Chuck Yung
EASA Technical Support Specialist

One of the unique motor applications we’re often called upon to service is the “shaker screen duty”or vibrator motor. See Figure 1. These are mechanically robust electric motors, fitted with large eccentric weights, designed to deliberately vibrate – a lot. The unusual application calls for some special considerations when repairing these motors. This article is intended to consolidate those tips in one place.

When dismantling the motor, the first step is to document the position of the eccentric weights on both ends, relative to each other, so the performance characteristics remain unchanged. Note that many of these are fitted with two weights on each end and that only one of the weights is keyed. The second weight can be shifted relative to the first to allow adjustment of the unbalance to suit the application. In some applications, for example, when shaking a product through a hopper, the weights might be adjusted to different settings to move materials of different density. See Figure 2.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Hace mucho tiempo, los motores de corriente continua funcionaban con baterías o con grupos motor-generador. Durante los últimos 50 años, la mayoría de los motores de corriente continua han funcionando con fuentes de poder de estado sólido - rectificando la corriente alterna en corriente continua. Cuando los motores comenzaron a funcionar con corriente rectificada, uno de los problemas detectados fue la presencia del "rizado" en los cables que se suponía tenían que entregar la corriente continua a la máquina. En ausencia de una norma específica, una pregunta muy frecuente es: "¿Cuánto rizado es demasiado?" Antes de tratar de sugerir una respuesta a esa pregunta, vamos a hablar de lo que es el rizado y de explicar por qué no es conveniente.

Mike Howell, PE
Especialista de Soporte Técnico de EASA

La mayoría de los centros de servicio de EASA encuentran muy pocas máquinas de flujo axial. Son tan raras, que vale la pena describir qué son y como se diferencian del típico motor o generador industrial de flujo radial. La Figura 1 muestra un corte de una máquina de flujo axial a la izquierda y una máquina de flujo radial a la derecha. Las zonas doradas representan los devanados del estator energizados y las verdes los bobinados del rotor o imanes permanentes. Tenga en cuenta que la máquina de flujo axial que se muestra tiene dos rotores; un devanado de rotor a cada lado del estator. La máquina de flujo radial es a lo que están acostumbrados la mayoría de los centros de servicio de EASA; un rotor separado de un estator por un entrehierro en dirección radial y un campo magnético que cruza ese entrehierro para vincular ambos devanados (o devanados e imanes permanentes) de manera que puedan producir un torque útil.

Chuck Yung
EASA Senior Technical Support Specialist

Cuando un cliente llama y quiere reemplazar su motor diesel o de gasolina por un motor eléctrico para impulsar una pieza de maquinaria, es fácil asumir que “los caballos de potencia son caballos de potencia”. ¡No tan rápido! Resulta que existen muchas formas diferentes para medir la potencia. El término caballo de potencia fue adoptado por James Watt a finales de 1700 para comparar la potencia de salida de las máquinas de vapor con la potencia de los caballos de tiro. Aparte de Norte América, la mayor parte del mundo utiliza el vatio para describir la potencia de salida, la cual es la unidad del Sistema Internacional de Unidades (SI). Desde 1700, tenemos hp mecánico, kW, hp métrico, hp eléctrico, hp hidráulico, hp de barra de tracción, hp de frenado, hp de eje e incluso variantes de hp fiscal. Dejando a los gobiernos que quieran sacar partido de ello. 

El propósito de este artículo es aumentar la conciencia sobre la cantidad de factores que se deben considerar al hacer este cambio aparentemente simple.

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. 

Cyndi Nyberg 
EASA Technical Support Specialist 

The basic definition of torque is the measure of the force applied to produce rotational motion, usually measured in pound-feet or Newton-meters. Torque is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied. 
Torque = Force x Radius 

Figure 1 illustrates the relationship between force and torque.

Obviously, if the force is in­creased, the torque will increase. If the magnitude of the force is main­tained, but the radius is increased, then the torque is also increased. 

Cyndi Nyberg
Former EASA Technical Support Specialist

Typically, motor currents of interest are the no-load current, full-load current, service factor current, and starting (or inrush) current.

You will know the full load current from the nameplate, and you can calculate the starting current from the Code Letter on the nameplate.

Service factor current may or may not be on the nameplate.

Matthew Conville, MBA, PE
EASA Technical Support Specialist

Before putting an AC machine into service, make sure its duty rating matches the application requirements. Otherwise, there’s a good chance excessive heat will degrade the machine’s windings.

Applications are not all created equal. For example, a crane motor doesn’t require the same duty rating as a punch press motor of equal horsepower that runs continuously. Likewise, a chop saw motor wouldn’t need the same duty rating as a pump motor that operates 24-7-365. If the motor must operate at variable speeds other than its nameplate base speed, its turndown ratio is another consideration.

NEMA Std. MG-1-1.40 and IEC Std. 60034-1, Clause 4 describe the duty classifications for the respective standards.

• NEMA duty classifications
• IEC duty types with "S" ratings
• Turndown ratios
• Questions to consider

READ THE FULL ARTICLE

A special discounted collection of 6 webinar recordings focusing on AC electric motor design.

Once purchased, all 6 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

The Basics: AC Motor Design
Presented July 2016

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

How Winding Changes Affect Motor Performance
Presented January 2019

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.

Motor Starting Capabilities and Considerations
Presented March 2014

This webinar addresses the topic of a three phase squirrel cage motor’s ability to successfully accelerate a driven load. Although a motor can drive a running load, that is not assurance that it has the capability to accelerate the load up to rated speed. The difference between success and failure is determined by some complex conditions. For example, the motor torque during starting is not constant, and unless the load is a pure inertia load (very rare), it does not have a constant speed-torque relationship. Key considerations addressed include acceleration time, acceleration torque, motor heating, stator and rotor limits, and torque variables.

Target audience: This presentation will be most useful for service center sales personnel, engineers, supervisors and managers. The content will be beneficial for moderate through highly experienced persons.

AC Motor Redesign: Speed Changes
Presented January 2015

This presentation 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 are performed using EASA’s AC Motor Verification & Redesign program, including use of the integrated motor winding database for locating comparative data. Examples will include other changes such as voltage, frequency and horsepower.

Magnetic Wedges
Presented January 2019

An increasing number of manufacturers are using magnetic wedges in their form-wound machines. When a winder fails to replace magnetic wedges in kind, the winding temperature rise can increase by 20°C, and the magnetizing current can increase by 20% or more.

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

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

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

Speed/Torque Curves
Presented March 2017

This recording covers:

• Starting torque
• Breakdown torque
• Full load torque
• Speed current curve
• Load torque curve
• Impact of reduced voltage start (autotransformer, PWS, wye-delta)
• Slot combination problems (noise, torque cusp, cogging)

It is very important to understand speed/torque curves and how they impact motor operation.

Target audience: Engineers, mechanics, winders and sales persons with fundamental knowledge of motor operation. 

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 

Chuck Yung
EASA Senior Technical Support Specialist

Redesigning electric motors has become commonplace for motor repair service centers. By changing one or more motor characteristics, service centers often can adapt motors to meet new requirements faster and more economically than they can obtain new ones.

This paper explains how to make any changes in the ratings of AC electric motors that are possible within design limitations. Examples of each redesign are included as a guide for making your own redesigns. Besides mathematical formulas, this section provides guidelines on the limitations for each type of redesign. These guidelines will also help you determine whether a desired new rating is possible before you strip a motor.

In most service centers, there are rules regarding what winding changes can be made, who can make them, and who must approve them. Make sure that redesigns are not made without going through the proper channels.

This paper gives a brief review of AC motor theory and operation that includes flux pattern, types of losses, NEMA design designations and test procedures. It also covers:

• Design considerations for slip-ring and synchronous motors
• Requirements for reduced starting voltage
• Formulas for redesigning polyphase and single-phase AC equipment.

This presentation 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 are performed using EASA’s AC Motor Verification & Redesign program, including use of the integrated motor winding database for locating comparative data. Examples will include other changes such as voltage, frequency and horsepower.

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

Chuck Yung
EASA Senior Technical Support Specialist

Air gap is the physical gap between a rotor and stator core in an AC machine, or between the armature and fields / interpoles in a DC machine. The role of the air gap is not as simple as it appears.

Topics discussed in this article include:

• Important principles (magnetic force and the amount of current to drive flux through air)
• Air gap in AC machines
• Air gap in DC machines

Presented by Chuck Yung
EASA Senior Technical Support Specialist

The physical air gap between the rotor or armature and the stator or field frame is complex and plays a critical role in the performance of AC and DC machines. Most repairers do not realize how little they understand about this subject.

This webinar will explain the role air gap plays in AC motor performance, how to recognize the symptoms of an uneven air gap, and share corrective measures. For DC machines, this webinar will cover the distinctly different role of the field air gap as opposed to the air gap of the interpoles.

• Air gap tolerance of AC machines
• Air gap tolerance of DC fields and interpoles
• Allowable runout of rotor / armature
• Recognizing the signs of air gap anomalies
• Corrective actions

Target audience
This webinar recording is of benefit to managers, supervisors, winders, mechanics and field service personnel.

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

Although aluminum magnet wire theoretically can be converted to copper magnet wire of about 5/8 of the original wire area, in some cases this is not advisable. In others, it may result in a change in the magnetic strength of a coil or winding. In this article we will address the most common aluminum-to-copper magnet wire conversions as well as how to deal with whether the wire area should be reduced.

Chuck Yung 
EASA Technical Support Specialist
 
When repairing motors, we often take the lead wire ampacity charts for granted, without giving much thought to how they were developed. Who .gured out how much current is acceptable for specific lead wire, and why are there different ratings for different types of insulation? 

It might be helpful to consider some of the variables that influence what looks – on the surface at least – like a simple subject. And as we will see shortly, “the surface” is one of the variables to consider. 

Since most electric motors and generators use lead cable rather than bus bar, the occasional motor with bus bar leads to questions about “circular mils per amp” for bus bar. Is the current density of bus bar com­parable to that for lead cable? 

Chuck Yung
EASA Senior Technical Support Specialist

While there are many similarities between 3-phase AC stators and DC armatures, there are some unique aspects to DC armature design; these can be extremely helpful to those who understand some little-known tips. My goal in writing this article is to share those tips.

Tom Bishop, P.E. 
EASA Technical Support Specialist
 
Have you ever had to deal with a rewound motor that had high no-load amps? That is almost a rhetori­cal question as most of us have experienced this situation. The focus of this article will be on steps to take before rewinding in order to avoid the condition of high amps after the rewind. 

Steps that should be performed on every AC stator rewind: 

1. Inspect the stator bore and rotor outside diameter for evidence of machining or damage. 
2. Record the original winding data exactly as found. 
3. Test the stator core before winding removal. 
4. Verify the winding data. 
5. Test the stator core after winding removal and cleaning. Applying these five steps will help avoid the vast majority of situations where a rewound motor will exhibit high no-load current. If these steps were not all followed and a motor has high no-load current, if possible, perform any steps above that were omitted. 

Gene Vogel
EASA Pump & Vibration Specialist

When repairing centrifugal and axial flow pumps, axial thrust is a concern. An understanding of the causes and the mitigating provisions of various pump designs will help repair technicians to ensure those provisions work properly. Various impeller designs, end suction and vertical turbine pumps will be a primary focus. 

Primary topics are: 

• Factors affecting the amount of axial thrust developed by an impeller 
• Review of some common mitigation designs 
• What repair technicians need to look for on various pump designs 

The mechanical pump components can be repaired without understanding the hydraulics of how a pump works. But it’s easy to miss important features that can affect pump performance and reliability.  

This presentation will be helpful for pump repair technicians and supervisor and engineers associated with pump repair.

Jim Bryan
EASA Technical Support Specialist

The squirrel cage induction motor (SCIM) functions by applying a voltage to the stator winding and inducing a voltage across the air gap in the rotor circuit. The squirrel cage rotor consists of a lamination stack with slots to ac­commodate some number of rotor bars and shorting (end) rings that tie all the bars together. The squirrel cage consists of bars and end rings that are typi­cally made from alloys of aluminum or copper. This squirrel cage is illustrated in Figure 1 with the lami­nation stack removed.

Cyndi Nyberg
Former EASA Technical Support Specialist

There are two main types of load that act on the bearings of a motor – radial and axial.

• Radial – A radial load is defined as a load that is applied perpendicular to the shaft. An example of a radial load would be an overhung load, such as with a sheave.
• Axial – An axial load, also referred to as thrust, is a load that acts parallel to the shaft on which the bearing is mounted. Just the rotor weight of a vertically mounted motor will cause a downward axial load on the bearing.

The type and magnitude of the load will determine what type of bearing should be used in the application. If the wrong type of bearing is used, it could lead to a motor failure in a short period of time.

Jim Bryan
EASA Technical Support Specialist (retired)

Rolling-element bearing construction has become a very precise and exacting process. Studies have shown that more than one-half of motors that come to service centers are because of worn out or failed bearings. This is understandable since this component is subject to wear and sometimes abuse. Bearing manufacturers are called upon to improve the quality and reliability of their product to increase the time in service before it becomes necessary to replace the bearings. Proper application and maintenance of the bearing is also a key to improved reliability. We will discuss in this article some of the components used to better understand what applications can be accommodated.

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.

Cyndi Nyberg
Former EASA Technical Support Specialist

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

Brick-type design
A brick-type winding uses two different sizes of wire arranged as shown in Figure 1. Rather than use one large rectangular wire for each turn, this example uses four smaller wires. When more than one conductor is used, each individual conductor must be insulated. However, it is not necessary to insulate every wire to achieve the required separation.

Luther (Red) Norris 
Quality Solutions Co. LLC 
Greenwood, Indiana 
Technical Services Committee Member
 
Brushless servo motors are being used in industry for many different applications. However, the primary industrial use for these motors is in automated machinery for the accurate positioning of the work piece or work tool. 

