176 Electrical Power Systems Technology
that require stable load current as the voltage changes. However, the self-
excited series-wound generator has very few applications.
Self-excited Shunt-wound DC Generator—connecting the field coils, the
armature circuit, and the load circuit in parallel produces a shunt-wound
DC generator configuration. Figure 7-15 shows this type of generator. The
output current developed by the generator (IA) has one path through the
load circuit (IL) and another through the field coils (IF). The generator is usu-
ally designed so that the field current is not more than 5 percent of the to-
tal armature current (IA).
In order to establish a strong electromagnetic field and to limit the
amount of field current, the field coils are wound with many turns of small
diameter wire. These high-resistance coils develop a strong field that is due
to the number of turns, and, therefore, they rely very little on the amount
of field current to develop a strong magnetic field.
With no load circuit connected to the shunt-wound DC generator, an
induced voltage is produced as the armature rotates through the electro-
magnetic field. Again, the presence of residual magnetism in the field coils
is critical to the operation of the machine. A current flows in the armature
and field circuit as long as there is residual magnetism. As the generated
current increases, the output voltage also increases, up to a peak level.
When a load circuit is connected to the shunt generator, the armature
current (IA) increases, because of the additional parallel path. This, then,
Figure 7-14. The output curve of a series-wound DC generator