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On airplanes SN 1455 and subsequent, a ground service bus is
incorporated to provide DC power to equipment required to perform
minimal servicing of the aircraft while on the ground. Use of the ground
service bus prevents the unnecessary powering of avionics equipment. In
the production standard configuration, only the wheel well lights, utility
lights and service lights receive power from the ground service bus. Other
items may be connected as desired by the operator during completion and
outfitting.
Selection of the ground service bus on or off is accomplished using the
GROUND SERVICE switch, located on the forward external switch panel.
See Figure 15. Whenever the GROUND SERVICE switch is selected to
ON, the ground service bus receives power from BATT 2. Other airplane
power sources may be connected as desired by the operator during
completion and outfitting.
A GND SVCE BUS annunciator, located in the cockpit overhead
annunciator panel and shown in Figure 17, illuminates amber when the
ground service bus is powered and airplane electrical power (battery power
minimum) is ON.
K. DC Bus Power Control Unit:
The DC Bus Power Control Unit (DCBPCU), located in the right avionics
rack, controls the connection of the DC power sources to the DC buses. By
providing automatic control capability over the DC power relays and
contactors, it controls the DC buses and batteries by switching DC bus
power to an alternate source should a malfunction occur. The DCBPCU
also provides power supply/voltage regulation, external power monitoring,
bus feeder fault protection, and manual or automatic control capabilities.
The DCBPCU also protects the DC buses from external DC overvoltage
and undervoltage, TRU undervoltage and overcurrent, Left, Right and
Essential DC bus undervoltage and overcurrent, and bus fault protection
on the main and essential DC bus feeders.
L. Power Distribution Box:
The Power Distribution Box (PDB), located in the right avionics rack, is the
load center of the electrical system. It serves as the terminal for all input
power and output to the buses and other loads in the aircraft. Power
switching to the DC buses is accomplished through relays within the PDB
that are controlled by the DCBPCU and converters. The PDB also provides
switching and control for the AC electrical system.
3. DC Electrical Power System Operation:
(See Figure 6.)
The flight crew controls the electrical power system through the EPMP. It consists
OPERATING MANUAL
2A-24-00 PRODUCTION AIRCRAFT SYSTEMS
Page 56
May 30/02
Revision 7
of 13 digital displays and 33 switchlights that allow the selection of electrical
power sources and display of voltages, amperages, frequencies and percentages
of total load.
When normally configured (L MAIN, R MAIN and ESS DC BUS switches selected
to AUTO; BATT 1 and/or BATT 2 switch(es) selected ON), the EPMP allows
automatic operation and selection of electrical power sources in order to minimize
flight crew workload. Manual operation is always available, however, in order to
hard-select or isolate power sources.
With an external DC power source available and the ELECTRIC MASTER AUX
PWR switch selected ON, external DC power is routed through the PDB to the
Left Main, Right Main and Essential DC buses.
With the alternators operating and the converters supplying power, selection of
the ELECTRIC MASTER LEFT PWR and RIGHT PWR switches to ON allows left
converter output to the Left Main and Essential DC buses and right converter
output to the Right Main DC bus.
If the APU is the only source of power and the ELECTRIC MASTER AUX PWR
switch is selected ON, the APU alternator powers the Left Main, Right Main and
Essential AC buses. The Left Main, Right Main and Essential DC buses in turn
receive power from the TRU.
The Essential DC bus provides power to equipment essential for safe flight.
Normally, the Left Main DC bus supplies the Essential DC bus but should it or the
Right Main DC bus not be available (and the Left Main, Right Main and Essential
AC buses are also not available), the main batteries are capable of powering the
bus through the Battery Tie bus. In this configuration, the Essential DC bus also
powers Phase A of the Essential AC bus through the E-inverter.
Illumination of the DC RESET amber switchlight indicates a transient problem,
bus fault or logic problem. If the problem is a Left Main or Right Main DC bus fault
or overcurrent condition, depressing the switchlight resets the system. If the
switchlight extinguishes, the fault has been cleared. If it remains illuminated, the
fault remains. If the problem is an Essential DC bus fault or overcurrent condition,
　
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