B737NG Electrical system Flashcards
What is the difference the amber “TR UNIT” light indicate in flight opposed to on the ground?
The TR UNIT light will only illuminate INFLIGHT if TR1 fails OR, if BOTH TR3 AND TR2 fails together. In other words the ‘TR UNIT’ light will always illuminate if TR1 fails, but will only illuminate INFLIGHT, if TR2 and TR3 fail together. On the ground ‘TR UNIT’ light will illuminate if ANY TR fails.
Does the amber ‘ELEC’ light operate in flight if a fault is encountered?
NO.
Incase of an electric overload, what will be the first thing to be shed?
The galleys and main bus on transfer bus 2 are shed first.
If the APU is the sole source of electrical power what difference does this make in flight compared to on the ground.
In flight, ALL galley and main busses are automatically shed. On the ground, the APU will attempt to supply full electrical load. In other words, partial power is supplied inflight.
If the BATT switch is selected to OFF, how can the STBY power supply power?
Switching the ‘STANDBY POWER’ switch to BATT
What is required in order to disconnect IDG’s?
Engine start levers must be in ‘IDLE’ detent with electrical power available.
What is the output of the IDG’s?
1. Phases?
2. KVA?
3. Voltage?
4. CPS?
3 phases, 90 KVA, 115 Volts AC & 28V DC @ 400 cycle AC power.
What will cause the IDG’s to automatically disconect?
High oil temperature or drive malfunction.
How is the IDG oil cooled?
Engine fan air and engine fuel flow.
What is difference between the “SOURCE OFF” light and the “TRANSFER BUS OFF” lights?
The SOURCE light refers to the power (generator) supplied to the bus. The BUS light refers to the busbar. So the source light can indicate a generator failure and the bus light can indicate a bus failure. The “SOURCE OFF” light can also indicate that the transfer bus is being powered thought the BTB by another generator until an AC power is manually selected.
What is the purpose of a Bus tie breaker (BTB)
The BTB allows one generator to supply power to both transfer busses.
Can the entire electrical system be powered from a single AC power source? (One generator)
Yes
How does the APU power the transfer busses?
Through bus tie breakers (BTB’s)
How many batteries does the VH-INU have?
Three. One main, one auxiliary and one dedicated battery that provides power to the Standby instrument (ISFD).
What does the AC power system consist of?
2 x Transfer bus, 2x Main bus, 4x Galley bus and 2x Ground service bus.
What powers the AC standby Bus?
Transfer bus 1 from either IDG or the Inverter from the Battery.
How can number 2 IDG power transfer bus 1 and vice versa?
Through the bus tie breakers (BTB’s)
Is it possible to power one transfer bus with external power and the other transfer bus with the APU’s generator?
No. The last selected power source will power (either GND or APU) both busses.
Is it possible to power one transfer bus with a respective IDG and the other transfer bus with the APU’s generator or external power?
Yes
If a transfer bus loses power from its respective IDG, do the BTB’s close automatically?
Yes, if the ‘BUS TRANSFER’ switch is in AUTO position.
How many transfer busses can the APU power in flight?
Two/Both
What happens if you take off with the APU powering both transfer busses and the APU shuts down/fails?
The IDG’s automatically connect o their respective transfer busses through the ‘Auto generator-online’ feature.
Can an IDG directly power the opposite transfer bus as it does with its respective transfer bus?
No, the opposite transfer bus receives power from the respective transfer bus through the bus tie breakers (BTB’s)
How are the IDG’s cooled/lubricated?
The IDG’s are cooled and lubricated using a self-contained oil system.
What causes the “DRIVE” amber caution light two illuminate? (1 item)
Low oil pressure, which is indicative of an IDG failure, engine failure or IDG disconnect.
What is the main source of AC power?
Generators.
What is the main source of DC power?
Transformer Rectifiers.
What is the electrical voltage?
28V DC & 115V AC
How are the Transformer Rectifiers (TR) powered?
From the Transfer busses.
Does the amber ‘ELEC’ light indicate a fault in the DC or AC system?
DC
How is TR1 powered?
Transfer bus 1
How is TR2 powered?
Transfer bus 2
How is TR3 powered?
Transfer bus 2 (Transfer bus 1 as backup)
What is the purpose of the CROSS BUS TIE relay?
To power DC BUS 1&2 in parallel, and isolate DC bus 1 from 2 during G/S capture. (Note: switching ‘BUS TRANSFER’ switch off, will also isolate DC BUS 1&2)
What will cause the Cross Bus Tie relay isolate DC bus 1 and 2?
Glide-slope capture and/or Bus Transfer switch is ‘OFF’
What is the voltage of the batteries and range?
24V, Range: 22-30V
What kind of batteries are used?
Nickel cadmium
How long can two fully charged batteries provide power to the standby system?
At least 1 hour
When is the switched hot battery powered?
Whenever the battery switch is ON
Can the hot battery bus be unpowered from the cockpit?
No. It’s directly connected to the battery.
How is the battery charger powered?
Main battery: AC ground service bus2
Aux Battery: AC ground service bus1
What is the secondary function of the Battery charger?
It becomes a fourth TR (Transformer Rectifier) which then powers loads that are connected to the hot battery bus and switched hot battery bus.
Which battery powers the standby system?
Main battery
Do the main and aux battery operate in parallel or series?
Parallel.
What is the voltage output of the standby system?
115V AC & 24V DC
Which switches ensure the standby power will automatically power the aircraft in the event of main power failure?
‘STANDBY POWER’ sw: AUTO, position & ‘BATT’ (DC) sw: ON
How does the batteries power the AC STANDBY bus?
Via a static inverter.
How do the batteries power the DC STANDBY bus?
Directly from the batteries.
Which busses must lose power before the standby power automatically kicks in?
AC transfer bus 1 or DC bus 1
How is the standby manually activated? Does the Batt switch have to be on?
Placing the ‘STANDBY POWER’ sw switch to BAT. No, the BAT switch can be on or off.
What happens when the ‘STANDBY POWER’ sw is placed to “OFF”? What indication will you receive?
BOTH AC & DC STANDBY busses are de-energised. Amber ‘STANDBY PWR OFF’ light.
What is the function of the Static inverter?
To convert 24V DC to 115V AC
How is power supplied to a Transfer Bus?
From a generator via a Generator breaker.
What will cause an IDG to automatically disconnect?
Generator drive malfunction. Amber ‘DRIVE’ light indicates low oil pressure.
Is the ‘Auto Generator online’ feature active whilst on the ground?
No
Will a high oil temperature in the IDG system cause the amber ‘DRIVE’ light to illuminate?
No, because the IDG should automatically disconnect!
What is the primary function of TR3?
To power the battery bus.
What is the secondary function of the TR3
A redundancy for TR2
What happens to flap indicator with loss of normal AC power (dual generator failure)
Indicator will freeze.