The brushless servo motor will have many features that are different than the standard AC induction or brush type DC motor. Most service centers are familiar with the operation and characteristics of three-phase induction motors and with DC motors with a commutator and brushes. 

The brushless servo motor will usually have a stator winding similar to a three-phase stator with three power leads. It will have a rotor that, instead of an induction squirrel cage rotor or a wound armature, will have permanent magnets that match the number of poles in the stator windings. 

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.   

Welcome by 2019-2020 EASA Chairman Brian Larry
Presentation by Tom Bishop, P.E., EASA Senior Technical Support Specialist

In 2003, EASA and AEMT (Association of Electrical and Mechanical Trades in the UK) issued a report that proved rewinding motors in accordance with prescribed good practices would maintain efficiency and reliability. But in recent years, claims abounded that premium efficient motors could not be rewound without degrading efficiency.

This recording discusses the latest EASA/AEMT research that included independent, third-party testing.

Gene Vogel
EASA Pump & Vibration Specialist

For many larger centrifugal pumps, there are options for installing “component” or “cartridge” mechanical seals. Understanding the advantages and limitations of each will allow you to recommend the best solution for customer applications.

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.

Mike Howell
EASA Technical Support Specialist

Before rewinding a stator, EASA strongly recommends winding data verification. This is a required criterion for rewinds covered under the EASA Accreditation Program audit checklist. With tools like EASA’s AC Motor Verification & Redesign program, this can be done easily within minutes. Additionally, the verification is an EASA member benefit provided at no additional charge by submitting an inquiry to EASA’s technical support staff. We see many cases where failure to invest a few minutes up front costs a service center an additional rewind. There are probably as many cases where service centers identify issues with the as-found winding data before investing time and materials. 

One of the most common winding data changes made by service centers is a wire size change. This is inherent to most redesigns where the number of turns per slot is changed. But it is also routinely done to accommodate a service center’s available inventory. Although this type of change is easily done in EASA’s verification & redesign program, there are various situations that restrict winders to pen and paper changes. And, as processes become more manual, they typically have a higher risk for error. Minimizing the manual calculations associated with this change can increase process efficiency while reducing errors.

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.

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.

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.

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

¿Cuáles son las condiciones normales para las que está diseñado un motor eléctrico? Esta es una pregunta que no surge muy a menudo, excepto cuando existe un problema con la aplicación.

La norma NEMA MG1 para motores y generadores proporciona detalles sobre este tema, definiendo las condiciones de servicio normales e inusuales. La norma IEC 60034-1, “Rotating Electrical Machines, Part 1 Ratings and Performance”, trata también algunas condiciones de aplicación en la cláusula 6, aunque no en la medida que lo hace la norma MG1. Nuestro enfoque estará basado en la norma MG1, ya que proporciona más detalles que la norma IEC 60034-1.

Cyndi Nyberg
Former EASA Technical Support Specialist

Most motors are run continuously with little variation in load. A continuous duty motor is energized and loaded for an extended period of time. When the motor is started, the temperature increases, and then the temperature stabilizes after some time.

If the motor was designed with a service factor, it is possible to run the motor at a higher-than-rated load for short periods of time without significant thermal damage to the windings, rotor or bearings. A motor to be used with a continuous load is sized based on that load rating.

There are, however, many applications where a motor is not loaded consistently throughout its duty cycle, or is energized intermittently.

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.

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

Cuando se energiza inicialmente un motor de CA a su voltaje nominal (y frecuencia), el motor toma varias veces la corriente nominal hasta que alcanza toda la velocidad de operación. Las consecuencias de la corriente de arranque incluyen: Breve sobrecalentamiento de los bobinados del estator y del rotor, disparos no deseados de los dispositivos de protección y caídas de voltaje en el suministro eléctrico.

De acuerdo con las normas NEMA MG 1 e IEC 60034-1, la corriente a rotor bloqueado es la corriente de estado estable a rotor bloqueado. Sin embargo, según la norma NEMA MG 1 clausula 12.36, al momento de la energización, existe un valor pico de medio ciclo que varía entre 1.8 y 2.8 veces la corriente de estado estable, en función del diseño del motor y del ángulo de conmutación. Un factor relevante en la amplitud de este valor pico instantáneo es el magnetismo residual en los núcleos del rotor y del estator y los ángulos instantáneos de los voltajes de fase aplicados. Aunque la medición de la corriente no sea lo suficientemente rápida para capturar el primer pico de medio ciclo, la Figura 1 ilustra un breve intervalo de tiempo cuando la corriente de arranque es transitoria, antes de alcanzar su estado estable. Esto se puede ver claramente a los 95ms, donde las amplitudes de las corrientes son diferentes en cada fase ya que se encuentran desfasadas entre sí.

Un término que debería evitarse o definirse es “Corriente de Inrush”. Dicha corriente no está definida en las normas NEMA o IEC. Por tanto, en algunos casos, podría significar la corriente a rotor bloqueado en estado estable y en otros podría ser el valor pico instantáneo de la corriente de arranque u otra cosa diferente. Con relación a la corriente a rotor bloqueado en estado estable, la norma NEMA MG 1 clausula 10.37.2 asigna letras para los kVA a rotor bloqueado por caballo de potencia medidos a voltaje y frecuencia nominal, tal como lo muestra la Tabla 1.

Diferencias en la Corriente de Arranque
Para apreciar mejor las diferencias en los dos tipos de corriente de arranque, evaluaremos un motor de 25 hp a 460 voltios con kVA a rotor bloqueado letra G. Incidentalmente, las letras más comunes para motores con potencias mayores o iguales a 10 hp (7.5 kW) son F y G. La Figura 2 muestra la fórmula para calcular la corriente a rotor bloqueado en un motor. Note que la c o rriente nominal del motor no se usa en la fórmula.

Por tal motivo, utilizar guías como: “La corriente a rotor bloqueado es 5 a 8 veces la corriente nominal” en el mejor de los casos es emplear valores estimados y de acuerdo con la fórmula de la Figura 2 no se puede confiar en su exactitud. Cuando la letra kVA (CODE) no se indique en la placa de datos del motor, un mejor enfoque para calcular la corriente a rotor bloqueado, siempre que sea posible, consiste en usar la fórmula de la Figura 2 y un rango guía. Suponga que el motor se encuentra en el centro de servicio. En ese caso, la corriente a rotor bloqueado se puede calcular siguiendo el procedimiento descrito en la sección “Need Locked-Rotor Current Only?” del artículo “Working with Motor Locked-Rotor Test Data” publicado en la revista Currents en febrero del 2016.

La corriente a rotor bloqueado calculada para el motor de 25 hp se encuentra entre 176 y 198 Amperios. Para determinar el valor pico instantáneo de la corriente de arranque potencial, multiplicamos los amperios a rotor bloqueado por 1.8 y por 2.8. El resultado es un rango entre 317 (1.8 x 176) y 554 (2.8 x 198) Amperios.

Dispositivos de protección
Los dispositivos de protección pueden ser fusibles o interruptores, siendo los fusibles sin retardo y los interruptores de disparo instantáneo o de tiempo inverso. La forma en que funcionan estos dispositivos puede explicar porque la protección interrumpe el circuito del motor durante el arranque.

Los fusibles sin retardo tienen una velocidad de respuesta rápida bajo condiciones de sobre corriente, proporcionando a los componentes del circuito una protección muy efectiva contra corto circuitos. Sin embargo, las dañinas sobre cargas temporales o sobre corrientes transitorias pueden causar interrupciones molestas a menos que los fusibles estén sobre dimensionados. Los fusibles son más adecuados para circuitos con cargas inductivas como motores o transformadores, que no estén sometidos a grandes sobre corrientes transitorias y a fuertes sobrecargas temporales. Para las cargas con motores CA, puede ser necesario sobredimensionar un fusible sin retardo al 300 por ciento de la corriente nominal del motor para poder soportar la corriente de arranque. Una mejor alternativa para aplicaciones con motores es la de un fusible con retardo de tiempo.

Los fusibles con retardo de tiempo se pueden dimensionar cerca de la corriente nominal del equipo para proporcionar una protección muy efectiva contra corto circuito y una protección confiable contra sobre cargas en circuitos sujetos a sobre cargas temporales y sobre corrientes transitorias. Dependiendo del tipo de fusible, en cargas con motores CA, un fusible con retardo se puede dimensionar al 125-175 por ciento de la corriente nominal para soportar la corriente de arranque. Comparado con los fusibles instantáneos, los valores de corriente más bajos pueden proporcionar una mejor protección contra corto circuitos con menos corriente máxima instantánea y una reducción potencial en el riesgo de arco eléctrico.

Tipos de Interruptores
Los interruptores de disparo instantáneo operan inmediatamente cuando la corriente del circuito alcanza el valor de disparo ajustado en el dispositivo. Estos interruptores son solo de disparo magnético y también se denominan Interruptores de protección para motores (MCPs por sus siglas en inglés). El circuito magnético del interruptor consiste en un núcleo de hierro con una bobina arrollada en el mismo, lo que crea un electroimán. La corriente de carga pasa a través de la bobina, por lo que el interruptor dispara cuando se presenta un corto circuito. Para soportar la corriente de arranque en cargas con motores CA, puede llegar a ser necesario dimensionar un interruptor de disparo instantáneo al 800 por ciento del valor nominal de corriente alterna (hasta 1700 por ciento en motores de alta eficiencia con Diseño B).

Los interruptores con retardo tienen un mecanismo que permite demorar la función de disparo del dispositivo. El tiempo de retardo necesario disminuye a medida que la corriente aumenta. Los interruptores de tiempo inverso son termo magnéticos. Este tipo de interruptores tienen dos mecanismos de conmutación: Un interruptor bimetálico y un electroimán. La corriente que excede el valor de sobrecarga del interruptor calienta el bimetálico lo suficiente para doblar una barra de disparo. El tiempo requerido por el bimetálico para doblar la barra y disparar el circuito es inversamente proporcional a la corriente. La parte magnética del interruptor funciona igual que en un interruptor de disparo instantáneo. Para soportar la corriente de arranque en cargas con motores CA, puede ser necesario ajustar un interruptor de tiempo inverso al 300 por ciento del valor nominal de corriente alterna.

Otro tipo de dispositivo de protección es un interruptor con unidad de disparo electrónica. El disparo de estos interruptores se pueden configurar con un tiempo de retraso largo, corto, instantáneo o disparo por aterrizamiento (L,S,I,G por sus siglas en inglés). Estas características permiten al usuario diseñar un disparo a medida para la aplicación. Si los interruptores se ajustan correctamente, los beneficios adicionales incluyen la reducción de la energía térmica en eventos potenciales con arco eléctrico y una mejor protección del motor.

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

When an AC motor is initially energized at rated voltage (and frequency), the current drawn is many times rated current until the motor attains full operating speed. Consequences of starting current include short time overheating of stator windings and rotors, undesirable operation of overload protective devices and a sag in the supply voltage.

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.

Bill Colton
Baldor Electric Co.
Commerce, California
Technical Services Committee Member

When selecting a drive for an ap­plication, there are many technical and commercial issues to explore in arriving at a choice. The scope of this article is to consider some of the techni­cal issues involved.

Let us assume that the motor is already in place and the customer has asked you to help select an adjustable speed drive. You have determined that the application is “constant torque.” (Constant torque is the same amount of full load RMS [root mean square] torque over the entire speed range required by the application.) 

Chuck Yung
EASA Senior Technical Support Specialist

Occasionally a customer wants a spare DC machine, and you find a replacement that is almost – but not quite – identical. Often, either the original or the spare is compound wound. The customer then asks: “What do the series fields do?” and “Can we just isolate the series leads?” 

There are a couple of considerations, but the answer is that “it depends.” If the nameplate is factory marked “Stabilized shunt” or “Stab shunt,” that tells us that the series contribution to total field flux is relatively small. In many applications (e.g., extruder), the relatively small series is not essential to successful operation of the motor.

Topics covered in the article include:

• Shunt and series field
• Flux contribution
• Higher percent compounding
• Inductive kick
• Shunt field failure

Mike Howell
Especialista de Soporte Técnico de EASA

La mayoría de los bobinados de los estatores de CA instalados por los centros de servicio de EASA son imbricados de doble capa, trifásicos y están balanceados. Pero ¿qué significa que estén balanceados? Si los devanados están balanceados, los voltajes generados en cada fase tienen la misma magnitud y el mismo ángulo de desfase (Ver Figura 1 ‒ Balanceado). Si hay alguna diferencia en la magnitud o en el ángulo de desfase, se trata de un devanado desequilibrado (Ver Figura 1 ‒ Desequilibrado). Está bien establecido que los devanados desequilibrados pueden causar vibraciones indeseables, ruido electromagnético y calentamiento adicional de los conductores debido a las corrientes circulantes.

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.

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

Occasionally an end user wants to take a motor designed for horizontal mounting and use it in a vertical position. This article addresses some of the key mechanical factors that should be considered when applying a horizontal ball-bearing motor in a vertical mounting position.

These key factors include:

• Axial thrust load capacity of bearing supporting rotor weight
• Rotor weight
• Weight of output shaft attachments
• Axial thrust from direct-connected driven equipment\
• Bearing lubrication paths
• Bearing lubricant retention
• Shaft up or shaft down orientation
• Ingress protection
• Locking axial thrust bearing

READ THE FULL ARTICLE

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

Occasionally an end user wants to take a motor designed for horizontal mounting and use it in a vertical position. In this article, we will address some of the key mechanical factors that should be considered when applying a horizontal ball bearing motor in a vertical mounting position. Figure 1 illustrates a horizontal motor in a vertical shaft down position.

