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.

Mike Howell
Especialista de Soporte Técnico de EASA

Las dos razones principales para realizar la prueba de núcleo del estator en el centro de servicios son (1) verificar que el núcleo del estator es apto para uso continuo y en caso de rebobinado y (2) verificar que el proceso de rebobinado no ha alterado de forma adversa la condición del núcleo del estator.

El propósito de este artículo es discutir como determinar, evaluar y comparar los resultados de la prueba de núcleo. Es muy importante comprender que la variación de los procedimientos de prueba puede invalidar la comparación.

David Sattler
L&S Electric, Inc.

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

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

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. 

Gene Vogel
EASA Pump & Vibration Specialist

A customer specifies that the rotor is to be balanced to 4W/N. Is that the 4W/N Military specification, or the 4W/N API specification?It could make a big difference. And, how do they compare to the ISO 1940/1 specification (G2.5, G1, etc.)? Fortunately, for symmetrical rotors, comparing the various standards is only a matter of a bit of easy algebra. For non-symmetrical rotors, the process gets a little more difficult because each of the specifications handles these cases differently. The other good news is that there are on-line references that provide graphic and tabulated comparisons.

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

Reconnections covered include:

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

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

Mike Howell
EASA Technical Support Specialist

The two primary reasons for performing stator core testing in the service center are (1) to verify that the stator core is acceptable for continued use and in the event of a rewind, (2) to verify that the repair process has not adversely changed the stator core condition. This testing can be done using a commercial core loss tester or a manual loop test using an appropriate AC source, cables and meters. Some typical reasons a manual loop test may be performed are: 

• Customer or service center preference / specs 
• Commercial core loss tester not available 
• Stator size is inappropriate for available commercial core loss tester 

Additionally, some service centers have forgone core loss testing on small stators for various reasons including difficulties with test configuration, calculations, cost or even appearance. The purpose of this article is to explore a low-cost test setup for loop testing small stators.

Matthew Conville, P.E.
EASA Technical Support Specialist

When we consider putting a machine into service, we must consider the duty rating of the machine. If we do not, there is a good chance that the machine being placed into service will have thermal degradation of the windings. Not every application is created equal. For example, a crane motor doesn’t need the same duty rating as a punch press motor that runs continuously, even though they may have the same horsepower ratings. Likewise, a chop saw motor wouldn’t need to have the same duty rating as a pump motor where the pump is operated continuously.

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. 

This webinar recording focuses on:

• Motor assembly issues
• Electrical and mechanical inspection
• Static and run testing
• AC motors with ball, roller and sleeve bearings

Target audience: This webinar recording is most useful for service center mechanics, supervisors and engineers. The content will also be beneficial for machinists, managers and owners.

A special discounted collection of 11 webinar recordings focusing on AC motor electrical procedures.

Once purchased, all 11 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

The Basics: Motor Repair Burnout Procedures
Presented October 2016

• Interlaminar insulation materials / properties of AC stators
• Core testing before and after
• Processing equipment, controls and records

The Basics: The Why and How of Core Testing
Presented October 2016

• The reasons for performing core testing and why they are important
• An explanation of the two core testing methods:
• Loop testing
• Use of a core tester
• How to properly perform a core test
• How to assess the results
• Stator Core Testing: Know What You Have Before You Wind It

Stator Core Testing: Know What You Have Before You Wind It
Presented April 2017

This presentation covers:

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

High Potential Testing of AC Windings
Presented December 2019

High-potential testing is routinely used to assess the ground insulation of AC stator windings in-process, after completion of a rewind and post-delivery. This webinar covers:

• Differences between AC and DC high-potential tests
• Sizing AC test sets when testing large windings
• What relevant standards address (and what they don’t)
• Communicating test requirements to all stakeholders
• When to test and at what levels
• How to evaluate results

Target audience: Beneficial for service center managers, supervisors and technicians responsible for high-potential testing.

Squirrel Cage Rotor Testing
Presented October 2014

Determining whether or not a squirrel cage rotor is defective is an issue that is a challenge to every service center as there is often no simple way to determine the integrity of a rotor. The primary focus of this session is to describe many of the available tests that can be utilized in the service center or at the motor installation site. In addition to conventional squirrel cage rotor testing methods such as the growler test, techniques that will also be covered are the use of a core loss tester, high current excitation, and spectrum analysis of vibration.

Target audience: This presentation will be most useful for service center and field technicians with at least 2 years experience, service center supervisors and managers, engineers, or anyone with previous experience dealing with suspected open rotor issues.

Evaluating High No-Load Amps of Three-Phase Motors
Presented December 2011

This presentation focuses on the steps to take before rewinding to avoid the undesirable situation of high no-load motor amps after the rewind.

The presentation covers the following steps that should be performed on every AC stator rewind:

• Inspect the stator bore and rotor outside diameter for evidence of machining or damage
• Record the original winding data exactly as found
• Verify the winding data
• Test the stator core before and after rewinding removal

Target audience: This is most useful for service center mechanics and winders with any level of experience, and service center supervisors and managers.

Insulation Technology Improvements and the Repair Market
Presented July 2019

Most modern rotating electric machines operate on the same principles their predecessors have for 100+ years. However, improvements in materials technology over that time have allowed for increasingly greater power density in machine design.

There is a natural time lag between OEM technology improvement and repair of equipment containing that technology. This session will explore some of these improvements and their implications for service centers attempting to provide a quality repair.

Target audience: This webinar will be appropriate for service center managers and technicians responsible for rewind activities.

Motor Temperature Rise and Methods to Increase Winding Life
Presented December 2018

This webinar discusses:

• Temperature rise: Method of detection, Insulation class, Enclosure, and Service Factor
• Increasing winding life: Insulation class, Cooling system, and Winding redesign

Target audience: This will be most useful for service center engineers, supervisors, managers and owners. The content will also be beneficial for mechanics and winders.

Air Gap: What It Is, What Does It Do, and Why Is It Important?
Presented October 2019

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 explains 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.

Troubleshooting AC Generators & Alternators
Presented May 2015

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

Core Repair and Restack Techniques
Presented April 2014

This webinar teaches:

• How to repair damaged stator cores and how to know when a restack is necessary.
• There are often cases when repairs can be accomplished without a labor intensive restack.
• When a restack is required, there are pitfalls to watch out for to avoid problems with geometry, vibration and core losses.

Target audience: This presentation is useful to the supervisor, winder and sales personnel who interact with the end user.

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.

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

This 4-page motor service order form provides fields to record:

• Customer contact information
• Nameplate data
• Reason for service
• Inspection activity checklist for the stator and rotor
• Incoming inspection notes
• Winding tests
• Rotor single-phase test
• No-load test
• Mechanical inspection before and after repair
• Winding tests after rewind but prior to treatment
• Winding tests prior to assembly
• No-load run test
• Shipping details

Presented by Matthew Conville, P.E.
EASA Technical Support Specialist

This webinar goes through the basics of what accessories may be needed for proper VFD control and power quality add-ons to improve motor driven system reliability. Just buying and installing a VFD isn’t enough to ensure proper operation of a motor driven system in its application, nor does it protect upstream and downstream devices from power quality issues. Topics include:

• Drive accessories
  • Operator panels, encoders, position encoders, communication devices
• Power quality accessories
  • VFD cables and EMC terminations
  • Input reactors and/or isolation transformers
  • Output filters (reactors, dV/dt, sinusoidal, inductive chokes, etc)
• Impacts on AC motors
  • Reduction in SF
  • Winding failures
  • Shaft voltage/bearing currents
  • Turn down ratios

This presentation will be useful for anyone new to VFD applications, or anyone in need of a refresher course. 

Gene Vogel
EASA Pump & Vibration Specialist

Proper alignment of direct-coupled machinery is an essential element in reliability of a new or repaired machine (motor, pump, gear case, etc.). One common impediment to achieving proper alignment and smooth opera­tion is a “soft foot” condition. 

A soft foot occurs when all the feet of a machine case do not sit flat on the supporting base so that tightening the foot bolts causes distortion of the ma­chine case. The source of the soft foot could be a baseplate which is not flat or machine feet which are distorted. Not only does this make it difficult to align the machine, but the casing distortion may add additional load to the bearings and create internal mis­alignment between the rotating and stationary elements of the machine resulting in poor performance and increased vibration.

This video walks through the steps to adjust and set end play on a typical vertical hollow shaft pump motor. Proper end play adjustment is important to keep the lower bearing from supporting the weight of the rotor and to allow for thermal growth within the motor.

The motor in this video has a thrust bearing in the top and a standard ball-type guide bearing in the bottom, which is typical of vertical pump motors. There are other bearing arrangements with somewhat different procedures for setting end play, but here we’ll be working with the most common arrangement and procedure. There are variations of this process, and some vertical pump motor bearing arrangements require special procedures, especially those with springs mounted under a spherical roller thrust bearing.

Topics covered include:

• Tools and supplies needed
• Basic principle of end play adjustment
• How to adjust end play
• How to measure and verify proper end play

Scott Clark, Ph.D., P.E.
Brandon & Clark, Inc.

Traditional rotor bar defect detection systems are often insufficient in sensitivity, record-ability and numerical analysis of test results. Many means of rotor defect detection require the motor to be fully assembled with a functional stator. These limitations have laid the groundwork for the development of a new rotor defect detection technique.

A new method termed Rotor Magnetic Field Analysis (RMFA) extends traditional induction motor rotor testing techniques with precision magnetic field measurements and data processing tools. This is the first new technology in rotor testing in more than three decades.

Ever had a customer return from camping and complain of a distinct odor of burnt electronics filling the air? The next thing that RVer knows, the water pump quits and the AC stops working. The consumer flips the switch for a circulating fan, but nothing happens. Even the stabilizer jacks will not operate.

If so, the culprit may be voltage variation from the incoming power source, which sometimes is hundreds of feet from the distribution transformer that supplies the varying demands of all the RVs connected to it. While that prime campsite might be perfect for the user, voltage variation can be hazardous for the RV’s electrical devices—especially its electric motors.

This article covers:

• Voltage variation
• High and low voltage effects on motor performace and reliability
  • Energy efficiency
  • Current
  • Temperature rise
  • Overload capacity
• Imporatnce of checking service voltage

READ THE COMPLETE ARTICLE

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.

Gene Vogel
EASA Pump & Vibration Specialist

La especificación ISO para balancear rotores rígidos (ISO 1940-1) fue innovadora cuando fue introducida hace varias décadas. Esta norma estableció los Grados de Calidad de Balanceo basada en la velocidad teórica que el centro de masa de un rotor se encontraría en espacio libre, girando a la velocidad de funcionamiento normal del rotor. Esta es terminología técnica difícil de expresar, pero un entendimiento práctico de la naturaleza de las fuerzas de desbalanceo es importante para aplicar las tolerancias de balanceo en rotores de diversas máquinas. Esto también ayuda a entender el impacto de los cambios fundamentales en la reciente norma de reemplazo: 21940-11: 2016.

Primero, vamos a clarificar la diferencia entre desbalanceo y vibración. Si una máquina tenía cierta cantidad de desbalanceo y fue asentada sin restricciones sobre un acolchado suave (una almohadilla de caucho), existirá cierta cantidad de vibración a 1x rpm. Atornille esa misma máquina a una fundación maciza y la vibración a 1x rpm será mucho menor. Así que no hay conversión directa de desbalanceo a vibración y viceversa.

Por consiguiente, para maquinaria en funcionamiento, las unidades de amplitud de vibración comunes de desplazamiento y velocidad no son medidas directas del desbalanceo, La cantidad de desbalanceo del rotor se puede describir como una cantidad de masa (peso) en un radio determinado.

El artículo continúa cubriendo:

• Unidades de desequilibrio
• Dos posibles aproximaciones para el uso de planos de cojinetes para evaluar la tolerancia de equilibrio
• Desplazamiento del centro de gravedad

Gene Vogel
EASA Pump & Vibration Specialist

The ISO balancing specification for rigid rotors (ISO 1940-1) was innovative when it was introduced decades ago. It established Balance Quality Grades based on the theoretical velocity the mass center of gravity of a rotor would encounter in free space, spinning at the rotor’s normal operating speed. That’s a mouthful of technical jargon, but a practical understanding of the nature of unbalance forces is important in applying balance tolerances to various machine rotors. It is also helpful in understanding the impact of fundamental changes in the recent replacement standard, 21940-11: 2016.

First, let’s clear up the difference between unbalance and vibration. If a machine had a certain amount of unbalance and was sitting unrestrained on a soft pad (a durometer pad), there would be a certain amount of vibration at 1x rpm. Bolt that same machine to a massive foundation and the vibration at 1x rpm would be much less. So there is no direct conversion from unbalance to vibration or vice versa.

Consequently, the common vibration amplitude units of displacement and velocity are not direct measures of unbalance for operating machinery. The amount of rotor unbalance can be described by an amount of mass (weight) at a certain radius.

The article goes on to cover:

• Unbalance units
• Two possible approaches to using bearing planes to evaluate balance tolerance
• Displacement of center of gravity

Tim Browne
Industrial Electric Motor Service, Inc.

Sospecho que casi todos en nuestra industria alguna vez han tenido el placer de reparar un motor “fabricado con requisitos especiales”. Este tipo de motor está construido para un propósito específico y tiene características que le pueden permitir funcionar bajo condiciones no habituales. Debido a la información limitada que algunos de ellos muestran en su placa de datos, la reparación de estos motores puede resultar un reto.

