Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

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

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.

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.

The webinar covers:

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

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

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

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

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

This presentation is aimed at the experienced technician and supervisor.

Chuck Yung
EASA Senior Technical Support Specialist

This paper covers:

• Interpreting AC and DC drop test results (Is that coil really shorted?)
• Differentiating between interpole and armature problems
• Locating an armature short/ground
• Locating shorted/open equalizers in an armature
• Working neutral: Did that motor arc when it left the factory? Let’s cure that problem!

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

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

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

Chuck Yung
EASA Senior Technical Support Specialist

Para la amplia variedad de aplicaciones de motores de CC, existen aquellas en las que se prefiere un motor shunt directo (straight shunt) y otras que parece que necesitan el mayor torque de arranque de un campo serie. ¿Por qué existen diferentes diseños de campo y son intercambiables? ¿Qué sucede con las placas de datos marcadas como “stab shunt” o “str shunt?” El propósito de este artículo es aclarar la confusión permanente sobre los tipos de campos, como también los beneficios de cada uno.

Un motor con solo campo shunt es llamado motor con bobinado shunt (o shunt directo), con placas de datos marcadas algunas veces como “str shunt”. El motor shunt permite un control de velocidad fácil sin requerir un drive sofisticado. La fuente de alimentación del campo podría ser tan básica como una fuente de CA variable (un variac) rectificada a través de un puente rectificador. Variando la corriente suministrada al campo shunt, se puede variar la intensidad del flujo de campo, proporcionando control de velocidad. Las extrusoras y una multitud de aplicaciones similares utilizan un simple motor shunt.

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.

Chuck Yung
EASA Senior Technical Support Specialist

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

Chuck Yung
EASA Senior Technical Support Specialist

Although the earliest practical DC motor was built by Moritz Jacobi in 1834, it was over the next 40 years that men like Thomas Davenport, Emil Stohrer and George Westinghouse brought DC machines into industrial use.

It’s inspiring to realize that working DC motors have been around for over 160 years. For the past century, DC machines over 30 or 40 kW have been cooled in the same manner – by mounting a squirrel cage blower directly over the commutator.

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.

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

Chase Fell
Precision Coil and Rotor

Los fallos a tierra, cortocircuitos y malas conexiones en las bobinas de los interpolos, campos serie y devanados de compensación de las máquinas de CC pueden causar problemas de funcionamiento que incluyen: Chisporroteo, flameo (flashover), frenado y fallos catastróficos. Algunas bobinas de campo shunt están bobinadas con muchas espiras y un alambre relativamente delgado y generalmente son excitadas con una fuente de CC independiente a la de la armadura. Por lo general, los campos serie, interpolos y devanados de compensación del circuito de armadura están bobinados con pocas espiras y alambre grueso, ya que por ellos circula la corriente de armadura. Para obtener resultados de prueba precisos asegúrese que los bobinados están limpios y secos y verifique visualmente las conexiones de los campos de baja resistencia. Para detectar problemas de calentamiento irregular o conexiones flojas o corroídas aplique voltaje CC a las bobinas de un estator de CC y realice una inspección termográfica. Compruebe que las marcas de los cables de salida sean las correctas. Estas deben coincidir con los datos de placa del fabricante original (OEM) o con las normas NEMA MG1 o IEC 60034-8, lo que aplique.

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.

Jerry Lipski
Jerry Lipski, LLC
Scheerville, IN

Ever run across brush arcing or vexing commutation issues? This paper, presented at the 2013 EASA Convention, covers:

• Definition of commutation
• Basic magnetism
• Commutation and AC in a DC armature core
• Brush construction
• The basic commutator and placement of carbon brushes
• Carbon brush arcing; what are the brushes telling you? + field case studies
• Sanding brushes
• Most common surface conditions
• Field experiences with drives
• Brushholders
• Slip ring application
• Field settings (neutral, tape method)
• Field/service center testing

Presented by Chuck Yung
EASA Senior Technical Support Specialist

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

This presentation covers:

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

This presentation will benefit service center technicians and supervisors.

Gary Braun
Brehob Corp.
Indianapolis, Indiana
Technical Education Committee Member

When servicing DC motors, one of the many tests we do to determine the condition of the commutator is to check it for loose bars.

