ATR 42 Model : 400/500
DC POWER
ELECTRICAL SYSTEM
P 4
NOV 99
001
1.06
.
20
DC SVCE BUS
The DC SVCE BUS supplies power in flight, and on ground during airplane servicing
operations.
The DC SVCE BUS can be supplied by :
- DC BUS 1. The master sw is the DC SVCE/UTLY BUS pb. When selected on, the
cabin attendant controls the DC SVCE BUS supply from a sw located on the cabin
attendant control panel.
- EXT PWR. Only the cabin attendant pb has control. The supply of the BUS may be
performed with batteries switched OFF.
GND HDLG BUS
The GND HDLG BUS supplies the DC loads required for airplane servicing on the
ground even with BAT sw selected OFF. Since these loads are not required during
flight, the GND HDLG BUS is deenergized in flight. The GND HDLG BUS can be
supplied :
- When EXT PWR is available, from DC SVCE BUS.
- When EXT PWR is not available, from HOT MAIN BAT BUS provided :
D
Cargo door operating panel door is open (micro switch), or
D
Refueling panel is open (micro switch), or
D
Entry door is open (micro switch).
TRANSFER
(see schematics p. 15 to p. 26)
With all switches in normal position, the DC power transfer is achieved by automatic
opening and/or closure of electrical contractors according to the particular electrical
conditions.
- On ground
D
When EXT PWR is connected (p. 15/16)
Note : The electrical power transfer is achieved in the same way as in flight as long
as EXT POWER is not connected.
- In flight
D
Both engine driven generator operating (p. 19/20)
* The engine driven generator 1 supplies the DC BUS 1,
* The engine driven generator 2 supplies the DC BUS 2,
* The BTC is open.
D
If one engine driven generator fails (p. 21/22)
* The BTC closes (BTC green flow bar illuminates),
* The entire electrical network is supplied by the remaining engine driven
generator.
D
If both engine driven generators fail (p. 23/24)
* DC ESS BUS, DC STBY BUS are supplied from the main battery, or from the
TRU, if selected ON.
* DC EMER BUS is supplied from the emergency battery or from the TRU, if
selected ON.
D
If both engine driven generators fail and TRU is inoperative (p. 25/26)
* When DC STBY BUS reaches undervoltage (amber UNDV light comes ON), this
bus may be recovered by selecting OVERRIDE pb.
AA
R
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