2-7
Figure 2-5.—Compound-wound dc motor.
When the shunt field is connected in parallel with the series field and armature, it is called a "long
shunt" as shown in figure 2-5, (view A). Otherwise, it is called a "short shunt", as shown in figure 2-5,
(view B).
TYPES OF ARMATURES
As with dc generators, dc motors can be constructed using one of two types of armatures. A brief
review of the Gramme-ring and drum-wound armatures is necessary to emphasize the similarities
between dc generators and dc motors.
GRAMME-RING ARMATURE
The Gramme-ring armature is constructed by winding an insulated wire around a soft-iron ring (fig.
2-6). 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.
Figure 2-6.—Gramme-ring armature.