We check for loose bars by lightly tapping the face of the commutator with a very small hammer. Then we check for suspicious sounds and move­ment or vibration of the bars as they’re struck. A loose bar will have a dull thud while tight bars will have more of a crisp “peck.” You should not feel any movement of the bar with respect to adjacent bars. 

Chuck Yung
EASA Senior Technical Support Specialist

One of the least understood parts of a DC motor is the commutator. With a little understanding and some helpful tips, commutator life can be maximized.

Commutators are made of copper bars* separated by insulation from each other and from the steel hub. Viewed from the end, each bar is wedge-shaped, tapered radially with the thickest portion towards the outside. The insulation material most often used is segment mica because it remains stable at the temperature and pressure required during assembly and operation. By alternating copper bars with mica segments, each bar is isolated electrically from the other bars. The resulting cylinder of bars and mica is mounted on an insulated steel hub.

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

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.
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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.

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Chuck Yung 
EASA Technical Support Specialist 

If you have ever tried to figure out the field re­sistance from the information on a DC motor nameplate, you probably wonder what in the heck the manufacturer was thinking! You know Ohms Law, but the nameplate information just doesn’t seem to follow it. 

Ohm’s Law: R = E/I 
I = E/R 
RI = E 
Where R = resistance E= voltage I= current

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.

This webinar covers:

• How much voltage output is too much?
• What can cause higher than desired output voltage?
• Brush spacing, brush seating, field or interpole spacing & polarity
• Interpole circuits

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

This inspection report helps record a DC motor's connection as it enters the service center. It is intended for use with 2-, 4- and 6-pole DC machines and includes space to:

• Draw and number the leads and jumpers
• Number of poles in series or in parallel
• Number of interpoles
• Number of series fields

This form will aid in collecting all needed information regarding a DC machine recieved for repair: nameplate data, armature coil data, armature dimensions, field winding data, field coil dimensions, general winding information as well as job and customer details.

This fillable PDF conveniently helps you save DC machine data for future reference. SImply copy the file or "Save As" to create a form for each motor you repair. The PDF includes a convenient button that can help you easily send DC data to EASA technical support.

This incoming inspection report provides a place to record basic DC motor conditions and test values, including:

• Customer information
• Armature voltage and amps
• Field voltage, amps ,etc.
• Electrical test information for the armature, fields, interpoles and series windings
• Brush and brushholder information

Chuck Yung
EASA Senior Technical Support Specialist

For the wide variety of DC motor applications, there are those where a straight shunt motor is preferred and others which seem to require the greater starting torque of a series field. Why are there different field designs and are they interchangeable? What about the nameplates marked “stab shunt” or “str shunt?” The purpose of this article is to clear up lingering confusion about the types of fields as well as the benefits of each.

A motor with only a shunt field is called a shunt wound (or straight shunt) motor, with nameplates sometimes labeled as “str shunt.” The shunt motor allows easy speed control without requiring a sophisticated drive. The field power supply could be as basic as a variable AC supply (a vari-AC) rectified through a bridge rectifier. By varying the current supplied to the shunt fields, the strength of the field flux can be varied, providing speed control. Extruders and a multitude of similar applications utilize the simple shunt motor.

This article discusses:

• When torque is needed
• Determining ampere-turns
• Using transformer test

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

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

Downloadable recordings in this bundle include:

The Basics: Understanding DC Motor Tests
Presented October 2016

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

Adjusting Brush Neutral
Presented June 2011

The webinar covers:

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

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

Carbon Brushes, Current Density and Performance
Presented June 2019

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

This presentation covers:

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

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

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

This presentation covers:

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

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

Final Testing of DC Machines
Presented September 2011

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

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

Advanced DC Testing
Presented April 2012

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

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

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

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

Chuck Yung 
EASA Technical Support Specialist 

EASA’s Engineering and Technical Support Department has received many calls over the past few months concerning repairs on DC motors. Most callers have asked for tips on troubleshoot­ing to make sure repairs are handled correctly. 

Prior to assembly, all windings should be tested for shorts, grounds and correct polarity. 

