Electrical Flashcards
737 draws DC power from _______ and a single______.
transformer rectifiers. Battery
IDGs provide power in the form of three phase, ________ alternating current.
115V, 400 cycle.
T/F: when one IDG is inop, the other can power the other bus as well.
True.
The APU generator can power both transfer buses on the ________ or in flight.
ground.
Which aircraft have auxiliary batteries?
tail 751 & 752.
Where is the hook up for the ground cart?
right side near nose gear.
What are two important principles for power on the 737?
different sources of AC power cannot be paralleled.
connecting a different source automatically disconnects and existing electrical power source.
What is the purpose of the AC and DC metering panel?
display AC and DC voltage and amperage and AC freq. Test functions are used by mx.
When does the BATT DISCHARGE light illuminate?
excessive discharge detected.
When does the TR UNIT light illuminate?
Ground: any TR unit has failed.
Flight: either TR1 has failed or both TR2 and TR3 have failed.
When does the ELEC light illuminate?
on the ground only: a fault in the DC power system or the stby power system.
When the BATTERY switch is off, and no other power sources connected, power is removed from which buses?
Battery Bus Switched Hot Battery Bus DC Stby Bus Static inverter AC Stby Bus
When the BATTERY switch is off, and other power sources are connected, power is removed from which buses?
Battery Bus and switched hot battery bus.
What does the CAB/UTIL switch do?
switches power on or off to galleys and cabin equipment when the AC transfer busses are powered.
When does the generator DRIVE disconnect light happen?
drive has been disconnected through use of the Generator drive DISCONNECT switch
IDG failure
engine shutdown
IDG automatic disconnect due to high oil temp
Can and IDG be reconnected in the air?
no
What are the conditions for the disconnect switch to work?
power is available
engine start lever in IDLE
If STANDBY POWER switch is in AUTO, how are busses transfered if all AC power lost?
AC stby bus powered by battery through static inverter
DC standby bus powered by battery
battery bus powered by battery
If you move the STANDBY POWER switch to off, what happens?
STANDBY POWER OFF light illuminates
AC standby bus, static inverter, and DC standby bus are not powered.
If you move the STANDBY POWER switch to BAT, what happens?
AC standby bus is powered by battery through static inverter
DC standby bus and battery bus are powered directly by battery
If the STANDBY POWER OFF light is illuminated, what busses are unpowered?
AC standby
DC standby
Battery bus
The DC cross tie opeartes as req’d to provide normal operations of the DC busses, or to isolate DC bus 1 from DC bus 2 _________.
when conducting an ILS approach.
What does TRANSFER BUS OFF light mean?
associated bus is not powered.
What does SOURCE OFF show?
no source has been manually selected to power the associated transfer bus.
manually selected source has been disconnected.
What does the ground service switch do?
allows the airplane to be serviced using external power by manually activating the ground service busses without energizing the AC transfer busses.
The AC STANDBY bus receives power from which bus?
AC TRANSFER BUS 1
When one generator fails or is disconnected, the system automatically ____________ in increments to bring the total load in line with capacity.
sheds electrical loads
With 1 IDG inop, what is the order of load shedding?
Galley on Trans Bus 2
Galley on Trans Bus 1
Main Bus 1
Main Bus 2
With the APU as the only elec source, which buses are shed?
galley busses and main busses are shed. If needed the IFE busses are also shed.
How many TRs are there? Where does their power come from?
3, AC Transfer buses
TR 1- AC Trans 1
TR 2& 3= AC Trans 2
How much power do the TRs supply?
28V DC power
How many volts is the battery?
24V DC power
What is the backup source of power for TR3?
AC Transfer bus 1.
The total DC load can be supplied by any ____ TRs.
2
Voltage range for the batteries is___ to ____ .
22V ; 30 V.
How long does power last for a single charged battery? Dual charged batteries?
30 min; 60 min
Which bus is always powered by the battery?
Hot Battery Bus, however, battery voltage must be above a specified minimum.
What bus powers the battery charger?
GND Service BUS 2. If 2 batteries installed, Aux battery powered by Batt Chgr on Gnd Service Bus 1
For batteries in TR mode what is being powered?
Hot battery bus and switched hot battery bus
The STBY power system provides _____AC and _____DC power to essential systems
115V; 24V
What are the components of the STBY power system?
Static inverter AC Stby bus DC stby bus battery bus Hot battery bus switched hot battery bus main battery (aux battery) if installed
If a/c is secured, to power down the a/c you do what?
APU switch OFF External power (if used) OFF BAT switch OFF
If both SOURCE OFF lights stay illuminated, what should you do?
Avoid icing conditions
Plan to land at nearest suitable airport
Fully charged battery will supply 30 min of power
If a TR UNIT light illuminates, what are you restricted to?
Don’t use AFDS Approach Mode
Autoland is not available
