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Electricity On Airliners  
User currently offlineFerroviarius From Norway, joined Mar 2007, 214 posts, RR: 0
Posted (2 years 2 weeks 1 day 23 hours ago) and read 3308 times:

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

11 replies: All unread, jump to last
 
User currently offlineLarshjort From Denmark, joined Dec 2007, 1351 posts, RR: 0
Reply 1, posted (2 years 2 weeks 1 day 22 hours ago) and read 3286 times:

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



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4
User currently offlineFerroviarius From Norway, joined Mar 2007, 214 posts, RR: 0
Reply 2, posted (2 years 2 weeks 1 day 22 hours ago) and read 3273 times:

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


User currently offlineLarshjort From Denmark, joined Dec 2007, 1351 posts, RR: 0
Reply 3, posted (2 years 2 weeks 1 day 22 hours ago) and read 3263 times:

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



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4
User currently offlineBMI727 From United States of America, joined Feb 2009, 15443 posts, RR: 26
Reply 4, posted (2 years 2 weeks 1 day 19 hours ago) and read 3144 times:

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.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (2 years 2 weeks 1 day 19 hours ago) and read 3123 times:

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.


User currently offlineAquila3 From Italy, joined Nov 2010, 243 posts, RR: 0
Reply 6, posted (2 years 2 weeks 1 day 6 hours ago) and read 2897 times:

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?



chi vola vale chi vale vola chi non vola è un vile
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 7, posted (2 years 2 weeks 13 hours ago) and read 2568 times:

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.


User currently offlineintsim From United States of America, joined Nov 2010, 97 posts, RR: 0
Reply 8, posted (2 years 2 weeks ago) and read 2338 times:

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


User currently offlinebikerthai From United States of America, joined Apr 2010, 2006 posts, RR: 4
Reply 9, posted (2 years 2 weeks ago) and read 2331 times:

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



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinepygmalion From United States of America, joined Jun 2006, 963 posts, RR: 38
Reply 10, posted (2 years 1 week 6 days 14 hours ago) and read 2161 times:

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.


User currently offlinebravogolf From United States of America, joined Apr 2005, 538 posts, RR: 1
Reply 11, posted (2 years 1 week 5 days 17 hours ago) and read 1956 times:

Quoting Ferroviarius (Reply 2):

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


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