Electrical Flashcards
Recall the function of the battery switch (OFF, ON)
OFF – battery connected to the battery direct bus only
(battery charging not affected)
ON - Connects battery to the DC transfer bus and the battery
direct bus (adds DC transfer bus)
Recall the function of the EMER PWR Selector (OFF, ARM, ON) and TEST conditions and messages
OFF - Emergency power is off. Resets the automatic emergency power system
ARM – Supplies emergency power automatically when power loss to the EMER AC or DC bus is detected
ON - Emergency power is on. The battery supplies power for AC EMER bus (through the static inverter) and DC EMER bus
• Emergency power can only be tested on the ground with both engines shut down. It is automatically tested when the switch is moved from OFF to ARM. During the test, the ON light illuminates and an EMER PWR TEST alert is displayed. A successful test is indicated when the ON light is extinguished and the alert is no longer displayed.
• Turn EMER PWR selector OFF if both pilots leave the aircraft and the APU is shut down.
Recall which buses are powered on EMER PWR and how long the battery can provide
power (4)
When activated, the emergency power system will provide power to the following buses for
approximately 60 minutes:
• Battery direct bus
• DC transfer bus
• Emergency AC bus (through emergency inverter)
• Emergency DC bus
Explain the function of the L/R BUS TIE Switches (OPEN, AUTO)
Open – Respective generator cannot power the
tie bus. Can also be used to reset a bus tie
lockout on the ground
AUTO – Generator bus to tie bus connection is
controlled automatically to meet aircraft power
requirements
Recall the function of the DC BUS TIE Switch (OPEN, AUTO)
OPEN - Opens all three DC bus tie relays
AUTO - DC bus tie relays are automatically controlled to
ensure all DC buses are powered
Recall the function of the L/R GEN Switches (RESET, OFF, ON)
RESET – Resets the generator
OFF – Disconnects the generator from the respective bus
ON – Allows an operating generator to supply power to its respective bus
Recall the function of the APU Power Switch (RESET, OFF, ON)
RESET – Resets the generator
OFF – Disconnects the APU generator from the tie bus
ON – Allows an operating APU generator to supply power to the tie bus
ON light illuminates blue when the APU generator is powering the tie bus.
Recall the function of the EXT Power Switch
OFF, ON
OFF – Disconnects EXT PWR from the tie bus
ON – Connects EXT PWR to the tie bus
Recall the function of the GND SERVICE ELEC PWR Switch (OFF, ON)
OFF - Neutral position for ground service power
ON - Connects external power to the AC ground service bus and powers the
DC ground service bus. EXT power switch is OFF. ON light indicates blue.
Recall the function of the GALLEY PWR Switch (OFF, ON)
OFF – Galley power is off
ON – Galley power is on. (In flight, if only one generator is providing
power to both generator buses, then system sheds the galleys to
conserve electrical power.) Can also be used to reset a galley load
shed.
Recall features of the No Break Power Transfer (NBPT)
• Normally, all electrical power source transfers will occur without power interruption
• Momentary breaks in power supply, however, may occur during the transfer of power
from the APU to an external source OR an unexpected loss of APU or IDG power,
such as flame-out or uncommanded shutdown.
