Electrical System Flashcards
What actions does switching the Bus Transfer switch to off do?
Isolates the AC transfer buses 1 & 2 if only one IDG is supplying AC power to both AC transfer buses.
DC cross tie relay opens isolating DC bus 1 & 2
When does a TR unit light illuminate?
In flight, TR unit 1 or both TR 2&3 fail.
On ground, if any TR unit fails.
What causes Drive light illumination?
Loss of oil pressure in respective IDG
Load shedding order single IDG operation?
Galleys and main bus on transfer bus 2
If overload still exists
Galleys and main bus on transfer bus 1
Still exists,
IFE
Load restoration?
If second power source is restored automatic load restoration is achieved.
If manual restoration is required cycle the cabin utility switch.
What happens at glide slope capture during an autopilot or flight director approach?
The cross bus tie relay opens isolating DC bus 1 & 2. This prevents a failure affecting both nav receivers and flight control computers
What are the two basic principles of the electrical system?
There is no paralleling of AC power sources
The source of power being connected to a transfer bus automatically disconnects the existing source.
How are the TR units powered?
TR1 - AC transfer bus 1
TR2 - AC transfer bus 2
TR3 - AC transfer bus 2 with 1 as backup source
What does the auxiliary battery do?
It is normally isolated from the power distribution system, however it operates in parallel with the main battery when powering the standby system
How long will the batteries supply standby power for?
60 mins minimum
With a loss of both AC generators what DC busses are powered and how?
The battery powers the…
Battery bus
DC standby bus
Hot battery bus
Switched hot battery bus
What does the main battery charger TR do?
Primarily charges the main battery. Once fully charged, provides power for all loads connected to the battery.
It also powers the battery bus if TR3 has failed
With the loss of AC transfer bus 1 or source powering DC bus 1, what powers the standby Ac and DC buses?
The main and auxiliary batteries and their chargers
What does electrical discharge light mean?
Excessive discharge from the batteries
What does positioning the standby power switch to BAT do?
Overrides the automatic switching and places the AC standby bus, DC standby bus and battery bus on standby power.
