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

6 presentations

$30 for EASA members

 

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

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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.

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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.

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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.

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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.

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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.

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

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

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.

Illustrates procedures for manufacturing random-wound interpole and main field coils for DC machines. Covers everything from removing old coils and taking data to installing and connecting new coils, including how to construct winding forms and jigs, how to shape coils to conform with the curvature of the field frame and how to insulate field coils. Both “wet” and “dry” winding techniques are illustrated.

This training film is archived here solely for historical purposes. The film was produced many years ago and does not meet EASA's current presentation standards. Some procedures may have also changed.

Covers all necessary steps for layer-winding DC field coils, how to layer-wind a shunt field coil, how to reinsulate an interpole field coil, and how to install large field coils in the frame.

This training film is archived here solely for historical purposes. The film was produced many years ago and does not meet EASA's current presentation standards. Some procedures may have also changed.

 

This training film is archived here solely for historical purposes. The film was produced many years ago and does not meet EASA's current presentation standards. Some procedures may have also changed.

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

The Institute of Electrical and Electronics Engineers (IEEE) standard for insulation resistance testing of mo­tor and generator windings that was published in 2002 has been revised. The 2013 edition was published in March 2014. 

The first change in the new docu­ment is a slight change in the title. It has changed from “IEEE Recom­mended Practice for Testing Insulation Resistance of Rotating Machinery” to “Recommended Practice for Testing Insulation Resistance of Electric Ma­chinery.” The reason for the change was to use the more prevalent IEEE term for motors and generators. Significant changes to clauses of the standard that affect service center repairs and testing are described in this article.