TM11-6125-256-34
Functioning of Equipment
Section I BLOCK DIAGRAM ANALYSIS
2-1. General
is applied through radio interference filter RF1 to the ac
power connector In addition a sample of the ac output is
a The motor-generator is divided into two sections
applied to voltage and frequency regulator assembly.
an electromechanical section, consisting of the motor and
the generator and an electronic section containing a
voltage and frequency regulator
b Electronic Section
Voltage and frequency
regulator assembly
controls the motor-
generator frequency output by controlling the strength of
the motor shunt field and thus governing the speed of the
rotating section The voltage output is regulated through
b The purpose, operation and interoperation of the
control of the current in the ac generator exciter
two sections (electronic and electromechanical) of the
motor-generator are explained in this chapter
NOTE
Familiarity with the equipment and its functioning is a
Type 4B48-6-A is used in PU-750()/A,
valuable tool in rapid and effective troubleshooting
type 4B93-1-A is used in PU-750A/A.
2-2. Block Diagram
(1) As the mechanical speed of the motor-generator
increases, the output frequency also increases To control
(fig (FO-1)
the frequency, the regulator controls the amount of
a Electromechanical Section
current flow through the motor shunt coils The speed of
the motor may be reduced by increasing the strength of
the motor shunt field
(1) The 28-volt dc input is applied to the
electromechanical section of the motor-generator
through the positive (+) terminal board to the motor
series field, the interpole windings, and the armature
(2) Once the ac voltage generated as a result of the
causing current to flow through the motor
residual magnetism in the exciter rises above a preset
level the voltage regulator supplies current to the exciter
This causes a further rise in the output voltage The
(2) The reaction of the magnetic fields established by
magnitude of output voltage Reducing the exciter
the current flowing through the motor causes the
current causes a reduction of ac output voltage Output
armature to rotate The motor starts as a series motor As
voltage is controlled by regulating the average current in
the motor speed increases, the armature voltage rises
the exciter
When the armature voltage reaches a predetermined
level, the armature voltage sensing relay and resistor
assembly energizes, causing series field cutout current
relay assembly, Type 1519-1-B, to close, shorting out the
series field With the series field shorted out, the motor
runs as a shunt motor The exciter field of the generator is
(3) The regulator performs the function of a rapidly
mechanically coupled to the armature of the motor by a
operating switch which interrupts the current flow in
common shaft, therefore, the exciter also rotates
both motor and generator field windings at a rate of 800
HZ (4B48-6-A) or 400 Hz (4B93-1-A). Control
(3) An ac voltage is induced in the ac field coils of
is accomplished with voltage-and frequency
the generator by the sweep of the exciter The exciter is
sensing circuits that establish the mag-
not energized at this time Residual magnetism in the
nitude of current required to produce the
exciter causes this voltage buildup The induced voltage
desired output and then vary the off-time
or the motor shunt coils and generator
exciter field stages.
