Chapter 6 - Electrical Flashcards
Battery Discharge (BAT DISCHARGE) Light
x2
- Illuminated (amber) – with BAT switch ON,
- excessive battery discharge detected.
TR UNIT Light
2 scenarios
Illuminated (amber) • On the ground • Any TR has failed. • In-flight • TR1 failed; or • TR2 and TR3 failed.
Electrical (ELEC) Light - Illuminated Amber
2x
A fault exists in DC power system or standby power system.
Note: Operates only with airplane on ground.
Battery (BAT) Switch - OFF
2x conditions
Normal power sources available
• Removes power from battery bus and switched hot battery bus
Battery is only power source
• Removes power from battery bus, switched hot battery bus, AC & DC standby
buses, static inverter.
Battery (BAT) Switch - ON
2x
• Provides power to switched hot battery bus
• Energizes relays to provide automatic switching of standby electrical
system to battery power with loss of normal power
CAB/UTIL Switch - OFF
2x
Removes electrical power from galley and cabin equipment systems
CAB/UTIL Switch - ON
supplies electrical power to galley and cabin equipment systems.
(IFE also 115v AC)
Generator Drive (DRIVE) Lights
4x
Integrated drive generator (IDG) low oil pressure caused by one of the following:
• IDG failure
• Engine shutdown
• IDG automatic disconnect due to high oil temperature
• IDG disconnected through generator drive DISCONNECT switch
Generator Drive Disconnect (DISCONNECT) Switches (guarded)
Disconnects IDG if electrical power is available and engine start lever is in IDLE.
IDG cannot be reconnected in the air
STANDBY Power Off (PWR OFF) Light
Illuminated (amber) – one or more of the following busses are unpowered:
• AC standby bus
• DC standby bus
• battery bus.
STANDBY POWER Switch (AUTO + AC busses powered)
- In flight, or on the ground, and AC transfer busses powered:
- AC standby bus is powered by AC transfer bus 1
- DC standby bus is powered by TR1, TR2 and TR3
STANDBY POWER Switch (AUTO + AC busses un-powered)
- In flight, or on the ground, loss of all AC power
- AC standby bus is powered by battery through static inverter
- DC standby bus is powered by battery
- Battery bus is powered by battery
STANDBY POWER Switch (BAT)
- AC standby bus is powered by battery through static inverter
- DC standby bus and battery bus are powered directly by battery
STANDBY POWER Switch (OFF)
- STANDBY PWR OFF light illuminates
* AC standby bus, static inverter, and DC standby bus are not powered.
Ground Power Available (GRD POWER AVAILABLE) Light
Illuminated (blue) – ground power is connected and meets airplane power quality
standards
Ground Power (GRD PWR) Switch
ON – if momentarily moved to ON position and ground power is available:
• removes previously connected power from AC transfer busses
• connects ground power to AC transfer busses if power quality is correct
TRANSFER BUS OFF Lights
Illuminated (amber) – related transfer bus is not powered.
SOURCE OFF Lights
Illuminated (amber) – no source has been manually selected to power the related
transfer bus, or the manually selected source has been disconnected
• if a source has been selected to power the opposite transfer bus, both
transfer busses are powered.
Generator Off Bus (GEN OFF BUS) Lights
Illuminated (blue) – IDG is not supplying power to the related transfer bus.
Generator (GEN) Switches (OFF)
Disconnects IDG from related AC transfer bus by opening generator circuit
breaker
Generator (GEN) Switches (ON)
Connects IDG to related AC transfer bus by disconnecting previous power
source and closing generator circuit breaker.
BUS TRANSFER Switch (AUTO)
BTBs operate automatically to maintain power to AC
transfer busses from any operating generator or external power
• DC cross tie relay automatically provides normal or isolated operation
as required.
BUS TRANSFER Switch (OFF)
isolates AC transfer bus 1 from AC transfer bus 2 if one IDG is supplying
power to both AC transfer busses
• DC cross tie relay opens to isolate DC bus 1 from DC bus 2.
APU Generator Off Bus (GEN OFF BUS) Light
Illuminated (blue) – APU is running and not powering a bus.
APU Generator (GEN) Switches (OFF)
APU generator powering both AC transfer busses
• moving a single APU GEN switch to OFF illuminates related SOURCE OFF light. APU continues to power AC transfer busses
• subsequently moving other APU GEN switch to OFF disconnects APU generator from tie bus and removes
APU power from AC transfer busses
• APU generator powering one AC transfer bus; IDG powering one AC transfer bus
• moving related APU GEN switch to OFF disconnects APU generator from tie bus and AC transfer bus. IDG powers AC transfer busses.
APU Generator (GEN) Switches (ON)
- Neither AC transfer bus powered by IDG – moving a single APU GEN switch to ON:
- connects both AC transfer busses to the APU generator
- disconnects external power, if connected
- opposite SOURCE OFF light illuminates until the other APU GEN switch is moved to ON.
- Both AC transfer busses powered by IDGs – moving an APU GEN switch ON:
- powers the related AC transfer bus from the APU generator
- other AC transfer bus continues to receive power from the IDG.
GROUND SERVICE Switch
Provides manual control of ground service busses. Enables servicing airplane using external power without activating AC transfer busses
Primary electrical power
Two engine integrated drive generators
(IDGs) which supply three-phase, 115 volt, 400 cycle alternating current
Source of DC Power
Transformer rectifier (TR) units and the main battery/battery charger
Backup power for AC & DC standby power
Main & auxiliary batteries
There are two basic principles of operation for the 737 electrical system:
- There is no paralleling of the AC sources of power.
* The source of power being connected to a transfer bus automatically disconnects an existing source
The electrical power system may be categorized into three main divisions:
The AC power system, the DC power system, and the standby power system.
APU Generator
The APU generator can supply power to both AC transfer busses on the ground or in flight. As the only power source, the APU generator can meet electrical power requirements for all ground conditions and most flight conditions.
External Ground Power
When connected, external power can supply power
to both transfer busses.
Ground Service
The switch provides ground power directly to the AC ground service busses for utility outlets, cabin lighting and the battery charger without powering all airplane
electrical busses. The ground service switch is a momentary push button and is overridden when both AC transfer busses are powered.
If the BUS TRANS switch is in the AUTO position and the source powering the transfer bus
is disconnected or fails, the source powering the opposite transfer bus automatically picks up
the unpowered transferred bus through the BTBs.
true
AC Transfer busses
Whenever external power is powering both transfer busses and the engine generator power is applied to its onside transfer bus, external power continues to supply power to the remaining transfer bus
In flight, one engine-driven generator drops offline and the BUS TRANSFER switch is in the AUTO position, what indications will the pilot see on the failed side?
SOURCE OFF and GEN OFF BUS are illuminated and the TRANSFER BUS OFF light remains extinguished.
Under which of the following conditions will the Cross Bus Tie Relay automatically open isolating DC bus1 from DC bus 2?
The bus transfer switch is positioned to OFF
With the STANDBY POWER switch in the AUTO position, the loss of all normal AC electrical power causes the battery to power the standby loads:
Both in the air and on the ground
AC amperage can be observed on the AC ammeter for the source selected by the AC meters
selector.
True
Illumination of the amber BAT DISCHARGE light indicates:
Excessive battery discharge is detected with the battery switch on.
In flight, an amber TR UNIT light illuminates if
TR 1 or TR2 and TR3 fails.