Electrical Flashcards
How many sources of AC Power?
Five (2 Engine Integrated Driven Generators (IDGs), 1 APU Generator, 1 Hydraulic Motor driven Generator (HMG), 1 External power)
DC power normally comes from 2 Transformer Rectifiers Units (TRUs) which are powered by their respective MAIN AC busses. If AC power is not available to operate the TRUs, then either the HMG or the MAIN BAT provides DC power (APU battery only provides power for the APU).
True
To what bus is the Utility Bus connected, when the Utility Bus switch is ON?
Arms the automatic operation of the AC And DC Bus Tie system
When does the Utility Bus OFF light illuminate
Whenever the bus is unpowered
With the Bus Tie switch in AUTO, what causes the AC Bus ISLN light to
Bus fault has occurred
What does the generator Control OFF light indicate ?
Generator Breaker open
Pushing a Generator Control switch off opens both the field and generator breakers.
True
Pushing the Generator Control Switch off opens the generator field.
True
Pushing the Generator Control switch off resets fault trip circuitry
True
Pushing the Generator Control switch off causes the Generator Control OFF and Generator DRIVE lights illuminated
False
What causes the Standby Power Bus OFF light to illuminate ?
Loss of power on either the Standby AC or DC Bus
The OFF position of the Standby Power Selector de-energizes the battery bus, standby AC Bus & Standby DC Bus.
False
What causes the Standby Power Bus OFF light to illuminate?
Loss of power on either the standby AC or DC bus
The OFF position of the Standby Power Selector de-energizes the battery bus, Standby AC bus & Standby DC bus.
False
Which of the following will cause the Generator DRIVE to illuminate
High oil temperature
You are preparing for the first flight of the day. You have just positioned BAT switch to ON. Why are the DRIVE lights ON?
Low oil pressure in both drives - normal until drives are operational
A generator Drive light can indicate a high or low drive output RPM
False
A generator Drive light can indicate low oil pressure
True
What can power a Utility Bus?
Respective Main AC Bus only
The Bus tie system parallels engine generators but prevents any other sources from being paralleled.
False
The APU can be used to power the LEFT Main AC Bus while the RIGHT engine generator is powering the RIGHT Main AC Bus.
True
The APU can be used to power the LEFT Main AC Bus while external power is powering the RIGHT Main AC Bus.
False
Which bus is powered automatically when external power is plugged in and available?
Ground Handling Bus
Source order for powering LEFT and RIGHT Main busses?
Respective IDG then APU Generator then Opposite IDG
The Ground Handling Bus powers the battery chargers.
False
The Ground Service Bus powers the cargo doors and cargo handling equipment.
False
What is the highest automatic priority on the LEFT Main AC Bus?
Left engine driven generator
The LEFT Main AC Bus can power the battery switch off
True
The standby buses can be powered from the LEFT Main AC and DC even with the Standby Selector OFF
False
With the APU supplying electrical power, what happens when the first engine is started?
The engine powers its respective buses only
What bus powers the fire extinguishers?
Hot battery bus
What bus powers most of the airplane fire detection systems?
Battery bus
What is closed by pushing the Generator Control switch ON before engine start?
Generator field only
Which has priority in supplying the ground handling bus, the APU or external power?
External power
Which of the following inhibits the APU Generator Control OFF light?
External power contactor being closed
Where is the external power receptacle?
Aft of the nose wheel well
When can the Ground Handling Bus be powered?
Only on the ground
What can power the Ground Service Bus?
APU, external power or an engine generator
What can power the Ground Handling Bus?
Only external power or the APU
When will the Utility Buses be shed during an engine start?
Only when the APU is supplying electrical and pneumatic power.
With the APU supplying both electrical and pneumatic power, what happens as the second engine is started?
Only the Utility Bus for the engine being started trips off
Three autopilots are armed for a triple channel approach. At 1200 ft RA, the LEFT generator is lost. As a result, the LEFT Main AC Bus is lost.
False
During a triple channel approach, the LEFT generator is lost at 140 ft RA. As a result the LEFT Main AC bus is lost.
True
What is required to enable the captain’s flight instrument transfer bus to transfer with the loss of the LEFT Main AC?
Only the LEFT Bus tie switch must be in AUTO
Which of the following arms the load shed system to trip off both Utility Buses with the loss of a Generator?
Both engine Generator Drive lights extinguished
Which of the following arms the load shed system to trip off Utility Buses when a generator is lost?
Both thrust levers in the takeoff range
In flight the LEFT engine is shut down. What electrical buses are lost?
Only the two Utility Buses
During a triple channel approach, the RIGHT generator trips off at 140 feet RA. As a result, the F/O’s primary flight instruments are lost.
False
What is required to enable the F/O’s instrument transfer bus to transfer with the loss of RIGHT Main AC?
Only the Right Bus Tie switch must be in AUTO
When electric power fails, what happens to the cockpit door lock?
It unlocks automatically
When APU GEN switch is positioned to OFF, APU GEN OFF light comes on. What condition might be indicated by the presence of both the ON flow bar & the APU GEN OFF light
The APB is open as a result of a fault
Right DRIVE light comes on. EICAS advisory message appears. What is the cause of these indications?
Either the RIGHT Generator Drive oil pressure is too low or the oil temperature is too high
Airplane is in flight. Electrical system is in normal flight configuration. STBY POWER OFF light comes on. EICAS advisory message appears. Which position of the STBY POWER selector will provide an alternate power source to the standby buses?
BAT
When is the Ground Service Bus powered?
Whenever the RIGHT Main AC Bus is powered
Concerning ‘Loadshedding’ during engine start.
Utility and galleys trip with engine start selector to GND (both for N°1, affected for N°2)
What buses can be powered by the HDG if the Main AC buses fail?
Standby AC, Standby DC, both battery buses and both instrument transfer buses
What signals the HDG to operate?
If primary power is lost on both Left and Right AC Main Buses, the HDG operates automatically
You are in flight. If the RIGHT engine Generator is lost + RIGHT Bus isolated on the EICAS. What will happen to the electrical system?
Right AC Bus will have no back-up power source
What does the STBY POWER OFF light indicate?
Either or both Standby Buses are unpowered
Which statement is true of the Ground Service Bus?
It can be powered from the Ground Handling Bus by using a switch on Flight Attendant’s panel
LEFT Main AC power is lost. What is the status of the STANDBY Buses?
RIGHT DC Bus powers LEFT DC Bus, STANDBY DC Bus and STANDBY AC Bus via static inverter
Which statement is true?
DC power normally comes from 2 Transformer Rectifiers Units (TRUs) which are powered by their respective MAIN AC busses. If AC power is not available to operate the TRUs, then either the HMG or the MAIN BAT provides DC power (APU battery only provides power for the APU)
What is the normal source of power for the STANDBY AC Bus?
LEFT Transfer Bus
The Ground Service Bus powers:
2 Battery chargers (MAIN + APU), Equipment cooling fan, LEFT forward pump, Main entry door & Passengers lights
Prior to establishing electrical power, the Main Battery powers the Hot Battery Bus and After establishing electrical power, Main Battery Charger powers the Hot Battery Bus.
True
The HDG produces power to:
Battery Bus and Hot Battery Bus, LEFT and RIGHT AC Transfer busses, Captain’s Instrument Transfer bus & Standby AC & DC busses
The HDG is operating while the gear is retracting.
False
BUS OFF light is illuminated. What does it mean?
Bus Tie Breaker is locked open because switch is OFF or Fault occurred
