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Factors to Consider When Testing DC Armatures

  • May 2021
  • Number of views: 2616
  • Article rating: 5.0

There are a lot of factors to take into consider when interpreting the bar-bar test or surge test. This articles reviews those factors.

Factores a Considerar al Probar Armaduras de CC

  • May 2021
  • Number of views: 2878
  • Article rating: No rating
Hay muchos factores a tener en cuenta al interpretar la prueba de barra-barra o la prueba de sobretensión. Este artículo revisa esos factores.

Two case history examples point to need for caution with metal spray

  • June 2018
  • Number of views: 2349
  • Article rating: No rating

Two case histories point out the need for caution when working with metal sprayed shafts:

  • Example 1: When measuring the bearing fit shaft size, the micrometer didn’t feel right; mushy, not solid, although the journal was very close to the specified size. After using two micrometers to experiment with one of these frosted fits, it was discovered that the measurement on one micrometer changed when tightening down the other micrometer and vice versa.
  • Example 2: The bearing journals on a large armature began to fail while the armature was coming up to speed in balance stand.

Power supply considerations when building a large growler

  • July 2017
  • Number of views: 2442
  • Article rating: 5.0

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.

Flashover: Causes and cures for damage to brushholders, commutators

  • April 2013
  • Number of views: 9769
  • Article rating: 3.3

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. 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.

How to strip an armature without degrading the core

A simple and efficient method to improve quality and save labor

  • January 2008
  • Number of views: 1936
  • Article rating: 5.0

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?

Surge testing of DC motor and generator armatures

  • July 2007
  • Number of views: 2615
  • Article rating: 5.0

In the April 2007 issue of CURRENTS, we covered surge testing anomalies, specifically for AC windings. The surge test can be used for DC windings as well. It can be a useful tool for evaluating armatures and some DC fields. A note of caution: If a winding does not have a minimum insulation resistance per ANSI/EASA AR100-2006, it is not safe to apply an overpotential test (surge or high potential). Surge testing shunt fields may not provide meaningful results if the surge pulse decays too quickly - if it dissipates through only the first few hundred turns. To obtain a test voltage high enough to test every turn would require too high a voltage. That high voltage would overstress the groundwall insulation.

Troubleshooting tips for armature rewinds

  • April 2003
  • Number of views: 1839
  • Article rating: 5.0

When an armature is rewound, there is always a slim chance that it may be connected incorrectly. If two coil leads are switched, or if the error results in an armature where each coil closes on itself, normal tests will detect the problem. The trouble arises when the misconnection results in a uniform winding. When that happens, the result may be—in effect—an accidental redesign for a different voltage.

A case of uneven brush wear

  • October 1998
  • Number of views: 3296
  • Article rating: 4.7

The brushes on a 4-pole, 700 hp DC motor were not wearing at the same rate. In this case, rapid brush wear occurred on two adjacent brush rows - one positive and one negative polarity. The other brushes had minimal wear. Electrical tests found no winding faults, and the air supply was clean. Most of us suspect low current-density when rapid brush wear occurs. A lightly loaded DC motor can "dust" a set of brushes in short order. Changing the brush grade (or removing some of the brushes) will usually solve the problem.

Training Film 14: Taking Data From a Hand-Wound DC Armature

  • June 1984
  • Number of views: 1173
  • Article rating: No rating

Describes the correct procedure for taking data from hand-wound DC armatures. Shows how to record the data on typical DC data sheets, and explains the terminology used describing DC data. Points out differences between lap and wave windings.

Getting The Most From Your Electric Motors

Getting The Most From Your Electric Motors - coverThis 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors.

This booklet covers topics such as:

  • Installation, startup and baseline information
  • Operational monitoring and maintenance
  • Motor and baseline installation data
  • How to read a motor nameplate
  • Motor storage recommendations



EASA/AEMT Rewind Study

EASA Rewind Study cover

The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors
Tests prove Premium Efficiency/IE3 Motors can be rewound without degrading efficiency.


ANSI/EASA AR100-2020

ANSI/EASA AR100-2015 cover

Recommended Practice for the Repair of Rotating Electrical Apparatus
This is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.



EASA Technical Manual

EASA Technical Manual cover

Revised May 2021
The EASA Technical Manual is the association's definitive and most complete publication. It's available FREE to members in an online format. Members can also download PDFs of the entire manual or individual sections.