After a DC motor is assembled and ready to test run, a few simple checks will greatly reduce the chance of motor problems.  The following procedures should be especially helpful to those shops that don’t have a dyna­mometer. 

Mike Howell
EASA Technical Support Specialist

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

Chuck Yung
EASA Senior Technical Support Specialist

More than 400 people have at­tended EASA’s Fundamentals of DC Operation and Repair Tips seminar since it was introduced in 2003. Even the most experienced and well-trained DC technicians will appreciate picking up some more testing tips. 

This webinar covers:

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

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

Presented by Chuck Yung
EASA Senior Technical Support Specialist

This webinar explains the DC redesign process along with the other factors often overlooked that should first be considered before a redesign.  As DC machines become difficult to source it’s not uncommon for an end user to ask about redesigning a DC motor that they have in storage, including changes in voltage for the shunt field and armature circuit.  Topics include:

• Shunt fields
• Reconnection for voltage change
• Change limitations
• Series fields  
• Cautions about circuit change
•  Armature circuit voltage change  
• Interpoles
• Brushes, boxes and current density
• Armature redesign considerations

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

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.

This presentation focuses on:

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

This presentation covers:

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

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

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

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

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.

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.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Cuando se prueban armaduras de CC, ya sea al entrar a reparación o una vez rebobinadas, una pregunta que escucho muy a menudo incluye la interpretación de los resultados de la prueba de impulso (barra-barra de alta frecuencia).

Chuck Yung
EASA Senior Technical Support Specialist

When testing DC armatures, whether incoming for repair or after completing a rewind, one question I often hear involves interpreting the surge test (or the high-frequency bar-to-bar test) results. There is a lot to our interpretation of the bar-bar test or surge test.

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.

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

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

Chuck Yung
EASA Senior Technical Support Specialist

There are times when a DC motor or generator experiences a catastrophic failure and the customer wants to know why it happened. One type of failure that seems to stimulate lively conversation is when the failure involves dramatic damage to the brushholders and commutator. The term “flashover” describes the appearance of the failure; the very name conveys an accurate mental image of the failure.  See Figure 1.

The questions that arise next are predictable: “What caused this?” and ”What can be done to prevent a recurrence?” Or, if the motor was recently repaired: “What did you do to my motor to cause this?!” The purpose of this article is to help you answer those questions.

The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Air is an electrical insulator, although the dielectric breakdown voltage of air is low compared to the insulating materials we use in electric motors. Inside an operating DC motor, we find heat, carbon dust and other contaminants, and perhaps even humidity. Each of these will reduce the dielectric strength of air.

As for Ohm’s Law, E/R = I; winders use this frequently to evaluate shunt fields and to extrapolate the temperature rise of those fields. But it also applies to the armature circuit. 
At the moment a DC motor is energized, before the armature starts to rotate, the armature current is limited only by the available kVA of the power supply. 

Consider the example of a 500 hp motor, with a 500V armature circuit. Static resistance of the armature-interpole circuit measured only 0.02 ohms, so the short circuit armature current could reach 25,000 amps if the drive has sufficient kVA: 500/0.02  = 25,000 amps.

Effects on armature
Fortunately, drives ramp up the armature voltage, rather than applying it instantly. As soon as the armature begins to rotate, the inductance provided by the armature becomes a factor in suppressing the armature current. Paraphrasing the now-defunct IEEE Standard 66: When voltage E is applied across a circuit consisting of a resistance and inductance L in series, the maximum rate of rise is given by the equation di/dt = E/L amperes per second; where E equals volts, and L equals henrys. In other words, the armature current decreases rapidly as the armature speed increases.

Every DC motor can be used as a generator, by driving it mechanically and applying current to the fields. When operating as a motor, there are times where the motor might be driven by an overhauling load (e.g., a loaded conveyor running downhill; or a hoist lowering a heavy load). When that happens, the counter-emf (electro-motive force) produced overcomes the applied emf, and flashover is likely. In layman’s terms, operating conditions cause the armature current to increase rapidly, and generated voltage/current trigger the flashover. 
A list of operating events that can cause a flashover is included in Table 1.