These key factors include:

• Axial thrust load capacity of bearing supporting rotor weight
• Rotor weight
• Weight of output shaft attachments
• Axial thrust from direct connected driven equipment
• Bearing lubrication paths
• Bearing lubricant retention
• Shaft up or shaft down orientation
• Ingress protection
• Locking axial thrust bearing

Gene Vogel
EASA Pump and Vibration Specialist

There are three fundamental parameters for machinery vibration data:  amplitude, frequency and phase. When testing machine vibration, amplitude and frequency are the two primary measurements for acceptance testing and for diagnostics. Both of these parameters have several units in which they can be recorded. 

Converting from one unit of measurement to another is not difficult if both amplitude and frequency data are available. In many cases, only amplitude measurements are available, without the needed frequency information, so conversion to other amplitude units is not possible. 

Knowing when conversion is possible and how to a apply conversion formulas is important when assessing customer specifications and analyzing diagnostic data.

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

De vez en cuando un usuario final quiere utilizar un motor diseñado para montaje horizontal en posición vertical. En este artículo, trataremos algunos factores mecánicos clave que deben ser considerados cuando se utiliza un motor horizontal con rodamientos de bolas en una aplicación en la que trabaja en montaje vertical. La Figura 1 ilustra un motor horizontal en posición vertical con el eje hacia abajo.

Los factores clave incluyen:

• Capacidad de carga axial del rodamiento que soporta el peso del rotor.
• Peso del rotor
• Peso de los elementos acoplados al eje de salida
• Empuje axial de los equipos de impulsión acoplados directamente
• Trayectorias de lubricación de los rodamientos
• Retención del lubricante de los rodamientos
• Orientación del eje: Hacia abajo o hacia arriba
• Protección contra ingreso
• Fijación axial del rodamiento de empuje

Jim Bryan
Especialista de Soporte Técnico de EASA (retirado)

Frecuentemente escuchamos decir a nuestros miembros, que uno de sus clientes le ha informado que un motor que había sido reparado, ahora se calienta. Nosotros siempre les preguntamos ¿Qué tan caliente? y por lo general responden “Bueno, no puedo mantener mi mano sobre él”.

Vamos a pensar un minuto en esta respuesta. La mano del ser humano típico, puede soportar una temperatura entre 60-65°C (140 -150°F), dependiendo de las callosidades, el dolor que pueda tolerar, cuantas personas estén observando, etc. Recuerden este número, mientras discutimos las temperaturas típicas de funcionamiento de un motor.

La norma NEMA MG1-2009 12.43 (ver Figura 1), define el aumento de temperatura para los motores a una temperatura ambiente máxima de 40 °C.

A special discounted collection of 6 webinar recordings focusing on DC motor electrical procedures.

Once purchased, all 6 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

The Basics: Understanding DC Motor Tests
Presented October 2016

• Ampere turns of the armature, field and interpole data
• Determining the best armature coil pitch
• Verifying interpole circuits
• Importance of brush angle
• Equalizers and armature windings

Adjusting Brush Neutral
Presented June 2011

The webinar covers:

• How to set brush neutral in DC machines.
• Several methods of setting brush neutral along with the benefits and drawbacks of each.
• Tips for permanent magnet and series-would machines.
• Tips on how to recognize problems and settings that affect brush neutral, and what to check if the neutral adjustment seems higher than usual.

Target audience: This presentation is most useful for service center and field technicians involved in the repair of DC machinery, service center managers engineers, or anyone involved in DC motor or generator repair, as well as those who are simply looking to expand their understanding.

Carbon Brushes, Current Density and Performance
Presented June 2019

The lowly brush is underrated and misunderstood. The brush grade, brush pressure and spring tension, as well as the effect of load and humidity are each important to brush performance in DC machines, wound rotor motors, and synchronous machines.

This presentation covers:

• Importance of brush grade
• Effect of humidity and load (current)
• Best practice method for removing brushes to improve performance
• Brush pressure & spring tension by application
• Supplemental cooling of slip ring / brush enclosures

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

Drop Testing of Fields and Synchronous Poles: Tips to Interpretation
Presented November 2011

This presentation covers:

• The basics of drop testing, as well as offers tips for interpreting the results.
• Both the AC and DC drop test are described as well as the advantages and drawbacks for each.
• For those cases where the drop test results are out of tolerance, this material will guide the technician in determining the reasons for the variation-how to recognize the difference between shorted coils and differences in iron, airgap or other influences.
• Rewind and assembly tips will also be discussed, where they influence the results of the drop test.

Target audience: This presentation is most useful for service center and field technicians with at least 5 years experience, service center managers, engineers, or anyone involved in DC motor or generator repair, as well as those who are simply looking to expand their knowledge.

Final Testing of DC Machines
Presented September 2011

To assure a quality repair, there specific tests (such as neutral-setting and interpole-armature polarity) that should routinely be performed on every DC machine. When done correctly, the simple procedures presented will prevent scenarios such as that late night phone call from an irate customer whose DC machine is "arcing like a fireworks show."

Target audience: Technicians with at least a moderate lever of experience in DC machine repair will benefit from this session.

Advanced DC Testing
Presented April 2012

This presentation shares tips that are not covered in “Fundamentals of DC: Operation and Repair Tips,” such as:

• Tips for interpreting armature and interpole tests
• Finding that ground in the newly rewound armature
• Interpreting questionable drop test results

It also covers final assembly tests including how to determine whether the cause of sparking is the interpoles or the armature.

Target audience: This presentation is aimed at the experienced technician and supervisor.

Mike Howell
EASA Technical Support Specialist

When rewinding the shunt fields of a DC machine, it is important to avoid making changes that could negatively impact performance. The recommended practice is to maintain the manufacturer’s winding configuration during the repair. That is, the field circuit connection, turns per coil, mean or average length of turn (MLT) and wire size should not be changed. However, service centers do sometimes encounter issues around wire size availability. The purpose of this article is to provide some guidance for making wire size substitutions when the original size is unavailable.

This webinar covers:

• Attraction / repulsion explanation as magnets
• Ampere-turns of armature, fields, interpoles
• Determining the correct interpole circuits
• Evaluation of armature designs
• How to recognize opportunities for improvement

Target audience: This webinar is intended for supervisors, winders and those desiring to learn more about DC machines.

Chuck Yung
EASA Technical Support Specialist

Sometimes when redesigning a motor, the desired speed requires more poles than are possible for the number of stator slots. Or, a motor arrives in the service center with a nameplate speed that does not seem to be compatible with the number of stator slots (e.g.,18 poles with 36 slots). In both cases, the answer may be a part-salient, part-consequent winding.

To understand how this winding works, let’s compare it to ‘normal’ winding designs. One winder’s trick for verifying the integrity of a connection diagram is to trace through each phase and “arrow-diagram” the groups. For a salient- pole winding, the polarities alternate with each physical group (Figure 1). With a consequent- pole connection, all the arrows point the same direction (Figure 2).

Gene Vogel
EASA Pump & Vibration Specialist

Whether it is a simple re-application of a pump from 50 Hz to 60 Hz (or vice versa), the repurposing of an existing pump, or the application of a new pump to an existing application, determining the proper trim for an impeller can be challenging. This presentation reviews: 

• Basic impeller design criteria 
• Methods of evaluating the head and flow and power implications of trimming impeller outside diameters

This recording will benefit pump technicians, engineers and sales personnel.

Chuck Yung
Especialista Senior de Soporte Técnico de EASA

Algunas veces cuando rediseñamos un motor, la velocidad requerida, necesita  más polos de los que son posibles de obtener con el número de ranuras del estator. O el motor ingresa en el centro de servicios con una placa que indica una velocidad que no parece compatible con el número de ranuras del estator (ej. 18 polos para 36 ranuras). En ambos casos, la respuesta puede ser un bobinado híbrido (o que funciona parcialmente con polos alternos y parcialmente con polos consecuentes).

This presentation focuses on:

• How to use basic design rules to verify data for fields, interpoles and armatures
• Verifying the correct armature coil pitch
• Special cases where you can improve on the original armature design
• What to do when the armature was received stripped, and the manufacturer no longer exists

REVISED September 2022!

The EASA Technical Manual, containing more than 900 pages of information specific to electric motor service centers, is available FREE to EASA members as downloadable PDFs of the entire manual or individual sections. The printed version is also available for purchase. Each of the 13 sections features a detailed table of contents.

VIEW, DOWNLOAD OR PURCHASE

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.

Jim Bryan
EASA Technical Support Specialist

What is voltage variation? Voltage variation is the deviation of voltage from the rated voltage; NEMA MG1 Section 12 allows a plus or minus 10% variation from rated voltage. That rat­ing assumes balanced voltages and acknowledges that motor performance will not necessarily be the same as at rated voltage.  Note: The tolerance for voltage unbalance is only 1%, an order of magnitude less than the 10% voltage variation tolerance. For more informa­tion on this subject, see the December 2007 edition of Currents for an article on voltage unbalance titled “Unbalanced Voltages and Electric Motors.”

En una máquina de C.A. el entrehierro es el espacio físico entre el núcleo del estator y del rotor o entre la armadura y los campos/interpolos de una máquina de C.C.

Los temas discutidos en este artículo incluyen:

• Principios importantes (fuerza magnética y la cantidad de corriente para conducir el flujo a través del aire)
• Espacio de aire en las máquinas de CA
• Espacio de aire en las máquinas de CC

Cyndi Nyberg 
Former EASA Technical Support Specialist 

Stator windings in three-phase motors are de­signed to have the amount of flux that the core needs to produce the desired output. The number of turns and size of wire are limited by the core dimensions. However, in the squirrel cage rotor, there are many more variables in the design. One of the variables is the shape of the rotor slot. Many rotor designs are skewed. So, why are ro­tors skewed? 

As the rotor turns, discontinuities on the sur­face of the rotor and stator disrupt the magnetic flux path of the motor. The flux path variation shows up in the form of harmonics that affect the performance of the motor. The difference be­tween the number of stator slots and rotor slots has a significant impact on the harmonics. The motor may be noisy, or there may be stray torques that lower the torque during starting or acceleration. The stator-rotor slot difference is why a motor winding that is redesigned for a dif­ferent speed may have problems, and why it is important to check the stator-slot-rotor-bar com­bination before proceeding with the redesign. 

This PowerPoint presentation is available for members to use to present the factors that should be considered when customers are faced with making the difficult decision to repair their existing motor or purchase a replacement.

The presentation is designed to help service center sales and marketing personnel answer these difficult questions for their customers:

• Is it better to repair or replace an electric motor that has failed?
• Will a repaired motor retain its efficiency?

Members are welcome to customize the presentation with their company logo, contact information and anything else that might help better inform their customers.

With this presentation, you will be able to discuss the complete repair/replace decision-making process from reviewing the application demands, failure assessment, factoring in efficiency, and motor repair/rewinding good practices.

The presentation also is helpful in explaining the value of working with an EASA accredited member (if you are accredited). If you’re not an EASA accredited member, you may remove this portion of the presentation.

DESCRIPTION
Filled with practical information, this 118-page handbook (3.5" x 6", 9cm x 15cm) makes a great “give-away” item for your customers and potential customers! Buy this great resource as is OR custom brand your company logo and information on the cover to turn it into a great marketing piece for your salespeople!

BUY COPIES OF THIS HANDBOOK

TABLE OF CONTENTS

MOTOR DATA–ELECTRICAL
Standard Terminal Markings and Connections
DC Motors and Generators (NEMA & IEC Nomenclature)
Field Polarities of DC Machines
General Speed-Torque Characteristics
Full-Load Efficiencies of Energy Efficient Motors
Full-Load Efficiencies of NEMA Premium™ Efficient Motors
Effect of Voltage Variation on Motor Characteristics
Power Supply and Motor Voltages
Effect of Voltage Unbalance on Motor Performance
Starting Characteristics of Squirrel Cage Induction Motors
Allowable Starts and Starting Intervals

MOTOR DATA–MECHANICAL
Suffixes to NEMA Frames
NEMA Frame Assignments–Three-Phase Motors
NEMA Frame Dimensions–AC Machines
IEC Mounting Dimensions–Foot-Mounted AC and DC Machines
IEC Shaft Extension, Key And Keyseat Dimensions–Continuous Duty AC Motors (Inches)
NEMA Shaft Extension And Keyseat
Dimensions–Foot-Mounted DC Machines (Inches)
NEMA Frame Dimensions–Foot-Mounted DC Machines (Inches)
NEMA Frame Dimensions–AC Machines (mm)
IEC Mounting Dimensions–Foot-Mounted AC and DC Machines (mm)
IEC Shaft Extension, Key and Keyseat Dimensions–Continuous Duty AC Motors (mm)
NEMA Shaft Extension and Keyseat Dimensions–Foot-Mounted DC Machines (mm)
NEMA Frame Dimensions–Foot-Mounted DC Machines (mm)

MOTOR CONTROLS
Power Factor Improvement of Induction Motor Loads
Capacitor kVAR Rating for Power-Factor Improvement
Full-Load Currents–Motors
Maximum Locked-Rotor Currents–Three-Phase Motors
NEMA Code Letters for AC Motors
Starter Enclosures
NEMA Size Starters for Three-Phase Motors
NEMA Size Starters for Single-Phase Motors
Derating Factors for Conductors in a Conduit
Allowable Ampacities of Insulated Conductors
Motor Protection Devices–Maximum Rating or Setting

TRANSFORMERS
Full-Load Currents for Three-Phase Transformers
Full-Load Currents for Single-Phase Transformers
Transformer Connections

MISCELLANEOUS
Temperature Classification of Insulation Systems
Resistance Temperature Detectors.
Thermocouple Junction Types
Dimensions, Weight and Resistance: Solid Round Copper Wire (AWG and Metric)
Square Bare Copper Wire (AWG)
Insulation Resistance and Polarization Index Tests
Properties of Metals and Alloys

USEFUL FORMULAS AND CONVERSIONS
Temperature Correction of Winding Resistance
Temperature Correction of Insulation Resistance.
Formulas for Electric Motors and Electrical Circuits.
Motor Application Formulas
Centrifugal Application Formulas
Temperature Conversion Chart
Conversion Factors
Fractions of an Inch–Decimal and Metric Equivalents

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

The International Electrotechnical Commission (IEC) standard 60529 “Degrees of protection provided by enclosures (IP code)” addresses the degrees of protection for electrical machines (motors and generators). The “IP” acronym means “International Protection,” but is sometimes referred to as “Ingress Protection.” The IP code is commonly displayed on metric machine nameplates, which are manufactured to IEC standards.

