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The RG Series is the revolving armature type, and the RGX Series is now the revolving field type. The differences between
these types and their features are described below. The construction of the revolving armature type is shown in Fig. 5- 15,
and that of the revolving field type in Fig. S- 16.
The basic operating principle of the generator is this. As a conductor moves in a magnetic flux (between poles N and S of a
magnet), a voltage is generated in the conductor and can be taken out as electric power. Generally, an electromagnet is used
for generators. The electromagnet consists of poles and field coils wound around them, and the poles become magnets as a
direct current runs through the field coils. The revolving armature type has static poles and a revolving armature which con-
sists of a conductor for taking electric power out. The revolution of the armature generates a voltage.
It was earlier explained that a conductor moves in a magnetic flux. Actually, however, a relative speed between the two is
sufficient for generating a voltage. That is, a voltage can also be generated by rotating the magnet while keeping the con-
ductor still.
The revolving field type falls in this latter category: The pole serving as an electromagnet rotattes, and armature which
consists of a conductor remains still.
The features of the revolving field type are as follows:
a)
b)
4
onlytwosliprings
As generator applications diversified, it became necessary for generators to meet increasingly varied conditions involv-
ing AC output, DC output, dual voltage, three-phase, and usefulness with induction motors. Accordingly, AC windings,
DC windings, auxiliary windings, etc. became necessary for generators. Because the revolving armature type takes elec-
tric power from the revolving part, it requires as many slip rings as the number of winding output terminals, and tbis
increases the generator dimensions. The revolving field type is small in size because it requires only two slip rings @r
feeding a current to operate the electromagnet.
Easy maintenance
As many brushes as the number of slip rings are necessary. The revolving field type is easier to maintain than the re-
volving armature type because it has fewer slip rings and brushes than the other.
Lightweight
The revolving armature type is heavy because it requires yokes to fm the poles and serve as flux passage. The revolving
field type is light in weight because the stator and rotor can be made by laminating steel sheets of the same material.
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