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Posted by Tomi Engdahl (194.29.197.1) on April 21, 2001 at 18:01:31:
In Reply to: Re: Three Phase Power posted by Kanonfodder on March 08, 2001 at 18:52:06:
: 3 phase power, typically used in aircraft (i.e. 110V 400HZ), is 3 separate sine waves of power exactly 120 degrees apart. If you use just one line of the power, then you will have 1 phase power running at 110 Volts. However, if you were to take 2 lines and combine them, you will get a line voltage of approx 210 volts (been a while and I forget the exact math for figuring 3 phase line voltage). Now you may be going WTF, but this is accomplished by those 120 phase differences. The biggest thing to remember is that you aren't comparing the 2 line voltage to zero, you are comparing the 2 line voltage to the difference between the remaining voltage. Also when you combine 2 lines, you have a 60 degree phase shift each way between the signals so you end up with a signal that is exactly 180 degrees out of phase from the remaining signal. So as an example if L(line)1 was at 30 degrees and 50 V, L2 was at 150 degrees and 50 V, L3 at 270 degrees and -110 V; you would have a line voltage of 210 V as compared to L3...
: Haven't messed with 3phase theory for a long time so some things might be slightly off, but thats it in a nutshell
Quite much right that your description.
Three phase is typically used in many other
places than aircrafts. In almost all areas
around the world, power is generated and
distributed as a three phase suppy.
The final distribution to in USA tends to
be be pretty much single phase to one
household and three phase only for heavy
applications (industrial, large motors, stage lighting).
In European countries there seems
to be mixture of single phase to house
or three phase to house.
For more material on power distribution networks
and three phase power I recommend reading
http://www.howstuffworks.com/power.htm