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Electricity On Airliners

Posted: Sat Mar 31, 2012 6:56 pm
by Ferroviarius
Good evening,

I am very much of a rail fan - and a very frequent air traveller.
While reading in a book on old electric high power locomotive - E 19, ref. , article in English on a somewhat less powerful sibling: http://en.wikipedia.org/wiki/DRG_Class_E_18 - the chapter about the transformers used, I discovered that there apparently had been detailed studies on whether to use copper or aluminum and how to form the coils.

How is this in modern airliners? I know that it was, e.g., necessary to replace CU wiring on the 380 with AL wiring in order to save weight.

What are the max. electric voltages and currents present during the operation of large frame airliners? How much heat has to be dissipated because of the warming of wiring? Are there large AC parts in the airlplane electrics or is it basically DC? Which types of transfomers are used, oil cooled or dry type?


Best wishes,

Ferroviarius

RE: Electricity On Airliners

Posted: Sat Mar 31, 2012 7:35 pm
by larshjort
A few old piston aircraft are still using 12 VDC, everything else runs 28 VDC and 115 VAC 400 hz. Some types including the A380 have started to use variable frequency instead, to save weight.

/Lars

RE: Electricity On Airliners

Posted: Sat Mar 31, 2012 7:44 pm
by Ferroviarius
Quoting Ferroviarius (Thread starter):
A few old piston aircraft are still using 12 VDC, everything else runs 28 VDC and 115 VAC 400 hz. Some types including the A380 have started to use variable frequency instead, to save weight.

Mange takk, Lars.
Why 400Hz (and not 50 or 60)? Is it to avoid un-wanted interferences?

Best,
Ferroviarius

RE: Electricity On Airliners

Posted: Sat Mar 31, 2012 8:17 pm
by larshjort
Det var så lidt.

I don't have a great knowledge about electrical stuff but I was told during my training that it would make both generators and power users lighter.

/Lars

RE: Electricity On Airliners

Posted: Sat Mar 31, 2012 10:40 pm
by BMI727
Quoting Ferroviarius (Reply 2):
Why 400Hz (and not 50 or 60)? Is it to avoid un-wanted interferences?

I think it's because some of the components are lighter and less bulky than other systems. There is still interference too. If you listen to radio communications from planes sometimes you can hear the hum in the background.

If you hear something similar to this:
http://www.youtube.com/watch?v=OUvlamJN3nM
then you're hearing the electrical system bleed through into the radio.

RE: Electricity On Airliners

Posted: Sat Mar 31, 2012 11:17 pm
by tdscanuck
Quoting Ferroviarius (Thread starter):
What are the max. electric voltages and currents present during the operation of large frame airliners?

Modern stuff gets up to about 235 VAC. The 787 also runs a 270 VDC system but it's the oddball.

Any one bus is carrying up to 250 KW, or about 1000 amps (over multiple phaes).

Quoting Ferroviarius (Thread starter):
How much heat has to be dissipated because of the warming of wiring? A

Wiring isn't so bad, it's the transformer/rectifier units, motor controllers (typically solid-state), lights, and avionics where most of the heat goes.

Quoting Ferroviarius (Thread starter):
Are there large AC parts in the airlplane electrics or is it basically DC?

Modern generators are all AC (either 400HZ or variable). That's used directly by large loads, or transformed/rectified to 28VDC for smaller loads. The 787 uses high voltage DC only as a intermediate step between 235 VAC and variable voltate/variable frequency AC for the big motors.

Quoting Ferroviarius (Thread starter):
Which types of transfomers are used, oil cooled or dry type?

As far as I know, they're all dry in modern designs. I assume that's for weight.

Quoting Ferroviarius (Reply 2):
Why 400Hz (and not 50 or 60)? Is it to avoid un-wanted interferences?

400 Hz lets you make many components smaller.

Tom.

RE: Electricity On Airliners

Posted: Sun Apr 01, 2012 12:08 pm
by Aquila3
Quoting Larshjort (Reply 1):
everything else runs 28 VDC

Is that with positive (+) to the ground ( more correctly tied to the chassis, in this case) , like some military telecom stuff?
And is the airplane frame used as a return path for the DC in order to save wiring?

RE: Electricity On Airliners

Posted: Mon Apr 02, 2012 5:06 am
by CM
Quoting Aquila3 (Reply 6):
Is that with positive (+) to the ground

Yes, the DC potential in the 28v systems is between the positive and a chassis ground.

Quoting tdscanuck (Reply 5):
The 787 also runs a 270 VDC system

Indeed, this system is an oddball. It is probably more precisely described as a ±270v DC system. In response to Aquila3's question above, the actual potential between positive and negative in this system is 540v. This voltage has no real distribution in the airplane; it simply runs in bus bars in the back of two equipment racks, running from Auto Transformer Rectifier Units into Motor Controllers which condition the power for running large motors.

RE: Electricity On Airliners

Posted: Mon Apr 02, 2012 5:48 pm
by intsim
Quoting BMI727 (Reply 4):
If you hear something similar to this:
http://www.youtube.com/watch?v=OUvlamJN3nM
then you're hearing the electrical system bleed through into the radio.

I seem to remember hearing ATC tell a pilot they had a lot of interference due to this. It most likely would have been a Tower due to not hearing SLC Center Controllers from the scanner I had.

Is it common for ATC to mention this to pilots?

Thanks

RE: Electricity On Airliners

Posted: Mon Apr 02, 2012 5:58 pm
by bikerthai
Quoting Ferroviarius (Thread starter):
I know that it was, e.g., necessary to replace CU wiring on the 380 with AL wiring in order to save weight.

Aluminum is also less prone to corrosion vs copper.

bt

RE: Electricity On Airliners

Posted: Tue Apr 03, 2012 3:46 am
by pygmalion
Quoting bikerthai (Reply 9):

Aluminum is also less prone to corrosion vs copper.

bt

but much worse in fatigue. All the exposed copper wire is plated in Tin or Al-Ni-Co alloys for corrosion protection. Some is even cap sealed over that in wet zones.

RE: Electricity On Airliners

Posted: Wed Apr 04, 2012 1:04 am
by bravogolf
Quoting Ferroviarius (Reply 2):

The higher the frequency the less iron is needed in the core of the transformers and motors thus saving weight.