A320 Emer Elec logic

[Down...2 greens]

Hi all,

A320 drivers will be aware of the electrical system's on-ground behaviour when in emergency configuration (Emer Gen supplying): namely, below 100kt the Battery Bus is recovered, below 50kt the AC ESS bus is lost (so all the screens go blank).

Can anyone shed (no pun intended) any light on the reasoning behind this design?

Cheers!

[CEJM]

Below 50kt you don't really need any of the screens which would be an unnecessary drain on the batteries.

The BAT Bus powers the DC ESS bus which enables you to use VHF1 and FLT Interphone.

Once you come to a stop, it is more important to be able to communicate (ATC, Fire crews, Cabin Crew and Pax) then having all your screens up and running.

REF: FCOM VOL 1 DSC-24-10-30-30 P18/22

[Down...2 greens]

From the FCOM schematics and description (rather than the simplified representation on the ECAM ELEC page) it looks to me like the DC ESS bus is powered directly from Bat 2 when on battery power only, and doesn't require the DC BAT bus. If that's the case I'm still not quite clear on the reason for all the on-ground switching, specifically:

1. What is the advantage of restoring the DC BAT bus <100kt?

2. Why is is AC ESS bus shed <50kt? One significant effect is the loss of ECAM, which might just be useful. The battery drain issue doesn't seem to be the answer, because the schematic shows the inverter powered exclusively by Bat 1 (so why not just keep the AC power for as long as that battery lasts - it wouldn't affect the comms equipment being supplied by Bat 2).

There's logic in it all somewhere, I'm sure!

[TyroPicard]

1. What is the advantage of restoring the DC BAT bus <100kt?
Both BATs are connected to DC BAT BUS and therefore DC ESS BUS, which is the important one.
Which also answers your q.2.
If you think in terms of FLY - NAV - COMM..... after landing..

Fly - stop on the runway or very close to it, for which you need power to ABCU, BRAKE PRESS indicator and Park Brake.
Nav - no external lights - no taxy.
Comm - VHF 1, FLT INT, CIDS, EXT HORN

Why do you need ECAM? The ENG FIRE lights still work, but not many pb's.