Chuck Yung 
EASA Technical Support Specialist 

While shaft currents are not a new problem (papers on the subject date back prior to 1930), what is “new” is our understanding of how to solve the problem. Shaft currents have been described as shaft voltages, circulat­ing currents, bearing currents and circulating voltages. This article will refer to the phenomenon as “shaft currents” because it is the current that causes the damage.

When a conductor is passed through a magnetic field, voltage is induced into the conductor. 

It is not the voltage that damages a bearing, but rather the current. (Fuses fail because the current is too high, not the voltage.) We don’t have a practical way to measure the current through the shaft, so we measure the magnitude of the voltage instead. 

This presentation introduces you to ANSI's new shaft alignment standard. Topics covered include:

• A discussion of alignment Quality grades, AL 1.2, AL 2.2, AL 4.5
• Shaft alignment tolerances
• Issues affecting measurements
• Conditions affecting alignment stability

Target audience: This presentation benefits service center technicians and supervisors looking to improve shaft alignment knowledge and skills. 

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

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

Cyndi Nyberg 
Former EASA Technical Support Specialist

There are a number of ways that the shaft of an electric motor can become magnetized in service. The most likely culprit is electric current through the motor and shaft, either from internal dissymmetry, welding or from a variable frequency drive. It can also be caused by electrical faults in the system, or even a lightning strike. 

We of course know that shaft voltages and the associated currents can cause bearings to fail. A typical ball bearing failure from shaft currents is shown in Figure 1. when a shaft is magnetized, it can further lead to bearing failures, unless something is done to elimi­nate the residual magnetism. The first reason for bearing failures is that the residual magnetism can cause shaft currents, which can quickly lead to bearing failures. But in addition, a magnetized shaft will attract bits of metal to the bearings. This reduces bearing life because it damages the bearing surfaces. 

The magnetism in the shaft may be strong enough that a screwdriver that sticks to the shaft. In fact, this is the most simple test to check for a magnetized shaft. 

Steve Skenzick
HPS Electrical Apparatus Sales & Service

En mi centro de servicio hemos visto problemas en ejes previamente reparados que fueron metalizados. En estos casos recibimos motores para revisión. Después de la inspección y de medir los ajustes de los rodamientos en el eje, encontramos algo que simplemente no se “sentía” bien. Podríamos decir por la apariencia que los ejes habían sido reparados antes de la revisión actual.

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

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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!

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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

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

Neville Sachs, P.E.
Applied Technical Services, Inc.,
Syracuse, NY

This technical paper, presented at the 2014 EASA Convention, will help you understand how and why shafts and fasteners fail. This paper covers:

• Discussion of material properties typically found in motor shafts, machine shafts and common fasteners
• Differentiating between overload and fatigue failures
• Understanding and identifying the difference between ductile and brittle materials, and how their fracture appearances differ
• A detailed explanation of how to identify fatigue failures, including the rate and direction of force application and the effect of stress concentrations
• Examples of several failure analyses

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

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

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

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

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

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

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

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

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

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Automatic alignment instruments are no substitute for the underlying process of aligning direct-coupled machines. This presentation explains the simple calculations that govern the alignment process. That understanding will allow technicians to use any alignment tool more effectively and deal with issues that confound the process.

En toda reparación mecánica, la capacidad para desmontar, reparar y volver a montar el motor de forma apropiada sin dañar innecesariamente ninguna de sus piezas es fundamental. Esto suena sencillo, sin embargo, durante el proceso de desarme se cometen demasiados errores costosos.

Si todos los motores entraran “como nuevos”, la tarea sería más simple, aunque esto no sería garantía de que el montaje del motor fuera adecuado.

Cuando un centro de servicio recibe un pago por reparar un equipo, quiere que este permanezca en funcionamiento, ya que, si el equipo falla dentro del período de garantía, deberá asumir el costo de volver a repararlo. Por lo que tiene sentido realizar la reparación correcta la primera vez.

