wound rotor). However, there are limits to the number of parallel circuits that can be used in an AC stator (or wound rotor) design. In this article, some of the potential problems associated with increasing the number of parallel circuits will be analyzed.

If the original design of a mo­tor has few turns with large wires, or many wires in hand, it may be easier to rewind if the number of parallel circuits can be increased (see Figure 1). Doubling the circuits, for example, doubles the turns per coil and cuts in half the wire size or the number of wires in hand. Of course, doubling the circuits also doubles the volts per coil.

This webinar recording covers: 

• Various types of AC motors and bases for operation
• Squirrel cage induction motor rotor design / construction
• Squirrel cage induction motor stator design / construction

This webinar covers:

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

This webinar covers:

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

Cyndi Nyberg 
Former EASA Technical Support Specialist 

To make more efficient use of time and materi­als, winders may want to increase the number of parallel circuits when winding an AC stator (or wound rotor). However, there are limits to the num­ber of parallel circuits that can be used in an AC stator (or wound rotor) design. In this article, some of the potential problems associated with increas­ing the number of parallel circuits will be analyzed. 

If the original design of a motor has few turns with large wires, or many wires in hand, it may be easier to rewind if the number of parallel cir­cuits can be increased. Doubling the circuits, for example, doubles the turns per coil and cuts in half the wire size or the number of wires in hand. Of course, doubling the circuits also doubles the volts per coil. 

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

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 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.

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.

Cuando un cliente solicita que un motor sea rebobinado para una nueva serie de condiciones, esto es lo que nosotros habitualmente le proporcionamos en la industria de los centros de servicio. No obstante, existen ocasiones en las que lo requerido por el cliente se puede llevar a cabo por reconexión; en algunos casos, esto se hace simplemente revisando los datos de placa del motor. El propósito de este artículo es identificar y explicar algunos de estos escenarios.

Las reconexiones cubiertas incluyen:

• Arranque por devanado partido (PWS)
• Un solo voltaje-12 cables
• 2 estrellas y 1 delta 230/460-575 voltios
• 380 voltios - 50 Hz y 460 voltios - 60 Hz
• 2300 y 4000 voltios

​Para una referencia adicional, ver "Variables a Considerar Cuando Cambiamos La  Frecuencia de  Un Motor Entre 50 y 60 Hz" publicado en Noviembre de 2008.

Gene Vogel
EASA Pump & Vibration Specialist

El software AC Motor Verification & Redesign (ACR-Motor Db) es una poderosa herramienta que permite a los centros de servicio satisfacer las necesidades de rediseño de estatores y rotores bobinados de CA de sus clientes. En la mayoría de los casos, los datos del bobinado se registran al momento de retirar el alambre, pero surgen situaciones en las que los datos originales no están disponibles, han sido registrados de forma incorrecta o que un centro de servicio haya desmantelado el devanado sin terminar la reparación. En estos casos, el centro de servicio debe realizar un rediseño “sin datos”. La ACR-Motor Db cuenta con ciertas características específicas para solucionar estos casos.

CÓMO CALCULAR UN DEVANADO A PARTIR DE UN NÚCLEO DESNUDO

Durante varias décadas, la base de datos de bobinados del programa de EASA (MotorDb) ha compilado los datos enviados por los miembros de EASA. Con más de 300.000 registros, es muy probable que en la MotorDb existan datos similares a los que se buscan. Simplemente, realizando una búsqueda en la base de datos utilizando las dimensiones del núcleo se obtienen varios devanados que coinciden. Para que se pueda usar en un rediseño, un bobinado de la base de datos no tiene que coincidir exactamente con la placa de datos del motor.

Cuando seleccione los datos de un bobinado, estos se pueden transferir automáticamente al programa de Rediseño donde se podrán realizar las modificaciones y ajustes necesarios para alcanzar los criterios deseados. Este proceso es fácil para la mayoría de los motores trifásicos de inducción.

El primer paso consiste en obtener un listado de datos posibles que se correspondan muy de cerca con las dimensiones del núcleo. Ingrese el largo del núcleo, el diámetro interior del núcleo, el número de polos y el número de ranuras en la Motor Db. A manera de ejemplo buscaremos un motor Marathon, 125 hp, 6 polos, 72 ranuras con las siguientes medidas de núcleo: 12” de largo y 14” de diámetro interior (ver Figura 1). La función Get Count rápidamente devuelve los posibles resultados, si estos son 50 o menos haga click en OK para obtenerlos. Estos se verán en formato de hoja de cálculo donde se pueden revisar en forma de columnas. Si los datos son muchos, añada más criterios de búsqueda para depurar los resultados.

En este caso, se encontraron 44 registros tal como se puede ver en la Figura 2. Ya que la hoja de cálculo se puede revisar por columnas, es conveniente verificar la AirDensity (AGD) y la Potencia (Pwr) para evaluar si existen datos que sean buenos candidatos para garantizar un rediseño exitoso. Para nuestro ejemplo existen 16 datos y 10 de ellos son motores Marathon de 125 hp. Así que, para este ejemplo, es posible que haya datos de fábrica disponibles.

Por supuesto, este no siempre será el caso. Supongamos que el motor del ejemplo fuese marca Siemens, que no está en la lista. Aún podemos elegir un fabricante diferente como base para nuestro rediseño sin datos. Seleccione uno de los devanados de la hoja de datos que se acerquen mucho a los criterios de los datos de placa deseados. Los datos completos se pueden ver en un editor (Figura 3).

