Section III. CIRCUIT ANALYSIS
2-7. Frequency Regulation (4B48-6-A)
2-6. Voltage Regulation (4B48-6-A)
(fig. FO-2)
(fig. FO-2)
a One side of the motor shunt field is connected to
a One side of the generator exciter field is connected
ground and the other side is connected to the collector of
to ground and the other side is connected to the collector
power transistor Q6 When the power transistor is on,
of power transistor Q5 When the power transistor is on
practically total dc voltages appears across the field
total dc voltage appears across the field When the
When the power transistor is off, total dc voltage appears
transistor Q5 is off, total dc voltage appears across
across transistor Q6.
transistor Q5
b The sensing voltage is taken from the top of voltage
adjust resistor R14 and the voltage at the emitter of
b Frequency regulation is accomplished by sensing
transistor Q1 The sensing bridge consists of resistors R1
the ac potential developed across a reactance transformer
R2, R3 and R14 and diodes CR3, CR4 and CR5 The
of a series LC circuit tuned to approximately 475 Hz The
voltage at the junction of resistor R3 and diode CR3 is the
LC circuit (capacitor C6 and inductor L2) operates at 400
voltage across the armature, less the drop across diode
Hz on the low side of the resonance curve The value of
CR21 The voltage at the junction of diode CR5 and
the ac potential developed is proportional to the
resistor R2 is the voltage across resistor R16 which, in
frequency and will continue to be constant for any one
effect is the difference between the input dc voltage and
frequency so long as the values of L and C remain
the fixed drop across diode CR23 Without any ac
constant This potential is then rectified (across resistor
voltage at the primary of transformer T1, transistor Q1 is
R5) and compared with another potential obtained by
cut off, causing transistor Q3 to conduct When the
rectification (across resistor R6) of the ac reference
transistor Q3 conducts transistor Q5 is cut off As a
voltage The two dc voltages are opposite to each other
result, no current is applied to the exciter As the ac
The voltage across resistor R6 and the voltage across
voltage generated as a result of the residual magnetism
resistor R10 aid in maintaining transistor Q2 cut off As a
and the exciter core rises a point is reached where the
result transistor Q4 is conducting and transistor Q6 is cut
base of transistor receives a voltage which is negative with
off As a result the shunt field is not connected As the
respect to the emitter voltage When this voltage is
motor speed increases the voltage across resistor R5
present transistor Q1 conducts transistor Q3 cuts off
increases until transistor Q2 switches into conduction
and transistor Q5 conducts With transistor Q5
With transistor Q2 conducting transistor Q4 is cut off
conducting current is applied to the exciter field and the
and transistor Q6 is conducting With Q6 conducting
voltage at the primary of transformer T1 rises further
current is applied to the shunt field The added field
The ac output voltage will continue to build up until the
current tends to slow down the motor When the
regulation point is reached At this regulation point the
frequency drops below 400 Hz the shunt field is then cut
voltage at the base of transistor Q1 goes positive with
out Due to the LC circuit of capacitor C6 and inductor
respect to the emitter voltage At this regulation point
L2, the shunt field voltage is switched on and off at an
transistor Q1 cuts off transistor Q3 conducts and
800-Hz rate, maintaining the output at 400 Hz
transistor Q5 cuts off This removes the exciter current
At this point transistors Q1, Q3 and Q5 rapidly switch
the exciter current on and off at the 800-Hz rate to
c Any increase in frequency will cause an increase in
regulate the output voltage
the on-time of power transistor Q6, resulting in a higher
average field current and a consequent reduction in
c The regulator reacts instantaneously to any change
frequency
in output voltage and maintains it constantly at a preset
value Free-wheeling diode CR19 is used to provide a
d The regulator reacts instantaneously to any change
path for the field current during the off time of power
in output frequency and maintains it constantly at a
transistor Q5
preset value