Chase Fell
Precision Coil and Rotor

Un aislante ideal no permite el flujo de la corriente de fuga. El factor de potencia de un aislante se define como el coseno del ángulo de fase entre el voltaje y la corriente. En un aislante ideal, la corriente adelanta al voltaje exactamente 90 grados y en este sistema ideal el factor de potencia sería cero. Los sistemas de aislamiento de las bobinas de los motores y generadores eléctricos tienen pérdidas inherentes que causan el flujo de corrientes capacitivas y resistivas (Ver Figura 1). Para estos aislamientos, el factor de potencia no puede ser cero. 

El factor de potencia tip-up (FP) se utiliza comúnmente para medir la calidad de las bobinas nuevas y devanados fabricados para motores y generadores de C.A. de 6 kV o tensiones superiores. En los sistemas de aislamiento modernos de los devanados estatóricos, el factor de potencia y el factor de disipación dieléctrica son casi los mismos (Ver Figura 2). La prueba de FP tip-up puede ser útil para verificar la calidad del proceso de fabricación del bobinado, el comportamiento del material aislante, la consolidación de los conductores, la uniformidad del encintado del muro aislante y la condición del curado de la resina. Una vez el sistema de aislamiento alcance el voltaje de inicio de efecto corona (CIV), la descarga parcial (DP) cortocircuitará efectivamente algo de la capacitancia del aislamiento y el factor de potencia aumentará. La prueba FP aplica a bobinas individuales tratadas con impregnación por presión y vacío (VPI) y bobinas resin-rich, así como también a bobinados completamente curados. La prueba de factor de potencia tip-up no aplica a pruebas en banco de bobinas VPI sin curar (verdes) o para evaluar bobinados completos pre-procesados VPI. 

En los centros de servicio, la prueba de factor de potencia tip-up puede ser útil para verificar la calidad de un sistema de bobinas recién instalado, incluyendo la eficacia del proceso VPI. La prueba FP de los bobinados en servicio puede establecer una medida de referencia para el mantenimiento por análisis de tendencias. Esta prueba FP en servicio puede identificar potencialmente el envejecimiento del muro aislante, ya que la capacitancia entre el conductor de cobre y el núcleo del estator, generalmente se reduce a medida que se presenta separación de las cintas (delaminación) y/o burbujas de aire en el aislamiento (voids), entre las bobinas y el núcleo. La separación de las cintas de aislamiento normalmente aparece o se acelera por el envejecimiento térmico o mecánico del bobinado. La separación de las cintas y/o las burbujas de aire en el aislamiento pueden ocasionar descargas parciales y el fallo prematuro del sistema de aislamiento.

By Mike Howell
EASA Technical Support Specialist

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

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

READ THE FULL ARTICLE

Tom Bishop, P.E. 
EASA 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. 

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

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

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

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

Chuck Yung 
EASA Technical Support Specialist 

A common observation about 2­-pole machines fitted with sleeve bearings is the inherent weak magnetic centering force. The classic symptom is chronic axial movement: a 2-pole rotor drifting “to and fro” from the established magnetic center position. This article addresses the numerous causes of this phenomenon, colloqui­ally referred to as “hunting.” Although the focus is on 2-pole motors, much of this information applies to sleeve bearing motors of any speed rating. Identifying the cause of a problem is good, but solutions are a lot more useful, so I’ve included those as well. 

We can use magnets to describe how a motor works. Opposite poles attract; like poles repel. The magnetic field rotating within the stator turns the rotor, and magnetic force affects the axial position of the rotor relative to the stator core. 

This presentation reviews the causes of axial thrust loading on bearings in motors and determine appropriate corrective actions. 

• Vertical mounting
  • Vertical turbine pump
  • Sheave
  • Fans
• External thrust loads
  • Fans
  • Misalignment
• Internal thrust loads
  • Bearing journal shoulder to shoulder
  • Bearing seat
  • Bearing caps
  • Wavy washer
  • Bearing housing taper
  • Thermal expansion
• Dissect a bearing

 Target audience: This presentation would benefit engineers and mechanics looking for the root cause of bearing failures.

Mike Howell
Especialista de Soporte Técnico de EASA

Para aquellos que trabajan casi exclusivamente con estatores trifásicos con devanados imbricados o concéntricos, las conexiones de los rotores bobinados con devanados ondulados pueden ser un reto. Esto es especialmente cierto, cuando los datos de conexión se pierden o cuando el fallo en el bobinado provoca daños en la conexión existente.

En estos casos, es conveniente contar con un método práctico que nos permita diseñar un diagrama de conexiones válido.

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.

Electric motor repair report form to collect basic motor, bearing, shaft, coupling information.

Mike Howell
EASA Technical Support Specialist

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

Presented by Chuck Yung
EASA Senior Technical Support Specialist

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

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

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

Storing an electric motor for more than a few weeks involves several steps to ensure it will operate properly when needed. For practical reason's, these are governed by the motor's size and how long it will be out of service. Factors like temperature, humidity and ambient vibration in the storage area also influence the choice of storage methods, some of which may be impractical for smaller machines or need to be reversed before the motor goes into storage. This article covers.

• Keeping good records
• Storage conditions
• Shafts and machined surfaces
• Bearing protection
• Special care for windings
• Carbon brushes

READ THE COMPLETE ARTICLE

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.

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

The tongue-in-check saying “If it’s in black and white, it must be right” is a helpful reminder that not everything we read (or hear) is accurate or complete. It’s always best to check sources and verify facts before accepting consequential statements as true. A similar adage underscores the importance of this advice in the digital age: “If it’s on the Internet, it must be true.” With these things in mind, here’s a random collection of common misconceptions about three-phase squirrel-cage motors and the facts that deny them.

Myths discussed include:

• Soft starting motors reduces utility demand charges.
• Higher current means a motor is less efficient.
• Power factor correction capacitors can reduce motor energy consumption.
• A motor can be loaded up to its service factor.
• A 230V motor can be used on a 208V electrical system.
• Oversized motors, especially motors operating at less than 60% of rated load, are not efficient and should be replaced with appropriately-sized premium efficiency (IE3) motors.
• It doesn't matter which of the three line-to-line voltages in a three-phase system you measure to see if a motor is supplied with the proper voltage.
• Hand contact on a motor surface is a reliable way to judge operating temperature.
• Winding burnout is the most common cause of motor failure.

READ THE FULL ARTICLE

Carlos Ramirez
Especialista de Soporte Técnico de EASA

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

El webinario incluye:  

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

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

Rob Boteler
Miembro del Comité de Gestión Energética de NEMA 

Las normas de eficiencia de los motores eléctricos están siendo modificadas en Canadá y México. La siguiente es una breve revisión de esos cambios que  permitirá a los miembros de EASA entender lo que les espera en estos países, en la eficiencia de los  motores con rango de potencias desde 1 hasta 500 hp.

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.

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

In this article, we will discuss testing of capacitors for electric motors in general and tests associated with specific uses of capacitors such as for power factor correction, and for electric motor starting (see Figures 1 and 2). For information on sizing power factor correction capacitors see Subsection 2.10 of the EASA Technical Manual, and for determining the correct size capacitor for a motor, see Subsection 2.11 of the EASA Technical Manual.

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

Para los centros de servicio, el manual Obteniendo Lo Máximo De Su Motor Eléctrico de EASA es una gran herramienta de mercadeo que pueden suministrar a sus clientes (usuarios finales). Como tal, este valioso documento de 40 páginas, proporciona a los usuarios finales información que les ayudará a obtener una operación más durable, eficiente y rentable de motores trifásicos de propósito general y de propósito definido con las siguientes características:

• Motores trifásicos de inducción de jaula de ardilla fabricados bajo normas NEMA MG1
• Potencias entre 1 y 500 hp (1 a 375 kW)
• Velocidades entre 900 y 3600 rpm (8-2 polos)
• Voltajes hasta 1000V, 50/60 Hz
• Todos los tipos de encerramiento estándar (DP, TEFC, WPI, WPII)
• Rodamientos de bolas y de rodillos y cojinetes de deslizamiento

La siguiente es una descripción general del contenido del manual indicando algunas formas de usarlo que pueden beneficiar a los usuarios finales, Ej. Sus clientes y sus clientes potenciales.

Instalación, arranque e información básica
La primera de las dos sesiones principales trata tres subtemas: Instalación del motor, arranque e información básica y al comienzo recomienda asegurarse de documentar el estado inicial del motor para establecer una base para compararla con resultados futuros. Además, los beneficios para el usuario final al seguir esta práctica, es que a menudo les permite detectar problemas pequeños o en formación, antes de que se conviertan en fallos caros y costosas pérdidas de producción.

El Apéndice A, “Datos básicos del motor y de su instalación” hace referencia a esto (ver Figura 1). Tomar los datos de placa y anotar los parámetros eléctricos y mecánicos al momento de la instalación y arranque del motor, permite que la información quede disponible para consulta, en papel o en formato electrónico, si es escaneada. La revisión de los datos del motor, incluyendo los de placa, puede proporcionar información sobre la idoneidad del motor para la aplicación.

Los puntos específicos a verificar son: Si el motor es adecuado para trabajar con un variador de frecuencia (VFD), si los rodamientos permiten instalarlo en una aplicación que requiere transmisión por correas, la accesibilidad a los puntos de lubricación y comprobar que las protecciones de sobre carga están bien calculadas para la potencia del motor. Los dos últimos puntos pueden resultar críticos si se trata de un motor de repuesto con una potencia nominal diferente a la del motor que está reemplazando.

Las consideraciones de la instalación, así como también la idoneidad de la fundación y de la base son importantes para la confiabilidad del motor. Una base débil o inadecuada puede distorsionar la carcasa, generar vibración o desgastar rápidamente los rodamientos.

El manual no solo proporciona detalles acerca de estos temas, sino que también cubre extensamente el alineamiento de los ejes, incluyendo el problema del pie suave, tolerancias y métodos de alineación para acoplamientos directos y para transmisión por poleas. El usuario final puede encontrar gran cantidad de información en tan solo unas pocas páginas del manual.

La información del manual procede de las consideraciones de instalación y de los procedimientos de arranque. En muchos casos, el motor que se está instalando ha estado almacenado. También se proporcionan detalles para ayudar a asegurarse que el motor funciona correctamente. Además del tema del almacenamiento, se incluyen otros relacionados con la lubricación y los lubricantes y la comprobación de la resistencia de aislamiento del bobinado (ver Tabla 1).

A continuación, se proporcionan recomendaciones para las pruebas de arranque previas a la operación del motor y se recomienda medir y registrar los niveles de vibración. Las pruebas recomendadas con el motor con carga incluyen medir los voltajes línea a línea, las corrientes de línea, la temperatura del bobinado (si es posible), la temperatura de los rodamientos y la temperatura ambiente. El manual sugiere que se registren dichos valores en la hoja de datos del motor para que sirvan como base para analizar las tendencias de futuras mediciones. Se suministran dos ejemplos para ilustrar la importancia de registrar los datos de referencia y sus tendencias.

Esta sección inicial concluye con la gestión total del motor. Generalmente, este tipo de programas rastrean las compras y los repuestos en una base de datos utilizando la información de la placa del motor y los datos de instalación / ubicación y aplicación. Por lo general, también realizan un seguimiento de los datos de referencia, mantenimiento, almacenamiento y reparación. Los principales beneficios para los usuarios finales son que dichos programas bajan los costos al reducir el tiempo de inactividad (los repuestos están disponibles) y el inventario es decreciente (identificación de los repuestos utilizados en múltiples ubicaciones).

Aquí, una consideración clave es determinar si la solución más rentable y confiable consiste en almacenar los motores de repuesto en el sitio o subcontratar el almacenamiento con un centro de servicio u otro proveedor. La gestión del motor y el almacenamiento de sus repuestos (y otros equipos) es una oportunidad adicional que tiene el centro de servicio para añadir valor al servicio prestado a sus clientes. Además, tener el motor de repuesto del cliente en sus instalaciones, brinda al centro de servicio una mejor oportunidad de recibir el motor que ha sido reemplazado para repararlo según sea necesario.

Seguimiento operacional​ y mantenimiento
La segunda de las dos secciones principales se ocupa del seguimiento operacional y el mantenimiento. Los temas principales incluyen condiciones específicas de la aplicación, mantenimiento preventivo y predictivo, inspección y pruebas y la relubricación de los rodamientos. Al utilizar las recomendaciones de esta sección, el usuario final puede prolongar la vida útil de sus motores, así como reducir el tiempo medio entre los fallos que requieren reparación.

Anomalías en el suministro eléctrico, como transitorios de voltaje, pueden dar lugar a transitorios de corriente y torques transitorios que pueden dañar no solo los devanados, sino también los componentes mecánicos del motor o del equipo accionado. Para ayudar al usuario final a evitar estos problemas, se suministra un listado que contiene diferentes apartados que identifican más de media docena de fuentes potenciales. Otra fuente de condiciones transitorias, que no es una anomalía, es el arranque del motor. El manual proporciona al usuario final una guía para manejar el arranque del motor y enfatiza la necesidad de limitar su número de arranques.