Los procedimientos de reparación, así como los propios motores, son afectados por los cambios en la tecnología. Este libro intenta incluir las últimas tecnologías comprobadas. En muchos casos, los métodos de reparación tradicionales aún pueden ser la alternativa más práctica. Las opciones presentadas a lo largo de este libro están destinadas a ayudar a los técnicos a seleccionar el método de reparación correcto, reconociendo que la decisión final recae en el propietario del equipo.

Algunas veces los métodos de reparación pierden popularidad, no porque aparezcan métodos mejores sino debido a técnicas deficientes. Otros métodos de reparación son adecuados para algunas aplicaciones, pero no para otras. Es trabajo del reparador decidir cuál será el mejor método para cada caso.

Este libro se encuentra dividido en secciones para los componentes básicos del motor con métodos de reparación y consejos dispersos por todas partes. Donde resulte práctico, se discuten también las causas de fallo. Esto ayudará a los técnicos a seleccionar el método de reparación más apropiado para cada aplicación en particular. La información presentada se basa en publicaciones de EASA y en revistas técnicas y literatura suministrada por fabricantes de motores, proveedores y centros de servicio establecidos.

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Tabla de contenido

• Terminología del motor
• Aplicaciones del motor y encerramientos
• Procedimientos de inspección y prueba
• Consejos para desmontar motores
• Rodamientos
• Alojamientos de rodamientos, orificios de eje, sellos y ajustes
• Ejes
• Rotores
• Ensamble del motor
• Accesorios y cajas de conexiones del motor
• Dinámica del motor
• Vibración y geometría del motor
• Corrientes por el eje/rodamientos
• Consideraciones especiales para motores a prueba de explosión
• Fallos en las componentes mecánicas
• Reparaciones misceláneas

Esta obra contiene muchas sugerencias sobre el manejo apropiado de las diferentes partes de un motor para minimizar los daños durante el proceso de reparación. Sin embargo, es imposible desarrollar un listado que las incluya todas.

En cambio, el principio básico de tomarse el tiempo para usar la herramienta adecuada y por lo general el procedimiento apropiado guiará a los técnicos por el camino correcto.

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.)

Download a FREE PDF using the link below or buy printed copies in EASA's Online Store

 

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

WARNING: HAZARDOUS AREA MOTORS Some elements of this Good Practice Guide To Maintain Motor Efficiency, particularly those concerning changes to windings, do not apply to hazardous area/explosion-proof motors (e.g., UL, CSA, IECEx). Do not use this guide for those types of motors.

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.)

Descargue un PDF GRATIS utilizando el link.

 

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

ADVERTENCIA: MOTORES PARA TRABAJAR EN UBICACIONES PELIGROSAS Algunos elementos de esta Guía de Buenas Prácticas para Conservar la Eficiencia del Motor, especialmente los relativos a los cambios en los bobinados, no aplican a motores que trabajan en zonas peligrosas/a prueba de explosión (ej., UL, CSA, IECEx). No use esta guía para este tipo de motores.

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.

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

When a shaft is in need of repair, often the first step is to determine the corrective method required. Econom­ics and best practices are typically sig­nificant factors in the decision-making process in selecting the method of repair. The types of shaft repairs that will be dealt with here are:  opposite drive end bearing journal, drive end bearing journal and a bent shaft. The objective is not to detail the repair processes, but to identify the most common methods appropriate to the types of repair and considerations associated with each method. Table 1 summarizes the methods for various load conditions.

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.

Eugene Vogel
EASA Pump & Vibration Specialist

It is common for vertical turbine pumps (VTP) to be designed with mul­tiple mixed flow impellers (sometimes 12 or more) and for the pump rotor to be supported by the vertical pump mo­tor.

Vertical pump motors can be solid shaft or hollow shaft. Solid shaft motors have an annular keyway in the shaft that is engaged by a solid coupling that supports the pump rotor. 