The NEMA MG1 Motors and Generators standards have adopted the IEC standards for the IP designations. Although not prevalent on NEMA machine nameplates, the inclusion of the IP marking is becoming more common. The purpose of this article is to describe the IP code designations and provide examples of the IP codes for common electrical machine enclosures.

Cyndi Nyberg Esau
Former EASA Technical Support Specialist

Most rotor, stator and armature laminations used in industrial electric motors and generators are made from non-oriented, cold-rolled electrical steels. However, there is a lot of variation in the specific properties in these electrical steels. This article will discuss properties of electrical steels, as well as the methods used to optimize the magnetic characteristics of the laminations, specifically through the annealing process.

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

Following the squirrel cage induction motor, what will come next? This webinar provides an overview of potential successor technologies.

• Permanent magnet (PM) motors
  • Hybrid permanent magnet (HPM) motors
  • Across the line start PM (LSPM) motors
  • High torque low speed PM motors
  • Surface permanent magnet (SPM) motors
  • Interior permanent magnet (IPM) motors
• Reluctance motors
  • Synchronous reluctance motors (SynRM)
  • Switched reluctance motors (SRM)
• Other motor technologies nearing reality
  • Amorphous metal designs
  • Axial flux ferrite PM motors

This webinar benefits anyone dealing with sales, service or repair of these and other emerging technology motors.

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

La norma 60529 de la International Electrotechnical Commission (IEC): “Degrees of protection provided by enclosures (IP code)” trata los grados de protección de las máquinas eléctricas (motores y generadores). La sigla “IP” significa “Protección Internacional” pero a veces se le conoce como “Protección contra Ingreso”. El código IP se muestra comúnmente en las placas de datos de las máquinas métricas, que son fabricadas con normas IEC. 

Las normas NEMA MG1 Motors and Generators han adoptado las normas IEC para las designaciones IP. Aunque no prevalecen en las placas de datos de las máquinas NEMA, la inclusión del marcado IP se está volviendo más común. El propósito de este artículo es describir las designaciones IP y proporcionar ejemplos de los códigos IP para los encerramientos de las máquinas eléctricas más comunes.

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

An old saying claims: “If it’s in black and white, it must be right.” Seeing something in writing makes it more believable than the spoken word. However, that does not mean it is true. We should always look for substantiation to back up statements, whether written or verbal.

A more recent saying is: “If it’s on the Internet, it must be true.” Apply that same fact-check here. Look for substantiation before accepting information gleaned from the Internet.  

Here is a random collection of some relatively common misconceptions about three-phase squirrel cage motor performance characteristics.

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 
EASA Technical Support Specialist 

Most of us involved in the repair of electrical equipment have a good understanding of how an electric motor works–especially the stator and ro­tor. But the fan can appear deceptively simple. Fans are pretty interesting, once we learn a few “affinity laws”—rules that also apply to blowers and impellers. This article will review some basic facts about fans that explain how small changes to a fan can make a BIG difference in the following critical areas: 

• Volume of air moved
• Static pressure
• Load
• Losses (efficiency)

These rules hold true for fan applications, im­pellers in pumping applications, and cooling fans on electric motors. When applied to the external fan of a TEFC (IP-54) motor, these rules offer some real opportunities for efficiency improvement. 

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.

This book ws developed in conjuction with EASA's two-day Fundamentals of DC Operation & Repair Tips seminar.

This book is not meant to replace the many good texts that cover the theory and design of DC machines, but to supplement them. Its purpose is twofold: to help the technician understand DC machine theory without complex formulae; and in a larger sense, to record in one place the repair procedures and tips usually learned the hard way during a long career of DC machine repair. It may take a decade or longer for a technician to become proficient and knowledgeable. We hope this book will cut many years from that timeline.

The text begins with DC theory (no math, we promise!), and then follows the logical progression of a DC machine through the service center. Disassembly, inspection and testing are covered in the initial chapters. 

Subsequent chapters are organized around the main parts of a DC machine. The final chapters cover assembly, final testing and application issues. Sections focusing on components explain how those parts work, how they are made and how they can best be repaired.

Repair tips gleaned from EASA members’ decades of experience are liberally sprinkled throughout the book. While many texts about DC machines explain how they should work, this is the first (to our knowledge) to discuss all the exceptions that a repairer is liable to run across during a lifetime of working with DC machines. These might otherwise be labeled “lessons learned the hard way,” except that the reader can benefit from having all these special cases collected in one source. When possible, it is better to learn by reading than by trial and error; otherwise, the first encounter with a unique design can result in a painful “learning experience.”

A DC machine can be used interchangeably as a motor or generator, simply by changing the connection. Any DC motor can be driven and used to produce power, and any DC generator can be motorized to provide mechanical power. Although this text predominately refers to “motor;” the material applies to both motors and generators.

As with the other EASA publications—Principles of Large AC Motors, Mechanical Repair Fundamentals of Electric Motors, and Root Cause Failure Analysis—each section is designed to stand alone. The small amount of duplication is intentional, to save the reader from flipping back and forth between sections.

Table of Contents - (Download the complete Table of Contents)

• Nomenclature and Nameplate Information
• DC Motor Theory
• Disassembly and Inspection
• Testing
• Armatures
• Commutators
• Frames
• Ventilation and Accessories
• Motor Assembly and Final Testing
• On-Site Troubleshooting
• Failure Analysis

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BOOK DOWNLOAD CD-ROM BOOK & CD-ROM

The repair of the various types of pumps represents an important segment of the service center repair market. Electric motors and pumps are the two most widely used industrial machine components.

Although there are two principle pump types (dynamic and positive displacement), this manual focuses on dynamic pumps and the fundamentals of dynamic pump repair. The information it contains will be helpful to both novice and experienced pump repair technicians, to supervisors and managers of pump repair operations, and to customer service and sales personnel who communicate with customers about pump repair issues.

Section 2 covers repair concerns and techniques common to most pumps, while the following sections focus on specific pump types and the unique concerns associated with repairing them. These sections include submersible pumps, vertical turbine pumps, end suction pumps and split case pumps. Where appropriate, these sections may reference the general repair information in Section 2.

Table of Contents- (Download the complete Table of Contents)

1. Nomenclature
2. General Pump Repair Procedures
3. Submersible Pumps
4. Vertical Turbine Pumps
5. End Suction Radial Split Pumps
6. Axial Split-Case Pumps
7. Seals
8. Pump Reliability
9. Glossary and Standards Organizations

Por Mike Howell
Especialista de Soporte Técnico de EASA

Los motores de reluctancia conmutada (SRM), también conocidos como motores de reluctancia variable (VRM), tienen su origen a mediados de 1830. Estos motores fueron usados como motores de tracción ferroviaria. Sin embargo, la electrónica de potencia necesaria para controlar satisfactoriamente los SRMs, no fue patentada hasta comienzos de los 70´s. Esto implicaba una conmutación electrónica sincronizada con la posición del rotor. Los centros de servicio están notando un incremento en el número de SRMs que reciben para reparar y algunos de los técnicos no están familiarizados con su funcionamiento. Como cualquier otra máquina rotativa, un conocimiento básico de los principios de funcionamiento puede ayudar a detectar problemas y durante la reparación. Uno de los puntos más críticos para el personal del centro de servicios es entender de antemano que estas máquinas no pueden ser operadas sin un drive especial, el cual normalmente necesita ser suministrado por el usuario final o el fabricante.

Mike Howell
Especialista de Soporte Técnico de EASA

Los avances en la electrónica de potencia en las últimas décadas han permitido el uso de una variedad de máquinas eléctricas rotativas que de otro modo no sería factible. Una de ellas se denomina máquina de reluctancia debido a la forma en la que dichas máquinas producen un torque electromagnético. Una máquina de reluctancia es una máquina eléctrica en la cual el torque se produce por la tendencia de su parte móvil a moverse a una posición donde se maximiza la inductancia del devanado excitado. En un artículo publicado en Currents en marzo de 2020, se trató el tema del motor de reluctancia conmutada (SRM), mientras que este artículo se centrará en el motor sincrónico de reluctancia (SynRM). Demos un vistazo a algunas de sus similitudes y diferencias.

Jim Bryan
Especialista de Soporte Técnico de EASA (retirado)

La fabricación de los rodamientos se ha convertido en un proceso muy preciso y exacto. Estudios han demostrado que más de la mitad de los motores ingresan en los centros de servicio debido a que sus rodamientos se encuentran desgastados o defectuosos. Esto es comprensible, dado que estos componentes están sometidos a desgaste y algunas veces al abuso. Los fabricantes de rodamientos están llamados a mejorar la calidad y la confiabilidad de sus productos para incrementar el tiempo de servicio, antes de que sea necesario reemplazar los rodamientos. Una aplicación adecuada y un buen mantenimiento también son claves para mejorar la confiabilidad. En este artículo discutiremos algunos de los componentes utilizados para entender mejor que tipo de aplicaciones pueden tener cabida.

Carlos Ramirez
Especialista de Soporte Técnico de EASA

Este webinario ayudará a los centros de servicio a navegar a través de los aspectos fundamentales del rediseño de motores de CA y ayudará a prevenir errores costosos asociados a los rediseños incorrectos. Los centros de servicio son contactados frecuentemente, para realizar rediseños y cambiar el voltaje, la frecuencia o la conexión del bobinado, entre otros.

El webinario incluye:

• Toma correcta de las medidas del núcleo
• La fórmula maestra
• Cambio en la conexión del bobinado
• Cambio de Paso (Pitch)
• Cambio velocidad o del número de polos
• Cambio de potencia

Este webinario está dirigido a bobinadores, supervisores y personal de ingeniería.

This 40-page booklet provides a great marketing tool for your service center! Use it to provide end users with information that will help them obtain the longest, most efficient and cost-effective operation from general and definite purpose electric motors with these characteristics:                                                                                                          

• Three-phase, squirrel-cage induction motors manufactured to NEMA MG 1 standards 
• Power ratings from 1 to 500 hp (1 to 375 kW)                                        
• Speeds of 900 to 3600 rpm (8 to 2 poles) 
• Voltages up to 1000V, 50/60 Hz 
• All standard enclosures (i.e., DP, TEFC, WPI, WPII) 
• Rolling element (ball and roller) and sleeve bearings

This booklet covers topics such as:

• Installation, startup and baseline information
  • Basic system considerations
  • Installation
  • Startup procedures
  • Baseline data
  • Total motor management
• Operational monitoring and maintenance
  • Application specific considerations
  • Preventive, predictive and reliability-based maintenance
  • Inspection and testing
  • Relubrication of bearings
• Motor and baseline installation data
• How to read a motor nameplate
  • Overview
  • Required information
  • Other terms
• Motor storage recommendations
  • Motor storage basics
  • Preparation for storage
  • Periodic maintenance

This resource is provided as a FREE download (use the link below). You can also purchase printed copies ready to distribute to your current or potential new customers. The cover of this booklet can also be imprinted with your company's logo and contact information (minimum order or 200). Contact EASA Customer Service for details.

READ MORE ABOUT THE FEATURES AND BENEFITS

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.

Mike Howell
EASA Technical Support Specialist

Reluctance machines offer simple construction, high power density and low cost. Over time, advancement in power electronics will increase the prevalence of these machines in a number of applications, creating repair opportunities for service centers. This recording explores features of synchronous and switched reluctance machines.

• Basic magnetic circuits
• Reluctance machines and torque production
• Slots, poles and phases
• Concentrated windings vs. lap or concentric windings
• Rewind, test and inspection

This recording will benefit service center managers, supervisors and technicians.

The purpose of this guide is to provide repair/rewind practices and tips that will help service center technicians and motor winders maintain or increase the efficiency, reliability and quality of the motors they repair.

Some of the included procedures derive directly from the 2019 and 2003 rewind studies by EASA and AEMT of the impact of repair/rewinding on motor efficiency. Others are based on the findings of an earlier AEMT study [1998] of small/ medium size three-phase induction motors and well-established industry good practices . 

The procedures in this guide cover all three-phase, random-wound induction motors. Much of the guide also applies to form-wound stators of similar sizes. 

(Note: This guide provides many specific procedures and recommendations. Alternative practices may accomplish the same results but must be verified.)

Table of Contents Overview

• Terminology
• Energy losses in induction motors
• Motor repair processes
  • Preliminary inspection
  • Dismantling the motor
  • Removing the old winding and cleaning the core
  • Rewinding the motor
  • Reassembling the motor
  • Confirming the integrity of the repair

El propósito de esta guía es suministrar prácticas y consejos de reparación/rebo­binado que ayudarán a los técnicos y a los bobinadores del centro de servicios a conservar o aumentar la eficiencia, confiabilidad y calidad de los motores que reparan.

Algunos de los procedimientos incluidos derivan directamente de los estudios sobre el impacto de la reparación/ rebobinado en la eficiencia del motor realizados por EASA y AEMT en los años 2003 y 2019. Otros se basan en los hallazgos del estudio previo efectuado por AEMT [1998] en motores trifásicos pequeños/medianos y en las buenas prácticas industriales bien establecidas.