La subsección sobre mantenimiento preventivo (PM), mantenimiento predictivo (PdM) y mantenimiento basado en confiabilidad (RBM) define y describe cada uno de ellos. Las técnicas de inspección y pruebas eléctricas y mecánicas y la evaluación de la condición física se identifican para PM, PdM y RBM [también denominado mantenimiento centrado en la confiabilidad (RCM)]. Incluso si un usuario final ya tiene un programa de PM, PdM o RBM, se puede beneficiar al consultar esta subsección ya que podría identificar los elementos que le faltan a su programa. Además, si un usuario final no está familiarizado con ninguno de estos programas, el manual proporciona información sobre el proceso inicial para obtener una operación más confiable del motor. Es decir, brinda una oportunidad para que el usuario final aproveche al máximo sus motores eléctricos y probablemente también el equipo acoplado.

En la siguiente sección sobre inspección y prueba de motores se incluye información adicional sobre PM, PdM y RBM. Muy a menudo escuchamos la frase “no pase por alto lo obvio”. Esto describe la importancia de la inspección física para detectar partes que falten, o que estén rotas o dañadas, trayectorias de circulación de aire bloqueadas y contaminantes. Cualquiera de estas condiciones podría llevar a un fallo prematuro y rápido del motor.

Las pruebas descritas en detalle incluyen la resistencia de aislamiento, la resistencia del devanado y el análisis de firma de corriente del motor (vea la Tabla 2). Cuando están disponibles en las normas industriales, se proporcionan criterios de evaluación para que el usuario final pueda determinar si sus niveles son aceptables o justificar una acción correctiva y se suministra información de seguridad relacionada con las pruebas de hipot y de impulso de los motores instalados. También se proporciona información sobre el análisis de vibraciones empleando un analizador de espectro.

Esta subsección final del cuerpo principal del manual brinda orientación para ayudar a asegurar un funcionamiento prolongado y confiable del motor. Las recomendaciones incluyen no solo relubricar los rodamientos, sino también monitorear los niveles de lubricante y verificar si hay fugas y contaminación. Se proporciona orientación para ayudar al usuario final a determinar el intervalo correcto de relubricación y el tipo y grado de lubricante cuando las instrucciones del fabricante del motor no están disponibles.

Se enfatiza la importancia de la compatibilidad de las grasas y se proporciona un cuadro de incompatibilidad. Un consejo sabio para la relubricación se encuentra en la frase: “La mejor práctica consiste en usar la misma grasa que ya existe en los rodamientos, siempre que sea adecuada para la aplicación.” Se proporciona una fórmula para determinar la cantidad precisa de grasa requerida como también un gráfico que ilustra los intervalos de relubricación en función del tipo y tamaño de rodamiento y la velocidad del mismo.

También se aborda la lubricación de cojinetes de deslizamiento y rodamientos lubricados con aceite, incluidos temas como la compatibilidad y viscosidad del aceite e intervalos de relubricación. También se describen temas específicos, como el tratamiento de las condiciones anormales y cómo reemplazar el aceite.

Apéndices
Los tres apéndices proporcionan información complementaria que puede ayudar al usuario final a obtener más de sus motores en términos de la conservación de los registros, la comprensión de la terminología y el almacenamiento del motor. El Apéndice A contiene un formato de dos páginas (vea la Figura 1) destinado a registrar los datos de placa del motor y los datos de las pruebas eléctricas y mecánicas. Inicialmente, el formato se puede usar para obtener información de referencia y que se puede actualizar posteriormente cuando se realicen trabajos de mantenimiento o reparación. Como tal, puede proporcionar información histórica invaluable para el usuario final y las empresas de servicio cuando sea necesario realizar un análisis simple o un análisis de causa raíz de fallo más completo.

La información en el Apéndice B es una compilación de términos clave asociados con los datos de placa del motor. (Nota: También hay un glosario de términos independiente al final del manual). Sin embargo, el valor real de esta información está en determinar el significado de los términos que a veces se malinterpretan. Conocer el verdadero significado y la importancia de estos términos puede ayudar a un usuario final a evitar un error costoso y a emplear tiempo excesivo en la compra de un motor que no es adecuado para una aplicación específica.

Según las consultas de los miembros de EASA, las recomendaciones de almacenamiento del motor, que son tema del Apéndice C, son una solicitud común de los usuarios finales. Por sí solas, estas recomendaciones de almacenamiento hacen del manual un valioso recurso para los usuarios finales. La última página de este apéndice resume la frecuencia con la que se deben realizar ciertas rutinas de mantenimiento durante el almacenamiento. Es raro encontrar esta información actividad vs tiempo en un solo lugar, que es algo que muchos usuarios finales apreciarán.

Mike Howell, PE
EASA Technical Support Specialist 

The insulation system chosen for any rewind should be suitable for the application, the voltage class, and the winding process capability of the service center. In most cases, adherence to “equal to or better than” selection is a good practice.

By Chuck Yung
EASA Senior Technical Support Specialist

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

Presented by Chuck Yung
EASA Senior Technical Support Specialist

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

The webinar recording covers

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

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

Chuck Yung
EASA Senior Technical Support Specialist 

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

Chuck Yung 
EASA Technical Support Specialist 

There are times when a winding cannot be processed through the burn­out oven, so it must be removed “cold.” The bond strength of most resins is approximately 8-10 psi (55-70 kPa), which means that a fairly large coil might have nearly 3,000 pounds (1350 kg) of bonding force with the slot. 

In those cases, there are some use­ful tips that can be used to reduce the difficulty in removing the coils. Many of the techniques in this article can be adapted for open slot wound rotors and armatures. 

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.

Tom Bishop, PE
EASA Senior Technical Support Specialist

Three of the most common three-phase motor problems we receive inquiries about are:

1. “The motor is drawing high no-load current.”
2. “The current of the three line leads is not balanced.”
3. “The motor is running hot.”

Even if you have never faced one of these issues, read on because it is almost inevitable that you will, and you will want to know what to do about it.

Presented by Matthew Conville, MBA, PE

Variable frequency drives (VFDs) are more common than ever before.  Sometimes when a VFD is introduced into a motor driven system, system reliability suffers. This recording addresses some of the common factors that reduce motor driven system reliability and how to correct them.

• Common failures in VFD motor driven systems
• How these failures can be corrected
• Questions to ask to before implementing a VFD to maintain system reliability

This recording is intended for inside sales, outside sales, sales managers, engineering, and field service technicians. 

Gene Vogel
Especialista de Bombas & Vibraciones de EASA 

Existen muchas causas comunes de vibración alta en la maquinaria rotativa; Demasiadas para enumerar aquí. Pero a menudo, lo que de otro modo sería un nivel aceptable de vibración se ve amplificado por la resonancia. Todas las máquinas son susceptibles a la resonancia. La resonancia ocurre cuando la frecuencia natural de algún componente de una máquina coincide con una fuerza excitadora. Cuando se produce resonancia, es la combinación de una fuerza excitadora y una frecuencia natural lo que da como resultado una alta vibración; ambos deben estar presentes en la misma frecuencia para que se produzca la resonancia. Cuando la resonancia causa una vibración excesiva, es importante identificar la frecuencia natural y la forma modal de la vibración. Una simple prueba de impacto (bump test), realizada a máquina parada, es un buen primer paso para identificar la frecuencia natural (Figura 1). 

Carlos Ramirez
EASA Technical Support Specialist

¿El motor consume mucha corriente en vacío, aunque los datos del bobinado son correctos? ¿El motor se calienta con carga de forma inusual? Estas son preguntas comunes que pueden ser resueltas verificando la condición del núcleo del estator. En este webinario discutiremos cómo realizar la prueba de lazo en el núcleo de un estator y cómo analizar los resultados obtenidos, proporcionando información sobre los equipos utilizados, consejos para reparar el núcleo del estator y otras pruebas alternativas.

El seminario incluye:

• Teoría de la prueba de lazo (“toroide”)
• Procedimiento de prueba
• Límites aceptables para las pérdidas y las temperaturas en el núcleo
• Equipo asociado
• Consejos para la reparación de núcleos dañados
• Pruebas alternativas

Este webinario es útil para supervisores, bobinadores y personal encargado de realizar las pruebas.

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.

Vicki Warren — Iris Power - Toronto, Ontario
Brian F. Moore – Georgia Power - Atlanta, Georgia
Jim Williams – Bradley’s Motors - Corpus Christi, Texas 
Special thanks to Gary Castle at Bradley’s Motors

Traditional tests of insulation resistance, polarization index (IEEE 43) and the controlled DC high voltage test (IEEE 95) have been effective in evaluating certain aspects of global vacuum pressure impregnation (GVPI) stator windings; however, they have not proven adequate for determining whether or not the insulation system is well-consolidated. Recently there has been the development of an IEC standard (IEC 60034-27) that defines the test procedures for performing off-line partial discharge testing as part of quality assurance testing. In addition, globally there has been a move towards using a dielectrics characteristic test, either power factor or dissipation factor, as part of the QA testing for GVPI systems. Partial discharge tests have proven to be effective in locating isolated problems that could lead to failure; whereas, the dielectrics characteristic tests provide a more general condition assessment. Based on experience to date, both are needed to fully evaluate how well the winding is consolidated. 

This paper, presented at the 2014 EASA Convention, describes research done by EASA service shops on the effectiveness and practicality of using offline partial discharge combined with a dielectrics characteristic test to evaluate the consolidation of stator windings in medium voltage machines manufactured by GVPI. Advantages and disadvantages of each test and industrial standards will be described as appropriate.

Presentado por Carlos Ramirez, EASA Technical Support Specialist

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

El webinar incluye:

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

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

Anthony Sieracki
Spina Electric Co.

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

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Uno de los temas más debatidos en nuestra industria es la comparación- y los procedimientos- de impregnación por presión y vacío (VPI) versus la inmersión y secado en horno. En este artículo, he ampliado la discusión para incluir bobinas semicuradas (B-stage) y el método de goteo (trickle). Los centros de servicio que cuentan con un tanque de VPI resaltarán rápidamente los muchos beneficios del VPI, como un mejor sellado de los devanados y una mejor transferencia de calor entre los conductores de los bobinados y la carcasa para mejorar la disipación de calor.

Los bobinados de pletina (solera/bobinas formadas) y de alambre redondo tienen dos problemas claramente diferentes. Para las máquinas con bobinas de pletina, la penetración de la resina es la mayor preocupación, lo que le brinda una clara ventaja al proceso VPI. En los bobinados de alambre redondo, la inquietud es la retención de la resina.

Jacob Snyder
Evans Enterprises, Inc.

When a modern temperature controlled (i.e., controlled pyrolysis) burnout oven is not available, the method described here can be used to process aluminum frame motors.

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.

Mike Howell
EASA Technical Support Specialist

Una de las actividades a realizar menos populares relacionadas con el tratamiento de los bobinados, es la preparación y la limpieza de los ajustes, agujeros roscados y superficies mecanizadas. Muchos centros de servicio invierten tiempo adicional durante la etapa de preparación para minimizar la etapa de limpieza. El enfoque más común para proteger estas superficies durante el tratamiento del bobinado consiste en utilizar compuestos para enmascarar o aerosoles de liberación de película seca.

Durante el último año, el departamento de soporte técnico de EASA ha recibido una serie de consultas por parte de los miembros buscando recomendaciones para reemplazar el producto “Special Masking Compound” de Famous Lubricants’ (ver Figura 1) que actualmente no se encuentra disponible. Se cree en estos momentos que el fabricante tiene la intención de continuar con la producción en el futuro, aunque el plazo se desconoce. Este problema específico conlleva a una pregunta más general: ¿Cuál es una buena práctica para escoger un producto para enmascarar estas superficies?

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
EASA Senior Technical Support Specialist

Cuando se considera la construcción de un gran growler para probar rotores y armaduras, la decisión inicial típica es seleccionar la potencia en kVA. La razón principal para esto es que el growler necesitará ser conectado a una fuente de alimentación que tenga suficiente amperaje. Para ayudar a simplificar el complejo proceso de diseño, en este artículo hemos seleccionado cinco potencias expresadas en kVA. Uno de los valores de potencia seleccionados cumplirá con las necesidades de la mayoría de los centros de servicios.

Este artículo abarca:

• Un ejemplo de diseño
• Determinación de las vueltas y el tamaño del cable
• Construyendo el núcleo
• Determinación de las dimensiones de la bobina

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.

Mike Howell
EASA Technical Support Specialist

One of the least popular tasks to perform related to winding treatment processes is preparation and cleanup of fits, threaded holes and machined surfaces. Many service centers invest additional time in the preparation stage so as to minimize the cleanup stage. The most common approach to protecting these surfaces during winding treatment is to utilize masking compounds or dry release sprays.

In the last year, EASA’s technical support staff has received a number of inquiries from members seeking replacement recommendations for Famous Lubricants' “Special Masking Compound” which is currently unavailable. It is believed at this time that the manufacturer intends on continuing production at some point in the future though the time frame is not known. This specific problem leads to a more general question: What is a good practice for choosing a product to mask these surfaces?

By Mike Howell
EASA Technical Support Specialist

Motors that meet the requirements of NEMA: MG1 Part 31 are designed for use with variable-frequency drives (VFDs). Motors that meet the requirements of NEMA: MG1 Part 30 may be suitable for inverter duty if appropriate measures are taken such as line conditioning. End users desiring speed and/or torque control often procure and install VFDs to modify existing applications where a standard-induction motor is in place. Frequently, they try to control costs by using the existing motor. There are a few areas of concern involving misapplication of a standard induction motor.

