Ferroviarius From Norway, joined Mar 2007, 234 posts, RR: 0 Posted (2 years 6 months 3 weeks 2 days 9 hours ago) and read 3440 times:
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?
Ferroviarius From Norway, joined Mar 2007, 234 posts, RR: 0
Reply 2, posted (2 years 6 months 3 weeks 2 days 8 hours ago) and read 3405 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?
BMI727 From United States of America, joined Feb 2009, 15778 posts, RR: 27
Reply 4, posted (2 years 6 months 3 weeks 2 days 5 hours ago) and read 3276 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.
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.
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
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.