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Identification
and Testing of DC Armatures
Background The IMA electrician must be able to properly troubleshoot dc motor and generator armatures. DC armatures may be the most difficult component of either ac or dc motors to correctly troubleshoot. Adding to this difficulty is the fact that the type of winding contained in the armature must be positively identified before actual testing procedures can be undertaken. This lesson presents dc armature terminology and identification, bar-to-bar testing procedures, and growler testing procedures. An important point to remember in this lesson is that there are only two types of armature windings, lap and wave. Each can be wound in various configurations. Armature winding terminology, definitions, and amplifying information Lap winding Definition: An armature winding where the leads of an individual coil are connected to
commutator bars that are adjacent or close to each other |
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| Amplifying information: If coil leads are connected to adjacent bars, the winding will be a simplex lap (figure at right).
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Click on image to
enlarge. Typical Simplex Lap-Wound DC
Armature |
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| If the total armature winding consists of two windings in series with coil leads connected to alternate bars, the winding will be a duplex single reentrant lap (figure at right). |
Click on image to
enlarge. Typical Duplex Single-Entrant Lap-Wound DC Armature
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| If the total armature winding consists of two separate windings insulated from each other and connected to alternate bars, the winding will be a duplex double reentrant lap (figure at right). |
Click on image to
enlarge. Typical Duplex Double-Entrant Lap-Wound DC Armature
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| Wave winding Definition: An armature winding where the leads of an individual coil are connected to commutator bars that are approximately two pole pitches apart
The figures shown in this lesson for wave windings are four-pole machine armatures. Wave windings will always have the same number of coils in series in one trip around the commutator as the main poles divided by two or P/2. Four-pole machines will have two coils in series, six-pole machines will have three coils in series, and so forth. |
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| Amplifying information: If the leads of the coils in series in one trip around the commutator are connected to adjacent bars, the winding will be a simplex wave (figure at right). |
Click on image to
enlarge. Typical Simplex Wave-Wound DC Armature
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| If the leads of the coils in series in one trip around the commutator are connected to alternate bars, the winding will be a duplex single-reentrant wave (figure at right). |
Click on image to
enlarge. Typical Duplex Single-Reentrant Wave-Wound DC Armature
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| If the total armature winding consists of two separate windings insulated from each other with the leads of the coils in series in one trip around the commutator connected to alternate bars, the winding is a duplex double-reentrant wave (figure at right). |
Click on image to
enlarge. Typical Duplex Double-Reentrant Wave-Wound DC Armature |
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More terminology, identifying windings  |
All
figures depicting wave windings are presented in simplified form.