Topics covered include:

• Speed-torque characteristics
• Shaft currents
• Installation

READ THE ARTICLE

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.

Jacob Snyder
Evans Enterprises, Inc.

El método aquí descrito se puede utilizar para procesar motores con carcasa de aluminio cuando no se tenga un horno moderno de quemado con temperatura controlada (es decir de pirolisis controlada).

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.

Presented by Mike Howell
EASA Technical Support Specialist

EASA’s Energy Policy states that members will strive to ensure that the methods, techniques and materials they use to service and rebuild rotating electrical machines will maintain or improve their energy efficiency, whenever possible. Controlling stator copper losses during rewinds is a significant part of that effort. This webinar recording looks at several aspects of winding design to prevent increased temperature rise and decreased efficiency.

• I²R losses and conductor area / length
• Eddy current losses and laminated conductors
• Circulating current losses and transposed conductors

This webinar recording will benefit service center managers, supervisors and technicians responsible for rewinds.

Carlos Ramirez
Especialista de Soporte Técnico de EASA

¿Recibió un motor antiguo bobinado con alambre de aluminio? Este webinario explicará como realizar la conversión adecuada de alambre de aluminio a alambre de cobre en máquinas de CA y CC, incluyendo ejemplos para el rebobinado de estatores y campos shunt.  Los temas cubiertos son:

• Sección de los alambre de cobre y aluminio 
• Alambres AWG y métricos 
• Devanados de motores de CA 
• Bobinas de campos shunt
• Ejemplos 

Este webinario está enfocado a bobinadores, supervisores e ingenieros.

Disclaimer: All video captions and translations are AI-generated.
EASA is not responsible for any inaccuracies that may occur.

Want to test your knowledge after watching the webinar?

TAKE THE QUIZ

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. 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

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

By Chuck Yung
EASA Senior Tecnical Support Specialist

The evolution of electric motor design as it pertains to cooling methods provides insights about better ways to cool machines in service. The array of methods engineers have devised to solve the same problems are fascinating yet reassuring because many things remain unchanged even after a century of progress. This article discusses how motors are cooled and how heat dissipation can be improved for applications that fall outside the normal operating conditions defined by the National Electrical Manufacturers Association (NEMA) Standard MG 1.

READ THE FULL ARTICLE

Chuck Yung
EASA Senior Technical Support Specialist

When a core loss test reveals localized hot spots, or visual inspection identifies physical damage, the ability to repair the damage in a cost-effective manner means the difference between repair or replacement.

Topics covered in this recording include:   

• What core loss flux level is correct?
• Clearing small localized hot spots
• What is the best way to clear surface shorting?
• Grinding versus spreading the laminations
• “Watt knocking” or physically manipulating the core
• Debunking the rusting myth — Coreplate, class F red insulator, waterglass
• Restack: complete or partial — Does lamination grade really matter? 

This presentation is intended for owner-managers, shop supervisors, machinists, service center technicians, and safety directors.

Chuck Yung
Especiaslista Sénior de Soporte Técnico de EASA 

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

Bret McCormick
Stewart's Electric Motor Works, Inc.

Paperwork.

No one likes it on the shop floor. Nobody wants to fill out forms. 

Like most service centers, we recognize that accurate paperwork is a necessary part of any effective system for achieving product quality. But in our experience, it’s always been difficult to develop easy-to-use forms that will streamline the process of moving jobs through the shop. With those thoughts in mind, we at Stewart's Electric Motor Works set out to find a better way to create user-friendly forms.

We started by cramming a lot of information onto a single sheet of paper and, after much discussion, eventually settled on a template that could be used to expand the paperwork of each department.

To simplify the process of making specific repair forms, we used the Tables function in Microsoft® Word to create more than 60 building blocks for capturing common information like nameplate data, flux densities, accessories, instructions/notes, and so forth. We also developed a small library of generic drawings (e.g., horizontal and vertical motors, rotors, armatures, pump components, etc.) that could be incorporated into forms as needed.

Now whenever we need a new form, we just paste the appropriate building blocks into the department’s template and save the document with a new file name. Then we move the blocks around on the page as needed, modifying the labels, cell sizes, and numbers of rows as necessary before saving the document again. With this procedure, it’s fairly easy to create or revise forms for all aspects of repair–from motor and pump inspection and disassembly to machine work, rewinding, reassembly and final testing.

Since this process works so well for us at Stewart’s Electric, it might be helpful to you, too. You can download and view our building blocks, illustrations and generic PDF forms by downloading the ZIP file below (ZIP is an archive file format that contains multiple files or directories that may have been compressed. If you are not familiar with extracting content from ZIP files, see this Microsoft Support page for instructions.)

To create your own form in MS Word®  or MS Publisher®, simply download the building blocks you need. Then cut, paste, resize and move them around on the page to make a form that best fits your company’s needs. (Tip: Ask your children or grandchildren if you need help learning how to cut and paste. :-)

The generic PDF forms may be what you need, so you may choose to use them “as is.” 

If you need more ideas on what to include on your forms, see Section 2.17 in EASA’s Technical Manual located online in the EASA Resource Library.

Download the file using the link below.

David Sattler
L&S Electric, Inc.

Unless great care is taken, pulling magnet wire from a motor stator often bends or splays the lamination’s end teeth. Bent teeth, or teeth that have been splayed outward at the ends of the core stack, will likely compromise the quality of the repair job. Studies¹ show that motor efficiency may be reduced by splaying end teeth. Even if that reduction in efficiency is slight, any reduction in efficiency results in higher costs and wasted energy.

Even though these performance reductions are seldom noticed by customers, our goal in motor repair is always to produce the highest quality rewind possible. Therefore, we have designed and implemented the use of disc clamps to hold the stator tooth tips in place while pulling magnet wire from the slots. The clamping fixtures described in the photos have helped ensure that we avoid damaging the stator teeth during the stripping process.

Chuck Yung
EASA Senior Technical Support Specialist 

Historically, one emergency repair used for large, low-speed machines (motors as well as generators) was to remove the damaged/failed coils from the circuit. Cutting out a single damaged coil permitted the machine to be quickly returned to service with minimal disruption.

As long as some basic principles are followed, this method can be safely used. It is still popular with operators of large, low-speed synchronous ma­chines. One common application for such machines is hydro power stations. There are many old hydro generators operating with a dozen or more coils bypassed. The underlying goal when cutting out coils is to minimize the negative side effects and keep coil groups intact for future removal.

WARNING: This procedure is not recommended for 2-pole machines. The odds of success are slim.

Chuck Yung
EASA Senior Technical Support Specialist

Flooding in the aftermath of tropical storms (hurricanes, monsoons and cyclones) with heavy rainfall will often shut down hundreds of plants along the Gulf Coast from Florida to Texas and other places around the world.

To get them up and running again, maintenance departments and motor repairers face the daunting task of cleaning muck and moisture from many thousands of electric motors and generators. See Figure 1. The process in such situations can take weeks, if not months, and requires special clean-up procedures for motors contaminated by saltwater.

Although the problems are huge, affected plants can get back in production more quickly by working closely with service center professionals and following a few tips that will make the cleanup more manageable. These include prioritizing motors and generators for repair or replacement, storing contaminated machines properly, and using proven methods to flush away saltwater contamination. Constructing temporary ovens on site or at the service center can also add capacity for drying the insulation systems of flooded motors.

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

A menudo, determinar la fuente del ruido en un motor eléctrico es más un desafío que corregirla. Sin embargo, un enfoque metódico puede reducir las causas posibles y por consiguiente facilitar la resolución del problema. Una advertencia aquí es que, si el ruido está relacionado con el diseño del motor, es decir, por un defecto de fabricación, puede que no sea posible o que no sea práctico obtener una solución.

En un motor eléctrico existen tres fuentes principales de ruido: Magnética, mecánica y por ventilación. Aquí discutiremos las causas y las características de cada una de ellas, proporcionando directrices para eliminar o reducir el ruido asociado con dichas fuentes.

Tom Bishop, P.E.
EASA Technical Support Specialist

Determining the source of noise in a motor is often much more challenging than correcting it. However, a methodical approach to investigating the noise can narrow down the possible causes and therefore make it easier to resolve the noise issue. There is a caveat. If the cause of the noise is due to something in the motor design, that is, a manufacturing defect or anomaly, a solution may not be possible or practical.

There are three primary sources of noise in a motor: magnetic, mechanical and windage. We will discuss the causes and characteristics of each and provide guidance in dealing with reducing or eliminating the noise associated with them.

Tom Bishop, PE
Especialista Sénior de Soporte Técnico de EASA 

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

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

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

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

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

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

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

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

General 

• Aislamiento Clase H o superior 

Alambre magneto 

• Inverter duty 

Sección del conductor 

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

Aislamiento 

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

Atado y soporte 

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

Impregnación 

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

Mike Howell, PE
Especialista de Soporte Técnico de EASA

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

Chuck Yung
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).

Richard Huber, P. Eng.
Richard Huber Engineering. Ltd
North Vancouver, BC
Canadá
Miembro del Comité Técnico de Servicios

Introducción
Recientemente trabajé en una máquina nueva de 13.8 kV de tensión nominal, enfriada por aire,   que producía grandes cantidades de ozono y tenía grandes niveles de descargas parciales. El problema básico con  los bobinados de esta máquina era  el espacio incorrecto entre las cabezas de bobina y los cables  de salida principales. También había poco espacio entre las series y las conexiones entre los  grupos del bobinado.

Chuck Yung 
EASA Technical Support Specialist 

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

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

Tom Bishop, P.E.
EASA Technical Support Specialist 

This article describes machine balancing of the rotating components of motors and generators, primarily rotors and armatures. The methods described here, in general, can be applied to on-site balancing if the rotating component is accessible. The intent is to describe the methods of attaching balance weights, not determining acceptable balance level or the location and amount of correction weight. 

The advent of computerized balancing machines has made the latter steps rather straightforward. However, the challenge of how to attach a weight in such a way that it will remain secure and not negatively affect machine operation remains at times a vexing problem. 

What is the purpose of dynamic balancing a rotating part? It is to reduce unbalance and consequently to bring vibration to acceptable levels to allow for normal bearing and other component life. The acceptable levels of vibration are described in EASA Tech Note 32, “Standards For Dynamic Balancing,” thus we won’t explain them here.

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.

Chuck Yung
Especialista Sénior de Soporte Técnico

Solía bromear con que si mencionas la palabra armónicos, los ingenieros se emocionan mientras que los ojos de los que no lo son se nublan. La verdad es que los armónicos se pueden entender fácilmente cuando se explican en términos sencillos. Estos son simplemente múltiplos de la frecuencia fundamental, con secuencia positiva, cero o negativa. La frecuencia fundamental es la frecuencia de línea, también llamada armónico de primer orden, que es de 60 Hz en América del Norte o de 50 Hz en la mayor parte del resto del mundo.

Otros armónicos (quinto, séptimo, etc.) se pueden ver como ese orden multiplicado por la frecuencia fundamental, o visualizarse como si tuvieran ese número de formas de onda en la misma distancia que una sola forma de onda de la frecuencia fundamental. Entonces, en un sistema de 60 Hz, el quinto armónico es 5x60 o 300 Hz. Habrá 5 formas de onda completas en el lapso de una sola forma de onda de 60 Hz. Cuando las porciones positiva y negativa de la onda sinusoidal son simétricas, los armónicos de números pares no existen.

Cualquier armónico que sea múltiplo de tres, en el mundo trifásico, es un armónico de secuencia cero; y, cuando estamos considerando un sistema de potencia sinusoidal, se cancela (a excepción de los alternadores síncronos, que están fuera del alcance de esta discusión).

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.”

Chuck Yung
EASA Senior Technical Support Specialist

I used to joke that if you mention harmonics, engineers get excited while the eyes of non-engineers glaze over. The truth is that harmonics can be easily understood when explained in layman’s terms. Harmonics are simply multiples of the fundamental frequency, with positive, zero or negative sequence. The fundamental frequency is line frequency – also called the first order harmonic -- that being 60 Hz in North America or 50 Hz in most of the rest of the world.

Other harmonic numbers (5th, 7th, etc.) can be viewed as that order times the fundamental frequency, or visualized as having that number of waveforms in the same distance as a single waveform of the fundamental. So in a 60 Hz system, the 5th harmonic is 5x60 or 300 Hz. There will be 5 complete waveforms in the span of a single 60 Hz waveform. When the positive and negative portions of the sine wave are symmetrical, even number harmonics are non-existent.

Any harmonic that is a multiple of three, in the three-phase world, is a zero-sequence harmonic; and, when we are considering a sinusoidal power system, cancels out (except for synchronous alternators, which are outside the scope of this discussion).

El Efecto de la Reparación/Rebobinado en la Eficiencia del Motor: Estudio de rebobinado realizado por EASA/AEMT y la Guía de Buenas Prácticas, ilustran que cuando la reparación/rebobinado de un motor eléctrico se realiza de forma correcta, no se degrada su eficiencia! y que esta tampoco se reduce después de varios reparaciones/rebobinados.

Basado en un estudio realizado en conjunto por EASA y la Association of Electrical and Mechanical Trades (AEMT) del Reino Unido, esta publicación concluye que empleando las mejores prácticas de reparación/rebobinado la eficiencia del motor se conserva. Además de una Síntesis, el informe proporciona todos los datos de prueba, mucha información relacionada con procedimientos de prueba y metodología, información de los procedimientos que utilizan buenas prácticas, lecturas complementarias y un capítulo entero sobre las consideraciones para reparar/reemplazar un motor.