Hollow shaft motors support and drive the pump rotor from the top by means of a head shaft fitted through the hollow motor shaft to the pump line shaft. In either case, there is an adjustment that lifts the pump rotor so it is supported by the motor shaft. This adjustment is obviously critical to the proper operation of the pump and motor and can have a significant effect on the motor load (current). Presented here are some of the main concerns for setting this pump lift ad­justment.

This video explains how to measure the diameter of a bearing journal accurately to within five hundred-thousandths of an inch or one-thousandth of a millimeter. This critical step will determine if the shaft needs any repairs for proper bearing fitment.

Topics covered include:

• Tools and supplies needed
• How to validate micrometer accuracy
• Minimum number of measurement locations
• How to measure a bearing journal

DESCRIPTION
This 94-page handbook (3.5" x 6", 9cm x 15cm) contains carefully selected materials designed to assist repair firms in their everyday work. Just as important, your customers and potential customers can use this pocket handbook as a handy reference for mechanical data for motors and driven equipment. 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!

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TABLE OF CONTENTS

Alignment
Alignment Information
Suggested Alignment Tolerances
ANSI/ASA Alignment Quality

Balancing And Vibration
Single-Plane Versus Two-Plane Balancing
Vibration Tests
Unfiltered Housing Vibration Limits
FFT Vibration Analysis
Vibration Constants
Vibration Conversion Factors
Electric Motor Vibration Diagnostic Chart

Motor Application Forumlas
Output
Shear Stress
Speed–AC Machinery 
Affinity Laws–Centrifugal Applications

Conversion Factors, Equivalencies & Formulas
Conversion Factors
Temperature Conversion Chart
Common Fractions Of An Inch–Decimal & Metric Equivalents
Prefixes–Metric System
Formulas For Circles

Bearings
Nominal Dimensions For Radial Ball Bearings
Nominal Dimensions For Cylindrical Roller Bearings
Radial Ball Bearing Fit Tolerances
Cylindrical Roller Bearing Fit Tolerances
Lock Nuts And Lock Washers For Ball Bearings

Motor Bearing Lubrication
Lubricating Oil Viscosity Conversions
NLGI Grease Compatibility Chart
Grease Classifications
Grease Relubrication Intervals

Metals And Alloys
Properties Of Metals And Alloys
Weight Formulas For Steel
Thermal Linear Expansion

Bolts
ASTM And SAE Grade Markings For Steel Bolts And Screws
Precautions For Tightening Bolted Joints
Bolt Tightening Torque Values
Tap Drills And Clearance Drills For Machine Screws

Keys And Keyseats
NEMA Keyseat Dimensions–Foot-Mounted AC & DC Machines
IEC Shaft Extension, Key And Keyseat (Keyway) Dimensions
Square And Flat Stock Keys
Standard Keyseat Sizes
Metric Keys–Standard Sizes

Belts And Sheaves
Pulley Formulas For Calculating Diameters and Speeds
Belt Installation
Belt Tensioning
Belt Deflection Force And Elongation Ratio
Standard V-Belt Profiles And Dimensions
V-Belt Sheave Dimensions
V-Belt Sheave Dimensions For AC Motors With Rolling Bearings
Application Of V-Belt Sheave Dimensions To AC Motors With Rolling Bearings
Mounting Of Pulleys, Sheaves, Sprockets, And Gears On Motor Shafts
Minimum Pitch Diameter For Drives Other Than V-Belts

Welding, Brazing And Soldering
Recommended Copper Welding Cable Sizes
Types Of Weld Joints 
Brazing
Basic Joints For Brazing
Soldering
Melting Temperatures Of Tin-Lead-Antimony Alloys
Flux Requirements For Metals, Alloys And Coatings

Slings, Wire Rope, Shackles and eyebolts
Types Of Slings
Typical Sling Hitches
Wire Rope
Spreader Bars
Lifting Capacity
Forged Shackles
Eyebolt Strength

Common Signals For Crane

Fundamental to every good mechanical repair is the ability to disassemble, repair and reassemble the motor correctly without unnecessary damage to any of the motor parts. This sounds simple, and yet too many costly mistakes are made in this process of taking things apart. If every motor repaired was in “as new” condition, the task would be much simpler. But this would be no guarantee that the reassembly would be correct.

