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TM 11-6130-377-14
the voltage of the + input as long as the +120 vdc input
charge on capacitor C28 holds transistor Q10 on, which
voltage remains below approximately 142 vdc.  If the
inhibits the voltage fault sensor circuits. U6-3 goes low
+120 vdc input voltage rises to approximately 142 vdc,
and provides a discharge path for capacitor C28 through
U9-6 goes low and Q9 turns on Q11 through R45.
resistor R42 and U6-3 to common. When capacitor C28
Transistor Q11 operates the shunt trip of CB1.
discharges to a voltage below the cutoff point of transistor
Q10 (approximately 50 milliseconds), the transistor turns
k.  Shunt Trip Relay Driver.  The shunt trip relay
off and removes the inhibit command from the voltage
driver consists of transistor Q11 and photocoupler U10.
fault sensors; that is, it allows the faults sensors to turn on
When transistor Q10 in the sensor delay circuit and
Q11 through Q9.  The total delay prevents the faults
transistor Q9 in the high and low voltage fault sensor are
sensors from reacting to transients that may be present at
held off, the shunt trip driver is off. After the sensor delay
the turn-on of the inverter.
has timed out, turning off transistor Q10, either sensor U8
h. Quarter-Start Generator. The quarter-start gene-
or U9 turning on allows the base of transistor Q9 to go
low. This action turns on transistor Q11 and energizes the
rator consists of U6 and U7. During the 2 second power-
shunt trip through connector J1 pin 5.  During parallel
on delay, U6-3 is off and transistor Q7 is on, grounding
operation, transistor Q9 turning on also forward-biases the
U7-5 and holding U7-6 low. With U7-6 low, U4-4 and -10
photodiode in the photocoupler (U10) and light from the
are low and the 60-Hz on U4-5 is inhibited. When U6-3
photodiode turns on the light-sensitive transistor.  The
goes low, transistor Q7 turns off and U7-5 goes high. The
photocoupler is not used during nonparallel operation.
next 120 Hz-clock from U3-8 through Q8 to U7-2 causes
U7-6 to go high and stay high. When U7-6 goes high, U4-
l.  Parallel Sensor Interconnection.
When the
4 and -10 go high and the 60-Hz signal is applied to Q4
inverter is connected for parallel operation of two units,
and Q5.
the photocoupler (U10) of the master inverter is
i.  Low Voltage Fault Sensor.  The voltage fault
connected to operate the slave inverter's shunt trip driver
and the photocoupler of the slave inverter is connected to
sensors monitor the +120 vdc input voltage at connector
operate the master inverter's shunt trip driver.  This is
J1 pin 2 through voltage divider R29 and R30. The low
accomplished by use of the cable between connector P2
voltage fault sensor consists of operational amplifier U8
of each inverter drive circuit board. The collector of the
and transistors Q9 and Q11. A reference voltage is set
photocoupler  transistor  of  the  master  inverter  is
up at the + input of the operational amplifier by
connected through P2 pin 1 to +5 vdc of the slave inverter
potentiometer  R32  and  resistors  R31  and  R33.
at connector P2 pin 3. The emitter of the master inverter
Potentiometer R32 is set so that the voltage of the + input
photocoupler transistor is connected through connector
is above the voltage of the - input as long as the +120 vdc
P2 pin 4 to the base of shunt trip driver transistor Q11 of
input voltage remains above approximately 95 vdc. If the
the slave inverter at connector P2 pin 9.  When the
+120 vdc input voltage drops to approximately 95 vdc,
master inverter photocoupler transistor turns on, the slave
the + input drops below the - input. This action causes
inverter +5 vdc is conducted to the .base of transistor Q11
the output to go low which turns on transistor Q9. When
in the slave inverter, causing the shunt trip drivers to
transistor Q9 turns on, Q21 is turned on through R45 and
operate simultaneously. The photocoupler of the slave
causes the shunt trip of CB1 to operate.
inverter operates the shunt trip driver of the master
j.  High Voltage Fault Sensor. The high voltage fault
inverter similarly, except that master inverter +5 vdc is
sensor consists of operational amplifier U9 and transistors
obtained at slave inverter connector P2 pin 10.  Other
Q9 and Q11.  The high voltage fault sensor operates
connections to connector P2 during parallel operation are
similar to the low voltage fault sensor, except that the
described in the parallel SCR driver input description.
amplified inputs are reversed. Potentiometer R37 is set
so that the voltage of the - input of the amplifier is below
Change 1

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