TM 5-6115-590-12
c. Power Unit electrical System (fig. 1-7 and FO-1).
The power unit electrical system consists of a 24V DC
system powered by batteries, a 120/240V AC single
phase, 60 Hz system powered by the engine driven 60
Hz generator, and a 120/208V AC three phase, 400 Hz
system powered by the engine driven 400 Hz generator.
The 24V DC system provides power for engine starting
and control, control power for the other power unit
systems (electrical, conditioned air and water) control
components, and emergency lighting power for other
elements of the MUST hospital. The 24V DC
emergency light power is distributed through the 60 Hz
system convenience receptacles and cable assemblies.
The 60 Hz system provides 60 Hz power to elements of
the MUST hospital as required. The 400 Hz system
provides 400 Hz power for operation of the conditioned
air system, water pumps, water hose heating, battery
changing, and for 400 Hz power requirements for other
elements of the MUST hospital. All of the electrical
systems incorporate safety devices to disconnect the
electrical output and prevent damage to components in
the event of an overload, undervoltage, overvoltage, or
underfrequency condition (except 60 Hz system). The
power unit includes electrical circuits for connection as a
standby unit and will automatically start and deliver
power should the operating power unit shut down. The
24V DC system also includes circuits and cable
assemblies for connection of an external source of 24V
DC power for starting. The power unit may also be
connected to another power unit to provide 24V DC and
400 Hz power to the nonoperating power unit for
operation of the ventilating fans in the nonoperating unit,
provided the cooled air system in the operating unit is
not operating.
(1) 24V DC Electrical System (fig. 1-7 and FO-1).
The 24V DC system provides power for engine starting
and for the switches, relays, contactors, solenoids, etc.,
which control operation of the engine electrical system,
60 Hz and 400 Hz electrical systems, conditioned air
system, and water system. The batteries which provide
the DC power will also provide up to one hour of
emergency light service to other elements of the MUST
hospital in the event of engine or electrical system
failure. The batteries are recharged through a
transformer-rectifier type battery charger powered from
the 400 Hz electrical system. Provisions are also
incorporated in the 24V DC system to connect an
external source of 24V DC power for engine starting in
the event the batteries are discharged.
(2) 60 Hz Electrical System (fig. 1-7 and FO-1).
The 60 Hz electrical system provides 120/240V AC, 60
Hz,
single
phase
output
power
for
external
requirements. The system consists of a brushless, self-
excited, air-cooled generator, a voltage regulator, a
generator protective panel, output power convenience
receptacles, and interconnecting wiring and connectors.
The 60 Hz system neutral conductor is not grounded.
Control components in the 60 Hz system are powered
from the 24V DC system.
Figure FO-1 Power plant electrical system
schematic
(Sheet 1 of 2)
(Located in back of manual)
Figure FO-1 Power plant electrical system
schematic
(Sheet 2 of 2)
(Located in back of manual)
(3) 400 Hz Electrical System (fig. 1-7 and FO-1).
The 400 Hz electrical system provides 120/208V AC,
400 Hz, three phase power for operation of the
conditioned air system compressors, condenser cooling
fans, air circulating fans, hot and cold water pumps, and
water hose heaters, 24V DC battery charger, and for
400 Hz power requirements in other elements of the
MUST hospital. The 400 Hz system consists of a
brushless, self-excited, air-cooled generator, voltage
regulator, generator protective panel, output power
receptacles, and interconnecting wiring and connectors.
The 400 Hz generator incorporates an integral cooling
fan and receives additional cooling air from the engine
cooling fan. The 400 Hz system neutral conductor is
grounded. Control components in the 400 Hz system
are powered from the 24V DC system.
d. Conditioned Air System (fig. 1-8, 1-9, and 1-10).
The conditioned air system supplies cooled air, heated
air, or ventilating air under slight pressure to other
elements of the MUST hospital. The system is a
recirculating system with recirculating fans in the return
air plenum. Adjustable vents in the return air
compartments permit adding make-up air to the system.
The conditioned air system consists of a cooled air
system, a heated air system, and a ventilating air
system. The three systems function independently but
use
some
components
interchangeable
between
systems. The four conditioned air outlets are located at
the rear of the power unit and provide connection
flanges for attaching the distribution ducts. The four
return air inlets are located on the right side of the power
unit and provide connection flanges for attaching the
return air ducts. Covers are provided for the outlets and
inlets when not in use. The four return air inlets are
provided with permanent high-velocity-type cleanable
air filters. Two temperature sensors are located at each
of the four return air inlets to provide temperature
control of the output air in response to temperature
changes in the return air. Also, a remote temperature
sensor may be connected to an electrical connector
provided on the return air inlet panel to provide
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