A320 electrical power transits
 

Hi gents,

Some folks including me, use a non-standard procedure in my company when disconnecting external power.

To avoid unwanted ECAM warnings and loud noises on the contactors, I momentarily switch off and on again one of the batteries and then remove external power.

Then the disconnection of the external power is done far more smoothly and with less probability of unwanted ECAM warnings.

I have no idea who told me that, many years ago. Nothing is written apparently, and no info that I can find anywhere in the FCOM.

Someone told me that this was a procedure back the old days.

Do you guys know info about that? Do you use it?

We need Chris Scott to answer this one.

Someone passed that as a piece of good advice to me. Never used it or seen it done except from that instructor, it's been 17 years since.

Apart from the regular switching over of the contacts, what noise are you referring to? ECAM messages on power transfer is also a mystery to me.

I’ve never heard of these problems or the technique.

It's not a technique I've ever heard of before in over 25 years working the type.
If you are getting constant ECAM messages then it sounds more like a fault with the power transfer (GPCU?) The aircraft was designed to be tolerant of transient power fluctuations. Unlike the later batch of electric aeroplanes that use a 'soft' transfer.

Do tell...?

Well,

If you switch off external power with higher loads (fuel pumps on) the noise on the contactor is louder. Also you see the monitors (PFD, ND, ECAM etc) to momentarily go off and on (like a white flash) and you can feel it hurts the plane. I dont know if thats a placebo on me, but I have encountered that many times. They dont happen all the time. We fly mixed fleet of 15 yrs old 320s but also NEO.

Regarding the ECAMs that sometimes accompany the above, I have seen many in my career that occurs when removing external power on high loads.

Examples that I have seen: SEC FAULTS(1,2 or 3 and sometimes two of them simultaneously), ELAC FAULTS, LG SYS DISAGREE, SMOKE LAV DET FAULT, FLAP SYS 1 FAULT and for sure some more, I cant remember all of them.

Its very rare, but happens. Calling the maintenance for clarifications and help, usually they guide you through MCDU system test pages. The tests pass almost all the time and the only solution is to completely power off the aircraft for 2-3 minutes and then power on again. Which is an issue if you have a fully boarded plane.

Then the problems disappear like magic. Its a known issue, happens rarely, but maintenance knows about it and its due to electrical switching. However doing this trick with the battery, saves the day and you feel the transit is a lot smoother.

By the way, not exactly relevant, but this morning the APU didnt pass the fire test during the preliminary, there was no response at all when pushing the test button. Maintenance advised to pull all the CBs behind and then push them on again. Problem solved.

It always makes me wonder why it is that if maintenance do any of the above, then legally, a log book entry is required with all the relevent documentation and approved data accompanying the sign off.
Pilots do it and there's no record or accumulated history of faults.
Go figure.

Its recorded in the logbook of course and the maintenance personnel is usually on the way if not already there. There is a database of class3 faults and all resets done. Phone calls is to rectify something sooner until the engineer arrives.

Did you write that with a straight face? Hahaha.

This explains it better than I could.

No-break power transfer

Well, most of the times :)

I think the contactors just move quicker. All the electrical switching on the A320 series is relay-logic so it will vary between aircraft.

Guessing that the trick of turning a battery on and off forces a battery to be connected to the DC network for a short period in order that the DC ESS bus is supplied while the electrical transfer takes place.

Always found that jabbing the EXT PWR button instead of a solid push resulted in a messy transfer but possibly placebo effect!

Not sure what you are talking about, the technique I described was shortly before disconnecting external power, switch off one of the batteries for 1-2 seconds, set on again the battery and then disconnect the external power.

For the record, that is not what I was shown on MSN 16xx by the gentleman who came with the aircraft.

So what was it?

If a battery is turned off and on again it undergoes a very short charging cycle. This means that when the EXT PWR button is pushed, there's no transient on the 28V supply because the battery is on the DC bus.

Normally the batteries aren't actually connected to the DC buses unless they're charging (you can tell in flight because the overhead lights dim slightly when a battery contactor closes).

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This could make sense.

Interesting topic! I remember on the older models the transient was so loud that it was very common that the captain will say just before shutting down the engines:” Mind your ears.” Basically we will remove our headset just before engines shut down to avoid the painful blast. The spurious ECAM warnings were common also. One of our old A321 was unique on his kind as it will very often have a “Stall Stall” aural warning during engines shut down. Now we only have NEOs and fairly new CEOs (MSN 4000+) All of them the transients are smooth.

Fun fact since Lantirn talked about the APU fire test:
Did you guys notice the warning related to the APU fire test during aircraft Setup in the last version of FCOM?

As licenced engineer on early A-320s (28 years ago) I can attest to many problems of power transfer during engine starts, resulting in ECAM warnings/faults etc. It was so common that often it was not written in ATLs at all, to be honest. Typical remedy was to reset related C/Bs, then run the test thru MCDU and worst case, power down entire airplane, even disconnect the batteries (to remove power even from hot bus) and reconnect after a minute. (did it with passengers on board once or twice) (eyesroll)

Interesting...Just checked that out!