Los procedimientos de esta guía cubren todos los motores trifásicos de inducción de alambre redondo. Mucha información también aplica a motores con bobinas preformadas (pletina o solera) de tamaños similares.

(Nota: Nota: Esta guía proporciona muchas recomendacio­nes y procedimientos específicos. Se pueden lograr los mismos resultados con otras prácticas, pero deberán ser verificadas.)

Tabla de Contenido

• Terminología
• Pérdidas de energía en los motores de inducción
• Procesos de reparación del motor
  • Inspección inicial
  • Desmontaje del motor
  • Remoción del antiguo bobinado y limpieza del núcleo
  • Rebobinado del motor
  • Montaje del motor
  • Confirmando la integridad de la reparación

The challenge for every motor repair firm is twofold: to repair the equipment properly; and to demonstrate to their customers by means of adequate testing and documenta­tion that rewound motors retain their operating efficiency. Following the guidelines in the “DOs” and “DON’Ts” below will help you accomplish both.

Numerous studies have been done to determine the effect rewinding has on motor efficiency. These studies identified several variables that can impact the efficiency of a rewound motor, including core burnout temperature, winding design, bearing type, air gap and winding resistance. The following guidelines were developed as a result of those studies, which found that the efficiency of both standard and energy efficient electric motors can be maintained during rebuilding and rewinding. 

To ensure that motors retain their efficiencies when rewound, EASA also strongly recommends that electric motor repair centers comply with ANSI/EASA Standard AR100: Recommended Practice For The Repair Of Rotating Electrical Apparatus and strictly adhere to the “DOs” and “DON’Ts” that follow. These guidelines, which contain safe values (based on available data) and correct procedures, apply to both energy efficient and standard motors. Further study of the matter continues, and these guidelines will be revised if additional information warrants.

Por Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Contrariamente a la opinión popular, no siempre, lo más grande es mejor. Un buen ejemplo es el motor eléctrico, el caballo de trabajo de la industria. Existe una tendencia natural a reservar un poco más de potencia, “por si acaso”.

Es por esto que la industria automotriz sigue vendiendo vehículos con motores de 300 hp, a pesar que el límite de velocidad está muchas veces por debajo de las 70 millas por hora. Pero así como sucede con estos depredadores de gasolina, el funcionamiento de un motor sobredimensionado puede costarnos dinero extra; algunas veces, una gran suma. Aquí presentamos un procedimiento sencillo para calcular los hp reales requeridos por una carga, sin emplear equipos e ingeniería costosa. Tenga en cuenta que las cargas se deben calcular, cuando el motor está demandando su máxima carga. Una carga que presenta amplias variaciones,  es buena candidata para un variador de velocidad electrónico (VFD).

This presentation covers:

• An explanation of partial discharge
• Description of the damage mechanism
• PWM drive and partial discharge
• How to evaluate partial discharge
• Repair tips for dealing with partial discharge

By Mike Howell
EASA Technical Support Specialist

Too often, replacement specifications for three-phase squirrel-cage induction motors cover only basic nameplate data such as power, speed, voltage, and frame size, while overlooking other important performance characteristics such as the design letter. This can lead to misapplication of a motor, causing poor performance, inoperability, or failures that result in unnecessary downtime. To avoid these problems, familiarize yourself with the following speed-torque characteristics and typical applications for design letters that NEMA and IEC commonly use for small and medium machines (up to about several hundred kilowatts/horsepower).

• NEMA Designs A and B, IEC Design N
• NEMA Design C, IEC Design H
• NEMA Design D

READ THE ARTICLE

Chuck Yung
EASA Senior Technical Support Specialist

Once upon a time, DC motors oper­ated from batteries or motor-generator sets. For the past 50+ years, most DC motors have operated from solid state power supplies – rectifying AC power to DC power. When motors began operating from rectified power, one of the problems experienced was the presence of AC “ripple” in the leads that were supposed to deliver DC power to the machine. Absent a spe­cific standard, a recurring question is: “How much is too much?” Before I try to suggest an answer to that question, let’s talk about what AC ripple is and explain why it is not desirable.

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? 

Tom Bishop, P.E.
EASA Technical Support Specialist 

Have you ever had to deal with chronic drive end ball bearing failures with a v-belt application? This article will take some of the mystery out of how to determine the load on a bearing, and how to increase the bearing capacity when necessary. The focus will be on bearing loading due to belt pull with v-belt drives. How to modify a motor to accept a cylindrical roller in place of a lower ca­pacity ball bearing will also be detailed. 

Calculating bearing load and life 
The calculation of bearing loading may at first appear to be a daunting task due to the many vari­ables involved. However, taken a piece at a time, the calculations are rather straightforward. An ex­ample will be used to illustrate this point. 

Jasper Fisher 
EASA Past Chairman (1999-2000)

One of the few dimensions on a mechanical drawing which is not directly determined by the designer, but is indirectly determined by the choice of gear pitch diameters of the driver and driven spur gears, is the gear center distance (C). This measurement is the center-to-center separation of the driver and driven gear set.

By Chuck Yung
EASA Senior Technical Support Specialist

There are several methods to operating a three-phase motor using single-phase power to make what would be an otherwise expensive and arduous process a little easier.

So, you told a neighbor you work with electrical equipment and now he thinks you can solve his problem because he or she bought a three-phase motor that can't run on single-phase power. Being asked to convert this motor already sounds like more trouble than it's worth. That's not quite true though. There are some methods to make the process easier.

These methods include:

• The phantom leg method
• Rotary phase converter method
• Variable frequency drive method

READ THE FULL ARTICLE

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.

Por Tom Bishop P.E.
Especialista Sénior de Soporte Técnico de EASA
 
Algunas veces, los cables de salida de los motores no se encuentran  identificados o sus marcas no  son legibles, por lo que se hace necesario  marcarlos para poder  conectar el motor adecuadamente  a la línea de alimentación. Este artículo se ocupará de cómo identificar  los cables de los motores eléctricos con 9 cables de salida y se  basa en la premisa de que ninguno de los  cables se encuentra marcado. Si alguno de ellos estuviera identificado, el procedimiento es el mismo, pero se requerirán menos pasos. Nota: Vea el artículo publicado en  mayo de 2008, en la revista Currents de EASA, titulado “Identifying Unmarked Leads Of 6-Lead Motors With 1 Or 2 Windings”.

Tom Bishop, P.E.
EASA Senior 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 article will address lead identification of three-phase motors with 9 leads, based on the premise that none of the leads are marked. If some of the leads are marked, the process is the same, but may require fewer steps. Note: See the May 2008 issue of Currents for the article “Identifying Unmarked Leads Of 6-Lead Motors With 1 Or 2 Windings.” 

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

Steps to determine characteristics needed for finding a replacement A motor is received from a customer with the request that it be replaced. However, it does not have a nameplate. The steps to determine the motor characteristics needed for identifying a replacement will be described here. These same steps can also be used in the case of repair of a motor without a nameplate, so that a new nameplate with key identification characteristics can be made and attached to the repaired motor. The focus of this article will be NEMA or IEC horizontal motors in standard frame sizes.

Bill Finley and Tyler Gaerke
Siemens Industry, Inc., Norwood, OH

There is always a need to push to higher and higher efficiencies. This can be seen in the revisions to IEEE 841 which pushed efficiencies up to NEMA premium levels. DOE has continued to pass legislation increasing efficiencies to higher levels up to 500 HP. There has also been action recently to establish higher minimum efficiency levels on machines as large as 2500 HP. Motor manufacturers have been motivated to find creative ways to increase efficiency levels through optimization of manufacturing processes, designs, active material increase and better more efficient materials such as magnetic sticks.

To better understand the steps required, it is helpful to understand, how losses are generated and to identify the levers that reduce these significantly, all at an acceptable cost for the investment of the motor. Life cycle costs should also be investigated. 

This paper investigates the impact on the motor performance during starting and normal operation by employing magnetic wedges versus non-magnetic wedges and other potential design changes. The type of induction motor, open (ODP, WPII) or enclosed (TEFC), along with the number of poles, influences the effect on the motor these design changes may have.

Magnetic forces (stresses) acting on the wedges are also investigated in this paper. This paper also discusses qualification processes that are necessary in order to avoid failures and ensure reliable magnetic wedge systems.

This paper covers:

• Designing and testing for NEMA and IEC premium efficiency levels
• History of high efficiency standards activities
• Industrial facility opportunities
• Magnetic wedges (purpose)
• Impact of magnetic wedges on motor performance
• Experimental data for different magnetic wedges
• Qualification of magnetic slot wedges
• Designing with magnetic wedges

Chuck Yung
EASA Senior Technical Support Specialist

One of the pleasures of helping EASA members is in discovering challenges or specific areas where we can improve on the original design of the motor manufacturer. The most recent of these, for me, has been a noticeable cluster of calls about motors with multiple windings. The call usually starts with something like this: "We wound this motor, and one speed was terribly burned." Another one I often hear is: "We rewound both speeds, and the surge test pattern for one speed indicates a winding problem." These are but a couple of examples of a design issue we are seeing with motors having more than one winding. While the use of variable-frequency drives (VFDs) is increasingly common, there are still applications using 2-speed, 2-winding motors. Cranes are a good example of one such application. When a core has more than one winding, the two windings behave as a transformer. Applying voltage to either winding induces voltage in the other winding because the two windings are inductively coupled. As long as both windings are connected 1 wye, and the leads of the second winding are left open, no magnetizing current is drawn by the second winding. When both windings are conventional and symmetrical, this arrangement works just fine. The problems start when either winding deviates from the symmetry that is so important to 3-phase motor performance.

Topics covered include:

• Transformer effect
• Visualizing the current flow
• Parallel circuits

Mike Howell
EASA Technical Support Specialist

Induction motors are most often applied to what are essentially constant speed drive applications. However, the use of induction motors in variable speed applications continues to grow, primarily due to technology advances in power electronics. This webinar will review speed control basics for induction machines.

• Wound-rotor motor speed control
• Squirrel-cage speed control by pole changing
• Squirrel-cage motor speed control by variable voltage, fixed frequency
• Squirrel-cage speed control by variable voltage, variable frequency

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.

This webinar recording covers:

• Insulation system versus insulation materials
• Stresses imposed on insulation systems
• Insulation system components / functions
• Typical testing of system components / functions

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.

Mike Howell, PE
EASA Technical Support Specialist

Unlike their AC counterparts, DC machines do not have rotating magnetic fields. Rather, there are fixed magnetic field axes for the field (direct axis) and armature (quadrature axis). Even though the armature is rotating, the magnetic field axis in the armature is fixed thanks to commutation, which allows the direction of current in an armature conductor to change as it passes from the region under one main field pole to the next.

Mike Howell, PE
Especialista de Soporte Técnico de EASA

A diferencia de sus homólogos de CA, las máquinas de CC no tienen campos magnéticos rotativos. Más bien, existen ejes de campo magnético fijos para el campo (eje directo) y la armadura (eje en cuadratura). Aunque la armadura esté girando, el eje del campo magnético de la armadura está fijo gracias a la conmutación, lo que permite que la dirección de la corriente en un conductor de la armadura cambie a medida que pasa debajo de un polo de campo principal al siguiente.

Much has been written in EASA publications and elsewhere about the consequences of excessive temperature on a motor’s performance. We know that excessive temperature and moisture are the largest contributors to bearing and winding failures. Understanding the source of the increased temperature will help us to correct the problem and improve the machine’s life expectancy.

A chart included in this article illustrates the theoretical impact of increased temperature on the life of the motor insulation system. This chart only addresses the impact of thermal aging and not various other conditions that will affectthe motor’s life. In other words, it says that for every 10ºC increase in operating tem-perature, the expected life is reduced by one-half. Conversely, if we can re-duce the temperature of the motor by 10ºC, we can expect the life to double. Note that this is true at any point on the curve. However, there is the rule of diminishing returns: at some point the cost of designing and operating a motor to run cooler out-weighs the benefts of doing so.  Here we will explore some of the factors that con-tribute to increased temperature.

Topics covered include:

• Overload
• Ventilation
• Voltage
• Electrical steel (core iron)
• Current density
• Circulating currents
• Harmonics

Chuck Yung 
EASA Technical Support Specialist 

Contrary to popular opinion, bigger is not al­ways better. A case in point is the electric motor, the workhorse of industry. There is a natural ten­dency to want a little extra power, “just in case.”

That’s why auto makers still sell cars with 300 hp engines, even though the speed limit may be under 70 miles per hour. But, just like those gas-guzzlers, operating an oversized electric motor may cost additional money; sometimes, a lot of money. Here is a simple procedure for determin­ing the actual hp required by a load, without expensive equipment or engineering. Bear in mind that loads should be determined when the motor is operating at its maximum load. A load that varies widely is a good candidate for a vari­able frequency drive (VFD). 

Contrary to popular opinion, bigger isn’t always better—especially when it comes to electric motors. Plant maintenance and engineering departments like having a little extra power available “just in case,” so they sometimes specify larger motors than applications require. But oversized motors cost more to operate—sometimes a lot more. Fortunately, there’s a simple procedure for determining the actual hp required by a load, without expensive equipment or engineering. Bear in mind that loads should be determined when the motor is operating at its maximum load. Loads that vary widely are good candidates for variable-frequency drives (VFDs), which offer the added benefit of controlling rate of production.

• Topics covered include:
• Estimating actual load
• Cost of "safety margin"
• Real life example
• Power factor and efficiency

READ THE FULL ARTICLE

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

The International Electrotechnical Commission (IEC) standard 60529, “Degrees of protection provided by enclosures (IP code),” addresses the degrees of protection for electrical machines (motors and generators). The “IP” acronym means “international protection” but is sometimes referred to as “ingress protection.” The IP code is commonly displayed on the nameplates of metric machines that are manufactured to IEC standards.

