-the menu mode.
R **ON A/C 401-499,
R A. Ground and Auxiliary Power Control Unit (GAPCU)
R (1) GAPCU functions
R The GAPCU controls both APU generator and external powers channels.
R In addition to the APU generator functions, the GAPCU has three
R different functions:
R - aircraft power supply control and network protection,
R - system test and self-monitoring relating to these functions
R - provide BITE and messages for the AC generation (GCU').
R NOTE : The GAPCU transmits command and data to and receives data from____
R up to the GCUs.
R The communication is made via 1553 serial data links.
R (a) Control and protection functions
R 1_ Control Unit Supply
R The control unit is supplied:
R - with 115 VAC/400 Hz, directly from the external power
R receptacle, by the voltage it has to analyse.
R The GAPCU generates 28VDC from this voltage. It is used:
R for its own needs (internal plus or minus 15 V, plus or
R minus 5 V and + 28 V supply), to supply the aircraft power
R supply control and indicating circuits (EPC, EXT PWR
R pushbutton switch, EXT PWR NOT IN USE indicator light and
R EXT PWR AVAIL caution light, flight/ground network
R contactors),
R - with 28 VDC from the normal aircraft electrical network and
R on the ground only.
R This dual supply constitutes the 28 V internal supply,
R peculiar to the control unit.
R 2_ Controls
R The GAPCU (in association with the EXT PWR pushbutton switch)
R controls the connection/disconnection of the external power
R to/from the aircraft electrical system.
R The necessary controls are achieved by means of relays.
R - The Interloch Monitoring Relay (IMR)
R This relay when energized, connects a holding supply to the
R GPU line contactor. It is energized when the following
R conditions exist:
R - external power Pin E voltage is higher than 12.6 Volts
R - external power protection latch is erroneous
R - interlock fault is erroneous:
R . the interlock voltage fault is detected when AC voltage is
R measured higher than 60VAC or DC voltage is measured higher
R than 45VDC.
R - The External Power Ready Relay (PRR)
R The PRR when excited enables the connection of the ground
R power unit to the aircraft network provided none of the
R following protections is actived:
R . over/undervoltage,
R . over/underfrequency,
R . incorrect phase order,
R . GAPCU internal fault.
R Any fault detection:
R - prevents the ground power unit from being connected to the
R aircraft network,
R - or causes it to trip if already in line.
R NOTE : When a fault is detected, the PRR is no longer excited____
R and/or inhibits illumination of the ON legend of the
R EXT PWR pushbutton switch.
R NOTE : The PRR also controls the illumination of the AVAIL____
R legend of the EXT PWR pushbutton switch in the cockpit
R and the EXT PWR AVAIL caution light in the external
R power receptacle housing.
R 3_ Protections
R - Over/underfrequency (OF, UF)
R The control unit permanently monitors the frequency of phase
R A voltage of the external power receptacle.
R The over/underfrequencies protection are triggered when the
R frequency becomes higher/lower than a certain threshold.
R - Over/undervoltage (OV, UV)
R The control unit permanently monitors the voltage of the
R three phases of the external power receptacle.
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