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

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

Determining the source of noise in an electric motor is often more challenging than correcting it. A methodical investigative approach, however, can narrow the possibilities and make it easier to resolve the issue—with one caveat. If the noise is due to something in the motor design (e.g., a manufacturing defect or anomaly), a solution may be impossible or impractical. With that in mind, let’s review the primary sources of noise in electric motors—magnetic, mechanical, and windage—as well as their causes and ways to reduce or eliminate them.

Areas examined in this article include:

• Magnetic noise
  • Slip noise
  • Skewing
  • Unequal air gap
• Mechanical noise
  • Loose stator core
  • Bearings
  • Airborne noise
• Windage noise

READ THE FULL ARTICLE

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.

A special discounted collection of 7 webinar recordings focusing on various aspects of electromechanical repair.

Once purchased, all 7 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

Time-Saving Repair Tips
Presented August 2014

This webinar shares:

• The secrets used by other service centers to gain a competitive edge in the repair process.
• Mechanical, winding and machining tips reduce repair time, help avoid unnecessary rework, and decrease turn-around time.

Target audience: Supervisors, machinists, mechanics, winders, and sales personnel who interact with the end user.

Repair Best Practices to Maintain Motor Efficiency
Presented June 2012

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.

Practical Problem Solving for the Entire Service Center
Presented August 2013

This presentation focuses on a report format developed by Toyota for a simple, yet methodical approach to document improvement. Whether you're dealing with problems related to sales, purchasing, repair or testing, if all team members can learn to speak the same, simple problem-solving language, they can tackle problems efficiently and effectively.

Target audience: This presentation is best suited for executives, managers, team leaders and front line supervisors from the office and service center who want to understand and implement such a program.

Induction Motor Speed Control Basics
Presented March 2019

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

AC Motor Assembly and Testing
Presented August 2018

This webinar recording focuses on:

• Motor assembly issues
• Electrical and mechanical inspection
• Static and run testing
• AC motors with ball, roller and sleeve bearings

Target audience: This webinar recording is most useful for service center mechanics, supervisors and engineers. The content will also be beneficial for machinists, managers and owners.

On-Site Testing & Inspection of Electric Motors
Presented July 2015

This webinar covers electrical testing and inspection of installed electric motors, including:

• Condition assessment for continued service
• Diagnostic fault testing and interpretation
• Physical inspection key points

Selecting Replacement DC and 3-Phase Squirrel Cage Motors
Presented September 2019

On many occasions, a different motor type is desired or needed. In these cases it is essential that the replacement motor provides the required performance, and do so reliably.

This presentation focuses primarily on the electrical aspects of selecting replacement motors. It also addresses speed and torque considerations.

• DC motor to DC motor
• DC motor to 3-phase squirrel cage motor
• AC motor to 3-phase squirrel cage motor

Target audience: Anyone involved with selecting replacement motors or diagnosing issues with replacement motor installations.

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.

Richard Huber, P. Eng. 
Richard Huber Engineering, Ltd. 
North Vancouver, BC
Canada 
Technical Services Committee Member

Introduction
Recently I worked on new air-cooled machines rated at 13.8 kV that generated large quantities of ozone and had very high partial discharge levels. The basic problem with the windings in these machines was incorrect spacing of the end turns and the main leads. There was also a lack of space between the series and group connections in the windings.

Spacing requirements
The spacing suggested here is a guide only and original equipment manufacturers (OEMs) and service centers may have their own guide for such values. It should be noted, how­ever, that if spacing is much reduced from that suggested here, there is a real risk that partial discharge activity will develop in the winding.

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

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

Kent Henry 
EASA Technical Support Specialist 

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

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

Mike Howell, PE
Especialista de Soporte Técnico de EASA 

El sistema de aislamiento escogido para cualquier rebobinado debe ser el adecuado para la aplicación, el voltaje y la capacidad del proceso de rebobinado del centro de servicio. En la mayoría de los casos, seleccionar una opción "igual o mejor" es una buena práctica.

Rob Boteler
Confluence Energy LLC

On October 22, the European Commission submitted its plan to expand motor and power converter efficiency regulations. As part of the EcoDesign directive, the Commission has been working on expanded motor and drive regulations for several years. The European Union directive will address both motors and variable frequency drives (VFDs) from .75 to 1,000 kW (1 to 1340 hp).

Efficiency directives in Europe are drafted by the Commission with individual countries responsible for enforcement. Unlike the USA where the regulation is promulgated and enforced at the federal level through the Department of Energy, each country within the EU has enforcement responsibility. Though some complain that the DOE rule making process is very lengthy and stressful, it does provide all interested parties with an opportunity to be heard. The EU Commission also has a process for the development of regulations, and many would argue that the manufacturers are somewhat less of an integral part of the EU process.  

The directive that will cover the new EU motor and power converter regulations is referred to as the “annex EN.” It has yet to receive its reference number. EC640/209, the current directive, will be replaced. 

Covered motor products
Beginning January 15, 2021, the energy efficiency of three-phase motors with a rated output equal to or above 0.75 kW (1 hp), and equal to or below 1,000 kW (1340 hp), with 2, 4 or 6 poles, which are not brake motors, increased safety motors, or other explosion-protected motors, shall correspond to at least the IE3 efficiency level. This should align with NEMA Premium 50 Hz.

Beginning July 1, 2022, the energy efficiency of three-phase motors with a rated output equal to or above 0.12 kW (0.16 hp) and below 0.75 kW (1 hp), single-phase motors with a rated output equal to or above 0.12 kW (0.16 hp), and increased safety motors with a rated output equal to or above 0.12 kW (0.16 hp) and equal to or below 1,000 kW (1,340 kW) shall correspond to at least the IE2 efficiency level.

Also, the energy efficiency of three-phase motors with a rated output equal to or above 0.75 kW (1 hp) and equal to or below 1,000 kW (1,340 hp) with 2, 4, 6 or 8 poles, that are not increased safety motors, shall correspond to at least the IE3 efficiency level. 

The directive includes AC motors that NEMA would describe as special or definite purpose, making this new regulation quite broad in the range of covered products. The EU directive does include motors that cannot be tested with the addition of a temporary endshield. 

The directive will not include air over (AO), totally encloseTENV, high ambient (60° C), high altitude (4,000 meters [13,000 feet]), low ambient (-40° C) and maximum operating temperature (400° C). Additionally, the directive exempts integral brake motors and integral motors and controls (IMACs). 

The directive does not include technologies other than AC. However, it is not clear if there is any distinction within the single-phase designs (cap start cap run, cap star induction run, etc.).

Covered variable speed drives 
The regulation covers variable speed drives with three phases input that are rated for operating with one motor within the 0.75 kW – 1,000 kW (1 to 1340 hp) motor rated output range, have a rated voltage above 100 V and up to and including 1,000 V AC, and have only one AC voltage output.

Variable speed drive (VSD) means an electronic power converter that continuously adapts the electrical power supplied to the motor to control the motor’s mechanical power output according to the torque-speed characteristic of the load driven by the motor, by adjusting the power supply to a variable frequency and voltage supplied to the motor. 

Product information requirements for motors 
According to the regulation, the product information requirements below shall be visibly displayed on the technical data sheet or user manual supplied with the motor; the technical documentation for the purposes of conformity assessment pursuant to Article 5; on websites of the manufacturer of the motor, its authorized representative, or the importer; and the technical data sheet or user manual supplied with products in which the motor is incorporated.

The exact wording used in the following list does not need to be repeated. The information may be displayed using clearly understandable graphs, figures or symbols rather than text: 

• Rated efficiency (ηN) at the full, 75% and 50% rated load and voltage (UN), determined based on the 50 Hz operation and 25° C ambient reference temperature
• Efficiency level: “IE2,” “IE3,” “IE4” or “IE5,” as determined as specified in the first section of this annex, followed by the term “-motor” 
• Manufacturer’s name or trade mark, commercial registration number and address
• Product’s model identifier
• Number of poles of the motor
• The rated power output(s) PN or range of rated power output (kW)
• The rated input frequency(s) of the motor (Hz)
• The rated voltage(s) or range of rated voltage (V)
• The rated speed(s) or range of rated speed (rpm) 
• Whether single-phase or three-phase
• Information on the range of operating conditions for which the motor is designed: 
  • altitudes above sea-level
  • minimum and maximum ambient air temperatures including for motors with air cooling
  • water coolant temperature at the inlet to the product, where applicable 
  • maximum operating temperature
  • potentially explosive atmospheres
• Information relevant for disassembly recycling or disposal at end-of-life; 
• If the motor is considered exempt from efficiency requirements in accordance with Article 4(2) of this Regulation: the specific reason why it is considered exempt. 

For motors exempt from the efficiency requirements in accordance with Article 4(2)(m) of this regulation, the motor or its packaging and the documentation must clearly indicate, “Motor to be used exclusively as spare part for” and the product(s) for which it is intended.

Efficiency requirements for variable speed drives 
Efficiency requirements for variable speed drives shall apply as follows: the power losses of variable speed drives rated for operating with motors with a rated output equal to or above 0.75 kW (1 hp) and equal to or below 1,000 kW (1,340 hp) shall not exceed the maximum power losses corresponding to the IE2 efficiency level.

Conclusions
This is the first regulation for VSD efficiency. Overall, the directive maintains references to IEC standards for both motors and VSDs that have been developed in collaboration with industry, regulators and energy advocates. Test methods will use IEC 60034, which delivers results similar to IEEE 112 or CSA 390.

The regulation in its entirety may be found at https://bit.ly/2PG0VaD.

The efficiency levels also reference IEC levels IE2 and IE3. Note that the directive includes a reference to IE4 and IE5 levels, which are not scheduled for implementation. Unlike NEMA, IEC has one efficiency table regardless of enclosure type calculated at 1.0 SF. 

One issue that will face motor manufacturers is the smaller size of IEC motors to power ratio. In some cases, this will force motors to jump one frame size. End-users and OEMs buying these higher efficiency motors will need to be cognizant of possible changes to the motor’s size that may cause form, fit and function issues in a specific application.

This presentation focuses on the steps to take before rewinding to avoid the undesirable situation of high no-load motor amps after the rewind.

The presentation covers the following steps that should be performed on every AC stator rewind:

• Inspect the stator bore and rotor outside diameter for evidence of machining or damage
• Record the original winding data exactly as found
• Verify the winding data
• Test the stator core before and after rewinding removal

This presentation is most useful for service center mechanics and winders with any level of experience, and service center supervisors and managers.

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

Determining the source of noise in a motor is often much more challenging than correcting it. However, a methodical approach to investigating the noise can narrow down the possible causes and therefore make it easier to resolve the noise issue. In this session we will address the causes and characteristics of the primary sources of noise in AC motors. Specific topics to be addressed:  

• Magnetic noise (aka “electromagnetic noise” or “electrical noise”) 
• Mechanical noise 
• Windage noise 
• Guidance for reducing or eliminating the intensity of these noise sources

This webinar recording is intended for mechanics, supervisors and testing technicians.

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

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

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

Tom Bishop
Especialista Sénior de Soporte Técnico de EASA

El problema más frecuentemente relacionado con la corriente alta en un motor, es la elevada corriente en vacío de los motores trifásicos. Este tema ya había sido tratado en tres artículos publicados anteriormente en la revista Currents de EASA, empezando con “Test Run Tips: Common Causes For High No-Load Current On Rewound Motors” (Junio de 2002); continuando con “Avoiding High No-Load Amps On Rewound Motors” (Febrero de 2004); y finalizando con “Taming Those Misbehaving Motors” (Diciembre de 2009). Este artículo cubrirá el amplio tema  de la corriente alta en vacio y el problema de la corriente con carga elevada en los motores trifásicos. También en él se consideran casos en los cuales existe una corriente en vacio menor que la esperada.

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

The most frequent concern about a motor with high current is high no-load current with a 3-phase motor. That topic has been addressed in three prior Currents articles beginning with “Test Run Tips: Common Causes For High No-Load Current On Rewound Motors” (June 2002); “Avoiding High No-Load Amps On Rewound Motors” (February 2004); and “Taming Those Misbehaving Motors” (December 2009). This article will cover the broad topic of high no-load current with 3-phase motors and the issue of high current with load with 3-phase motors. Also considered will be cases of lower than expected no-load current.

Presented by Tom Bishop, PE
EASA Senior Technical Support Specialist

This recording covers the broad topic of high no-load current with 3-phase motors and the issue of high current with load with 3- phase motors. Also covered are the cases of lower than expected no-load current. 

Primary topics are:

• High no-load current – motor not rewound
• High no-load current – rewound motor
• High current with load

This presentation is intended for mechanical technicians, winders, supervisors, engineers and managers. 

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

Service centers routinely check the shaft extension runout of motors and generators. When there are issues associated with them, or when applicable, the coplanarity of the mounting feet and the amount of end foat of horizontal sleeve bearing motors and generators are checked. A common point about all three of these dimensions is that they are checked with the machine assembled; that is, no disassembly is required. There are many other mechanical tolerances associated with motors and generators, such as bearing fits. However, the focus of this article will be the three tolerances just mentioned. Rather than referring to both electric motors and generators, for brevity the term “machine” will be used.