The NEMA MG1 Motors and Generators standards have adopted the IEC standards for IP designations. Although not prevalent on NEMA machine nameplates, the inclusion of the IP marking is becoming more common. In light of this, this article reviews IP code designations and examples of the IP codes for common electrical machine enclosures.

• IP characteristic letters
• IP characteristic numerals
• Typical IP codes

READ THE FULL ARTICLE

Jim Bryan
EASA Technical Support Specialist (retired)

La placa de datos de un motor eléctrico revela mucha información valiosa acerca de la capacidad y desempeño de la máquina. Las normas NEMA MG1-2014 (National Electrical Manufacturers Association Motors and Generators 1) e IEC 60034-8 (International Electrotechnical Commission) brindan información que se debe incluir en la placa de datos para cumplir con las normas.

By Mike Howell
EASA Technical Support Specialist

Right-sizing of three-phase induction motors for different applications – and striking a balance between reliability and efficiency – isn’t always easy, but it can be cost-effective. Before the days of comprehensive predictive and preventive maintenance programs, the conventional approach to reliability was conservatism, both in design and in application. That’s to say that on a 25 hp application, you’d find a very conservatively designed 60 hp motor that was really 75 hp “under the hood.” And yes, the motor would last a very long time, but it would have an inflated (and often ignored) operational cost. Many of these robustly engineered applications are still out there, and it can be well worth the effort to identify and correct them.

Some of the topics covered include:

• New vs existing applications
• Determining the actual load
• Determining typical loading by measuring the average input power
• Line amps
• Locked-rotor amps
• Starting torque
• Special applications

READ THE FULL ARTICLE

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

The wires that are associated with most motor and generator windings are copper magnet wires. For some special application machines, there are other wire types that have been used, such as Litz wire (very fine woven strands) or lead wire. In this article, we will address some issues relating to magnet wire type conversions and combinations.

The term magnet wire brings to mind the thought that the wire is somehow “magnetic,” which is not the case. The reason for the name is that it is wire used in magnetic coils. Thus, they are coils that make use of electro-magnetism. The two physical types are round and rectangular magnet wire. Strictly speaking, square wire is a form of rectangular wire. Having mentioned round and rectangular wire, we will move on to our first topic: the conver­sion of rectangular to round wire.  

An increasing number of manufacturers are using magnetic wedges in their form-wound machines. When a winder fails to replace magnetic wedges in kind, the winding temperature rise can increase by 20°C, and the magnetizing current can increase by 20% or more.

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

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

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

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.

Rick Hoadley
ABB

Whenever an application engineer is planning on installing adjustable speed drives for AC motors, line current harmonics and reflected waves are two factors that need to be addressed. Four basic questions should be answered in order to successfully commission the drive system:

1. What is my power system like today
2. What impact will the additional drives have on the power quality for the other equipment
3. If needed, what harmonics mitigation method should be used
4. How long and what type of cable is used between the drive and motor

This paper, presented at the 2013 EASA Convention, deals with understanding IEEE Std 519 and various mitigation methods in order to meet those recommendations. It also reviews the types of filtering that is available to reduce the reflected waves seen at the motor terminals.

Topics covered include:

• Overview of drives topologies
• The differences between 6,12,18 pulse and active front end drives
• How the differences in drives relate to harmonics generated
• Filters on either end of the drive to mitigate the effects of harmonics, as well as voltage spikes and other potential damaging effects on the motor

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

Un viejo dicho dice: “Si está en blanco y negro debe estar bien”. Ver algo por escrito lo hace más creíble que si se escucha verbalmente. Sin embargo, eso no significa que sea verdad. Siempre deberíamos buscar una justificación que soporte un testimonio, sea escrito o verbal.

Un dicho más reciente dice: “Si está en internet debe ser cierto”. Aplique el mismo concepto aquí. Busque una justificación antes de aceptar información obtenida por internet. Aquí tenemos una colección de algunos de los conceptos errados más comunes acerca de las características de desempeño de los motores eléctricos tipo jaula.

Tom Bishop, P.E. 
EASA Technical Support Specialist 

Motors built to National Electrical Manufacturers Association (NEMA) standards use alphabetical letter codes on the nameplate to designate a number of alternating current (AC) motor characteristics. These characteristics are the code, design, and insulation class.

Read the nameplate carefully as these designations are easily mis­interpreted. Similarly, re-confirm these data items when your customer provides them. For example, the letter “B” could designate a design code, insulation class or kVA code (though highly improbable.) What do these different designations mean? 

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

Correct interpretation of five operating parameters for NEMA, IEC induction motors When someone reads an electric motor nameplate, the normal assumption is that the information can be used at face value. That applies to some but not all of the nameplate information. For example, the power rating (hp or kW) and frame size are specific to the motor. However, ratings such as voltage, frequency, current, speed (rpm) and efficiency have tolerances associated with them. Our focus in this article will be to discuss the correct interpretation of each of these five operating parameters for induction motors of both NEMA and IEC design. Topics discussed include: Voltage and frequency - NEMA MG1-12.44 and IEC 60034-1.7.3 Current - NEMA MG1-12.47 and IEC 60034-1 Speed (rpm) - NEMA MG1-12.46 and IEC 60034-1-12.1 Efficiency - NEMA MG1-12.58 and IEC 60034-1 Note: The letter codes for insulation class, design and kVA code that appear on NEMA motor nameplates are addressed in "Motor Nameplate Letter Code Designations" in the March 2009 issue of Currents.

Jim Bryan
EASA Technical Support Specialist (retired)

The nameplate of an electric motor reveals much valuable information about the capability and performance of the machine. NEMA MG1-2014 (National Electrical Manufacturers Association Motors and Generators 1) and IEC 60034-8 (International Electrotechnical Commission) provide information required to be included on the plate to conform to the standards. 

This varies by the type and size of the motor. For instance, rated field and armature voltages are required for direct current (DC) motors but obviously are not required for alternating current (AC) motors. A table is included that lists the basic requirements applicable to motors. Not all motors will comply with these requirements. These include motors built before the implementation of the standards or outside the jurisdiction of the standards agencies.  Some motors, such as synchronous and wound rotor motors, will have additional requirements. To cover all these is beyond the scope of this article.

Topics covered include:

• Identification
• Power
• Maximum ambient
• Speed
• Phase and voltage
• Code letter
• Design letter
• Efficiency and service factor
• DC motors
• Power factor
• Altitude

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

This webinar addresses the topic of a three phase squirrel cage motor’s ability to successfully accelerate a driven load. Although a motor can drive a running load, that is not assurance that it has the capability to accelerate the load up to rated speed. The difference between success and failure is determined by some complex conditions. For example, the motor torque during starting is not constant, and unless the load is a pure inertia load (very rare), it does not have a constant speed-torque relationship. Key considerations addressed include acceleration time, acceleration torque, motor heating, stator and rotor limits, and torque variables.

Target audience: This presentation will be most useful for service center sales personnel, engineers, supervisors and managers. The content will be beneficial for moderate through highly experienced persons.

Tom Bishop. P.E. 
EASA Technical Support Specialist 

It should not be assumed that because a motor can drive a running load, it also has the capability to accelerate the load up to rated speed. During starting, a mo­tor must deliver the energy required to accelerate the load. To do this, the motor torque must exceed that needed to ac­celerate the load. The motor torque value in excess of the load torque requirement is termed the “torque available for ac­celeration,” as shown in Figure 1. 

Though this explanation appears to be relatively simple and straightfor­ward, there are some complex condi­tions. Namely, that the motor torque during starting is not constant, and unless the load is a pure inertia load (very rare), it does not have a constant speed-torque relationship. Therefore, the torque available for acceleration is the difference between the speed-torque curves for the motor and the load. 

This presentation begins with an overview of ambient, winding temperature rise, and winding temperature. It also covers factors for motor temperature rise limits such as motor size (medium or large), insulation class rating, service factor and the enclosure. The final part of the presentation addresses detectors for measuring winding temperature, namely thermostats, resistance temperature detectors (RTDs), thermocouples and thermistors.

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

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

It’s impossible to balance line-to-line voltages perfectly in three-phase circuits, so they typically differ by a few volts or more. However, if voltage unbalance exceeds 1%, it can markedly decrease the performance and energy efficiency of three-phase motors while increasing the likelihood of premature failure. Avoiding these issues requires a proactive approach that includes installing adequate protective devices and periodically checking for voltage unbalance at the motor terminals.

The article covers:

• What it is
• Common causes
• Effects of unbalanced voltage
• Testing for unbalanced voltages and single-phasing
• Ways to correct unbalanced voltages

READ THE FULL ARTICLE

By Mike Howell
EASA Senior Technical Support Specialist

Process downtime is expensive—even more so when it’s unexpected. So, when an electric motor fails, we tend to pull, repair, or replace it, and move on as quickly as possible. In doing so, however, we may miss an opportunity to capture basic information that could help improve the reliability of the application. With a little planning, these data can be gathered with no delay in startup.

Topics covered include:

• Collect initial data
• Don't destroy two motors
• Help your service center

READ THE FULL ARTICLE

Chuck Yung
EASA Senior Technical Support Specialist

How much no-load current should I expect when testing a motor? We would like to have a ratio of no-load amps / full-load amps, for quality control purposes. Many of us expect a motor to draw approximately one-third of rated current, when operating from rated voltage on our test panel. That is a good rule of thumb - most of the time. While there are lots of exceptions, most of them are predictable.

The intent of this article is to explain why those statements are valid and, in the process, to offer practical guidelines for assessing no-load current. Many of us apply these principles daily. 
Knowledge is power. We should, whenever possible, improve our knowledge by gathering facts: 

• Use the AC Motor Verification & Redesign Program to check densities before rewinding the motor. 
• Keep records of tests for comparison of identical machines. 
• Get information from the manufacturer to supplement your records.

Topics covered in this article include:

• Practical guidelines
• Effects of applied voltage
• Different designs affect rule
• Flux and air gap
• Number of poles
• Considering scale, manufacturing tolerances
• Exceptions to every rule

​Este folleto de 40 páginas ofrece una gran herramienta de marketing para su centro de servicio! Lo utilizan para proporcionar a los usuarios finales con información que le ayudará a obtener la, operación más eficiente y rentable de propósito más larga de los motores eléctricos generales y definidas con estas características:

• Trifásica, motores de inducción de jaula de ardilla fabricados con las normas NEMA MG 1
• Los valores de potencia de 1 a 500 CV (1 - 375 kW)
• Velocidades de 900 a 3600 rpm (8 a 2 polos)
• Tensiones de hasta 1000 V, 50/60 Hz
• Todas las cajas estándar (es decir, DP, TEFC, WPI, WPII)
• Rodando elemento (bolas y ruedas) y los cojinetes de manguito

Este folleto cubre temas tales como:

• Instalación, puesta en marcha y la información de base
• monitoreo y mantenimiento operativo
• Datos del motor y la instalación de línea de base
• Cómo leer una placa de identificación del motor
• recomendaciones de almacenamiento del motor

Este recurso se ofrece como una descarga gratuita (utilizar el enlace más abajo). También puede comprar copias impresas listo para distribuir a sus actuales o potenciales nuevos clientes. La portada de este folleto también se puede imprimir con el logotipo e información de contacto de su empresa (pedido mínimo o 200). Póngase en contacto con Servicio al Cliente EASA para más detalles.

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.

Chuck Yung
EASA Senior Technical Support Specialist

Concerns about partial discharge (PD) used to be limited to repairers and users of machines rated over 7 kV. PD is a common consideration for machines rated 11 kV and higher. This article will describe PD, explain how to detect it, and offer repair solutions.

What is partial discharge?
Air, like Nomex^®, Mylar^®, mica and Dacron^®, is an insulator. Like any insulation, it will break down electrically if subject to too high an im­pressed voltage. Air is capable of with­standing approximately 75 volts/mil (3000 volts/mm), as compared to mod­ern insulating materials rated many times higher. (See Table 1.)

Cyndi Nyberg 
Former EASA Technical Support Specialist 

Power factor can be best explained with a short illustration. Figure 1 below shows the three ele­ments to consider. First, true power, measured in kW, is the power that does useful work. Reactive power, measured in kVAR, is the power that is stored and returned by all inductive machines, such as motors and transformers. The apparent power, measured in kVA, is the voltage multiplied by the current in the system. Even though the true power is doing the work, the power company has to dis­tribute the apparent power. 

Mathematically, the power factor is the cosine of the angle between the true and apparent power. Power factor is defined as the ratio of true power used in an electric circuit to the apparent power, or the power that is apparently being drawn from the source. In a sense, apparent power is “bor­rowed” from the power company. Since AC power is continuously reversing, the borrowed power is sent back to the system every time the al­ternating current reverses. 

Gene Vogel
EASA Pump & Vibration Specialist

Probablemente todo el mundo se encuentra familiarizado con el impacto de los esfuerzos de la eficiencia energética en nuestra industria. Esto ha sido una preocupación y un incentivo para la innovación en los motores eléctricos. Los miembros de EASA y los fabricantes han sido moldeados por las fuerzas gubernamentales y del mercado, destinadas a reducir el uso de la energía eléctrica. Los motores eléctricos son un objetivo primordial de estos esfuerzos "verdes".

Pero el panorama comercial y regulatorio se encuentra en constante evolución y el horizonte que se vislumbra incluye un nuevo enfoque para las bombas y los sistemas de bombeo. El Departamento de Energía de los EE. UU. (DOE) está implementando normas de eficiencia para las bombas rotodinámicas (bombas de flujo centrífugas y axiales). Las normas tendrán poco efecto en el mercado de reparación mientras que los fabricantes se verán directamente afectados. Pero la eficiencia de una bomba es muy diferente a la de un motor eléctrico.