Los datos originales estaban en la base de datos así que no será necesario ningún rediseño ya que el motor se puede rebobinar usando directamente estos datos. Sin embrago, este no siempre es el caso y el software de EASA tiene una función en la MotorDb que permite transferir los datos a la función ACR la cual permite efectuar el rediseño. Los datos enviados a la función ACR crean un nuevo registro en el que todas las opciones de rediseño quedan disponibles. Retomando nuestro ejemplo, suponga que fuese necesario un rediseño para 575 V. Los datos disponibles en la MotorDb son solo para 230 o 460 V. La Figura 4 muestra un registro de la MotorDb enviado a la función ACR para poder realizar el rediseño de 460 a 575 V.

El bobinado fue rediseñado para 575 V y se cambió la conexión de 6 Y a 3 Y manteniendo los voltios por bobina dentro de los límites aceptables (Ver Figura 5).

La combinación entre la EASA Winding Database y el Verification and Redesign program es una solución sencilla para afrontar los retos de los bobinados sin alambre. Para ver las instrucciones paso a paso, vea el video tutorial, How to calculate a winding from a bare core disponible en go.easa.com/wbc.

Jim Bryan
EASA Technical Support Specialist (retired)

The connection of a three-phase motor is one of the many variables a motor designer can use to optimize the performance and life of the machine. The designer determines whether to use a wye or delta connection and how many parallel circuits to maximize current density (circular mils per amp or cm/A) while optimizing flux densities and manufacturability.

In three-phase motors, the square root of three is an important number. Because of the phase relationships of the three windings shown in Figure 1, the voltage and current are intertwined with this factor. In the delta winding, the phase voltage is applied to each phase winding but the current has two possible paths. Due to the phase relationship of the winding, the current is not split in two but by the square root of three (1.73). The opposite is true for the wye connection; the phase voltage impressed on each phase is the line voltage divided by 1.73, and the phase current equals the current in each coil. This is the reason that wye wound motors have fewer turns of heavier wire than do delta-connected motors.

Chuck Yung
Senior Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO

In the paper "Unusual Winding Connections & Layouts," presented at the EASA Convention 2008, Chuck Yung explores various unconventional winding designs encountered in three-phase motors. These designs often appear to violate standard rules but ultimately adhere to the principles of symmetry and electrical balance. The paper reviews several exceptions to common winding rules and provides insights into how these designs function effectively.

Yung begins by discussing the fundamental rules of motor design, emphasizing symmetry in slot spacing, phase sequence, pole distribution, and the number of slots being divisible by phases and poles. He explains that deviations from these rules can lead to issues such as circulating currents, higher losses, electrical noise, and negative torque. However, certain designs manage to work despite appearing asymmetrical.

One notable exception is the use of unequal grouping, where parallel circuits do not have the same number of coils. This can be mitigated by ensuring that each circuit has the same total number of turns, even if the number of coils differs. Another exception involves equalized connections, where jumpers connect points of equal electrical potential within parallel circuits to reduce circulating currents.

The paper also covers part-salient, part-consequent windings, which combine salient-pole and consequent-pole designs to achieve a desired number of poles using an existing lamination stamping. This hybrid approach allows for the creation of motors with unconventional slot-to-pole ratios.

Interleaved windings are another unconventional design discussed by Yung. These windings divide each group into subgroups and parallel them, effectively doubling the number of circuits. Proper interleaving requires that the electrical center of each subgroup coincides to prevent circulating currents and ensure efficient operation.

Interspersed windings, primarily used in two-pole machines, are designed to reduce the adverse effects of harmonic waveforms. By interspersing coils of adjacent groups, the winding behaves as if each coil has a longer span, improving motor performance by reducing harmonic distortion.

Yung emphasizes the importance of understanding these unusual winding connections and layouts to avoid repeat failures and improve motor efficiency. He advises service centers to proceed with caution when encountering unfamiliar designs and to consider the motor's history and performance when making repairs.

Key Points Covered:

• Fundamental rules of motor design and the importance of symmetry
• Exceptions to common winding rules, including unequal grouping and equalized connections
• Part-salient, part-consequent windings for unconventional slot-to-pole ratios
• Interleaved windings to double the number of circuits
• Interspersed windings to reduce harmonic distortion in two-pole machines

Key Takeaways:

• Unusual winding designs can function effectively despite appearing asymmetrical.
• Ensuring equal total turns in parallel circuits can mitigate issues with unequal grouping.
• Equalized connections reduce circulating currents and improve efficiency.
• Part-salient, part-consequent windings allow for unconventional slot-to-pole ratios.
• Proper interleaving prevents circulating currents and ensures efficient operation.
• Interspersed windings improve motor performance by reducing harmonic distortion.
• Service centers should proceed with caution when encountering unfamiliar winding designs and consider the motor's history and performance.

Presented by Mike Howell
EASA Technical Support Specialist

EASA Internal Connection Diagrams for Three-Phase Electric Motors is available to members as a free PDF download and contains hundreds of connections, as well as templates for windings up to 30 poles. This webinar recording shows how to access it and provide examples of how to use it.

• Three-phase connection basics
• Accessing the resource from different devices
• Understanding and using the templates provided
• Examples of completed diagrams  

This webinar recording is intended for personnel responsible for taking data or connecting windings.

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. 

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

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

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.

The Basics: Motor Connections
Presented November 2016

This webinar covers:

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

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

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

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

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.

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.

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.

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. 

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.

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).