AC Generators
AC GENERATOR THEORY
AC GENERATOR THEORY
AC generators are widely used to produce AC voltage. To understand how these
generators operate, the basic theory of operation must first be understood.
EO 1.2
Given the speed of rotation and number of poles,
CALCULATE the frequency output of an AC generator.
EO 1.3
LIST the three losses found in an AC generator.
EO 1.4
Given the prime mover input and generator output,
DETERMINE the efficiency of an AC generator.
Theory of Operation
A simple AC generator consists of:
Figure 3 Simple AC Generator
(a) a strong magnetic field, (b)
conductors that rotate through that
magnetic field, and (c) a means by
which a continuous connection is
provided to the conductors as they
are rotating (Figure 3). The strong
magnetic field is produced by a
current flow through the field coil
of the rotor. The field coil in the
rotor receives excitation through
the use of slip rings and brushes.
Two brushes are spring-held in
contact with the slip rings to
provide the continuous connection
between the field coil and the
external excitation circuit. The armature is contained within the windings of the stator and is
connected to the output. Each time the rotor makes one complete revolution, one complete cycle
of AC is developed. A generator has many turns of wire wound into the slots of the rotor.
The magnitude of AC voltage generated by an AC generator is dependent on the field strength
and speed of the rotor. Most generators are operated at a constant speed; therefore, the generated
voltage depends on field excitation, or strength.
Rev. 0
Page 5
ES-10
