(
If
this
section is to be used
with
equipment
or
apparatus
that
is associated with earlier
or
later
issues
of
the
circuit schematic drawings, reference
should be made to the SDs and CDs to determine
the
extent
of the changes and the manner in which
the section may be affected.
1.05
The voltage
that
is applied to
the
L3
coaxial
cable is
determined
by
the
length
of
the
power section. A power section is the series loop
through the center conductor
of
two coaxial lines
with the primary windings ofthe auxiliary transformer
at
each
repeater
point
connected in
series
with
the center conductor
of
the two coaxial lines. The
voltage
that
is applied to the
L3
coaxial cable is
obtained by stepping up the output voltage
of
each
motor-alternator and automatically regulating the
stepped up output to maintain a constant alternating
current
for
the
coaxial lines.
The
approximate
constant
current
used on
the
coaxial lines is 1.5
amperes for a
PSI
system
or
1.6
amperes
for
a
PS2 system. The alternating
current
for a power
section
is
held
constant
by
the
two
variable
motor-driven
autotransformers
in
the
associated
PWR
CONT
(power
control)
bay.
One
of
the
autotransformers
is used for coarse
adjustments
and
the
other
autotransformer
is
used
for
fine
adjustments. The coarse-adjust autotransformer is
controlled
by
a voltage relay and the
±3
percent
cams
of
the
fine-adjust
autotransformer.
The
fine-adjust
autotransformer
is controlled
by
an
electronic-regulating circuit. Both the coarse-adjust
and fine-adjust autotransformers respond to voltage
drops
across
a
resistance
that
is in
series
with
the L3 coaxial lines.
1.06
Each
motor-alternator
in
the
combination
plant
consists
of
a
de
motor,
an
ac motor,
and a self-excited alternator mounted on a common
shaft. .The motor-alternator, under manual control,
is
started
and
brought
up to normal
speed
and
voltage limits by the de motor. The drive is then
transferred
manually to the ac motor for normal
operating conditions. When
the
alternator
is on
ac drive, the field
of
the
de
motor is connected to
the
battery
through
a high
resistance.
An ac
power failure or low voltage condition automatically
disconnects the ac power from the ac motor, applies
battery
to the de motor, and short-circuits the high
field resistance
causing
the de motor
to
operate
and provide alternator drive.
1.07
The regular and emergency motor-alternators
in
the
plant
are
driven
by
the
ac
motors
ISS
3, SECTION 167-676-301
under
normal
operating
conditions. A
voltage
transfer
control circuit causes the motor-alternator
drive to automatically
transfer
from the ac motors
to the de motors when the ac input voltage drops
below approximately 80 percent
of
nominal value.
When
the
ac
input
power
is
restored,
the
motor-alternators will automatically
transfer
from
the de motors back to the ac motors when the ac
input
voltage
has
been
at
least
90
percent
of
nominal value for approximately 1 minute.
If
the
motor-alternator fails to keep
the
output
voltage
about
225
volts, the voltage relays will cause the
motor-alternator to
transfer
to the de motor.
If
the output voltage from a
regular
motor-alternator
drops below
205
volts
for
more
than
112
second,
the voltage relays will cause the load to
transfer
from the
regular
motor-alternator to the emergency
motor-alternator.
1.08
The emergency motor-alternator is used
as
a common emergency motor-alternator for a
combination of from
one
to six regular motor-alternators
and inverters. Under normal operating conditons,
the emergency motor-alternator
runs
continuously
at
no load and will automatically replace any
regular
motor-alternator
or
inverter
that
fails, goes low in
supplying outputvoltage,
or
is removed from service
for maintenance.
1.09
If
the
motor-alternators in
the
plant
were
operating
on
the
de motors (due to
an
ac
power failure) and all
the
motor-alternators were
transferred
back to
the
ac
motors
at
the
same
time (ac power restored),
the
resulting load
surge
might reduce the ac input voltage to the ac motors
below the line monitor
transfer
point. This could
cause
the
motor-alternators to
transfer
back and
forth repeatedly.
To
prevent the ac input voltage
to
the
ac
motors
from
dropping
below
the
line
monitor
transfer
point,
an
alternator-sequencing
circuit restores the motor-alternators in the
plant
to
ac
drive
sequentially
on
an
individual
basis
following
an
ac
power
failure
(ac
power
now
restored). The emergency motor-alternator would
be the first unit to
transfer
back to ac drive.
1.10
The plantcontains an originating TRANSFER
CONTROL
bay
and
as
many
SUPL
(supplementary) TRANSFER CONTROL
bays
as
required. The originating TRANSFER CONTROL
bay contains
the
common control circuit
that
is
used to
automatically
transfer
the
load
from
a
faulty
regular
motor-alternator to
the
emergency
motor-alternator and also contains the circuits
for
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