Figure 1.16. Alternating-Current Generator.
b. Direct-current generator. The direct current supply described in the preceding paragraph is
not practical in commercial use, because the voltage reaches zero twice in each revolution of the
generator and the power output would be too small. A practical generator must therefore have many
coils, each coil being connected to a pair of commutator segments, so that the output of current from
them overlaps and provides a continuous flow. A direct-current generator is one of three types,
depending on whether the fields are connected in series, shunt, or a combination of the two. A series-
wound generator has field winding in series with the armature; a shunt-wound generator has its field in
parallel with the armature; and a compound-wound generator has both.
c. Alternator. An alternator is provided on some locomotives to supply ac power to fans and
blowers. The stator contains the two-phase output winding, and the fields are wound on the rotor.
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