B747 & A340 Electrical Systems

[alastairg100]

Hi I was just wondering if you would be able to explain the B747-400 Electrical Systems panel and A340 one in more detail.

I have been given these pictures;
B747;
B747.jpg picture by alastairg100 - Photobucket

A340;
A340.jpg picture by alastairg100 - Photobucket

I understand that they are both on the ground running off ground supply, with no generators or APU on.

I was just wonderin if someone could elaborate more and explain what the controls do and when in the start up procedure the aircraft would have this set up

Thanks

[SMOC]

You can't have that scenario on the 744, engines 1,2 & 3 are running powering their respective busses and EXT pwr 1 on the bus. It's flight sim crap.

[NSEU]

Alastair, I have a 370 page paper manual describing the electrical system of the 747-400.. and it still only scratches the surface!

This is probably too much to ask of the ladies and gentlemen here

Some Microsoft Flight Sim add-on's may have free manuals which help explain the system (I think PMDG has one).

Of course, you need to know about basic electrics, otherwise the expressions used in these manuals will be meaningless (i.e. know what generators, inverters, transformers, rectifiers, busses, etc, are).

Rgds
NSEU

[mustafagander]

As SMOC says, the displayed set up is not possible

All Boeings I have known from B707 on have a protection which trips off EXT PWR when a GEN comes on line to that bus. End of story. The diagram reminds me of something out of a training leaflet to show what the indications are for various power breakers made or open but not an operational scenario.

The B747 electrical system is fairly simple. 4 AC buses, each powered by an engine driven alternator and 4 DC buses fed by TRUs. Both the AC and DC systems are tied/paralleled to avoid out of phase stuff and to load share. Some important equipment is fed from stand by, essential or direct from the ships battery depending on its importance. These buses are sourced from whatever power is available, generally automatically. The APU just runs the ship on the ground prior to engine start. NB this is VERY simplified!!! It just goes to show that Westinghouse got it right first time in the 1950s!

[EEngr]

As a few others have pointed out: EXT PWR 1 cannot be connected to the buses at the same time they are fed from engine generators. Interesting note: EXT PWR 1 indicates that the external power contactor is closed ("ON" illuminated) but ext power 1 is not available ("AVAIL" not illuminated). This should not be possible.

EXT PWR 2 shows "AVAIL" but its contactor is open. This is a realistic scenario (ext power plugged in but not on the buses).

[SloppyJoe]

A340. From left to right top to bottom.

Silver bat switch: 1, 2, apu. Selects what bat voltage is displayed in lcd next to it.

Bat 1, Bat 2, APU Bat push buttons: Turns bats on or off.

Galley: Turns off power to galleys.

Commercial: Turns off power to almost everything in the back, including galleys.

AC ESS FEED: Switches feed of AC ESS BUS from AC BUS 1-1 to AC BUSS 2-4

Bus Tie: In is auto, computers auto configure contactors in case of failures or switching power sources. Out opens all contactors so each bus is isolated. Used to find out what may be causing smoke.

IDG 1, 2, 3, 4: Used to disconnect the gen from the engine. Physically disconnects its drive.

Gen 1, 2, 3, 4, APU GEN push buttons. Turns off a generator. Or turns one on if you had turned it off. Normally left in all the time.

Ext A/B push buttons: When ext power is avail can push button to connect it to aircraft buses.



This is how the panel would look like with all engines running on ground or in flight with no failures.

[spannersatcx]

EXT PWR 1 indicates that the external power contactor is closed ("ON" illuminated) but ext power 1 is not available ("AVAIL" not illuminated).

That's correct, avail or on but not both.

[NSEU]

There was a modification on the 747-400 to extinguish the AVAIL light if the ON light came on.

I don't know if this modification was carried out on all aircraft, so both Spanners and EENGR, may be correct.

Rgds
NSEU

[EEngr]

There was a modification on the 747-400 to extinguish the AVAIL light if the ON light came on.

Thanks. That was probably done after my time. At any rate, having external power and generator power on the same buses is not allowed, so the graphic is suspect.