Newsgroups: alt.engineering.electrical
Subject: Re: why three phase system is not preferred in aircrafts power circuits....
References: <5deba331-ad64-4d6b-8ad1-2bb795345278@t12g2000prg.googlegroups.com>  <[email protected]>   <[email protected]>    
James Sweet  writes:

> [email protected] wrote:
> > On Fri, 20 Jun 2008 09:57:13 -0700 VWWall  wrote:
> > | [email protected] wrote:
> > | |> I'm curious how hard it might be to make a computer PSU that
> > would run on
> > |> any frequency from 50 Hz to 400 Hz (or maybe wider), compared to just the
> > |> 50 Hz to 60 Hz range.
> > | | Most ATX power supplies use a simple rectifier first stage, fed
> > directly | from the power line.  This is switched to a "doubler"
> > when the 120/240V | switch is set to 120V. This charges a capacitor,
> > which supplies DC to | the switching circuits.  The newer ones work
> > from 90-270V input and rely | on the switching stage(s) to
> > accommodate the varying DC developed.
> > | | There is nothing inherently related to the input frequency,
> > unless it's | the PF correction in some newer supplies.
> > So I can run them from 0.25 Hz power, then?
> > FYI, most of my PSUs do not have that "115/230" switch.  They are
> > labeled
> > "100-240V 50/60Hz".  So it's safe to run it on 400Hz in an airplane?
> >
> 
> 
> If you had large enough filter capacitors in the input circuit then
> yes, you could run it at 0.25 Hz, but where are you going to find
> that? A standard switchmode PSU will work fine on any realistic
> frequency, I don't think anywhere is less than 50Hz anymore, or
> greater than 400Hz.

In some countries there is still electrical railway systems  
operating at 16.7 Hz electrical power. Many other countries 
run their electrical transis with 25 kV 50 Hz power.

http://www.3phasepower.org/3phasefrequency.htm 
"The countries Germany, Austria, and Switzerland use a traction power
network  for railways, distributing single-phase AC at 16.7 Hz. A
frequency of 25 Hz was used for the German railway Mariazeller Bahn
and some railway systems in New York and Pennsylvania (Amtrak) in the
USA."

http://en.wikipedia.org/wiki/Utility_frequency#Railways
"Germany, Austria, Switzerland, Sweden and Norway use traction power
networks for railways, distributing single-phase AC at 16. Hz. "


Then there are those special applications where DC power is
used and ditributed. DC is commonly found in many low-voltage
applications, especially where these are powered by batteries. 
Telephone exchange communication equipment, such as DSLAM, uses
standard -48V DC power supply. Positive 12V, 24V, 48V, 110V and 
220V voltage power supplies (battery backed up) are used in 
by control systems used by electrical utilities and some 
industrial automation applications. 
An electrified third rail carrying a DC is used to power both 
underground (subway) and overground trains (for example 
use 600V-1200V DC 
http://www.nycsubway.org/tech/power/rotary.html
http://en.wikipedia.org/wiki/Third_rail ).
 


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/