# Gramme Ring and Drum Wound Armature in DC Motors

- Link: https://studyelectrical.com/2019/11/gramme-ring-and-drum-wound-armature-in-dc-motors.html
- Published: 2019-11-28T15:18:47+00:00
- Author: Tesla

A DC motor can be made using different types of armatures based on its application.
There are 2 types of armatures.

 1. Gramme Ring Armature
 2. Drum Wound Armature

## Gramme Ring Armature

The Gramme-ring armature is constructed by winding an insulated wire around a soft-
iron ring.

![Gramme ring armature winding](https://studyelectrical.com/wp-content/uploads/2019/
11/Gramme-ring-armature-winding.png)

Gramme ring armature winding

Eight equally spaced connections are made to the winding. Each of these is connected
to a commutator segment. The brushes touch only the top and bottom segments. There
are two parallel paths for current to follow — one up the left side and one-up the
right side.

These paths are completed through the top brush back to the positive lead of the
battery.

To check the direction of rotation of this armature, you should use the right-hand
rule for motors.

Hold your thumb, forefinger, and middle finger at right angles. Point your forefinger
in the direction of field flux; in this case, from left to right. Now turn your 
wrist so that your middle finger points in the direction that the current flows 
in the winding on the outside of the ring. Note that current flows into the page(
away from you) in the left-hand windings and out of the page (toward you) in the
right-hand windings. Your thumb now points in the direction that the winding will
move.

The Gramme-ring armature is seldom used in modern DC motors. The windings on the
inside of the ring are shielded from the magnetic flux, which causes this type of
armature to be inefficient.

The Gramme-ring armature is discussed primarily to help you better understand the
drum-wound armature.

## Drum Wound Armature

The drum-wound armature is generally used in AC motors. It is identical to the drum
winding discussed in the chapter on DC generators.

![Drum wound armature of dc motor](https://studyelectrical.com/wp-content/uploads/
2019/11/Drum-wound-armature-of-dc-motor-1.png)

Drum wound armature of dc motor

If the drum-wound armature were cut in half, an end view at the cut would resemble
the drawing in the figure (view A),  (view B) is a side view of the armature and
pole pieces.

Notice that the length of each conductor is positioned parallel to the faces of 
the pole pieces. Therefore, each conductor of the armature can cut the maximum flux
of the motor field. The inefficiency of the Gramme-ring armature is overcome by 
this positioning.

The direction of current flow is marked in each conductor in the figure (view A)
as though the armature were turning in a magnetic field. The dots show that current
is flowing toward you on the left side, and the crosses show that the current is
flowing away from you on the right side.

Strips of insulation are inserted in the slots to keep windings in place when the
armature spins. These are shown as wedges in the figure (view A).

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