DC GENERATOR CONSTRUCTION
Figure 12 Compounded DC Generator
Series-wound and shunt-wound
generators have a disadvantage in
that changes in load current cause
changes in generator output voltage.
generators are used require a more
stable output voltage than can be
supplied by a series-wound or shunt-
wound generator. One means of
supplying a stable output voltage is
by using a compound generator.
The compound generator has a field
winding in parallel with the
generator armature (the same as a
shunt-wound generator) and a field
winding in series with the generator armature (the same as a series-wound generator) (Figure 12).
The two windings of the compounded generator are made such that their magnetic fields will either
aid or oppose one another.
If the two fields are wound so that their flux fields oppose one another, the generator is said to be
differentially-compounded. Due to the nature of this type of generator, it is used only in special
cases and will not be discussed further in this text.
If the two fields of a compound generator are wound so that their magnetic fields aid one another,
the generator is said to be cumulatively-compounded. As the load current increases, the current
through the series field winding increases, increasing the overall magnetic field strength and
causing an increase in the output voltage of the generator. With proper design, the increase in
the magnetic field strength of the series winding will compensate for the decrease in shunt field
strength. Therefore, the overall strength of the combined magnetic fields remains almost
unchanged, so the output voltage will remain constant. In reality, the two fields cannot be made
so that their magnetic field strengths compensate for each other completely. There will be some
change in output voltage from the no-load to full-load conditions.