6. Electrical Flashcards
TR UNIT Light
- On the ground: Any TR failed,
- In flight: TR1 or TR2 and TR3 failed
ELEC Light
- Fault exists in DC or Standby Power system,
- Operates only on the ground
BAT Switch OFF
- Removes power from Battery Bus and Switched Hot Battery Bus during normal operation,
- Removes power from Battery Bus, Switched Hot Battery Bus, DC Standby Bus, Static Inverter and AC Standby Bus when Battery is only power source
CAB/UTIL Switch ON
Supplies power to:
- All 115V AC Galley Busses
- Recirculation Fans,
- Door Area heaters,
- Drain Mast heaters,
- Lavatory Water heaters,
- Logo lights,
- Potable Water Compressor,
- Shaver outlets,
- LED Cabin Lighting
DRIVE Light
IDG Low Oil Pressure caused by:
- IDG failure,
- Engine shutdown,
- IDG automatic disconnect due to high oil temperature,
- IDG disconnected through DISCONNECT switch
DISCONNECT Switches Operation Requirements
Disconnects IDG if:
- Electrical power is available and,
- Engine Start Lever is in IDLE
STANDBY PWR OFF Light
One or more of the following busses are unpowered:
- AC Standby Bus,
- DC Standby Bus,
- Battery Bus
STANDBY POWER Switch
AUTO:
- Automatic switching from normal to alternate when,
- Power from AC Transfer Bus 1 or DC Bus 1 is lost
BAT:
- Overrides automatic switching and,
- Places AC, DC Standby Busses and Battery Bus on Battery power,
- BAT switch maybe On or OFF (if OFF Switched Hot Battery Bus is not powered)
OFF:
- STANDBY PWR OFF light illuminates,
- AC Standby Bus, Static Inverter and DC Standby Bus are not powered
BUS TRANSFER Switch
AUTO:
-DC Cross Tie Relay automatically provides normal or isolated operation,
OFF:
- Isolates AC Transfer Bus 1 from 2 if one IDG is supplying power to both AC Transfer Busses,
- DC Cross Tie Relay opens to isolate DC Bus 1 from 2,
- Inhibits AC Transfer Bus 1 to supply TR3
AC Power Supply
- 2 IDGs produce 115V, 400Hz,
- IDGs supply their own busses and also opposite bus as well in case of an IDG failure,
- APU operates a generator and can supply both AC Transfer Busses
Basic Principles of Electrical System
- No parelleling of the AC sources of power,
- The source being connected to a Transfer Bus automatically disconnects an existing source
Ground Service
Without powering all airplane busses, it provides power directly to the AC Ground Service Busses for:
- Utility outlets,
- Cabin lighting,
- Battery charger
AC Power System
- Each consists of: Transfer Bus, Main Bus, 2 Galley Busses and Ground Service Bus,
- Transfer Bus 1 also supplies power to the AC Standby Bus,
- If AC source of a Transfer Bus fails or disconnected, that bus can be powered by any available source via BTB,
- BTB: Bus Tie Breaker,
- It’s not possible to power one Transfer Bus with External Power and one another with APU,
- If an Engine Generator no longer supplies power, BTB automatically closes to allow the other Generator to supply both Transfer Busses
Generator On-line Feature
- In case airplane takes off with APU powering both Transfer Busses,
- If APU is shut down or fails, Engine Generators automatically connected to their related Transfer Busses,
- Occurs only once in flight
Automatic Load Shedding
Engine Generators:
- Galley and Main Bus on Transfer Bus 2 are shed first,
- If an overload still sensed, Galley and Main Bus on Transfer Bus 1 are shed,
- If an overload still sensed IFE Busses are shed,
- Manual restoration of Galley and Main Busses can be attempted by recycling CAB/UTIL switch
APU Generator:
- Inflight if APU is the only electrical power source,
- All Galley and Main Busses are automatically shed,
- If an overload still sensed, both IFE Busses are automatically shed,
- On the ground APU attempts to carry a full electrical load,
- If an overload is sensed, Galley and Main Busses are shed until the load is within limits,
- Manual restoration of Galley and Main Busses can be attempted by recycling CAB/UTIL switch
IDG
- Integrated Drive Generator,
- Contains the Generator and Drive in a common housing,
- Lubricated and cooled by self-contained oil system,
- An integral electro-mechanical disconnect device allows for a complete mechanical isolation of the IDG
DC Power Supply
- 28V DC Power is supplied by 3 TR units, which are energized from the AC Transfer Busses,
- Battery provides DC Power when no other source is available
TR
- Transformer Rectifiers,
- Converts 115V AC to 28V DC,
- Any 2 TRs are capable of supplying the total connected load
TR Power Sources
- TR1: Transfer Bus 1,
- TR2: Transfer Bus 2,
- TR3: Transfer Bus 2 and backup from 1 (When BUS TRANSFER Switch in AUTO)
TRs Power Output
Under normal conditions:
- DC Bus 1, 2 and DC Standby Bus connected via the Cross Bus Tie Relay,
- TR1 and 2 supplies DC Bus 1 & 2 and DC Standby Bus,
- TR3 supplies the Battery Bus and serves as a backup for TR1 & 2
Cross Bus Tie Relay Open
When:
- BUS TRANSFER switch OFF,
- G/S capture during F/D or Autopilot ILS approach: this isolates DC busses to prevent a single failure from affecting both navigation receivers and FCCs
Battery Power Supply
- Dual 24V Nickel-Cadmium batteries, man and auxiliary, located in the Electronics Compartment,
- Battery voltage range: 22-30V,
- Can supply any part of the DC system,
- Auxiliary operates in parallel with the Main Battery when Battery is powering Standby System,
- At all other times Auxiliary Battery is isolated from power distribution system,
- Two fully charged batteries supply Standby Power for a minimum of 60 minutes,
DC Busses Powered From Battery During Standby Operation
- Battery Bus,
- Hot Battery Bus,
- Switched Hot Battery Bus,
- DC Standby Bus
Switched Hot and Hot Battery Busses Power
- Switched Hot Battery Bus: Powered when Battery switch is ON,
- Hot Battery Bus: Always connected to Battery
