Jeffrey Angus wrote:

On 1/22/2011 6:37 PM, David Nebenzahl wrote:

On 1/22/2011 5:27 AM PeterD spake thus:

On Fri, 21 Jan 2011 18:09:26 -0800, David Nebenzahl
wrote:

The discussion started with a mention of 2-phase power. Turns out
that in the world of electrical power, this has a specific meaning.
It refers to a now-obsolete system of generating power in 2 phases
that were 90° apart, and was used at Niagara Falls:

http://www.3phasepower.org/2phasesystems.htm

And of course there's 3-phase power, widely used today.

The problem is this: several people, myself included, contend that
the two "legs" of power produced by a center-tapped transformer do,
in fact, constitute two separate phases of power, 180° apart. (This
is how household power is delivered in North America, with a
step-down xfmr at the power pole delivering 240 volts in the form
of 120-0-120.)


Well, if you want to be correct, the house power is split phase, and
not two phase. I suppose there is an arguement that it is two phase,
but say that to a power engineer and you'll get the old raised
eyebrows response!


Welllll ... that's pretty much what I wrote. So I take it you agree with
me that it is, in fact, 2-phase power, correct?


In a word, no.

Power distribution being what it is, the 240/120 transformer on the
pole is sourced with _ONE_ phase of the 3-phase feed for the area.
That there is a center tap allowing for 120/120 or 240 loads is
immaterial. It's STILL single phase.

Jeff


Oh, so now that we have a CT as a neutral (common), how do you explain
the two different phase angles we now have ?

Last time I went to school, phase count was the number of
phase angles you have that are unique in degrees.

does not matter how you derived it..

If I plug in an inverter that operates from a single phase circuit
and it generates 3 phases that are 120 degree's apart, does that mean
it much be single phase because it started from a single phase source?


Jamie