Electrical Flashcards
BAT DISCHARGE Light
Excessive battery discharge
TR UNIT Light
On ground – any TR unit failed
In flight – TR1 failed, or TR2 and TR3 failed
ELEC Light
On ground only – fault in DC or Standby power system
DRIVE Light
IDG low oil pressure, caused by
• IDG failure
• IDG automatic disconnect due to high oil temp
• IDG manual disconnect thru DISCONNECT Switch
• Engine shutdown
STANDBY PWR OFF Light
AC Standby, DC Standby, or Battery Bus not powered
TRANSFER BUS OFF Light
Transfer Bus not powered
SOURCE OFF Light
No source selected or last selected source disconnected
GEN OFF BUS Light
IDG not powering the related Transfer Bus
APU GEN OFF BUS Light
APU running but not powering a bus
GRD POWER AVAILABLE Light
Ground power of acceptable quality connected to aircraft
Which buses are controlled by the OFF and BAT positions of the STANDBY POWER Switch?
OFF position AC Standby Bus, DC Standby Bus
BAT position AC Standby Bus, DC Standby Bus, and Battery Bus
What happens when the BUS TRANSFER Switch is placed in OFF?
- Isolates AC Transfer Bus 1 from AC Transfer Bus 2 if one IDG is supplying power to both AC Transfer Buses
- Isolates DC Bus 1 from DC Bus 2 by opening the Cross Bus Tie Relay
If the APU is the only available power source (ground or flight), what happens if the BUS TRANSFER Switch is placed in OFF?
It arms each BTB to open if its related APU GEN Switch is moved to OFF
What is required for the Switched Hot Battery Bus to be powered?
BAT Switch must be ON
Must the BAT Switch be ON to connect ground power to the buses?
Yes
Is it possible to use APU and ground power simultaneously?
No
With the APU powering the buses, the first engine is started. What happens when its GEN Switch is placed ON?
That IDG powers its related Transfer Bus (GEN OFF BUS Light extinguishes), while the other Transfer Bus continues to be energized by the APU generator
Describe the “automatic on-line” feature of the engine generators:
If you forget to connect the engine generators to the buses and takeoff using APU power, and later lose the APU generator (due to failure or shutdown), the IDGs will connect to the buses automatically…one time only, and only in flight.
Which lights illuminate on the electrical panel to indicate a failed IDG?
GEN OFF BUS
SOURCE OFF
DRIVE
What are normal AC voltage and frequency indications?
- 115 ± 5V (110-125V for APU generator with buses loaded)
* 400±10CPS
What are normal DC voltage indications?
26 ± 4V (up to 33V battery voltage during primary charge cycle)
What is the normal power source for the Battery Charger?
Ground Service Bus 2
What is the normal power source for the AC Standby Bus?
AC Transfer Bus 1
What is the normal power source for the DC Standby Bus?
TR1, 2, and 3
What is the normal power source for the Battery Bus?
TR 3
What is the normal power source for the Hot Battery Bus?
Battery/Battery Charger
What is the normal power source for the Switched Hot Battery Bus?
Battery/Battery Charger
Describe automatic load shedding when buses powered by a single engine generator:
Galleys, main buses, and IFE buses shed incrementally based on actual load sensing. Automatic restoration occurs as capacity restored.
Describe automatic load shedding when buses powered by the APU generator only (in flight):
All galleys and main buses may shed, followed by both IFE buses if required.
Describe automatic load shedding when busses powered by the APU generator only (on ground):
APU attempts to carry full load. If an overload is sensed, APU sheds galleys and main buses until load within limits.
Note: Manual restoration of galley and main buses can be attempted by cycling CAB/UTIL Power Switch to OFF, then back ON.
When will emergency exit lights automatically illuminate, if armed?
With loss of AC power or DC Bus 1
Which buses remain powered after loss of both engine generators?
- Battery Bus
- Hot Battery Bus
- Switched Hot Battery Bus
- DC Standby Bus
- AC Standby Bus
When may circuit breakers be pulled and reset?
When specified in a procedure
What requirements must be observed when resetting a circuit breaker in flight?
- Reset only if specified in a procedure or required for flight
- Cooling period of 2 minutes must be observed
- Maximum of one reset may be attempted unless essential for safety of flight
- Do not reset (even once) a galley CB
What requirements must be observed when resetting a circuit breaker on the ground?
- CB tripped for unknown cause may only be reset after Maintenance has determined cause of trip and that CB may be safely reset
- CB may be cycled (pulled and reset) as part of an approved trouble-shooting procedure, unless specifically prohibited for existing conditions
Is an AML entry required for any circuit breaker trip?
Yes
