Electrical Systems

[TC-DCA]

Hi everyone !
First of all, I'm sorry for my level of English.
I'm 16 years old and I am an enthusiast of aviation, as you can guess.

I am studying the systems of various aircraft as the A320, B737 NG, and the B777, I have already studied with details the Hydraulic systems, the Air Systems and others systems of these three types aircrafts.
I am now studying the ELECTRICAL SYSTEM but he raises me problem, I meet some difficulties.
Thus I write you to understand much better the Electrical System of the B737, 777 and A320.
I read the FCOM's of all these 3 planes, (the ELECTRICAL Chapter) and I also downloaded documents from "Smartcockpit" website but I didn't understand the systems.
The A320 does not raise me problem, but I do not understand well the 2 others aircraft.




As you can see on the image above, on A320, during flight, 2 generators come from engines, and thus feed the AC 1 and the AC 2, 116 V of the AC 1 and the AC 2 are converted to 28V via the TR'S 1&2 and the TR's feeds the DC 1&2, and DC 1&2 feeds the battery, correct ? It is the same on the B737 NG and the 777 ? Or small difference ?

Question: Did electric system of 777 and 737 NG have big differences compared with that of A320? And what is the DC, the DC ESS, the DC BAT BUS ?
The systems of 320 are easier for me to study compared with the 737 NG and the 777. I do not understand well thus I would be very satisfied if you help me.

Here's what I already know :

I 'll tell you about the " Electrical Systems " , including descriptions of the various switches on different planes like the 737 , A320 and B777 .

So first of all , I put below the ELECTRICAL PANEL 3 aircraft, then I'll describe the switches.

Electrical Panel of 737




Electrical Panel A320




Electrical Panel 777




So here for pictures of the panels. Now I will explain what are these switches , starting with the 737 and comparing the result with the A320 and 777.


STANDBY POWER:
When in guarded position, this is in AUTO position. This is in case of power loss.
The batteries feeds AC&DC when the 2 Generators is lost and when APU is not available, but the batteries feeds AC&DC for maximum 60 minutes ! Correct ?

2 Disconnect switch
Disconnects IDG.IDG cannot be reconnected in the air.
IDG drive engine generator to AC.


GEN 1&2
GEN's are Integrated Drive Generator (IDG)
OFF – disconnects IDG from related AC transfer bus by opening generator circuit
breaker.
ON – connects IDG to related AC transfer bus by disconnecting previous power
source and closing generator circuit breaker.


APU GEN 1&2
APU GEN's are Integrated Drive Generator (IDG)
ON - APU GEN is active.
OFF - APU GEN is not active.

BUS TRANSFER SWITCH or BUS TIE.
AUTO (guarded position) – BTBs operate automatically to maintain power to AC
from any operating generator (APU or GEN from engine or external power).
In the case of a failure of GEN 2 for example, we just have AC 2, and the BUS TIE alows the AC 2 to supply AC 1. Right ?
OFF – isolates AC 1 from AC 2 if one IDG is supplying power to both AC 1&2.

So for the 737 , we learned all that , so now we will compare our 737 to the A320 !

First, there are not two switches " GUARDED " called DISCONNECT . Why ? Answer:
There are 2 well , but they are called differently : IDG 1 & 2 !

Secondly, there is a switch called BUS TIE on the A320 and there is not the 737. Why ? Answer:
There are about 737 too, but it is called BUS TRANSFER simply !

Third, there is a switch named AC ESS FEED OVRD on the A320 and there is not the 737.
What is the AC ESS FEED ? answer:
AC Essential ALTN Switch - Pushing the AC ESS FEED switch Enables the AC ESS Bus to be powered via AC Bus 2 INSTEAD of AC Bus 1 . A white boxed ALTN Will illuminate light on the switch. Normally AC ESS Bus is Supplied from AC Bus 1 .

FAULT - An amber FAULT light indicates the AC ESS bus is not Electrically powered
So I can not tell you that it is unfortunately , but you can see it is normally begged by AC BUS 1 , but can also be begged by AC BUS 2 ALTN mode.
I don't understand what is this exactly unfortunately.

I will now compare the 737 and 320 at 777 !

First, we can see on the 777 2 SWITCH BACKUP GEN , they do not exist on the 737 and 320.
Why ? What is it? If two of the IDG ( generators ) and APU is inoperative , the backup generator supplies the essential equipment of the airplane .
I do not want to explain in more detail because it is a bit complicated.

Secondly, there are two switches named DRIVE L & R , they are named "disconect" on the 737 and IDG on the 320.

Third and finally, there are 2 switches on the BUS TIE 777 , and there is only one on the 737 and 320. Why ? I don't know.

I want to talk about the Ram Air Turbine ( RAT) also , they do not appear on the ELEC panel but also relates to the supply. It is a small propeller that comes at the loss of 2 generators or hydraulic .

So the 320 has it , and in the case of loss of 2 generators, it unfolds automatically and pressure the BLUE system and power the EMERGENCY GENERATOR via a hydraulic motor , which power AC ESS &DC ESS and what to get our flight controls (ailerons , elevators ..) . Right ?

The 777 also has one, which pressurizes the C1 and C2 circuit for flight controls necessary ahead ( ELEVATORS , Ailerons ... ) and also the RAT powers the STANDBY POWER when you do not have APU which allows us to be electrically powered , AC&DC. Right ?

The 737 did not , simply because the 737 uses APU in the case of loss of 2 generators, or at worst a STANDBY POWER that operates using batteries of the aircraft (MAX 60 MIN !) This supplying AC , and for the flight controls, there is the hydraulic STANDBY which operates the rudder and reverses as well as the LE FLAPS / SLATS.
For flight controls ( Ailerons and ELEVATORS ) is done in manual reversion by pilot forces , yes, because the 737 is not a FBW !

And I am still sorry if I make faults when writing.

[Officer Kite]

You're not really 16 are you