Topics covered include:

• Shaft extension runout tolerance
• Coplanarity of mounting feet tolerance
• End float

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.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist
​ EASA’s Getting The Most From Your Electric Motors is a great marketing tool for service centers to provide to customers (end users). As such, this valuable 40-page booklet provides 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 MG1 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

The following is an overview of the contents of the booklet indicating some of the ways that using it can benefit end users, i.e., your customers — and potential customers.

Installation, startup and baseline information
The first of the two major sections addresses three subtopics: motor installation, startup and baseline information. Early on it recommends making sure to document the motor’s initial condition to establish a baseline for comparison with future results. Among the benefits to the end user by following this practice is that it’s often possible to recognize small or developing problems before they lead to costly motor failures and downtime.

Reference is made to the “Motor and installation baseline data” sheet (see Figure 1) found in Appendix A. Recording the nameplate data and pertinent electrical and mechanical parameters at the time of installation and startup makes that information available for reference in hard copy or, if scanned, electronic format. Review of the motor data, including the nameplate information, can provide insight into the motor’s suitability for the application.

Specific items to check include motor suitability for use with a variable frequency drive (VFD), bearing suitability if the application is a belt drive, lubrication points accessibility, and verifying that the motor control and overload protections are sized properly for the motor rating. The last two points can be critical if the motor is a replacement and of a different power rating than the motor that it replaced.

Installation considerations such as the adequacy of the foundation and base are important for motor reliability. A weak or otherwise inadequate base can result in frame distortion, rapid bearing wear and vibration.

The booklet not only provides details on these topics, it extensively covers shaft alignment, including the issues of soft foot, alignment tolerances, and alignment methods for direct-coupled and for belt-drives. The end user can find a great deal of installation related information in just a few pages of the booklet.

The information in the booklet proceeds from the installation considerations to startup procedures. In many cases the motor being installed had been in storage; details are provided to help assure that the motor functions properly. Among the storage related topics are lubrication and the lubricant, and checking winding insulation resistance (see Table 1).

Next, recommendations are provided for pre-operation startup tests. Measuring and recording vibration levels is recommended. Recommended tests with the motor under load include line to line voltage, line currents, winding temperature (if possible), bearing temperature and ambient temperature. The booklet suggests these baseline values be recorded on the motor data sheet as a basis for future trending measurements. Two examples are provided to show the importance of recording baseline and trending data.

The section on motor installation, startup and baseline information concludes with the topic of total motor management. These programs typically track purchases and spares in a database by nameplate information, facility/location, and application. Usually they also track baseline data, maintenance, storage and repair. The primary benefits for the end users are that such programs lower costs by reducing downtime (spares are readily available) and decreasing inventory (identification of spares used in multiple locations).

A key consideration here is whether the most cost-effective and reliable solution is to store spare motors on site or to outsource storage to a service center or other vendor. Motor management and spare motor (and other equipment) storage is yet another opportunity for a service center to provide a value-added service for their customers. Further, having the customer’s spare motor at your facility provides a better opportunity to receive the replaced motor to perform the needed repairs.

Operational monitoring and maintenance
The second of the two major sections deals with operational monitoring and maintenance. Primary topics include application-specific conditions, preventive and predictive maintenance, inspection and testing, and bearing relubrication. By making use of the advice in this section the end user can extend the useful life of their motors, as well as the mean time between failures requiring repair.

Abnormalities in the electrical supply such as transient voltage can result in transient currents and torques which can damage not only windings but also mechanical components of the motor or driven equipment. To help the end user avoid these abnormalities, a bullet list identifies over a half-dozen potential sources. Another source of transient conditions that is not an abnormality is motor starting. The booklet provides the end user with guidance in dealing with motor starting and emphasizes the need to limit the number of motor starts.

The subsection on preventive maintenance (PM), predictive maintenance (PdM) and reliability-based (RBM) maintenance defines and describes each. Electrical and mechanical test and inspection techniques and physical condition assessments are identified for PM, PdM and RBM [also termed reliability-centered maintenance (RCM)]. Even if an end user already has a PM, PdM or RBM program, they can benefit from review of this subsection as it may identify missing elements in their program. Also, if an end user is not familiar with any of these programs the booklet provides information to get them started on the path to more reliable motor operation. That is, it provides an opportunity for the end user to get the most from their electric motors and probably the connected equipment as well.

Additional information on PM, PdM and RBM is included in the subsequent section on motor inspection and testing. All too often we hear the statement “don’t overlook the obvious.” That describes the importance of physical inspection in detecting missing, broken or damaged parts, blocked airflow paths and contaminants. Any one of these conditions could lead to premature and perhaps rapid motor failure.

Tests that are described in detail include insulation resistance, winding resistance and motor current signature analysis (see Table 2). When available from industry standards, criteria for evaluation are provided so that the end user can determine if their levels are acceptable or warrant corrective action. Cautionary information is provided regarding high-potential and surge testing of installed motors.  Information about vibration analysis using a spectrum analyzer is also provided.

This final subsection of the main body of the booklet provides guidance to help assure long and reliable motor operation. Recommendations include not only relubricating bearings, but also monitoring lubricant levels and checking for leaks and contamination. Guidance is provided to help the end user determine the correct relubrication interval and the lubricant type and grade when the motor manufacturer instructions are not available.

The importance of grease compatibility is stressed, and a grease incompatibility chart is provided.  Sage relubrication advice is given in the statement: “The best practice is to use the same grease that’s already in the bearings–provided it’s suitable for the application." A formula is provided to determine the precise amount of grease required; a graphic illustrates grease relubrication intervals based on bearing type, size and speed.

Oil-lubricated sleeve and rolling element bearing lubrication is also addressed, including topics such as oil compatibility, viscosity, and relubrication intervals.  Specific topics such as dealing with abnormal conditions and how to replace oil are also described.

Appendices
The three appendices provide supplementary information that can help the end user get more from their motors in terms of record-keeping, understanding motor terminology and storage. Appendix A contains a two-page data form (see Figure 1) intended for use in recording motor nameplate data and electrical and mechanical test data. Initially the data form can be used for baseline information, and then updated when maintenance or repairs are made. As such it can provide invaluable historical information for the end user and service firms when it becomes necessary to perform a simple failure analysis or more comprehensive root cause failure analysis.

The information in Appendix B is a compilation of key terms associated with motor nameplate data. (Note: There is also a standalone glossary at the end of the booklet.) However, the real value of this information is in determining the meaning of terms that at times are misunderstood. Knowing the true meaning and importance of these terms can help an end user avoid a costly and time-consuming mistake in purchasing a motor that is not suited for a specific application.

Based on member inquiries, motor storage recommendations, which are the topic of Appendix C, are a common end user request. These storage recommendations alone make the booklet a valuable resource for end users. The last page of this appendix summarizes how often to perform certain storage maintenance routines. It is rare to find this time versus task information all in one place, which is something many end users will appreciate.

Ordering information
Printed copies of Getting The Most From Your Electric Motors booklet can be purchased in EASA’s Online Store or you may download a PDF copy for FREE.

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

This article addresses electrical testing and inspection of installed 3-phase squirrel cage motors. The main purposes of testing installed electric motors are condition assessment for continued service or to diagnose suspected faults. The emphasis here will be on diagnostic electrical testing and interpretation, as well as physical inspection key points. Note: Most of the tests and inspections described in this article can also be performed on 3-phase wound rotor motors, and induction and synchronous generators.

By Chuck Yung
EASA Technical Support Specialist 

Most EASAns are familiar with the basics of rotor rebarring.  We know that the endrings and bars are not always the same material, and understand the importance of maintaining the cage resistance.  For those of us who only occasionally rebar rotors, here are a few tips to assure a quality repair. 

Gene Vogel
Especialista de Bombas y Vibraciones de EASA

El programa de Verificación & Rediseño de Motores C.A. de EASA- Versión 4, lanzado en mayo, es una actualización fácil de usar de la Versión 3 y de la Versión 2 más antigua del programa. El diseño y las funciones del nuevo programa están adaptados de la Versión 2 más antigua, por lo que los usuarios se podrán mover a través de él en una curva de aprendizaje fácil. En la Versión 4 del programa también existen funciones que ayudarán al reconocimiento de aspectos del proceso de rediseño, que pueden haber sido pasados por alto. Si su programa está operativo, continúe leyendo para aprender acerca de estas funciones.

Al ingresar un nuevo diseño, la Versión 4 del programa proporciona un campo para identificar el cliente por su nombre o por un número. Un “Nuevo” botón permite al usuario introducir los datos del cliente sobre la marcha, pero se considera práctico que haya ingresado antes los datos de sus clientes habituales. Los elementos del menú Database -> Customer, le permiten ganar tiempo al gestionar su lista de Clientes. Por tanto los clientes se pueden ingresar fácilmente por nombre o ser seccionados desde una lista de nombres desplegable.

Utilice el teclado o el ratón
Al ingresar los Datos del Bobinado Original, algunos usuarios prefieren el teclado mientras otros se sienten más cómodos moviéndose por los campos con el ratón. El programa soporta ambos métodos. Con el tabulador se accede a los campos de los datos (shift-Tab para devolverse). Cualquier campo que cuente con flechas para ajuste de valores se puede configurar con las teclas situadas Arriba-Abajo del cursor o se pueden escribir los valores. El botón de opción y las casillas de verificación se pueden ajustar con la Barra Espaciadora. Con el ratón, solo manipule las flechas para ajustar los valores o haga clic en cualquier campo y escriba el valor. También puede situar el cursor encima de un ícono para ver su descripción (ver Figura 1).

Una vez ingresados los datos, al oprimir el botón Calculate (Calcular), se visualiza una tabla de selección con las posibles opciones de rediseño. Dicha Tabla es flexible y se puede ampliar para incluir más columnas (clic derecho). Estas columnas se pueden ordenar haciendo clic sobre sus encabezados. Hay varias opciones disponibles para ver los diferentes números de circuitos (ver Figura 2).  En la ayuda (HELP) del programa o en la página web de EASA: http: //www.easa.com/resources/software/ac-motor-verification-redesign, existe un buen video tutorial sobre cómo utilizar esta Tabla de selección. A menudo, la elección de los parámetros de rediseño implica comparar diferentes opciones. El programa permite al usuario escoger y ver múltiples opciones desde la tabla de selección – solo sostenga la tecla CTRL y haga clic en las filas deseadas. Las diferentes opciones de rediseño se pueden seleccionar con las pestañas situadas en la parte inferior de la pantalla. Para comparar los parámetros críticos en forma de columnas, seleccione en el menú Rediseño la opción Side-by-Side.

Además, justo encima del botón Calculate situado en la página del motor Original, existen los botones denominados Round Turns (Redondear Espiras) que sirven para ajustar el número de espiras: Integer (entero) o Half-Turn (promedio). Al escoger la opción Half (promedio) se incluyen esas opciones en la tabla de selección. Por ejemplo, si una máquina de 4 polos, 48 ranuras, 12 grupos, 4 bobinas por grupo tiene 7.5 espiras (half turns), esta podría ser rebobinada con 7-7-8-8 espiras y paso 1-11 ó utilizando 7-8-7-8 espiras y paso 1-12.

Datos de rebobinado integrados
Algunas veces, cuando los datos no están disponibles o son sospechosos, se requieren los datos de rebobinado para un “núcleo sin alambre”, Los Datos de Rebobinado de EASA- Versión 4, integrados al programa de rediseño, pueden ayudar en estos casos. Al encontrar en la base de datos un motor con parámetros similares, estos datos se pueden usar como base para diseñar el bobinado del “núcleo sin alambre”. Al localizar en la base de datos un motor adecuado, la opción del menú MotorDb -> Send to ACR, convierte los datos de ese motor en un nuevo caso de rediseño y no es necesario volver a escribir los datos. La página web de EASA cuenta con un video tutorial de este sencillo proceso.

Es común experimentar con diferentes parámetros del bobinado como el número de espiras, el paso y las conexiones. La mejor alternativa consiste en utilizar el botón Calculate para desplegar la tabla de selección y escoger la opción deseada; el resultado del rediseño se abrirá en una nueva pestaña como Rewind option # (ver Figura 3). La opción de Rebobinado Manual proporciona un cuadro de diálogo para ajustar esos valores. Sea precavido a la hora de rediseñar bobinados manualmente, ya que es posible ingresar valores “imposibles” como 4 circuitos con 6 polos, lo que el programa no permitiría normalmente.

Ajustes del tamaño del alambre
Uno de los ajustes más comunes es el del tamaño del alambre. La ranura de un bobinado puede estar muy floja o muy apretada, o el tamaño del alambre escogido podría no estar disponible en la cantidad suficiente de hilos en paralelo. El programa proporciona una calculadora poderosa para escoger la combinación entre dos tamaños (calibres) de alambre incluyendo el cálculo del porcentaje del cambio. Los valores de los nuevos tamaños de alambre calculados se ingresan automáticamente en el rediseño con los valores nuevos de CM/A (A/mm2) (ver Figura 4).

