TM 1-1520-238-T-6
9–5
SECTION I.
Equipment Description and Data
9–1.
EQUIPMENT CHARACTERISTICS, CAPABILITIES, AND FEATURES
9–1
a. Characteristics.
(1) The ac electrical power generation system generates and distributes ac electrical power required to
operate the helicopter systems. AC electrical power is supplied to two transformer/rectifiers (T/R) which produce
28 VDC for systems requiring dc power. The dc electrical power generation system rectifies 3-phase, 115/200
VAC, 400 hertz (Hz) power to provide 28 VDC to the helicopter circuits requiring dc voltage. Major components of
the system consist of two T/Rs and a dc bus tie contactor. The battery supplies dc voltage for APU starting and
emergency operation in case of total electrical system failure. The external power system allows external ac
electrical power application for systems operation and/or checkout. The ground service utility receptacle provides
aircraft ac and dc power for lights, hand tools, etc.
b. Capabilities and Features.
(1) AC Electrical Power.
AC electrical power generation consists of two identical and redundant
electrical power systems. The system generates 3-phase, 115/200 VAC, 400 Hz ac power at 35 Kilo-Volt Amperes
(KVA). Either system is capable of supplying all electrical power requirements. If either system malfunctions,
automatic switching ensures continued electrical operation. The system is monitored internally and electrically
shuts down if an overvoltage, undervoltage, underfrequency (on ground only), or an overcurrent fault is detected.
(2) DC Electrical Power.
Each T/R is capable of providing 28 VDC at 250 amperes. DC electrical power
generation maintains output voltage limits of 25 to 29 VDC at loads of 10 to 250 amperes. Each T/R provides its
own forced air cooling and radio noise suppression. In the event of an over temperature condition, which is
normally due to failure of the cooling fan, a thermal sensor is activated. The thermal sensor completes a circuit to
light the appropriate HOT RECT indicator on the pilot caution/warning panel. The dc bus tie contactor connects
the output of the T/R to the emergency dc bus, dc bus 1, dc bus 2, and dc bus 3. The contactor connects dc
busses 1 and 2 in the event one T/R is not operating and prevents paralleling of the T/R outputs.
(3) External Power.
The external power system supplies 3-phase, 115/200 VAC, 400 Hz ac power to
aircraft ac distribution points. All major components are line replaceable units (LRUs). The system monitors input
external power for over/under voltage, over/under frequency, and phase sequence. If a fault is detected, the
system electrically disconnects external power.
(4) Battery and Battery Relay.
The battery is connected to the emegency dc bus when the battery relay
is energized by 18 VDC or greater. The battery supplies 24 VDC and contains 19 individual removable cells of
1.25 volts per cell.
(5) Battery Charger.
The battery charger completely recharges a discharged battery within 2 hours.
Charging is stopped if battery temperature rises above 122 5 F (50 3 C) and resumes charging when the
temperature drops below 115 5 F (46 3 C). Battery charging is stopped if an open or short circuit occurs in
the battery temperature transducer circuitry. Battery charging is stoped or inhibitted if the tenth cell voltage falls
below or exceeds 45 to 60% of battery terminal voltage for more than 3 0.6 minutes. Battery charging is stopped
when external power is applied to the helicopter to prevent buildup of explosive gases.
