12.5.6.2 Starter/Generators
The starter/generators are located on the accessory gearbox of each engine. Each starter/gener-
ator serves as a starter motor and will revert to generator operation if the DC GEN switch is in the
ON position and the engine speed exceeds 50% NH following successful engine start. Each gen-
erator output is monitored and controlled by its Generator Control Unit (GCU). After engine start,
the GCU ensures the generator supplies 28.5 VDC (400 Amps max) to its feeder bus regardless
of load.
The EPCU will then monitor and control the DC EPGDS. The EPCU will turn on the #1 DC GEN
or #2 DC GEN caution lights in the event the DC generator is disconnected from its feeder bus. If
a generator overheat condition occurs, the appropriate caution light #1 DC GEN HOT or #2 DC
GEN HOT will come on. The light will go out when the temperature drops below the overheat
condition.
12.5.6.3 Transformer Rectifier Units
Located in the nose, the two Transformer Rectifier Units (TRU) change three-phase, 115-volt,
variable-frequency AC input power into 28 VDC (300 Amps max) nominal output. The TRUs are
unregulated but provide DC power in the range of 26 to 29 VDC during operation.
Under normal conditions, each TRU powers its respective secondary bus. The L TRU or R TRU
caution light comes on if either TRU is off line or failed. The L TRU HOT or R TRU HOT caution
light comes on if the sensor in either detects an overheat condition. The light will go out when the
temperature drops below the overheat condition.
The two TRUs alone are capable of powering the entire DC system.
12.5.6.4 Auxiliary Power Unit (APU) Starter/Generator
The APU Starter/generator is located in the tail cone section of the aeroplane. The APU is
designed to supply 28VDC to the essential main, and secondary DC buses on the ground.
A Contactor allows the connection of the APU Starter/generator to the right main feeder bus for
APU starting and powering of the aeroplane DC buses. Its control is achieved from the APU
GCU.
After the APU is started, the starter/generator is available to supply power in parallel with the bat-
teries to start the aeroplane engines.
Dash8 - Q400 - Electrical
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