If the interpoles are not correctly adjusted to maintain brush neutral throughout the operating load range, the shifting neutral results in arcing as the load increases outside the black band region. That can, in and of itself, trigger a flashover. (The black band region can be described as this: Weakening / strengthening the interpoles, independent of all else, until the brushes begin to spark produces a band within which no sparking occurs. That band is referred to as the “black band.” For more information, see the Assembly and Final Test section of Fundamentals of DC Operation and Repair Tips.)

Preventive measures
Working to help your customer understand the basics of how a DC motor operates can go a long way towards helping them avoid problems. One of my most vivid “triggers” of a flashover is the customer who installs a newly rebuilt compound motor with more than 50% compounding. (The percent compounding describes the percentage of total field flux contributed by the series fields, at full load.) They check rotation and discover that the motor needs to be reversed. We all know that the correct way to do this is to swap the A1 and A2 leads (the large wires that are thoroughly taped). But, says the customer, it is so much easier to swap the shunt field leads (they are smaller, and probably held in a terminal strip by screws) instead. That shortcut has worked in the past — on straight shunt motors.

With a compound-wound machine, this time-saving shortcut changed the motor from a cumulative connection to differential. The motor runs fine unloaded, and even with a moderate load. But when the load is increased to the point that the series overpowers the shunt fields, catastrophe occurs. Since this is a newly rebuilt motor, there is a very good chance that your customer will blame you. After all, you just rebuilt the motor. So it is important to educate the customer to avoid just such a situation. (And yes, I have had many, many calls where a newly installed motor failed exactly as just described.)

If someone blames a flashover on “drive settings,” that implies that the drive is accelerating or decelerating the motor too rapidly. If so, a competent drive technician should be able to adjust that to reduce the chance of flashover. Blaming the drive may instead mean that the motor is in an application calling for a regenerative drive, but the customer replaced the drive with a less expensive model that cannot handle the regenerative mode. (And the customer might not admit having done so until you press the issue.) One example would be a compound wound motor driving a roller coaster. When the cars are coasting downhill, the regenerative mode is used to prevent dangerous over-acceleration.

A compound wound motor, in such an application, requires a drive that has connection points for the shunt, armature and separate series field leads. This is to permit the motor to operate with a cumulative connection in both directions of rotation. If a compound wound motor is operated from a drive with only shunt- and armature circuit leads, in a reversing application, it will be cumulative in one direction but differentially compounded in the opposite direction. The higher the percent compounding, the greater the risk of speed instability and/or flashover. See Table 2.

Specific to any DC motor, there are several preventive measures to reduce the chance of a flashover. The first of these is to simply chamfer the end of the commutator bars. Voltage stress varies exponentially to the inverse of the radius. Chamfering the customary square corner at the end of the commutator to a 1/16” (1.6 mm) radius reduces the voltage stress to approximately 15%, significantly reducing the opportunity for flashover to occur. See Figure 2.

Add flashover protection
If a customer has chronic issues with flashover, take a lesson from the traction motor industry and add flashover protection. Install four equally spaced short lengths of angle iron in line with the end of the string band area. The bolted connection must be electrically sound and the edge closest to the commutator must be bare metal (no paint or other coating). The bare metal provides a reliable path to ground, if an arc is to occur, thus minimizing damage to the costly brush boxes and commutator. See Figure 3.

Flashover detection is commercially available and reliable. It has long been known that, at the moment a flashover begins, the field polarity reverses. Automated instrumentation, by monitoring the polarity of the field current, can shut the motor down before the fault current causes damage.

If the application is a fan, blower or downhill conveyor, where the motor might start while the load is free-wheeling in reverse, the solution could be a brake – either mechanical or otherwise, interlocked with the drive to release the brake when the motor starts. One option the end user might consider is to use the shunt fields as the dynamic brake. If they do so, the field current should not exceed 1/3 of the rated shunt field current. Otherwise, the shunt fields might overheat and fail prematurely.

The manufacturer has more latitude than we do as repairers, so it is common to see larger machines designed with a compensating winding (a.k.a. “pole face bars”), imbedded in the face of each field pole to effectively extend the influence of the interpoles. Those compensating windings, just like interpoles, must be connected correctly so as to yield the correct interpole strength. Misconnected interpoles or compensating windings (i.e., the wrong number of circuits) radically change performance and are much more likely to spark and/or flashover.