En el programa de rediseño existe un buen número de opciones convenientes. Las dimensiones del núcleo se pueden escribir en fracciones como 3 11/16, o emplear matemática simple para convertir los valores; 3.5 x 25.4 (conversión de pulgadas a mm). En el menú de Tools (Herramientas) existe una opción disponible para Definir los Tamaños de Alambre Disponibles de tal forma que solo aparecerán los alambres que se encuentren en inventario. Este listado trabaja en conjunto con la casilla de verificación de Solo Tamaños de Alambre Disponibles (Wires Sizes: Only Available), localizada en la página del Motor Original justo arriba del botón Calculate. Existen Valores Pre-establecidos para los datos de los Motores Originales. En el menú Tools seleccione Motor Defaults e ingrese cualquier dato que pueda ser usado con frecuencia. Los datos de entrada comunes son hp – kW y los calibres de los alambres AWG o Métricos. Guarde y cierre el Motor Pre-establecido  y estos valores serán fijados por defecto para nuevos rediseños. El menú Reference tiene un conjunto de calculadoras sencillas y varias tablas comúnmente utilizadas, como los datos del Alambre Magneto Redondo y las Corrientes Trifásicas a Plena Carga. También, en el menú Reference existe una versión en PDF del manual de Rediseño de Motores C.A. que tiene muchas fórmulas básicas usadas para el cálculo de rediseños. Las tablas de conversión de Concéntrico a Imbricado también están ahí, estas son usadas por algunos miembros para revertir una conversión de Imbricado a Concéntrico. Para obtener más información a cerca de la conversión a bobinados concéntricos, contacte al Soporte Técnico de EASA.

Una vez se haya calculado el rediseño de un Motor Original, los datos del Motor Original se aseguran y no pueden ser editados sin borrar los rediseños. Esto es para prevenir que esté presente un rediseño que no coincida con el Motor Original. El menú Editor -> Allow Edits permite la opción de Borrar todos los Rediseños (Delete all Redesigns) o de Clonar el Motor (Clone Motor). Al seleccionar Clone Motor se creará un nuevo Motor Original en los que los datos se pueden editar. Esto es útil en escenarios de “simulación” y para motores con varios bobinados en los cuales la mayoría de los datos físicos de cada bobinado son los mismos.

A lo largo de la búsqueda de datos de motores similares en la base de datos de bobinados y durante el rediseño de múltiples motores, puede haber un número de motores abiertos en cualquier momento. Las pestañas arriba del editor muestran la identificación del motor con un ícono para el tipo de dato. Cuando existen varias pestañas, al hacer clic derecho en cualquiera de ellas, se visualizarán las opciones para cerrar las pestañas que no son necesarias: Cerrar las otras (Close Others), Cerrar las Pestañas a la Izquierda (Close Tabs to the Left), Cerrarlas Todas (Close All).

La ayuda del programa cuenta con información útil para el rediseño de bobinados en las secciones de Concepts y Task. Los vídeos de los tutoriales están disponibles en la web de EASA y se puede acceder a ellos a través de la pantalla de Bienvenida del programa, en el menú Ayuda. Los tutoriales y la Ayuda son recursos útiles cuando surgen preguntas. Por supuesto, el soporte técnico de EASA también puede responder inquietudes relacionadas con las características y funciones del programa o ayudar con cuestiones de rediseño.

Nota del Editor: Los que habían comprado la Versión 3 recibieron automáticamente en mayo la Versión 4. De lo contrario, el programa se puede adquirir utilizando el formulario adjunto. 

Mike Howell
Especialista de Soporte Técnico de EASA

La mayoría de los centros de servicio realizan algún tipo de prueba por comparación de impulsos, aunque la terminología y la metodología pueden variar. En términos simples, se comparan las respuestas o formas de onda obtenidas al aplicar  pulsos con tiempos rápidos de subida y si existe una diferencia excesiva, la unidad bajo prueba podría estar defectuosa. La forma de onda producida por el pulso es exclusiva de la unidad bajo prueba, que por ejemplo podría ser el devanado de un estator. La forma de onda será función de la resistencia, capacitancia e inductancia del circuito bajo prueba y un buen número de variables pueden afectar esas características.

Una dificultad o reto de la prueba por comparación de impulsos ha sido su subjetividad. Es decir, que para quienes realizan la prueba no siempre es fácil obtener la misma conclusión al comparar dos formas de onda. Durante las dos últimas décadas, varios fabricantes de equipos han comenzado a utilizar métodos analíticos para evaluar los resultados de la prueba por comparación de impulsos. El objetivo es eliminar tanto como sea posible la mayor cantidad de subjetividad, de tal forma que el operador pueda decidir de forma sencilla lo que debe hacer con la unidad. El método de análisis más utilizado, en diferentes formas, es el Error de Relación de Área (EAR) .

¿Necesita estar capacitado en EAR para poder realizar las pruebas por comparación de impulsos de forma satisfactoria? No, pero si usted cuenta con dicha formación, un conocimiento básico de los datos reportados por el equipo le puede ayudar a tomar una decisión bien fundamentada.

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.

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.

Chase Fell
Precision Coil and Rotor

An ideal insulator allows no leakage current to flow. The power factor of an insulator is defined as the cosine of the phase angle between voltage and current. For an ideal insulator, the current leads the voltage by exactly 90 degrees and the power factor for this ideal system would be zero. Coil systems in electric motors and generators have inherent losses causing capacitive and resistive current flow. For this insulation, the power factor cannot be zero. 

The power factor (PF) tip-up test is commonly used as a quality measurement for new coils and windings manufactured for AC motors and generators rated 6 kV and higher. For modern stator winding insulation systems, the power factor and the dielectric dissipation factor are very nearly the same. PF tip-up testing can be useful to verify the quality of the winding manufacturing process, insulation material performance, consolidation of conductors, uniformity of groundwall taping and state of resin curing. Once an insulation system reaches corona inception voltage (CIV), partial discharge (PD) will effectively short out some of the capacitance of the insulation and the power factor will increase. PF testing is applicable to individual vacuum pressure impregnation (VPI) coils and resin-rich coils as well as cured complete windings. Power factor tip-up testing is not applicable for bench testing of green VPI coils or evaluating pre-processed complete VPI windings. 

The power factor tip-up test can be useful in the rewind shop to verify the quality of a newly-installed coil system including the effectiveness of VPI processing. PF testing of in-service windings can set a baseline measurement for maintenance trending. The in-service PF tip-up test can potentially identify groundwall insulation aging since the capacitance between the copper conductor and the core is generally reduced as delamination and/or air pockets become present in the insulation between the coils and the core.

Mike Howell, PE
EASA Technical Support Specialist

The phase balance test is briefly described in section 4.2.8 of ANSI/EASA AR100-2020. Other names for this test include open stator impedance test, ball test, small rotor test and dummy rotor test. The phase balance test is used in some form by many service centers both as a troubleshooting test and a quality control check before winding treatment. The typical approach is to apply a reduced and balanced three-phase voltage to the stator winding terminals with the rotor removed and then to evaluate the resulting current balance and magnitude. Acceptance criteria differ, but it is a reasonable expectation that the current should be balanced within 10% of the average current.

Winding RTDs are resistance-based temperature monitoring devices. Aside from just reporting winding temperature, here are some tips for maximizing the benefit of RTDs. Place six RTDs, spacing them uniformly around the core so there are two per phase. Provide a location map, numbering the RTDs, starting with the number 1 RTD in the 12:00 position. Number the RTDs clockwise facing the connection end.

Knowing where each RTD is located (which phase, as well as the physical location in the stator) provides some powerful diagnostic ability. Possible causes for deviation in temperature are:

• Two RTDs reading high, and both in the same phase: Check for voltage / current unbalance; higher current in one phase causes higher temperature in that phase.
• If the number of circuits is half the number of poles, circulating currents can occur. This situation can be exacerbated by uneven airgap which cause a further temperature increase. The corrective action, in this case, is to use the appropriate extra-long jumpers when connecting the winding.
• Higher temperature indicated in adjacent RTDs may indicate obstructed ventilation. Some possible causes are clogged filters, missing soundproofing, displaced weather-stripping, poorly positioned air baffles, or a missing J-box cover.
• Some manufacturers place all six RTDs across the 10:00 to 2:00 portion of the winding, to report more uniform temperatures. By distributing the RTDs symmetrically around the stator -- instead of just on the top -- the reported apparent temperatures often look alarming. Before returning the motor, let the end-user know where they were originally, and explain that the symmetrical placement will yield more realistic results.

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.

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

Mike Howell
EASA Technical Support Specialist

For those who work almost exclu­sively with lap or concentric wound three-phase stators, wave wound rotor connections can be a challenge. This is especially true if connection data gets lost or if an existing winding con­nection is damaged during a failure. In these cases, it is useful to have a practical method for laying out a valid connection diagram.

When installing winding Resistance Temperature Detectors (RTDs), divide the number of stator slots by the number of RTDs to install (usually six) and mark the slots accordingly. For example, a 72-slot stator with six RTDs would position an RTD in every 12th slot. That results in two RTDs per phase. Be sure to number the RTDs and provide a map of their locations to aid the customer in interpreting temperature differences. For example, unbalanced voltage might result in higher temperature in two RTDs in the same phase, while obstructed ventilation is likely to cause higher temperature in two or three adjacent RTDs.

One anomaly is WPI or WPII (weather protected) enclosures, where the top hood is integral to airflow. Some manufacturers place all six RTDs across the top of the windings (from the 10:00 - 2:00 positions) so that all RTDs are within the area receiving better cooling. This is not deceptive; it’s just meant to avoid a customer asking questions about temperature differences. For repairers, it’s a talking point with your customer when rewinding such a motor. Do they want the RTDs evenly spaced, recognizing that they will see the differences in actual operating temperature? Or do they want them placed as the manufacturer did? Better to have that conversation first, rather than raise doubts after the motor returns to service.

Note that, depending on the coils/ group and pitch, an RTD might be between top and bottom coils of the same phase, or of different phases.

Chase Fell
Technical Education Committee Chair
Jay Industrial Repair

High potential (hipot) testing procedures for motor and generator windings are usually performed with 50/60 Hz AC or DC as the power source. Hipot testing is a critical step in validating the quality of new windings. AC and DC hipot tests are also useful to understand the condition of aged insulation for machines in service. DC hipot testing is widely used in motor repair because the equipment is portable, and the steady state test current comes mostly from leakage through the insulation.

When a breakdown occurs, DC causes less damage to material adjacent to the fault when compared to AC tests. A disadvantage of DC testing is the voltage is not distributed in the same way as what the winding sees with AC. Specifically, the DC test stresses the end turns much higher.

AC hipot testing is much more consistent with the voltage stress of the machine in service. Studies have shown that the AC hipot test can reveal insulation defects that are left undetected with DC tests. An AC test can better detect voids and delamination inside the insulation system. The disadvantage of the AC test at power frequency is when the size of the test set and/or complexity of the setup becomes problematic in motor repair and in the field.

High-potential testing is routinely used to assess the ground insulation of AC stator windings in-process, after completion of a rewind and post-delivery. This webinar covers:

• Differences between AC and DC high-potential tests
• Sizing AC test sets when testing large windings
• What relevant standards address (and what they don’t)
• Communicating test requirements to all stakeholders
• When to test and at what levels
• How to evaluate results

Beneficial for service center managers, supervisors and technicians responsible for high-potential testing.

Often an overhung fan is balanced in a single plane, only to find that the vibration has shifted to the outboard bearing. Attempts to use standard two-plane techniques may result in calculated correction weights that are very large and produce poor results. There are more effective ways to approach this common problem. This presentation shows a methodical approach and techniques for tackling this difficult balancing problem.

Target audience: This presentation is intended for field service balancing technicians, supervisors and managers.

Jim McKee (deceased)
Alabama Electric Motor Service
Sheffield, Alabama 
Technical Education Committee Member 

There seems to be a long and never ending list of equipment and facilities needed by most EASA service centers. But often we are constrained by cost, available space, and more urgent priorities that keep us from fulfilling some of these needs. One such (almost mandatory) need is a vacuum pressure impregnation (VPI) system. 

Normally there are two ways to provide this service. One way is to have another EASA service center do the VPI process for you. Another is to buy your own system at a consider­able capital investment. 

There is also another option. We decided that the way to provide VPI processing was to build our own system. Most EASA service centers have a talented collection of people with numerous skills. Ours is no exception. We felt that we had the skills in house to do the job. All we needed was some hardware and to do a bit of research into how the process works. 

Gene Vogel
EASA Pump & Vibration Specialist 

There are many common causes of high vibration on rotating machinery; too many to list here. But often, what would otherwise be an acceptable level of vibration is amplified by resonance. All machines are susceptible to resonance. Resonance occurs when the natural frequency of some machine component coincides with an exciting force. When resonance occurs it is the combination of exciting force and a natural frequency that results in high vibration; both must be present at the same frequency for resonance to occur. When resonance does cause excessive vibration, it is important to identify the natural frequency and the mode shape of the vibration. A simple bump test, conducted with the machine not running, is a good first step in identifying the natural frequency (Figure 1).

This presentation demonstrates an easy-to-build temporary oven that can be constructed in the service center or in site. The recording covers:

• Materials to use and where to obtain
• Heating: electric, propane, or other?
• Measuring winding temperature
• Regulating oven temperature
• Storage of the parts when not in use
• Safety concerns and cautions

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

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

The Electrical Apparatus Service Association (EASA) has published two documents to help users and service providers ensure that motor repairs performed reflect good practices that maintain or improve a machine's energy efficiency and reliability: ANSI/EASA Standard AR100-2015: Recommended Practice for the Repair of Rotating Electrical Apparatus and the "Good Practice Guide" of the 2003 study The Effect of Repair/Rewinding on Motor Efficiency, by EASA and the Association of Electrical and Mechanical Trades (AEMT). These documents serve as tools by which service centers and end users can speak the same language when it comes to level-setting service and performance expectations on motor repair and rewind.