​There is usually an easy way and a hard way to remove and install parts. Brute force is seldom the easiest or the correct way. The old saying of “don’t force it, get a bigger hammer” is seldom the best way.

When a service center is paid to repair equipment, the service center wants it to stay in operation. If the equipment fails again—within the warranty period—the service center pays to repair it again. It makes sense to repair it correctly the first time.

In order to improve equipment, it is important to know how and where it operates. Without understanding why a motor fails, it is impossible to deliberately improve its mean time between failures.

To do this, there must be communication between the service center and the motor user. Not only does this help the repairer decide the best course of action, but it helps the user appreciate the professionalism of the service center.

Repair procedures, like motors themselves, are affected by changes in technology. This book attempts to include the latest proven technologies. Time-honored methods of repair, in many cases, may still be the most practical option. Options presented throughout this book are intended to help the technician select the appropriate repair method, recognizing that the ultimate decision rests with the equipment owner.

Repair methods sometimes fall into disfavor, not because better methods are introduced, but because of poor techniques. Other repair methods are well-suited to some applications but not to others. It is the job of the repairer to decide what is the best method for each case.

This book is divided into sections for basic motor components with repair methods and tips dispersed throughout. Where practical, reasons for failures are also discussed. These will aid the technician in selecting the most appropriate method of repair for each unique application.

The information presented draws from EASA publications, IEEE publications, technical journals and literature supplied by vendors, motor manufacturers and established service centers.

This book contains many suggestions on how to correctly handle the various parts of a motor during the repair process so as to minimize damage. However, it is impossible to develop an all-inclusive list. Instead, the basic principle of taking the time to use the correct tool and correct procedure will usually lead the technician down the right path. Always remember, if it has to be forced beyond reason, it might be that neither the proper tool or procedure is being used or something is wrong with the parts. Step back and ask “What am I overlooking?”

Table of Contents

1. Motor Nomenclature
2. Motor Applications and Enclosures
3. Test and Inspection Procedures
4. Motor Disassembly Tips
5. Bearings
6. Bearing Housing Repair, Shaft Openings, Seals and Fits
7. Shafts
8. Rotors
9. Motor Assembly
10. Motor Accessories and Terminal Boxes
11. Motor Dynamics
12. Vibration and Motor Geometry
13. Shaft/Bearing Currents
14. Special Considerations for Explosion-Proof Motors
15. Failures in Mechanical Components
16. Miscellaneous Repairs

This book is available as part of EASA's Fundamentals of Mechanical Repair seminar.

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Chuck Yung
Especialista de Sénior de Soporte Técnico de EASA

Una de las cosas más mundanas de las que debemos preocuparnos como reparadores es el almacenamiento de los motores y para muchos, almacenar motores grandes para clientes importantes representa ganancias. Para todos nosotros, ser conscientes de cómo nuestros clientes almacenan los motores que les reparamos es crítico desde el punto de vista de la satisfacción del cliente. Es probable que un motor mal almacenado sufra fallos en el devanado o en los rodamientos, y no queremos reclamos por garantía poco realistas sobre algo que está fuera de nuestro control.

Nuestras principales preocupaciones al almacenar motores, especialmente a largo plazo, son los devanados, los rodamientos y el pandeo del eje.

Gene Vogel
EASA Pump & Vibration Specialist

Shaft alignment is a critical step in the installation of rotating machinery, in a new installation or a repaired machine. Skipping or botching this step can decrease operating efficiency and shorten machine life. The procedure for aligning two rotating machines requires measuring their relative shaft positions and adjusting one or both machine cases, usually by shimming at the feet. Until recently, though, how closely the shafts need to be aligned was an open question. That changed with the publication of American National Standards Institute/Acoustical Society of America (ANSI/ASA) standard 2.75-17. Here is a summary of what it covers and how it will benefit users involved with shaft machinery alignment.

