On Thursday, November 28, 2013 11:38:40 AM UTC-5, bud-- wrote:
On 11/27/2013 6:35 PM, wrote:
Neither will the IEEE power engineers:
http://ieeexplore.ieee.org/xpl/artic...number=4520128
"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."
Not obvious what the author has in mind in the minimal summary of his paper.
It's clear to me:
"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. "
He's saying that in fact you have two phases and that's how
you have to analyze it.
He clearly says the standard way of looking at split-phase, 3-wire
supplies is they are single phase.
He didn't say that at all.
Everyone here but you (that has
provided an opinion) agrees with that.
The author suggests a departure where the 2 hot wires are considered
separate phases for "modeling".
He did not say it's just for modeling.
And for modeling, if you are looking at
the *currents* in the 3 wires, you have to consider them separate phases
because the currents will be 180 degrees out of phase only if the loads
are resistive. Not obvious what the author is saying beyond that.
So, how can you consider them separate phases if they are
really not separate phases?
But, alas, I don't see where the author's suggestion has been accepted.
The paper confirms what the rest of us have been saying.
How about these white papers from electrical eqpt manufactuers that
clearly talk about two phases being present:
http://www.behlman.com/applications/AC%20basics.pdf
http://www.samlexamerica.com/support...Circuit s.pdf
Are they wrong too?
My service panel is "single phase". If I replaced it, the only panels
manufacturers have are "single phase". The 2-pole breakers for them are
"single phase".
I propose we resolve this by using L1, in my L1-N-L2 service, as the
reference. L1-N and L1-L2 are in phase.
The standard real 2-phase supplies have 2 transformers 90 degrees apart
with the centertaps connected. Does this then have 4 phases?
In a 3-phase wye system are there 6 phases at the transformers (each
transformer has 2 ends)?
No because the logical reference point to look at phases
is from the neutral common point. You have 3 phases, differing by 120 degrees.
Similarly, the logical reference point in a split-phase service is
the neutral common point. From that perspective, you have two phases
present. Since you brought up 3 phase, what about the other thread
I started where I used 3 phase to show how you can get to split-phase
and how it looks like two phases? A lot of people looked at that post, but
no one wants to comment? Here it is again:
Let's start with a 3 phase wye power source. For anyone
not familiar, here's a diagram of it, it's fairly straightforward:
http://central-energy.com/AppNotes.html
It's the first diagram that shows a 3 phase wye power source.
Let's assign Phase A as the reference point and make it 0 deg.
Phase B is 120 deg off from Phase A. Phase C is 240 deg off from
Phase A. You can see those 3 waveforms on a 3 input scope,
one input attached to each phase, the scope reference point tied
to the neutral. I believe everyone here is in 100% agreement that you
have 3 phases present there. Let's put that power source inside a box
and I run those 4 wires out of the box, I have 3 phases.
For convenience, let's assign each of the 3 voltage sources in
the box to be 120V. So, we have 3 phases emerging from the box,
with 120V between any phase and neutral. All this I hope we
agree is still 3 phase.
OK, so now, lets just leave everything as it is, but only run
Phase A and B and the neutral out of the box. How many phases
do I have now? I would hope that you would agree that I have
two phases, Phase A at 0 deg, Phase B at 120 deg. Again, I can
see exactly that on a scope.
Now, lets change the source for phase B so it's at 90 deg. How many
phases do I have coming out of the box? My answer: two. Change B to
175 deg. How many phases do I have? My answer: two. Change
B to 185 deg, how many phases do I have? My answer: two.
Now change Phase B to 180 deg and how many phases do I have?
My answer: two.
And if I have two there, how exactly is what's coming out of
that box any different than the 3 wires coming into a split-phase
240/120V service? You have a neutral and two phases 180 deg
apart coming out of the box. Between Phase A and neutral you
have 120V. Between
Phase B and neutral you have 120V. Between phase A and Phase B
you have 240V. What's coming out of that box
is identical in every way to what's delivered with a 240/120V
split-phase service. If I hooked either the box or the 240/120V
split-phase service up to your house, there is absolutely
nothing different in terms of current flow, voltage, etc
that is going on at the panel. You could not tell the difference.
Another way of looking at it. I could replace the power source
in the box with a center-tap transformer that delivers 240/120V
split-phase and you could not tell the difference. The electrical
charecteristics on the 3 wires coming out would be EXACTLY the same.
My position is clear. The 180 deg phase relationship is just
one special case of the various possibilities. You can still
view it as two phases, treat it that way from an engineering
analysis basis, etc. The opposing view is apparently that
something magical happens at 180 deg, so that it can no longer
be referred to as 180 deg out of phase, it must only be called
"opposite" or some other imprecise non-engineering term. In fact,
no one who says I'm confused has yet given their definition of "phase",
though I've asked 10 times now. How can you even talk about
something, when no one will define it?