Incluso los estamentos reguladores que escriben los requisitos de eficiencia para las bombas entienden que es el sistema al que está conectada la bomba lo que determina su eficiencia. Tanto Hydraulic Institute (HI) como CSA Group tienen iniciativas en camino para establecer normas para medir y reportar la eficiencia de los sistemas de bombeo.

Este interés emergente en la eficiencia de las bombas y de los sistemas de bombeo, crea oportunidades para los miembros de EASA involucrados en la reparación de bombas que representan a los proveedores o que puedan estar moviéndose en esa dirección.

Gene Vogel
EASA Pump & Vibration Specialist

Everyone is probably familiar with the impact of energy efficiency efforts on our industry. For electric motors, this has been both a concern and an incentive for innovation. EASA members and manufacturers have been shaped by the governmental and market forces aimed at reducing electrical energy usage. Electric motors are a primary target of these “green” efforts.

But the commercial and regulatory landscape is ever evolving, and the horizon coming into view includes a new focus on pumps and pump systems. The U.S. Department of Energy (DOE) is implementing efficiency standards for rotodynamic pumps (centrifugal and axial flow pumps). The standards will have little effect on the pump repair market, while pump manufacturers are directly affected. But pump efficiency is very different from electric motor efficiency.

Even regulators writing the efficiency requirement for pumps understand that it is the system to which the pump is connected that dictates the efficiency of the pump. Both the Hydraulic Institute (HI) and the CSA Group have initiatives in progress to set standards for measuring and reporting pump system efficiency.

This emerging interest in pump and pump system efficiency creates opportunities for EASA members involved in pump repair, who represent pump vendors, or who may be moving in that direction.

Jim Bryan
Especialista de Soporte Técnico de EASA

 El motor de inducción de jaula de ardilla funciona cuando se aplica tensión al bobinado del estator que induce, a través del entrehierro un voltaje en el circuito del rotor. El rotor de jaula de ardilla está formado por un núcleo o paquete magnético con ranuras que alojan un determinado número de barras conductoras y anillos de cortocircuito que fijan todas las barras entre sí. La jaula de ardilla está hecha con  barras conductoras y anillos generalmente fabricados con aleaciones de cobre o aluminio. En la Figura 1 se puede apreciar una jaula de ardilla sin el núcleo o paquete magnético.

Las versiones impresas y en forma de descarga del valioso manual didáctico / recurso de EASA, “Principios de Motores C.A. Medianos y Grandes”, se encuentran ahora disponibles en inglés y en español. El manual incluye gráficos e ilustraciones, fotografías y mucha información técnica sobre máquinas C.A., incluyendo como funcionan, información específica sobre los tipos de encerramientos, fabricación de componentes y aplicaciones.  Muchos de los principios incluidos en el libro aplican a todos los motores C.A., especialmente a aquellos accesorios que fueron asociados en el pasado con las máquinas más grandes (como encoders, RTDs, termostatos, calentadores de espacio, sensores de vibración, etc.).

Las versiones  forma de descarga ofrecen funciones prácticas ya que contienen toda la información que contiene el manual impreso, pero en formato PDF, fácil de usa, ya que contiene marcadores que permiten a los lectores navegar rápidamente por el documento y “saltar” a la página deseada.

Las secciones del manual incluyen:

• Terminología y Definiciones del Motor
• Tipos de Encerramientos de Motores
• Aplicaciones Típicas para Motores
• Consideraciones de Manejo y Seguridad
• Teoría Básica del Motor
• Normas para Motores
• Estatores
• Rotores de Jaula de Ardilla
• Ejes
• Lubricación y Rodamientos
• Accesorios del motor & Cajas de Conexiones
• Procedimientos de Inspección y Prueba
• Alineamiento del Motor, Vibración y Ruido
• Procedimientos de Almacenamiento
• Máquinas Sincrónicas

COMPRAR

This version of Principles of Medium & Large AC Motors manual is now available to address applicable IEC standards and practices. This 360-page manual was developed by industry experts in Europe along with EASA's engineering team. (The "original" version of this book based on NEMA standards remains available as a separate document.)

This manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, information on enclosures, construction on components and applications. Many of the principles included apply to all AC motors, especially those with accessories that are associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters and vibration sensors).

While the manual covers horizontal and vertical squirrel-cage induction motors in the 37 to 3,700 kW (300 to 5,000 hp) range, low- and medium-voltage, most of the principles covered apply to other sizes as well. 

This valuable instructional/resource manual is available in printed and downloadable versions, and focuses primarily on IEC motors.

Sections in the manual include:
(Download the PDF below for the complete Tables of Contents)

• Motor nomenclature & definitions
• Motor enclosures
• Typical motor applications
• Safety & handling considerations
• Basic motor theory
• Motor standards
• Stators
• Squirrel cage rotors
• Shafts
• Bearings & lubrication
• Motor accessories & terminal boxes
• Test & inspection procedures
• Motor alignment, vibration & noise
• Storage procedures
• Synchronous machines

BUY A COPY FOR YOUR OFFICE

PRINTED BOOK DOWNLOADABLE PDF

This book is also available focusing on NEMA Standards — in both English and Español.

NEMA - English NEMA - Español

This valuable instructional/resource manual is available in printed, downloadable and CD-ROM versions.

For this second edition, this 320-page manual has been reorganized, updated with new information, including revised standards and published articles, and edited extensively. The manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, specific information on enclosures, construction of components and applications. Many of the principles included apply to all AC motors, especially those with accessories that were associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters, vibration sensors, etc.).

While the manual covers horizontal and vertical squirrel-cage induction motors in the 300 to 5,000 horsepower range, low- and medium-voltage, most of the principles covered apply to other sizes as well.

This manual focuses primarily on NEMA motors.

Sections in the manual include:

• Motor nomenclature & definitions
• Motor enclosures
• Typical motor applications
• Safety & handling considerations
• Basic motor theory
• Motor standards
• Stators
• Squirrel cage rotors
• Shafts
• Bearings & lubrication
• Motor accessories & terminal boxes
• Test & inspection procedures
• Motor alignment, vibration & noise
• Storage procedures
• Synchronous machines

BUY NOW

BOOK DOWNLOAD CD-ROM BOOK & CD-ROM

This book is also available focusing on IEC Standards ... IEC VERSION

This three-part series focuses on the pump selection process.

• Part 1 - Pump System Basics
  Whether for a new pump application or for a pump replacement, it is important to understand the full range of expected operating conditions, and the system parameters dictated by those conditions. The machine mounting method, its vertical location relative to the liquid level, and environmental conditions must also be considered. This presentation addresses those concerns and introduces the process of properly selecting a pump for a particular application.
• Part 2 - Pump System Concerns
  When requesting a proposal for a new or replacement pump, a customer may provide you with specific pumping parameters, such as required head, flow and NPSH – or not. It is helpful when specifying a pump, to understand the system parameters that determine those required pumping parameters. This presentation will go over the basics of determining system parameters for pump applications.
• Part 3 - Series and Parallel Pumps
  There are many guidelines for designing multiple pumps for a single system. The most basic concern is to understand the requirements when multiple pumps are arranged in series and/or in parallel. Also, the design of systems has been become more flexible with the availability of variable speed drives, which are often applied in multiple pump installations. This presentation addresses those concerns and sheds some light on issues that result from misapplication.

This presentation takes the mystery out of pump curves and provides viewers with the necessary knowledge to determine pump operating points, efficiency and horsepower. The exclusive parameters that determine if a pump is likely to cavitate are also discussed.

Target audience: This presentation is intended for application engineers, sales personnel, managers and interested pump technicians and supervisors.

Reclosure occurs when power to a motor is briefly interrupted and restored before the magnetic field has fully collapsed in the motor’s winding. If this occurs while the applied power is out of phase with the collapsing field, significant damage can result. This webinar will address how this can happen and what measures can mitigate damage potential.

Topics covered include:

• Reclosing a switch or breaker before the magnetic field collapses
• Utilities’ automatic reclosure
• Contactor “chatter”
• Determining the time constraint
• Remedies: Time delay; Zero crossing

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 

Cyndi Nyberg 
Former EASA Technical Support Specialist 

Have you ever wondered why the shaft of an electric motor is often larger than that of the driven equip­ment? One reason for this is that the standard shaft sizes specified for the standard NEMA frame machines are larger than the minimum required, as we will see in the examples below. Manufacturers tend to design using an ample safety factor. Given the dire consequences if a shaft breaks, that is understandable. 

Even so, the difference between a T and TS shaft can raise questions for those unfamiliar with mechanical design. It is important that the shaft is large enough to (a) transmit the required torque without exceeding the maxi­mum allowable torsional shearing stress for the shaft material, and (b) prevent torsional deflection, or twisting, during service. All this, with a substantial safety factor. 

There are certain repair processes, such as winding removal and replacement, that can impact the efficiency and reliability of electric motors. Prudent repair practices must not increase overall losses, and preferably should maintain or reduce them.

This presentation explains how those repair processes affect efficiency and reliability, and gives the best repair practices in order to maintain or improve efficiency.

Target audience: This presentation is most useful for service center inside and outside sales representatives, customer service personnel, engineers, supervisors and managers. The content will be beneficial for beginners through highly experienced persons.

Chuck Yung
EASA Senior Technical Support Specialist

When a customer calls and wants to replace his diesel or gasoline engine with an electric motor to drive a piece of machinery, it’s easy to assume that “horsepower is horsepower.” Not so fast! It turns out that there are many different ways to measure power. The term horsepower was adopted by James Watt in the late 1700s to compare the output of steam engines to draft horses. Aside from North America, most of the world uses the International System of Units (SI) unit watt to describe power output. Since the 1700s, we have mechanical hp, kW, metric hp, electric hp, hydraulic hp, drawbar hp, brake hp, shaft hp and even variants of taxable hp. Leave it to governments to want a piece of the action.

The purpose of this article is to increase awareness about the many factors which must be considered when making such a seemingly simple substitution.

Gene Vogel
EASA Pump and Vibration Specialist

Resonance is a property of all mechanical structures. It can be described as a sensitivity to a certain vibration frequency. For machinery such as electric motors, pumps, turbines, etc., it becomes a problem when small vibratory forces from the machine operation are amplified by mechanical resonance. The result can be very severe vibration levels, even when the exciting forces are small. Often resonance is encountered when a speed change has been implemented, as with retrofitting a VFD or operating a 50 Hz motor on 60 Hz power.

The most common example of resonance is when the structure supporting a machine is resonant at or near the rotating speed of the machine. Even slight vibratory forces from residual unbalance and misalignment will excite the resonant base structure, resulting in severe vibration. The machine components can also be resonant. There are many examples of 2-pole electric motors where a resonant endbracket caused very high axial vibration at 1 x rpm or 2 x rpm.

A second category of resonant conditions occurs when the resonant component is the rotating element of the machine. This is common with gas and steam turbines, centrifugal pumps and 2-pole electric motors. While the result is similar (high vibration when a certain operating speed is reached), this is a more complex phenomenon. When the operating speed reaches the resonant frequency of the rotating element, the rotating element actually distorts and the vibratory forces increase significantly.

There is a need to distinguish between these two types of resonance. The first, where a supporting structure or non-rotating machine component is resonant, is usually referred to as a “structural resonance.” The second, where the rotating element is resonant, is known as the “rotor critical speed.” This leaves the term “critical speed” (without the word “rotor”) somewhere in limbo.

Technically, a critical speed could be either a structural resonance or a rotor critical speed. For the sake of clarity it’s best to avoid using that term. The simple term “resonance” can be applied to both conditions to avoid confusion.

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

The EASA/AEMT Rewind Study was published in 2003, prior to the introduction of premium efficient (IE3) motors. The recently completed follow-up study evaluated motors with premium efficiencies to confirm that, as with the earlier study, the efficiency of these motors can be maintained during rewind and repair by using established good practices.

This webinar covers the results and the technical details of this most recent study.

It will benefit service center managers, customer service representatives, sales representatives, supervisors and technicians.

Chuck Yung 
EASA Technical Support Specialist 

One of the more common sources of exaspera­tion for a winder is rewinding a motor that has odd turns. How would you like to find a better way to deal with odd turns? Here are some tips to make life easier for the winder: 

This webinar recording covers: 

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

Cyndi Nyberg 
Former EASA Technical Support Specialist 

When manufacturers design a motor, there are many variables. For a given stator, the winding has to conform to some fairly rigid rules, and there is not a lot of variance, even among different manufacturers. However, the rotor de­sign is wide open. The variables in the rotor design include: the number of bars, bar material, bar shape, end ring design, skew, air gap, and construction (cast or fabricated). All of these will ultimately have an impact on the speed torque characteristics of a motor. 

Unfortunately, because of the rotor design, it is difficult to alter the basic shape of the speed torque curve of a motor in for repair by modifying the stator winding. Modifications can be made to the rotor such as changing the bar material or size, and changing the end ring design, but it is difficult to determine the actual effect they will have on the operating characteristics. 

Jim Bryan
EASA Technical Support Specialist (retired)

The most stressful time for electric motors is during starting. The speed-current curve in Figure 1 illustrates why. At starting, the motor current is the highest it will ever be. This is referred to as starting or locked rotor current. These different terms describe that when the shaft speed is zero, the current is maximum. Note also the impact of applied voltage to the current characteristics. This will be discussed later.

Many performance parameters of the motor are directly proportional to the current. The parameter of most concern in this article is the heat produced which is proportional to the square of the current as represented by P = I²R. Where P is the power lost in heat (kilowatt-hours [kW•h]) due to the square of the current flow (I²) through a resistance (R). Once the motor has been successfully started, the load current level is reached and the cooling circuit of the motor is able to dissipate the additional heat produced by the starting current. Restarting the motor before this additional heat has been dissipated means more heat in the form of kW•h will be added on top of that which is there. Each subsequent start before the additional heat has been dissipated will add more heat — raising the temperature until some component in the motor reaches its failure point.

