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* There is no power between the BTBs.
The EPC opens if any one of these occur:
* Quality of external power is bad
* Ground power switch is put to OFF position
* A protective function occurs
* You remove the external power plug
* The interlock pins do not have continuity
* Another power source selection trips (opens) the EPC.
Protection
The BPCU protects the external power channel and isolates the
channel if a failure occurs. The BPCU monitors these
parameters of external power:
* Current
* Voltage
* Frequency.
Current Protection
The BPCU has protection logic for these types of current faults:
* Overcurrent
* Unbalanced phase current
* Phase sequence.
The BPCU opens bus tie breaker 2 (BTB 2) if there is an
overcurrent condition. The BPCU then opens BTB 1 if the
condition continues. Finally, the BPCU opens the EPC if there is
still an overcurrent condition.
The EPC opens if the BPCU finds an unbalanced phase current
condition. The BPCU will not close the EPC if a phase sequence
fault is true.
The BPCU also uses current information to remove power (load
shed) to the galley and main buses. See the AC Electrical Load
Distribution section for more information. (SECTION 24-50)
Voltage Protection
The BPCU has protection logic for these types of voltage faults:
* Overvoltage (high voltage)
* Undervoltage (low voltage)
* External power plug fault.
The BPCU opens the EPC if an overvoltage or undervoltage
condition happens. The BPCU will not let the EPC close if there
is an overvoltage or undervoltage condition.
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EFFECTIVITY
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The BPCU monitors the voltage and polarity at pins E and F of
the external power panel. The BPCU opens the EPC or prevents
the EPC from closing if there is a fault condition.
Frequency Protection
The BPCU opens the EPC or prevents the EPC from closing if
there is an under frequency (low frequency) condition.
The BPCU opens the EPC or prevents the EPC from closing if an
there is an over frequency (high frequency) condition.
Indication
The blue GRD POWER AVAILABLE light comes on to show the
external power is connected and power quality is in limits. The
BPCU supplies power for the light. The light comes on for these
conditions:
* There is continuity through pins E and F at the external
power connection
* Connected external power quality is in limits.
The amber CONN light comes on to show that external power is
connected. The light is not an indication that power quality is
good. The light is neon and receives AC power directly from the
external power feeder lines in P92 PDP 2.
The white NOT IN USE light comes on to show that the ground
service buses and transfer buses do not receive power from the
external power source. The light comes on when these
conditions are true:
* Continuity through pins E and F (external power plug
connected)
* Ground service relays are de-energized, and
* EPC is open.
Interfaces
The R47 external power sensing relay energizes to supply entry
way lighting to the passenger entry door areas. This relay
receives power from the BPCU.
See the Lights chapter for more information about these lights.
(CHAPTER 33)
The refueling power control relay (R11) energizes to supply
power to the fueling station. This relay receives power from the
BPCU.
See the Pressure Refueling section for more information about
the pressure refueling system. (SECTION 28-21)
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