174 Electrical Power Systems Technology
Self-excited Series-wound DC Generators—Since DC generators pro-
duce direct current, it is possible to extract part of the output of a genera-
tor to obtain excitation current for the field coils. Generators that use part
of their own output to supply the excitation current for the electromagnet-
ic field are called self-excited DC generators. The method used to connect the
armature windings to the field windings determines the characteristics of
the generator. It is possible to connect armature and field windings in se-
ries, parallel (shunt), or series-parallel (compound).
The self-excited series-wound DC generator has its armature windings
connected in series with the field coils and the load circuit, as shown in
Figure 7-13. In this generator, the total current flowing through the load
also flows through the field coils. The field coils are, therefore, wound
using only a few turns of low-resistance large-diameter wire. A sufficient
electromagnetic field can then be produced by the large current flowing
through the coils.
Figure 7-12. Simplified illustration of a separately excited DC generator: (A)
Pictorial diagram, (B) Schematic diagram