• The need for a standard
• Purpose and scope
• Tolerances
• Alignment principles
• Alignment quality grades
• Making machine moves

READ THE FULL ARTICLE

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

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

Las secciones del manual incluyen:

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

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

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

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

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

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

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

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PRINTED BOOK DOWNLOADABLE PDF

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

NEMA - English NEMA - Español

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

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

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

This manual focuses primarily on NEMA motors.

Sections in the manual include:

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

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BOOK DOWNLOAD CD-ROM BOOK & CD-ROM

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

 

Eugene Vogel
Especialista en Bombas y Vibraciones de EASA

Es común que las bombas de turbina vertical (VTP) se encuentren diseñadas con varios impulsores de flujo mixto (algunas veces 12 o más) y que los rotores de las bombas estén soportados por los motores verticales. Los motores de las bombas verticales pueden ser de eje macizo o hueco. Los motores de eje macizo tienen una cuña o chaveta anular (en forma de anillo) en el eje, para asegurar un acoplamiento sólido que soporta el rotor de la bomba.

Los motores de eje hueco soportan y accionan el rotor de la bomba desde la parte superior, mediante un cabezal de eje que está asegurado al eje lineal intermedio (line shaft) a través del eje hueco del motor. En cualquiera de los casos, existe un ajuste que eleva el rotor de la bomba para que quede soportado por el eje del motor.

Obviamente este ajuste es crítico para el funcionamiento adecuado de la bomba y el motor y puede llegar a tener un efecto significativo en la carga del motor (consumo de corriente en amperios). En este artículo se presentan algunos puntos importantes para ajustar la elevación del eje de la bomba.

Cyndi Nyberg 
Former EASA Technical Support Specialist 

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

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

This book was developed to help electric motor technicians and engineers prevent repeated failures because the root cause of failure was never determined. There are numerous reasons for not pursuing the actual cause of failure including:

• A lack of time.
• Failure to understand the total cost.
• A lack of experience.
• A lack of useful facts needed to determine the root cause.

The purpose of this book is to address the lack of experience in identifying the root cause of motor failures. By using a proven methodology combined with extensive lists of known causes of failures, one can identify the actual cause of failure without being an “industry expert.” In fact, when properly used,  this material will polish one’s diagnostic skills that would qualify one as an industry expert.

The book is divided into the various components of an electric motor. In addition to a brief explanation of the function of each component and the stresses that act upon them, numerous examples of the most common causes of failure are also presented.

For this second edition, the manual has been reorganized and updated with new information including a new approach to methodology, new case studies and a new section covering synchronous machine failures. This could not have been done without many contributions from EASA members and the Technical Education Committee. 

The all new “Root Cause Methodology” section goes into great detail explaining that effective root cause failure analysis must take place within the context of a practical problem-solving methodology or framework. It covers a modified Plan-Do-Check-Act process that emphasizes the importance of planning and the related problem-solving methodology components. This section also explains A3, a high-level reporting tool that is very effective for problem solving.

In addition, besides a systematic approach to problem solving, root cause failure analysis of motors and motor systems requires familiarity with contributing factors attributable to various kinds of applications, environments and industries. This includes how various stresses can affect motor components and the reciprocal impact the motor system may have on the motor. This section includes a table with a detailed summary of motor stresses. 

There also is a new section on “Synchronous Machine Failures” and an expanded “Case Studies” section. Readers are guided through eight case studies.

With 328 pages, the book provides extensive information, including a wide range of failures, the likely causes listed, and the methodology for confirming the probable cause of each failure. 

Members may purchase a printed manual and/or a PDF download. The printed manual is in black and white, while the download shows most of the failure photos in color.  

