>>From: Dunst, Mordecai[SMTP:mdunst@smtplink.coh.org]
>>Can someone give me a simple clear explanation of 3phase electricity?
It's easier with a graph but bear with me. Imagine single phase AC as a
sine wave, centered around 0 volts. It climbs up to a maximum, then
returns to 0 volts and drops to its most negative. The peaks are at +/-177
Volts giving an average of 110 VAC (more or less).
2 phase AC (in most houses with 220 service) consists of two such sine
waves, 180 degrees out of phase with each other. Each wave referenced to
ground would be at 177V max (110 VAC average), but they are 'mirror' images
of each other and if you look between the two the average would be 220 VAC
(both are zero V at the same time, then one climbs to its maximum while the
other climbs down to its most negative). It looks like a bunch of ellipses,
peaks and troughs each at 177 V, and double that if you were to measure
from a peak to a trough.
3 phase is three such sine waves, each 120 degrees out of phase with the
others. Because they are out of phase they don't add directly or cancel
each other out; the result is something in between. In this case, a 208
VAC wave.
I have a simple excel graph that shows this, but don't want to post it to
the list as it is 40Kb. Anyone who wants it, let me know.
Mark Miller
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