Electrical Flashcards
How much and what type of electrical power do each of the IDGs provide?
115V AC.
What are the 2 operating principles of the 737 electrical system?
- AC power sources do not run in parallel.
- Connecting a new source of power, automatically disconnects the current source.
What bus does the AC transfer bus 1 power, that bus 2 does not?
AC Standby Bus.
What is the purpose of the generator “on-line” feature?
It automatically connects the engine generators in the event the APU is accidentally powering both transfer busses at takeoff, and subsequently fails.
With regards to Automatic Load Shedding (during single generator operation); what is the order of bus shedding?
(1) Galleys & Main Bus on TB2.
If an overload is still sensed:
(2) Galleys & Main Bus on TB1.
Overload still exists:
(3) IFE Bus.
When the APU is the only source of electrical power, what sequence does Automatic Load Shedding follow if an overload is sensed?
(1) All Main & Galley Busses.
(2) Both IFE Busses.
During a flight, the generator DRIVE light illuminates. What does this indicate?
Low oil pressure on the associated generator.
During a flight you have had to disconnect a generator using the drive disconnect switch.
Can you reconnect the generator in flight?
No.
How much DC power do each of the TRs provide?
28V.
Where does TR3 normally receive power from? And where can it receive back-up power from?
Transfer Bus 2.
Back-up from Transfer Bus 1.
What connects DC bus 1, DC bus 2 and the DC STBY bus to each other?
The Cross Bus Tie Relay.
Which bus does TR3 provide power to?
The battery bus.
Under what conditions will the Cross Bus Tie Relay move to open?
(i) Glideslope capture during a FD/AP ILS/GLS approach.
(ii) Bus Transfer switch positioned to OFF.
During a flight, the TR UNIT light illuminates, what could this indicate?
Either:
(i) TR1 has failed.
or
(ii) Both TR2 & TR3 have failed.
What is the capacity and type of battery on the aircraft?
What is the batteries voltage range?
What is the minimum standby power time available from the battery?
(i) 24V Nickel-Cadmium Battery.
(ii) Range of 22 - 30V
(iii) A minimum of 30 minutes.
How long can the ISFD remain powered on after loss of power?
Up to 150 minutes.
Which bus powers the AC Standby Bus?
AC Transfer Bus 1.
What powers the DC Standby Bus?
TR1, TR2 & TR3.
What powers the battery bus?
TR3.
What powers the hot battery bus and switch hot battery bus?
Battery/Battery Charger.
What does placing the standby power switch to BAT do?
It overrides automatic switching and sets the standby busses and battery bus on battery power.
During taxi, the TR UNIT light illuminates. What does this indicate?
At least one of the TR UNITS have failed.
Will the overhead ELEC light only illuminate on the ground, or in the air?
On the ground.
What other battery bus is also powered whenever the battery switch is ON?
The Switched Hot Battery Bus.
What components are used to convert the AC power to DC power?
The Transformer Rectifier Units (TRs).
In the event of a loss of all engine and APU electrical power, how is power provided to the AC STBY BUS?
Power is provided from the Battery via an Inverter.
During a total electrical failure; if the standby power switch is positioned OFF, which busses are de-energised?
The AC STBY BUS and DC STBY BUS.
What is the alternate power source for standby power?
The Battery.
How are the IDGs lubricated and cooled?
By a self-contained oil system.
With STANDBY POWER SWITCH in AUTO, if there is a complete electrical failure, how does the system receive electrical power? And how does the AC STANDBY BUS receive its power then?
From the BATTERY, and the INVERTER converts the DC power from the battery to AC for the AC STANDBY BUS.
What does the the STANDBY POWER OFF light illuminated indicate?
That the AC and DC STANDBY bus are not powered.