The limiting factor as determined by the design is the temperature increase resulting in component failure in a squirrel cage induction motor of one of three components: the winding, the rotor bars or the rotor shorting end rings. Depending on the design, the thermal “weak link” could be any of these.

Jim Bryan
EASA Technical Support Specialist (retired)

There are many misconceptions about Service Factor (SF) in the industry. Some feel it is meant for temporary excursions into overload conditions; others consider it to be an allowance for permanent overload. The truth is that it is neither. As defined in the EASA Technical Manual and NEMA MG1, the definition of service factor is:

"A multiplier which, when applied to rated power, indicates a permissible power loading that may be carried under the conditions specified for the service factor."

The NEMA MG1-2011 theory of SF says that a motor is thermally capable of overload to that point within the insulation class at normal service conditions.

Since any increase in load increases the current, this overload will increase the operating temperature of the motor. For every increase of 10ºC, the motor winding expected life is reduced by one-half. It does not matter what the source of that increase in temperature is; overload, poor ventilation, low voltage or high ambient temperature are just a few.

Gene Vogel
EASA Pump & Vibration Specialist

Service centers are often called on to provide replacement pumps or pump motors or to advise on pump retrofit and re-application projects. A good understanding of the parameters that govern pump performance is essential to help customers with these opportunities. The information here relates to rotodynamic pumps (centrifugal and axial flow impellers) and not to positive displacement pumps.

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.

By Chuck Yung
EASA Senior Technical Support Specialist

It’s fair to say that one’s outlook on life is colored by experience. A good example of this with sleeve bearing motors is the question, “What’s the proper clearance between a shaft and the sleeve bearing it rides in?” Chances are each of us has a rule of thumb for this, probably related to shaft diameter. Some of these may look familiar:

• One thousandth, plus 1 per in. of diameter
• Two thousandths, plus 1 per in. of diameter
• 0.0015 in. per in. of diameter
• 0.002 in. per in. of diameter

They can’t all be right, yet many of us may have used one of these rules (probably not the same one, either!) with great success. Which one, if any, is correct? The answer depends on the application.

READ THE FULL ARTICLE

Tom Bishop, P.E.
EASA Technical Support Specialist 

The speed-torque characteristics of three-phase motors are an important consideration when selecting a replace­ment. If an incorrect design type is chosen for the new motor, the motor may not start the load, or the motor may draw excessive starting current and consequently trip overload protective devices. When it comes to repair, at times a squirrel cage rotor is determined to have an open circuit and will need to be rebarred. 

It is the rotor bar and end ring material and physical shape that have the greatest effect on starting as well as running performance. Simply put, the rotor design determines motor Association) standards fall into four major categories, or design types. These are identified on the motor nameplate as design A, B, C and the less common D. There was a design E designation that NEMA withdrew a few years ago. What are the differ­ences between the design types? We will define the starting characteristics and examine these different designs. Note: IEC (International Electro-technical Commission) motors do not have design type designations. 

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.

Mike Howell
EASA Technical Support Specialist

Aside from managing his family’s brewery in England, J.P. Joule did some pretty amazing work in physics dur­ing the mid-nineteenth century. Joule discovered that the rate at which heat is produced by a steady current in any part of an electric circuit is proportional to the resistance and the square of the current. So, the I²R loss of a conductor is not creatively named.

How does this apply to motor stator windings? The stator I²R loss is typically the largest contributing factor to the stator winding tempera­ture rise and the largest detractor of efficiency.

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.

By Mike Howell
EASA Technical Support Specialist

The switched reluctance motor (SRM), also known as the variable reluctance motor (VRM), originated in the mid-1830s. It was first used as a locomotive traction motor. However, the power electronics necessary for satisfactory control of SRMs were not patented until the early 1970s. This entailed electronic commutation synchronized with rotor position. Service centers are seeing an increase in the number of SRMs received for repair, and some of the technicians encountering them are unfamiliar with how they work. As with any other rotating machine, a basic understanding of operating principles can be useful in troubleshooting and repair. One of the most critical things for service center personnel to understand upfront is that these machines cannot be operated without a special drive, which typically would need to be supplied by the end-user or the manufacturer.

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.

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 presentation covers: 

• What is classic pump cavitation?
• The NPSHA – NPSHR relationship
• How to identify the evidence of cavitation
• Other types of cavitation

Chuck Yung
EASA Senior Technical Support Specialist

Anyone who has spent much time reading the EASA AC Motor Redesign book, or motor design textbooks, will recall that there are certain stator-rotor slot combinations that can detract from the performance of an electric motor.

Cyndi Nyberg 
Former EASA Technical Support Specialist 

NEMA MG-1-12.45 states that motors shall operate successfully under running conditions at rated load with a variation in the voltage or the frequency up to the following: 

• Plus or minus 10 percent of rated voltage, with rated frequency. 
• Plus or minus 5 percent of rated frequency, with rated voltage. 
• A combined variation in voltage and frequency of 10 percent (sum of total values) of the rated values, provided the frequency variation does not exceed plus or minus 5 percent of rated frequency. 

Austin Bonnett
Austin Bonnett Engineering, LLC
Gallatin, Missouri
EASA Education and Technology Consultant

The three-phase squirrel cage in­duction motor is a very robust machine that can operate over a wide range of voltage conditions;  it is the workhorse of the industry. However, for optimum performance and life expectancy, the voltage supply should be a balanced three-phase sine-wave voltage, and its magnitude should be as close to the nominal voltage stated on the motor nameplate as practical. 

Jim Bryan
EASA Technical Support Specialist

When designing or redesigning an electric motor, there are many trade-offs. For instance, opening up the air gap to improve power factor might diminish the efficiency. For every action taken in adjusting the motor’s design, there is a reaction at some other point that affects the motor’s performance.

One of the critical considerations involves the interaction of the turns per coil and pitch. As you shorten the pitch, it requires more turns to generate the same torque. But, as you increase the number of turns, the wire takes up more space in the slot. The way to overcome this problem is to decrease the wire size. But decreasing the wire size decreases the current density, in­creasing the I²R losses and operating temperature. 

By Jim Bryan
EASA Technical Support Specialist (retired)

Much has been said and done to produce the "perfect" fit for rolling element bearings in motors and other rotating equipment. Assembly of these machines requires that either the inner fit to the shaft (journal) or the outer fit to the housing (bore) is able to slide; so if one fit is tight, the other must be loose. While "tight" and "loose" are relative terms that must be defined in the quest for the perfect fit, any fit that's too loose or too tight can lead to early bearing failure and costly downtime.

A tight (interference) fit is usually recommended for motor bearing journals. Standard fits for radial ball bearing journals range from j5 to m5; the standard housing fit is H6. These are the "standard" fits and may be different depending on the machine designer's understanding of the application.

READ THE FULL ARTICLE

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

Aunque la tracción magnética desbalanceada puede afectar a otras máquinas eléctricas rotativas, como los motores y generadores de CC y monofásicos, nuestro enfoque en este artículo se centrará en los motores jaula de ardilla trifásicos. Los dos temas principales son: La tracción magnética desequilibrada (UMP) y el descentrado del rotor (pullover). Para mayor claridad, comenzaremos por definir y explicar brevemente estos términos.

Richard Huber, P.E.
Richard Huber Engineering, Ltd.

Transformers are fundamental to an industrial or utility distribution or transmission system. This article will present basic transformer information that may help the reader appreciate how they operate and their many features. 

Many people consider a transformer to be one of the more basic of electrical machines. As a result, many of the design and operational characteristics are taken for granted. From time to time, it may be beneficial to review these characteristics and refresh one’s understanding. Some of the basic concepts are discussed in the following sections. 

Most of the information presented here will be limited to transformers with two separate windings.

Topics covered in the article include:

• Transformer design—how a transformer works
• Volts, amps and flux
• Wind polarity
• Excitation current
• Regulation and efficiency
• Winding taps
• Types of transformers
• Wound cores and stacked cores
• Shell type and core type transformers
• Single-phase and three-phase transformers
• Dry type and liquid filled transformers
• Isolating and shield transformers
• Auto transformer

This recording covers theory of operation, inspection, operation and troubleshooting tips for AC generators and alternators. For the supervisor, field service technician or service center personnel, generators can present unique challenges. Topics covered include:

• Theory of operation
• Testing tips
• Stator winding cautions
• How to interpret the exciter motor connection
• In-shop and on-site testing methods
• How to test the voltage regulator
• How to test a generator without a regulator

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

Although unbalanced magnetic pull can affect other rotating electric machines such as DC motors and generators and single-phase motors and generators, our focus in this article will be on three-phase squirrel cage induction motors. The two main topics are unbalanced magnetic pull (UMP) and rotor pullover. For clarity we will begin by defining and briefly explaining these terms.

Herb Prychodko 
Kentucky Service Co., Inc.

Lexington, Kentucky The advent of Variable Frequency Drives (VFDs) has allowed many applications to take advantage of the increased controllability of AC motors. This has resulted in a large increase in the use of these devices. However, an unwanted consequence of using VFDs is the distortion of the supply’s fundamental sine wave, commonly referred to as line harmon­ics. There are two types of harmonics, current and voltage. Remedial methods for both will be covered in this article.

Tom Bishop, P.E. 
EASA Technical Support Specialist 

How do we know if a motor is operating within its temperature rating? The simple answer, and a good one, is that the National Electrical Manufacturers Association (NEMA) has defined temperature rise for electric motors in Motors and Generators, NEMA standard MG 1-1998. In this article we will focus on temperature rise and tem­perature sensing of three-phase induction motors. 

We will begin by identifying some key terms. Temperature rise is the increase in temperature above ambient. Ambient temperature is the tempera­ture of the air (or other cooling medium) in the area surrounding the motor, frequently termed “room temperature.” The sum of the ambient temperature and the temperature rise is the overall, or “hot,” tem­perature of a component. Insulation temperature classes are based on the overall temperature. For ex­ample, a Class B winding system is rated 130ºC. The normal maximum ambient, per NEMA, is 40ºC. The temperature rise limit for the Class B winding would be estimated at 90ºC (130-40). 

Chuck Yung
EASA Technical Support Specialist

Member Question: We recently received a rotating frequency converter for repair. It appears to be a wound-rotor motor coupled to an induction motor. The drive motor is not the same speed as the wound-rotor motor. How does this work?

The rotating frequency converter is exactly as you describe. Usually the drive motor has fewer poles than the wound-rotor motor, so the wound-rotor motor is driven faster than its synchronous speed to increase the frequency of the output.

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.

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

What are the normal conditions for which a motor is designed? This is a question that does not often come up except when there is an issue with a motor application.   

The NEMA MG1 motor and generator standards provide details on this subject by defining usual and unusual service conditions. The IEC 60034-1 standard, “Rotating Electrical Machines, Part 1 Ratings and Performance,” also addresses some application conditions in clause 6, though not to the extent given in MG1. Our focus here will be on MG1 since it provides greater detail than IEC 60034-1.

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

We in the apparatus repair business don’t always realize how global our work is until a cus­tomer sends in a motor to be redesigned for use on a different frequency. The most common frequen­cy conversion requests are between 50 and 60 hertz (Hz). Motors intended for use in North America typically are rated at 60 Hz, whereas most of the remainder of the globe uses 50 Hz. 

The speed of a three-phase mo­tor is determined by the number of poles and the frequency. As much as we are aware of this relationship, it remains a mystery to most end users. How often have you had a customer simply request changing a 4-pole motor from 50 to 60 Hz? They want to maintain the speed at about 1500 rpm. Not only is it impossible, there are other considerations related to the type of load that must be taken into account. 

Chuck Yung
EASA Senior Technical Support Specialist

Vertical motors differ from horizontal motors in numerous ways, yet some view them as “just a horizontal motor turned on end.” The obvious differences are the (usually) thrust bearings, with arrangements varying from single- to three-thrust bearings with different orientations suited for specific load, rpm and applications.

Less obvious differences are in the ventilation arrangements, shaft stiffness, degrees of protection and runout tolerances. This session will include:

• Bearing systems: Single, double or more?, Thrust direction, Angle of contact and rpm, Spherical thrust bearings, hydrodynamic
• Ventilation and cooling
• Operating environment, and enclosures: Enclosures (degrees of protection), ODP, TEFC, WPI, WPII (IP equivalents)
• Oil types and quantity: Bearing load and operating temperature, Consideration of speed, Sizing and adding cooling tubes
• Runout tolerances and repair methods: Upper bearing housing, Bearing carrier and shaft, Bottom bracket flange, Best practice methods for re-machining

This recording will benefit the service center owner, supervisor, technicians, sales personnel and customer.

Mike Howell, PE
EASA Technical Support Specialist

Most EASA service centers encounter very few axial-flux machines. They are rare enough that it is worthwhile to describe what they are and how they differ from the typical radial-flux industrial motor or generator. Figure 1 shows a cutaway of an axial-flux machine on the left and a radial-flux machine on the right. The gold regions represent the energized stator windings and the green regions represent the rotor windings or permanent magnets. Note that the axial-flux machine shown has two rotors; a rotor winding on either side of the stator. The radial-flux machine is what most EASA service centers are accustomed to; a rotor separated from a stator by an air gap in the radial direction and a magnetic field that crosses that air gap to link both windings (or windings and permanent magnets) in a way that can produce useful torque.

Jim Bryan
EASA Technical Support Specialist

We often hear from members that a customer has reported that a motor that has been repaired is now run­ning hot. We always ask how hot and the reply frequently is:  “Well, I can’t hold my hand on it!” Let’s think about that answer for a minute. The typical human can tolerate about 60-65ºC (140-150ºF) depending on calluses, threshold of pain, how many people are watching, etc. Remember that number as we discuss typical motor operating temperatures.

​

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