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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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.

Chuck Yung
EASA Senior Technical Support Specialist

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

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.

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.

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

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

Helpful tools

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

This video shows how to adjust the brush neutral position of a DC machine to prevent sparking at the brushes at full load. An accurate neutral setting promotes good commutation and efficient machine operation. It also minimizes commutator wear while maximizing brush life. For this video, we’re using the AC method of setting brush neutral.

Chuck Yung
EASA Senior Technical Support Specialist

We all know that stator cores should be burned at a controlled temperature to prevent lamination deterioration that can lead to harmful eddycurrent losses. But what about armatures? While that DC machine is energized by direct current, it is also true that the armature itself sees alternating current as the current in each coil reverses while passing from pole to pole. 

A temperature-controlled burnout oven permits us to cremate a stator without worry, but an armature is another story. Because the commutator is integral to the armature, and cannot be easily removed, some repairers resort to a hand-stripping operation. Careful use of a torch to warm the windings accelerates the stripping job, but controlling the core tempera­ture can be difficult. And stripping a large armature without heat is all but impossible by conventional methods. 

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

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.

Chuck Yung 
EASA Technical Support Specialist 

Have you ever wondered about the purpose of the shims found under the interpoles in most DC machines? Those shims are used by the manufac­turer to adjust the interpole strength. If they are lost, left out or mixed up, the result will be a DC motor or generator that arcs – especially when loaded.

Chuck Yung 
EASA Technical Support Specialist 

We have a DC motor that arcs when loaded. We checked all the usual suspects: brush neutral, interpole polarity relative to the armature, brush spacing around the commutator, etc. How can we determine the correct interpole circuits? 

I’m excited to be able to share a brand new DC repair tip. A conversa­tion with two EASA members led to a method for determining whether the interpoles are connected with the correct number of circuits. 

Not only is this new method easy, it’s a refinement of the interpole polarity test we routinely perform on every repaired DC machine. To explain why this method works, let’s review some design basics and then use that information to determine the correct interpole circuits.

Mike Howell, PE
EASA Technical Support Specialist

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

Mike Howell, PE
Especialista de Soporte Técnico de EASA

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

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

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

Topics covered include:

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

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

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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.  

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.

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.

Chase Fell
Precision Coil and Rotor

Ground faults, short circuits and bad connections in interpole coils, series coils and compensating windings cause performance problems in DC machines, including brush sparking, flashover, stalling and catastrophic failure. Shunt coils have many turns of relatively small wire and are usually excited by a DC source independent of the armature. Series, interpole and compensating coils in the armature circuit usually are wound with a few turns of heavy wire as these coils carry armature current.

For accurate test results, make sure windings are clean and dry. Verify connections of low resistance fields by visual inspection. Apply DC voltage to an assembled field frame and perform a thermography scan to detect problems including uneven heating and loose or corroded connections. Verify that the terminal lead markings are correct. Lead marking should conform to the original equipment manufacturer (OEM) nameplate, NEMA MG1 or IEC 60034-8, whichever is applicable.

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.

Presented by Ashutosh Kumar
Karsten Moholt AS

Learn how a fellow EASA service center interpreted different maintenance philosophies and put their own development in that curve. Their evolution has gone from workshop to predictive maintenance and beyond–to proactive maintenance, including 3D scan/print and the Internet of Things (IoT)

This recording addresses how the modern toolbox has changed–from an adjustable spanner (wrench) to sophisticated sensors. IoT is just a new tool in the box.

Mike Howell
Especialista de Soporte Técnico de EASA

Diferentes normas relevantes incluyendo la IEC 60085 y la IEEE 1 definen de forma similar los materiales electro aislantes (EIM) y los sistemas de aislamiento eléctrico (EIS). Resumiendo, los EIM son materiales idóneos para separar las partes conductoras a diferentes voltajes y los EIS son estructuras aislantes que contienen uno o más de estos materiales.