Sections in the manual include:

• Root Cause Methodology (all new)
• Bearing Failures
• Stator Failures
• Shaft Failures
• Rotor Failures
• Mechanical Failures
• DC Motor Failures
• Synchronous Machine Failures (all new)
• Accessory Failures
• Case Studies (expanded)
• References

This book is available as part of EASA's Root Cause Failure Analysis seminar.

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PRINTED COLOR BOOK DOWNLOADABLE PDF PRINTED COLOR BOOK & PDF

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DISCOUNTED BLACK & WHITE BOOKS!
Prices are now DISCOUNTED on remaining black & white books while supplies last! If you have already purchased a black & white manual and are interested in the color version, please contact EASA Customer Service (+1 314 993 2220).

B&W BOOK B&W BOOK & DOWNLOAD

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Presented by Chuck Yung
EASA Senior Technical Support Specialist

This webinar explains what shaft currents are, what causes them, and differentiates between the two common causes:

1. Circulating currents which affect DC motors and AC motors not operating from a drive
2. Shaft currents caused by operation from a VFD, and how to tell the difference between the two.

This webinar also discusses and compares methods to mitigate shaft currents and explains why the different causes of shaft currents require different solutions. It covers:

• Shorted rotor iron
• Uneven air gap
• Unbalanced voltage
• What type of grounding brush works best?
• Role of carrier frequency in causing shaft currents
• How to recognize the problem on site
• Insulation thickness, capacitance, and types of insulated bearings

This information is useful to engineers, service center managers, mechanics and anyone interacting with customers.

Presented by Gene Vogel
EASA Pump & Vibration Specialist

There are heat methods and press methods for straightening shafts. This webinar reviews those methods, their pros and cons, and when one method or another may be applicable.

• Various shaft bend modes and how to identify them 
• An illustration of an effective method using heat to straighten a shaft 
• A description and precautions for use of a press to straighten a shaft 
• An explanation of how metallurgy impacts shaft straightening

This webinar is intended for service center engineers, machinists and mechanics.

The slender dimensions of many pump shafts make them susceptible to distortion, which affects pump performance and reliability. This recording presents a methodical approach and effective techniques for measuring and correcting shafts which are bent or twisted.

Target audience: This presentation is intended for service center supervisors, managers and machine shop technicians.

Jasper Fisher 
Rexel Motor Repair 
Alton, Illinois 
Technical Education Committee Member 

Like most maintenance and repair tasks, a successful outcome is gen­erally predicated on good planning and preparation. The first steps in the process are often the most critical. 
When preparing to remove a shaft from an armature (Figure 1) or rotor core (Figure 2), first measure and record the location dimensions of all shaft-mounted components. This in­
cludes materials such as bearing spacer collars, flingers, and removable cool­ing fans and the shaft-to-core location dimensions. 

A common reference measurement is from the outer edge of the lamina­tion stack to a bearing journal shoulder and/or the shaft extension end. These location measurements should be made to 1/32” +/-1/64” (0.8 mm +/-0.4 mm) (or better) and be permanently recorded in the job record. 

Steve Skenzick
HPS Electrical Apparatus Sales & Service

At my service center, we have seen problems with previously repaired shafts that were metal sprayed. In these cases we received motors for overhaul. Upon inspection and measuring the bearing shaft fits, we found something that just didn’t “feel” right. We could tell from the appearance that the shafts had been repaired prior to the current overhaul.

Cyndi Nyberg
Former EASA Technical Support Specialist 

Shaft failures are not an everyday occurrence, but when they come in, it can be an interesting challenge to determine the cause of failure. Regardless of what caused the shaft to fail, what actually happens when it bends or breaks? 

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

Two common scenarios that service centers deal with regarding belt drive applications are failure of a motor drive end ball bearing or breakage of the shaft at the drive end bearing shoulder. The cause of these failures often is over-tensioning of the v-belts. However, there are many other faults or undesirable practices that can lead to premature bearing failure, belt wear and sheave wear. 

