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BPCU uses its inputs from components and other control units.
Fail-safe functions are in the system to allow power distribution
if the BPCU fails.
BPCU Power Supplies
The BPCU gets power from these three sources:
* External three-phase AC power
* 28v dc from the battery
* 28v dc from DC bus 1.
BPCU Inputs
The BPCU receives these inputs:
* Ground power switch position
* Bus transfer switch position
* Line voltage at a point between the external power panel and
the EPC
* Signal from the current transformer (CT) that is proportional
to the current flow through the feeder wires
* Continuity circuit through pins E and F at the external power
panel (interlock)
* Bus tie breaker 1 (BTB 1) and BTB 2 positions
* Generator control breaker 1 (GCB 1) and GCB 2 positions
* Auxiliary power breaker (APB) position
* Air/ground
* Ground service relays position
* Ground service switch position
* EPC position
* APU generator switch positions (from AGCU)
* Source off signals from GCUs
* Autoland signal from flight control computers (FCCs).
AIRPLANES WITH GALLEY SWITCH;
* Galley switch position
AIRPLANES WITH CAB/UTIL AND IFE/PASS SEATS SWITCHES;
* Cab/Util switch position
* IFE/Pass Seats switch position
BPCU Outputs
The BPCU supplies these outputs:
* GRD PWR AVAILABLE indication on the P5-4 module
* Indication at external power panel (P19)
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EFFECTIVITY
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* Close command to EPC
* Power to refueling relay
* BTB close command (through GCUs)
* Breaker open command (through GCUs)
* APB hold off command
* BPCU fail-safe command to GCUs
* APU configuration load shed information to APU electronic
control unit (ECU)
* Load shed (to galley and main bus load shed relays)
* Ground service relays.
Protection
The BPCU uses inputs to monitor the electrical system. If
necessary, the BPCU removes loads from some buses (load
shed) to protect the system. The BPCU opens the EPC if the
problem continues. See the EPC control and protection page in
this section for more information.
BPCU Fail-Safe
The BPCU has protection to fail-safe the power channel if the
BPCU loses control or protection capability. A signal goes to the
GCU of the power channel. A fail-safe condition will do these
functions:
* Open the EPC
* Make the NOT IN USE light on the external power panel go
off
* Make the GRD PWR AVAILABLE light on the P5 panel go off
* Remove power to the galleys and main buses
* The BPCU sends a fail-safe signal to GCU 2. GCU 1 signal
has 200 millisecond time-delay
* GCU 2 closes BTB 2 if the BUS TIE is de-energized
* GCU 1 closes BTB 1 if transfer bus 1 needs power
* Apply APU power manually if the tie bus is de-energized
* Make the BPCU FAULT light on the face of the BPCU come
on
* Prevent the operation of the fueling power control relay
(R11).
Built-In Test Equipment (BITE)
The BPCU has BITE to help you do troubleshooting of the
external power system. See the TRAINING INFORMATION
POINT page in this section for more information.
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EXTERNAL POWER - BUS POWER CONTROL UNIT (BPCU) - GENERAL DESCRIPTION
EFFECTIVITY
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Control
The BPCU closes the EPC when all of these occur:
* Ground power switch on P5 is in the ON position
* External power quality has correct voltage and frequency
* The interlock pins (EF) have continuity
* No protective functions occur
　
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