Como en cualquier sistema, existe una interacción entre los materiales usados y los diseñadores de los sistemas de aislamiento cuidan todos los detalles para evitar que esta interacción produzca resultados indeseados. Por ejemplo, es posible que dos materiales (EIM) clasificados individualmente como clase H (180ºC) tengan vida térmica en un sistema (EIS) limitado a una clase térmica F (155ºC).

Mike Howell
EASA Technical Support Specialist

Relevant standards including IEC 60085 and IEEE 1 have similar definitions for electrical insulating materials (EIM) and electrical insulation systems (EIS). To summarize, EIM are materials suitable for separating conducting parts at different voltages, and EIS are insulating structures containing one or more of these materials.

As with any system, there is an interaction between the materials used, and the insulation system developers take great care to ensure that this interaction does not lead to undesirable outcomes. For example, it is possible for two materials (EIM) classified individually at thermal class H (180°C) to have thermal endurance in a system (EIS) limited to thermal class F (155°C). Far worse outcomes could exist if material compatibility is an issue. At the service center level, our resources are generally insufficient for these types of insulation system development activities. For this reason, two approaches often seen are (1) relying on a third party (e.g., resin manufacturer) to provide a qualified insulation system bill of materials, or (2) applying commonly used materials based on their individual ratings. The first approach is strongly recommended, and the second approach can lead to disaster.

Lubrication is a vital part of any machine that moves. Understanding the mechanism that grease and oil use to provide that lubrication is important so that the maximum life of the equipment can be achieved.

This presentation discusses ways to get the most benefit from the lubricant by choosing the proper oil or grease and properly maintaining the equipment.

Critical to the process are compatibility, re-lubrication quantity and frequency and avoiding contamination.

Target audience: This presentation is most useful for service center and field technicians, service center managers and engineers desiring to specify the proper lubricant and help motor users understand proper re-lubrication for the best effect.

Jim Bryan
EASA Technical Support Specialist (retired)

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

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

Topics covered include:

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

This valuable resource is available only to EASA Members.

Active and Allied members can download this software for FREE!

This version of the EASA Motor Rewind Database software takes a large leap forward with the data that it provides members. Most notably, it now has the ability to connect to a live, ever-expanding online database of more than 250,000 windings. This live database will be continuously monitored, updated and corrected as needed by EASA’s Technical Support Staff. Using the online database guarantees you’ll have the most up-to-date information available at all times. If your computer does not have an Internet connection, the software will automatically switch to the static, local database that was included and loaded during installation. (Note: The local database does not receive updates.)

The database includes:

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

Tom Bishop. P.E. 
EASA Technical Support Specialist 

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

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

Jim Bryan (retired)
EASA Technical Support Specialist

As with most tasks, there are many ways to terminate motor leads and each one has a following who believe it is the best method. Here we will discuss some of these procedures and outline a few of the advantages and disadvantages of each. We will not consider the starting method or internal connection of the motor, but only the methods used to connect the motor leads to incoming power.

Topics covered include:

• Types of terminations
• Insulating the joints
• Medium voltage stress cones
• Recommended torque values for lugs and split bolts

JD McGlone
Technical Education Committee Member
JCI Industries, Inc.

As EASA members, we have the technical skills, knowledge and support to do almost anything in the electromechanical repair industry. Rail work is no different.

Over the past several years, I have been involved with the short line railroad industry, completing repair work and field service. Most EASA members are likely aware of these opportunities, but some may not be.

Tom Bishop
EASA Senior Technical Support Specialist

When considering building a large growler for testing armatures and rotors, the initial decision typically is to select a kVA rating. A primary reason for this is that the growler will need to be connected to a power supply of sufficient ampacity at the supply voltage. To help simplify a complex design process, four kVA ratings have been selected for this article. One of the selected ratings should fit the needs of most service centers.

This article covers:

• A design example
• Determining turns and wire size
• Building the core
• Determining coil dimensions

By Jim Bryan
EASA Technical Support Specialist (retired)

The Institute of Electrical and Electronics Engineers (IEEE) has published a new standard: IEEE Std. 3004.8-2016, “Recommended Practice for Motor Protection in Industrial and Commercial Power Systems.” If you’re an electrical professional who deals with a broad spectrum of motor protection schemes, including low- and medium-voltage AC and DC motors, then you need to become familiar with this standard.

