EXCITER CONTROL FIELD
T1 T2 T3
TERMINALS
AC OUTPUT
TERMINALS
EXCITER
EXCITER
A LT E R N ATO R
FIELD
A R M AT U R E
A R M AT U R E
WINDINGS
WINDINGS
(3-PHASE)
ROTOR
SHAFT
SLIPRING
R O TAT I N G
AC
BRUSHES
FIELD
G E N E R ATO R
E X C I T E R G E N E R ATO R
WINDINGS
A
T Y P I C A L A C G E N E R ATO R
( S C H E M AT I C )
EXCITER CONTROL FIELD
T1 T2 T3
TERMINALS
AC OUTPUT
TERMINALS
A R M AT U R E
ROTOR
SHAFT
SHAFT MOUNTED
AC
R O TAT I N G R E C T I F I E R S
G E N E R ATO R
E X C I T E R G E N E R ATO R
B
B R U S H L E S S G E N E R ATO R
( S C H E M AT I C )
ASf07030
Figure 7-30.--Ac generator schematic drawings.
The number of windings is fixed, and the demand
windings. When the generating field is rotated, its
is for constant frequency; therefore, a constant speed.
magnetic flux is passed through and across the
Thus, the only practical remaining method for voltage
generator armature windings.
control is to control the strength of the rotating
The armature illustrated is wound for a three-phase
magnetic field. In views A and B of figure 7-30, you
output. Remember, a voltage is induced in a conductor
can see that by varying the exciter armature dc output
if it is stationary and a magnetic field is passed across
voltage, the ac generator field strength is also varied.
the conductor, the same as if the field is stationary and
The ac generator voltage regulation is obtained by
the conductor is moved. The alternating voltage in the
controlling the output of the exciter. The exciter output
ac generator armature windings is connected through
is controlled by varying the current flow through the
fixed terminals to the ac load. View B is a simplified
exciter field windings. Therefore, the essential
schematic of a brushless generator using diodes
function of the voltage regulator is to use the ac
instead of brushes and slip rings.
generator output (which it is designed to control) as a
sensing influence to control the amount of current the
AC VOLTAGE REGULATION.--The amount
exciter supplies to its own field. The most widely used
of voltage induced into the ac generator windings
ac regulator is the solid-state voltage regulator.
depends mainly on three things--the number of
conductors in series per winding, the speed of the
P H A S E S E QU E N C E C O N T RO L . -- W h e n
generator, and the strength of the magnetic field. Any
high-capacity ac power systems became a part of naval
of these could be used to control the generator output
aircraft, accompanying problems developed in both
voltage.
the aircraft and the ac system in the form of electrical
7-21