Also, a little more than a year ago, EASA launched its electric motor repair accreditation program, based on AR100 and the "Good Practice Guide." The program benefits both end-users and service providers by ensuring that electric motor repairs conform to the good practices identified in the aforementioned documents."

Electric motor efficiency can be maintained during repair and rewind by following defined good practices. This article builds on my previous discussion of PM and PdM for three-phase squirrel-cage motors ("PM and PdM for electric motors") by outlining some of the expectations and good practices for repairs of these types of motors.

READ THE FULL ARTICLE

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

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

Helpful tools

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

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

There is much discussion in the industry about how to properly electrically test AC stator and wound rotor windings. Topics include test voltage, procedure, frequency and when to perform the various tests. This article describes how the following standards address these questions:

• NEMA MG 1-2011
• (MG1) IEEE 43-2000
• (IEEE 43) IEEE 62.2-2004
• (IEEE 62.2) IEEE 522-2004
• (IEEE 522) IEEE 1068-2009
• (IEEE 1068) ANSI/EASA AR100-2010
• (AR100) CSA C392-2011 (C392)

These standards are regularly reviewed and coordinated, so some of the information may not match the old yellowed reference taped to your toolbox lid. These updated references should replace anything dated previous to the dates indicated on the standard. AR100 Section 4.3.1 lists the recommended tests for stator and wound rotor windings. They are insulation resistance (IR), winding resistance, growler, phase balance, surge comparison, polarity and ball rotation tests. This article covers the IR, winding resistance and surge tests. Noticeably absent from this list is the ever popular high potential (hi-pot) test. Topics covered also include:

• IR (or megohm) test
• Polarization index test
• Winding resistance test
• Surge comparison test
• Hi-pot test.

Presented by Carlos Ramirez
EASA Technical Support Specialist

Is the motor drawing high no-load amps and winding data are correct? Are you experiencing unusual heating of the stator under load? Those common questions can be answered by checking the stator core condition. This presentation will discuss how to perform a stator core test using a loop test. It also will explain how to analyze the results, providing information about the associated equipment, tips for repairing core damage and explain other alternatives for stator core testing.

The presentation covers:

• Loop test theory
• Testing procedure
• Acceptable limits for losses and core temperatures
• Associated equipment
• Tips for repairing core damage
• Alternative stator core test

This presentation will be useful for supervisors, winders and test technicians.

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

LEARN MORE

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

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

Specific changes addressed will include:

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

Target audience: Service center technicians and supervisors.

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.” 

Pat Douglas Kirby Risk
Mechanical Solutions & Service

Shaft currents have always been a concern for large motors due to magnetic asymmetries within the motor. Manufacturers strive to keep these to a minimum.

With the widespread use of Variable Frequency Drives (VFDs), shaft current issues have become a concern in all sizes of motors. If these currents are discharged through the bearings, electrical discharge machining (EDM) occurs. Proper installation of VFDs can play a large part in mitigating issues with shaft currents. 

Many end users are not aware of shaft currents or their destructive paths. All too often they think that the motor bearings keep failing because the motor repair was not completed properly. 
Service centers need to be on the lookout for these issues when repairing a customer’s equipment. Many repairs arrive at the service center with no history and no hint of what the problem with the motor might be. The technicians have to do an “autopsy” of the motor to be sure the causal problem is repaired and not just the symptom.

Chuck Yung 
EASA Technical Support Specialist

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

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

Mike Howell, PE
EASA Technical Support Specialist

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

Topics include:

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

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

There are changes in the National Electrical Code that EASA members need to know about. View this webinar to learn:

• The background behind these changes
• The 2020 change impacting reconditioned motors
• How the changes will be interpreted
• What the changes mean for the electric motor service industry

Mike Howell
EASA Technical Support Specialist

As service organizations, we should examine every phase of our projects and the related decisions we make in terms of SQDC (safety, quality, delivery and cost) every time and in that order.

• Safety – keep people safe
• Quality – fulfill requirements
• Delivery – meet time commitments
• Cost – achieve strong business results

When operational excellence principles have been adopted, organizations typically find that if they properly and intentionally attend to safety, quality and delivery, then cost can more easily be controlled leading to predictable and satisfactory business results.

Often times, the projects that are most difficult to manage properly are the ones that divert from the norm, removing us from our standard business activities. Approximately 48% of EASA service centers report providing at least one type of fieldservice as a standard business activity. These fieldservice activities are primarily vibration analysis, alignment, balancing and thermography.

A less common activity is the on-site stator rewind. Certainly, there are classes of machines (e.g., large generators) that are almost always wound on-site and there are service organizations that specialize in these activities. However, most service centers perform on-site stator rewinds infrequently and even then, many of the personnel required for the scope of work are not the personnel usually involved with fieldservice work. When working on-site and out of our element, how do we ensure the safety of all people affected by our work while delivering a quality product on-time and on-budget?

One way to mitigate risks associated with these types of projects is quality planning.

Chuck Yung 
EASA Technical Support Specialist 

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

Chuck Yung
EASA Senior Technical Support Specialist

One of the more mundane things we as repairers must be concerned with is motor storage. For many of us, storing large motors for major customers is its own profit center. For all of us, being aware of how our customers store the motors we repair and send to them is critical to customer satisfaction. A poorly stored motor is likely to suffer winding or bearing failure, and we don’t want unrealistic warranty claims over something outside our control.

Our primary concerns when storing motors, especially long-term, are windings, bearings and shaft sag.

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

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

It’s a striking fact that operating a three-phase induction motor at just 10°C above its rated temperature can shorten its life by half. Whether your facility has thousands of motors or just a few, regularly checking the operating temperature of critical motors will help extend their life and prevent costly, unexpected shutdowns. This article will show you how to go about it.

READ THE FULL ARTICLE

Art Godfrey (retired)
Birclar Electric & Electronics
Romulus, Michigan

Introduction
Modern variable frequency drives (VFDs) offer an almost dizzying range of capabilities that include output fre­quencies into the hundreds of hertz. It can be tempting to use a standard AC induction motor with one of these VFDs. But doing so requires a thorough understanding of the intended applica­tion and how the VFD will affect the motor. Since the most popular VFDs sold today are pulse-width modulated (PWM) type, the comments and recom­mendations in this article will assume that is the type used.  Also, motor volt­age will be 600 volts or less.

This presentation covers the following topics:

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

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

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.

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

Este artículo cubre las pruebas eléctricas y la inspección de motores trifásicos jaula de ardilla que han sido instalados. Los principales objetivos al probar los motores en el sitio de trabajo son: Evaluar su condición para garantizar su funcionamiento continuo odiagnosticar presuntos fallos. Aquíharemos énfasis en las pruebas y enla interpretación de los resultados, asícomo también, en la inspección física de los puntos clave. Nota: La mayoría de las prue­bas descritas también se pueden realizar a los motores con rotor bobinado y en los gen­eradores sincrónicos y de inducción. 

This webinar covers:

• Types of tests: Insulation resistance, Polarization index, High potential, Surge, Partial discharge test
• Testing of machines: Motors (AC and DC), Generators (AC and DC)

Target audience: This webinar will be most useful for service center supervisors, electromechanical technicians, winders and field service personnel.

Chuck Yung
EASA Technical Support Specialist

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

Published: August 2006 & Revised: September 2024

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

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

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

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

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

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

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

This webinar recording reviews the failures associated with 3-phase motors on Variable Frequency Drives (VFDs) and how to rewind to limit future failures. The transient over-voltages produced by the VFD can cause the winding insulation to break down. Motor manufacturers and service centers have recognized that the winding insulation system must be enhanced to help withstand the effects of being used on a VFD. Topics include:

• Brief overview of the transient voltage phenomena
• Materials for an inverter-duty winding system
• Processes for an inverter-duty winding system
• Other considerations: cables, VFDs

This webinar is intended for winders, shop supervisors and engineering staff.

Tom Bishop, PE
EAS A Senior Technical Support Specialist 

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

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

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.

Presented by Mike Howell
EASA Technical Support Specialist

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

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

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

Mike Howell, PE
EASA Technical Support Specialist

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

Tim Browne
Industrial Electric Motor Service, Inc.

I suspect that just about everyone in our industry at one time or another has had the joy of repairing a “purpose-built” motor. This kind of motor is built for a specific purpose and has characteristics that may allow it to operate under non-standard conditions. Due to the limited information that some of them display on the nameplate, the repair of these motors can be somewhat of a challenge.

Sometimes these motors possess differences such as the color of paint, the shaft size, the bearing size, or type. It can be the operating temperature and at times it can be the motor in its entirety. Following are a few useful tips we use when repairing a motor with so many question marks.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

A menudo, las inundaciones producidas por las intensas lluvias de las tormentas tropicales (huracanes, monzones y ciclones) colapsan cientos de plantas industriales a todo lo largo de la costa del golfo de México, desde la Florida hasta Texas y en otros lugares del mundo.

Para retomar las actividades productivas, los departamentos de mantenimiento y los reparadores enfrentan la difícil tarea de limpiar la suciedad y desalojar la humedad en miles de motores y generadores eléctricos. Ver Figura 1. El proceso en tales situaciones puede tomar semanas o meses y requiere procedimientos especiales para limpiar los motores contaminados con agua salada.

Aunque el problema es enorme, las fábricas pueden volver a producir más rápidamente aunando esfuerzos con centros de servicio profesionales y siguiendo algunos consejos que facilitan las tareas de limpieza. Estos incluyen, priorizar los motores que requieren ser reparados o reemplazados, almacenar adecuadamente las máquinas contaminadas y utilizar métodos contrastados para eliminar la contaminación con agua salada. Fabricar hornos provisionales in situ o en el centro de servicio también puede aumentar la capacidad de secado de los sistemas de aislamiento de los motores inundados.

Chuck Yung
EASA Senior Technical Support Specialist

There are applications where the end float inherent to a sleeve bearing machine is not desirable, and some means of limiting the axial movement is needed. This is usually accomplished by selecting an appropriate coupling and relying on the driven equipment to prevent axial movement of the motor shaft. 

The gear-hub style of coupling can be end-float limited by installing a “hockey-puck” spacer. The grid-style coupling can be limited by spacers inserted on both sides. 

Regardless of coupling style, unless the driven equipment has some internal means to limit end float, there are circumstances where some external means of preventing axial movement is needed.

Por Steven Carbone
Miembro del Comité de Educación Técnica
Industrial Electro-Mechanics

En el actual entorno competitivo cada vez mayor, los usuarios finales buscan centros de servicio de máquinas eléctricas rotativas que aumenten su oferta de valor agregado. Una de las formas más fáciles para que un centro de servicios logre esto es efectuando una inspección minuciosa y detallada de los equipos que reciben para reparación. Los resultados de dicha inspección permiten mejorar la confiabilidad de los equipos que se logra a través de los resultados de la evaluación y las recomendaciones que ofrece el centro de servicio para prevenir fallas recurrentes y mejorar el tiempo medio entre fallas.

Por Gene Vogel
Especialista de Bombas y Vibraciones de EASA

Realizar una correcta alineación de las máquinas acopladas de forma directa es un elemento esencial para garantizar la confiabilidad de operación de una máquina nueva o reparada (motor, bomba, caja de engranajes, etc.). Uno de los impedimentos comunes para lograr una alineación adecuada y un correcto funcionamiento, es el denominado  "pie suave".

John Allen
Sheppard Engineering

Clachan Hydro Power Station (HPS) went into service in 1956. Clachan HPS is located on Scotland’s west coast about 40 miles north of Glasgow. The underground power station is at the head of Loch Fyne sea loch. See Figure 1. The tailrace discharges into the Fyne River, a salmon fishing river. Loch Fyne has a renowned fishery and seafood restaurant within a mile.

The 900 ft (275 m) head vertical shaft Francis turbine driven 50 MVA, 40 MW 428.6 rpm 11 kV generator was designed by English Electric. The generator stator was recored and rewound in 1984 by Peebles Field Services (acquired by Dowding & Mills in 1998).

During the 1984 rewind, the original split core stator was rebuilt as a complete annulus. And the Class B winding was replaced by a resin rich Class F epoxy winding. The turns were insulated with Samicaflex insulation tape and the slot cell would typically have been an S5 mica tape; this is a 180g/m2 epoxy mica tape on a glass fabric. The dielectric stress for the slot cell (wall) insulation was very conservative at 41.9 v/mil (1,650 v/mm).

The rewind used 5 mm (0.197”) epoxy glass wedges with Nomex 410 packing and 4 mm (0.157”) phenolic glass coil separators. The punched slot width was 22.15 mm (0.872”) which would typically have resulted in a built slot width of 21.8 mm (0.858”) and the specified slot cell width was 21.1 mm (0.831”).

As part of Scottish & Southern Electric (SSE) program of power station refurbishment, Clachan HPS was refurbished in 2000. The program included refurbishment of the generator stator with an option to rewind if the partial discharge levels could not be improved. 

Dowding & Mills refurbished the generator stator, re-insulated the rotor and replaced the DC exciter with a brushless excitation system. They also replaced the complete station control systems together with all the low voltage (LV) and high voltage (HV) electrical installations.

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.