Due to practical space limitations, this article won’t be exhaustive in its coverage but will deal with common scenarios other than motor bearing failure and shaft breakage.

This presentation covers:

• Shaft material and specs
• Shaft coupling types
• Machining for shafts
• Bronze, plastic, graphite and cutlass bearing options
• Bearing clearance concerns and reference data 
• Bearing housing fits

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

The rules of thumb often applied to journal bearings in horizontal machines don’t apply to vertical machines. Vertical turbine pumps are a common example.

This presentation explains the characteristics of bearings in these pumps and provide examples of manufacturers specifications.

In addition, specialty bearing materials will be discussed in regard to applications, specifications and installation.

Target audience: This webinar is most useful for service center technicians and engineers. The content is beneficial for supervisors and managers who are responsible for pump failure analysis and testing.

9 presentations

$45 for EASA members

 

A special discounted collection of 9 webinar recordings focusing on a wide variety of vibration, balancing and alignment topics.

Once purchased, all 9 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

An Overview of Vibration Tolerances
Presented August 2019

When it comes to machine vibration, “how much is too much” depends on a number of factors. Knowing which standard and/or tolerance applies requires a working knowledge of the standards and some basics of vibration terminology. This  presentation provides an overview of where and how NEMA, IEC, ISO and Hydraulic Institute standards may apply to machines commonly encountered in EASA service centers.

• NEMA, IEC, ISO and Hydraulic Institute standards
• Basic vibration terminology
• What standard applies?

Target audience: Service center managers, engineers, in-shop and field service technicians can benefit from a clearer understanding of vibration standards and terminology.

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Basics of Machinery Foundations and Bases
Presented November 2012

A faulty machine foundation or base can lead to excessive vibration and premature failure. This presentation explains the fundamentals of machinery foundation construction and how to identify and troubleshoot machine base problems, including basic vibration techniques and ODS analysis.

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Fundamentals of Shaft Alignment
Presented November 2012

Automatic alignment instruments are no substitute for the underlying process of aligning direct-coupled machines. This presentation explains the simple calculations that govern the alignment process. That understanding will allow technicians to use any alignment tool more effectively and deal with issues that confound the process.

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Shaft Alignment
Presented March 2016

This webinar recording provies a straightforward look at the simple relationship between shaft centerlines that is known as shaft alignment. Bypassing the common discussion of laser and manual instruments, this presentation gets to the heart of the shaft alignment process. Topics covered will include:

• Fundamental concepts
• How to visualize machine case position
• Practical solutions for moving machine cases
• Applying tolerances
• The foot-base-foundation connection

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ANSI's New Shaft Alignment Standard
Presented July 2018

This presentation introduces you to ANSI's new shaft alignment standard. Topics covered include:

• A discussion of alignment Quality grades, AL 1.2, AL 2.2, AL 4.5
• Shaft alignment tolerances
• Issues affecting measurements
• Conditions affecting alignment stability

Target audience: This presentation benefits service center technicians and supervisors looking to improve shaft alignment knowledge and skills. 

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How to Balance Overhung Fans
Presented October 2011

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.

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Vibration on Belt Driven Machines
Presented June 2013

This presentation focuses on:

• Identifying belt vibration
• Identifying pulley pitch line run-out vibration
• Other vibration sources
• ODS analysis

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The FFT (aka Spectrum): What It Is and Ways to Use It
Presented July 2012

This presentation examines:

• How the spectrum is generated from the vibration signal
• The effect of f-max ad resolution settings
• Averaging techniques
• Scaling and demodulation

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Vibration Problems on Vertical Motors and Pumps
Presented December 2010

When motors are installed on top of vertical pumps, high vibration is a common problem. The problem may be mechanical, hydraulic or structural.

This presentation provides an understanding of the nature of this style pump and the various forces essential to diagnosing and correcting vibration problems on vertical pump motors.