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.

By Jim Bryan
EASA Technical Support Specialist (retired)

The effects of excessive temperature on motor performance are notorious. After moisture, they are the greatest contributor to bearing and winding failures. Understanding the source of increased temperature is key to correcting the problem and improving the reliability of your facility’s motor fleet.

Topics in this article cover:

• Overload and service factor
• Ventilation
• Voltage variation
• Electrical steel
• Current density
• Circulating currents
• Harmonics

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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 Senior Technical Support Specialist

I’ve often commented on how for­tunate we are to work on such a variety of electric motor designs. One day, you are working on a new design some designer has recently created, and the next day you are repairing a motor that could be in a museum. It’s fascinating to see the different ways engineers have devised to do the same thing, and yet reassuring to see how many things remain unchanged even after a century of electric motors. 

One aspect of electric motors that could be placed in both categories is the way an electric motor is cooled. This article takes a look at how motors are cooled and how we can improve cool­ing for some of the special applications we encounter.

Jim Bryan
Especialista de Soporte Técnico de EASA (retirado)

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

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

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

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

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

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

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

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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

This webinar discusses:

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

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

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

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

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

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

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