ATR 42-500, Manual

Page: 49 / 129

G - Electrical systems
p. 48
G.
Electrical systems
4. ACW schematic
ATA 24
NP=0 NP=0
ACW supplied by the External Power
– When the ACW GPU is available ( AVAIL ) but not ON, the GPU supplies only the ACW
Service Bus, if the GND Service Bus switch, on the flight attendant panel, is ON.
– When the ACW GPU is ON , the GPU supplies through the BTC, the ACW BUS 1, the ACW
BUS 2 and the ACW SVCE BUS.
– Even if one ACW generator is available, the GPU has always the priority.
ACW
GEN 1
ACW BUS 1 ACW BUS 2 TRU
ACW
GEN 2
SVCE BUS
ACW
GPU
NP=0 NP=0 in hotel mode
NP<20% with prop feathered
ACW in Hotel mode or with the propeller feathered
NOTE: An ACW Generator is available if the NP is above 66%.
– When the right engine is running in hotel mode, the NP=0.
– When the engines are running but the propeller is feathered, the NP is bellow 20%
In both cases the ACW Busses are not supplied
ACW
GEN 1
ACW BUS 1 ACW BUS 2 TRU
ACW
GEN 2
SVCE BUS
ACW
GPU
NP=0 NP=70.8%
The propeller unfeathered and one ACW GEN on line
On ground, when the propeller is unfeathered, the engine is running on fuel governing mode.
The fuel governing mode, maintain a minimum NP of 70.8%, in order to have the ACW
available (ACW GEN on line at 66%)
The ACW GEN supplies, the ACW BUS 2 and ACW BUS 1 through the BTC, but the SVCE
BUS is shed (one generator is not able to supply all the busses)
CAUTION: on ground in case of an EEC or PEC fault, the fuel governing mode is lost and the
ACW generator is not available (NP<66%)
ACW
GEN 1
ACW BUS 1 ACW BUS 2 TRU
ACW
GEN 2
SVCE BUS
ACW
GPU
09T2253_ATR_systems42_72PEC_AtoH.indd 48 19/05/10 11:05