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labeled COCKPIT DEFOG OR DEFROST and CABIN
AIR. By pulling the DEFOG or DEFROST handle, heater
or ventilating air is directed to the cockpit nose enclosure
ducting. The airflow is directed to the transparent portion
of the jettisonable doors and nose enclosure providing
defrosting as well as additional forward cockpit section
heating. When the CABIN AIR handle is pulled, heated
or ventilating air flows through the ducting to the cabin.
2-10-5. Cabin Heat Controls.
Fourteen manually adjustable outlets are provided in the
cabin for the comfort of the passengers.
2-10-6. Heater Caution.
NOTE
Since the HEATER HOT caution will not extinguish
until the temperature in the combustion
chamber is below 177C, it may take several
attempts at restarting the heater before
HEATER HOT caution extinguishes.
A heater caution capsule labeled 712 HEATER HOT,
714A HTR HOT is on the master caution panel (fig.
2-14-6). This caution indicates failure of the automatic
temperature control circuit. If air temperature in the heater
rises to 177C, an overheat switch deenergizes the
automatic temperature controller relay, shuts off the
heating system, except the blower, and activates the
712 HEATER HOT, 714A HTR HOT caution. The heating
system will not operate until the blower has lowered
the heater temperature to normal and the HTR START
switch is pressed. Even though the temperature in the
combustion chamber has lowered, the 712 HEATER
HOT, 714A HTR HOT caution will not extinguish until the
HTR START switch is pressed.
TM 1-1520-240-10
2-11-1
SECTION XI. ELECTRICAL POWER SUPPLY AND DISTRIBUTION SYSTEMS
2-11-1. Electrical Power Supply System.
Alternating current (AC) is the primary source of power
to operate the electrical and electronic equipment. Three
AC generators, two driven by the aft transmission and
one driven by the APU, produce 115/200-volt 3-phase
400-Hz power. The system develops 28-volt DC through
two transformers rectifiers (RECT) one each in the forward
section of the left and right fuselage pods. DC is
also supplied by a 24-volt nickel-cadmium battery.
Both 115/200-volt 3-phase AC and 28-volt DC can be
supplied by operating the APU or by connecting an AC
external power source to the external power receptacles
(fig. 2-11-1). If the APU is running or AC external power
is connected, DC power is supplied by the helicopter
transformer rectifiers (RECT). If only DC external power
is supplied, AC power is not available on the helicopter.
Circuits are protected by circuit breakers (fig. FO-2 and
FO-5). The electrical load is divided between the two AC
generators (fig. FO-3 and FO-6). Should one generator
fail, the other will automatically take over the entire load.
When APU is running, its single generator powers the
entire load.
Figure 2-11-1. External Power Receptacles
2-11-2. AC System.
The AC system supplies 115/200-volt three-phase
400-Hz power from No. 1 AC generator to No. 1 threephase
AC bus and from No. 2 AC generator to the No. 2
three-phase AC bus (fig. FO-3 and FO-6). The AC equipment
is powered by these buses. Some of the equipment
is operated by 115-volt single-phased AC and some
equipment by 26-volt AC power supplied through the
transformers.
The AC system is protected from overvoltage, undervoltage,
and underfrequency conditions by generator control
units. The generators will be disconnected from the
AC buses any time the RRPM drops below 82 to 85
percent for more than 3 to 7 seconds. The AC power
distribution system has four power sources, a contactor,
control circuit, an AC power transfer circuit, and two AC
buses.
The No. 1 and No. 2 generator power sources are two
main generators driven directly by the aft transmission.
The APU generators is driven directly by the APU. The
external power source is an AC power supply connected
to the helicopter.
No. 1 and No. 2 generators feed their respective buses.
If No. 1 and No. 2 generator fails (or are shut down), the
failed generator is isolated from its bus and the operating
generator feeds both buses. When No. 1 or No. 2 or both
generators are operating, APU generator and external
power are blocked from the AC buses.
When the APU generator is operating and the main generators
are shut down (or rotors turning below about
84%) or switched off, the APU generator feeds both buses.
When the APU generator is operating, external power
is blocked from the AC buses. When external power
is applied to the helicopter (GEN APU, GEN 1, and GEN
2 are OFF), the external power source feeds both buses.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
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