On Monday, July 30, 2018 at 7:38:44 PM UTC-4, wrote:
On Mon, 30 Jul 2018 13:06:50 -0700 (PDT), trader_4
wrote:

Abstract:
Distribution engineers have treated the standard "singlephase" distribution transformer connection as single phase because from the primary side of the transformer these connections are single phase and in the case of standard rural distribution single phase line to ground. However, with the advent of detailed circuit modeling we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary. Which now brings into focus the reality that standard 120/240 secondary systems are not single phase line to ground systems, instead they are three wire systems with two phases and one ground wires. Further, the standard 120/240 secondary is different from the two phase primary system in that the secondary phases are separated by 180 degrees instead of three phases separated by 120 degrees. What all of this means is that analysis software and methods must now deal with an electrical system requiring a different set of algorithms than those used
to model and analyze the primary system. This paper will describe the modeling and analysis of the single-phase center tap transformer serving 120 Volt and 240 Volt single-phase loads from a three-wire secondary.

W. H. Kersting
Milsoft Utility Solutions, USA

When I read that I see him say he is talking about "modeling" not
reality.
My suggestion is maybe his software model needs to be adjusted to more
closely reflect reality.

Good grief. It's not an issue of software modeling. It's an issue of
what the circuit really is, how it really behaves. From a circuit
standpoint, you don't need to know if it came from a transformer or
if it came from a synthesized electronically generated source from
a battery. The 240/120 service looks like TWO ideal voltage sources,
that are 180 deg out of phase or equivalently, of opposite polarity
sharing a common neutral. There is no other way to model it. That's
all he's doing. That's what everybody does, because that's what it
is, what it behaves like. If you feel otherwise, show us your alternate
model.


Would you be happier if I found a half dozen articles by credentialed
people who explain why this is single phase?
I have certainly been in quite a few CEU seminars given by
professionals who explain it in very precise terms not software
models.
Perhaps this is just too complicated for homeowners to grasp. That is
why we say "hire an electrician".

Back to the disparaging remarks I see. And still no answers to the very
simple questions a student would ask a teacher:


Define one phase, two phase, N phase power.

The 100 year old two phase power was with a 90 deg phase difference.

Put two windings on the same shaft at the generator and feed it to the
house over three wires, shared neutral, with a 90 deg phase
difference between the two coils. Would there then be two phases entering
the homeowner;s house?

Yes or no?

Would there still be two phases there if I rotate one generator coil
so that it's 179 deg phase difference instead of 90?

Yes or no?


If it's 180 phase difference, then what? Is that still two phases?

So I run that into a house as 240/120, how many phases now?


And if that is still two phases, then it's electrically identical to
what's coming into the house from the center tapped transformer.
Electrons and engineering don't care how it was created, only what is
actually there.


Let's say I have a black box that has five phases coming out of it, at 120,
150, 180, 210, 240. They are electronically synthesized as you would in
a uninterruptable power supply. Do you need to know what power source
it uses? Why does it matter if it's powered
by a DC battery, single phase or 3 phase? Is the 180 one not a legitimate
phase, just because it's at 180?

The other poster raised another good point. If there are not two phases
present, if they are not of opposite polarity, then I should be able to
take any two receptacles in a house and parallel them. Instead with
some combos I get 240V? Two 120V circuits with voltage waveforms that are
out of phase by 180 with a shared neutral gives you exactly that.