READ THE ARTICLE

Chuck Yung
Especialista Sénior de Soporte Técnico de E ASA

Chuck Yung
EASA Senior Technical Support Specialist

This presentation examines features, benefits and drawbacks of both conventional and alternative methods of cleaning electric motors.

Methods covered include:

• Immersion tanks
• Steam cleaning
• Parts-washing machines
• Pressure washers
• Abrasives
• Ultrasonic devices

Environmental options for handling waste by-products are also addressed. If you are considering changing your cleaning methods, this webinar is for you.

John Allen
Sheppard Engineering

La Central Hidroeléctrica de Clachan, comenzó a funcionar en 1956. Esta central subterránea se encuentra localizada en la costa oeste escocesa, a unas 40 millas del norte de Glasgow y en la cabecera del lago salado Loch Fyne. Ver Figura 1. El ducto de descarga vierte el agua dentro del rio Fyne, en el cual se pesca salmón. Loch Fyne cuenta en una milla con pesca reconocida y marisquerías de renombre.

La turbina Francis de eje vertical con salto de agua de 900 pies (275 m) que acciona un generador de 50 MVA, 40 MW 428.6 rpm 11 kV fue diseñada por English Electric. En 1984, el núcleo del estator fue reconstruido y el estator fue rebobinado por Peebles Field Services (adquirida en 1998 por Dowding & Mills).

Durante el rebobinado de 1984, el núcleo original fabricado en secciones, fue reconstruido totalmente en forma de anillo y el bobinado Clase B fue reemplazado por un bobinado epóxico resin-rich Clase F. Las espiras fueron aisladas con cinta Samicaflex y el aislamiento a tierra generalmente estaba fabricado con cinta de mica S5; esta es una cinta de mica de 180g/m2 sobre un tejido de fibra de vidrio. La rigidez dieléctrica del aislamiento a tierra (Pared de aislamiento) de 41.9 v/mil (1,650 v/mm) era muy conservadora.

Durante el rebobinado se utilizaron cuñas epóxicas de vidrio de 5 mm (0.197”) con un relleno de Nomex 410 y separadores de bobinas de vidrio fenólico de 4 mm (0.157”). El ancho de la ranura perforada era de 22.15 mm (0.872”), lo que normalmente habría dado lugar a un ancho de ranura construida de 21.8 mm (0.858”) y el ancho de la pared de aislamiento especificada era de 21.1 mm (0.831”).

Como parte del programa para el reacondicionamiento de centrales eléctricas de la Scottish & Southern Electric (SSE), La Central hidroeléctrica de Clachan fue reacondicionada en el año 2000. El programa incluía el reacondicionamiento del estator del generador con la opción de rebobinarlo, si no se podían mejorar los niveles de descargas parciales. 

Dowding & Mills reacondicionó el estator del generador, re-aislando el rotor y reemplazando la excitatriz de CC por un sistema de excitación sin escobillas. Ellos también cambiaron completamente los sistemas de control de la estación, conjuntamente con todas las instalaciones eléctricas de bajo y alto voltaje.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Aunque el primer motor de C.C. práctico fue construido por Moritz Jacobi en 1834, fue durante los 40 años siguientes que hombres como Thomas Davenport, Emil Stohrer y George Westinghouse fabricaron máquinas de C.C. para uso industrial.

Es inspirador darse cuenta que los motores de C.C. han estado trabajando por más de 160 años. Durante el siglo pasado, las máquinas de C.C. con potencias por arriba de los treinta o cuarenta kW han sido refrigeradas de la misma forma, montando un soplador de aire de jaula de ardilla directamente en el colector.

Chuck Yung
EASA Senior Technical Support Specialist

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

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

This presentation covers:

• Who can perform repairs on hazardous location motors?
• What does it take to be certified?
• UL Files: Manufacturer and Rebuild Class, division, group and zone
• Temperature codes CSA, IECEx, FM and other third parties

Target audience: This will benefit service center management for firms that are interested in learning more about servicing hazardous location motors.