APU - CONTROLS AND INDICATORS
Continental
Rev. 12/01/00 #29 Flight Manual
APU - CONTROLS AND INDICATORS
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ELECTRICAL
TABLE OF CONTENTS
ELECTRICAL SYSTEM ..................................................................... 1
AC Power Generating System ..................................................... 1
AC Power Distribution System ..................................................... 2
DC Power Distribution.................................................................. 3
Emergency AC and DC Power Supply ......................................... 4
Continental
Rev. 12/01/00 #29 Flight Manual
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ELECTRICAL SYSTEM
The airplane electrical power system consists of a 115/200 volt, 400-Hz, 3-phase AC power generating and distribution system that furnishes power to the AC and emergency AC busses. For control circuits, lighting, and other load devices requiring DC power, 115-volt AC from the AC distribution busses is converted to 28-volt DC by transformers-rectifiers (TRs).
For instrument power, 115-volt AC from the AC busses is reduced to 28-volt AC by single phase transformers.
Power for certain portions of the DC system is supplied by a battery, when the main power distribution system is de-energized. In addition, power for APU starting is supplied by the battery.
An inverter, powered from the battery direct bus, supplies single phase 115-volt, 400-Hz AC power for emergency use when all other sources of AC power have been lost. The inverter also supplies AC power to the refueling system or ignition system when normal electrical power is not available.
A battery charger, powered from an AC bus, maintains the battery in a charged condition.
AC Power Generating System
AC power is normally supplied by any two of three AC generators, one on each engine and one on the auxiliary power unit (APU). Each generator is rated at 40-kva continuous output and is capable of supplying sufficient power for operation of essential electrical systems in the event of loss of the other two generators.
The APU generator is mounted directly on the APU and is driven at a constant speed by the APU governing system. The APU generator may be substituted for an engine generator or may be used for ground electrical power.
Each engine-driven generator is driven though a constant-speed drive (CSD), which converts the variable speed output of the engine to a constant speed. The CSDs and electronic units maintain a constant voltage and frequency output from the generators regardless of varying engine speeds and electrical loads.
Continental
Rev. 12/01/00 v#29 Flight Manual
An oil indicating system for each CSD shows the oil outlet temperature and the oil temperature rise across the drive. Each CSD has a disconnect switch which will uncouple the CSD from the engine if required. When disconnected, a CSD must be engaged manually at the engine, after engine shutdown.
Fault protection is incorporated in each generator control circuit to automatically remove the generator from its bus and de-energize the generator in the event of certain circuit malfunctions. Pulling the ENG FIRE handle will also de-energize the generator. The generator may be restored to operation by the reset function of the generator switch when the malfunction is corrected. (ENG FIRE handle must be reset first, if pulled.)
A generator may be reset only once for a given fault. If a fault trips the generator after reset, the fault should be located and corrected before attempting to place the generator on its bus again.
AC Power Distribution System
The AC power distribution system is divided into two separate systems operating independently of each other, but with crosstie capabilities. The right and left engine-driven generators supply power directly to the respective systems. Power from the APU generator may be selected to either or both generator busses, or directly to the ground service bus when only ground service power is required.
The left and right generator busses supply heavy 3-phase loads, such as galley power and cooling fans. The generator busses supply subordinate left and right AC busses respectively. The subordinate AC busses supply lighter 3-phase loads such as fuel pumps, transformer-rectifiers (TRs), and single phase AC circuits. The right generator bus also supplies the ground service bus.
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