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Two phases or not?

D

David Nebenzahl

Jan 1, 1970
0
I'm posting this to try to settle an argument going on in another
newsgroup (alt.home.repair) about phases in electrical power.

Over there, someone posted a question about GFCI breakers that morphed
into a discussion of multiphase electrical power. A disagreement arose
thereafter about whether a center-tapped transformer actually delivers
two separate phases of electricity or not. I'd like to get opinions
here, since at least some folks here have engineering backgrounds: over
there (a.h.r.), not so much. People there tend to be more electrician
types, rather than EEs and such.

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.)

Now it's true that in the electrical industry, this is called
"split-phase" power, and if you tried to tell the guy behind the counter
at the electrical supply house that it's 2-phase, he'd look at you funny.

However, I (and others) say that this is, in fact, true 2-phase power,
even if it's not called that. It just happens to be trivially easy to
generate it from a single phase, as it only involves inversion. (Unlike
3-phase, which requires rotary converters or electronic devices to
generate from single-phase power.)

Take, for example, any push-pull amplifier with a phase inverter or
phase splitter in front of it: it generates two separate phases out of a
single phase.

So, what do y'all say?


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.
 
P

Phil Allison

Jan 1, 1970
0
"David Nebenzahl"
I'm posting this to try to settle an argument going on in another
newsgroup (alt.home.repair) about phases in electrical power.

Over there, someone posted a question about GFCI breakers that morphed
into a discussion of multiphase electrical power. A disagreement arose
thereafter about whether a center-tapped transformer actually delivers two
separate phases of electricity or not. I'd like to get opinions here,
since at least some folks here have engineering backgrounds: over there
(a.h.r.), not so much. People there tend to be more electrician types,
rather than EEs and such.

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.)

Now it's true that in the electrical industry, this is called
"split-phase" power, and if you tried to tell the guy behind the counter
at the electrical supply house that it's 2-phase, he'd look at you funny.

However, I (and others) say that this is, in fact, true 2-phase power,
even if it's not called that. It just happens to be trivially easy to
generate it from a single phase, as it only involves inversion. (Unlike
3-phase, which requires rotary converters or electronic devices to
generate from single-phase power.)

Take, for example, any push-pull amplifier with a phase inverter or phase
splitter in front of it: it generates two separate phases out of a single
phase.

So, what do y'all say?


** It's clearly two phase power, no doubt about that.

There are two AC waves that differ only in phase and if both "phases" are
loaded equally, the neutral current is zero.

So it is completely analogous to three phase power.

The 90 degree system is just an obsolete odd ball only a moronic pedant
would even mention.



..... Phil
 
J

Jamie

Jan 1, 1970
0
David said:
I'm posting this to try to settle an argument going on in another
newsgroup (alt.home.repair) about phases in electrical power.

Over there, someone posted a question about GFCI breakers that morphed
into a discussion of multiphase electrical power. A disagreement arose
thereafter about whether a center-tapped transformer actually delivers
two separate phases of electricity or not. I'd like to get opinions
here, since at least some folks here have engineering backgrounds: over
there (a.h.r.), not so much. People there tend to be more electrician
types, rather than EEs and such.

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.)

Now it's true that in the electrical industry, this is called
"split-phase" power, and if you tried to tell the guy behind the counter
at the electrical supply house that it's 2-phase, he'd look at you funny.

However, I (and others) say that this is, in fact, true 2-phase power,
even if it's not called that. It just happens to be trivially easy to
generate it from a single phase, as it only involves inversion. (Unlike
3-phase, which requires rotary converters or electronic devices to
generate from single-phase power.)

Take, for example, any push-pull amplifier with a phase inverter or
phase splitter in front of it: it generates two separate phases out of a
single phase.

So, what do y'all say?
I do industrial EE work and terminology can really
get screwed up at times.

You have a CT (center Tap) this gives you 2 phases, using the
CT as the common, which of course are 180 degrees apart. How ever,
if you need 230 volts, you would need to use the 2 outer legs which
will only give you a single phase for that circuit. Hence, only
one winding over all. CT means nothing here.

To qualify for a phase, it must has a common or an opposing leg.

Lets look at a floating Delta 3 phase system, even though it has
no common to qualify it as 3 circuits 120 degree's out of phase, it
does have 3 separate windings, each 120 degree's out and can supply
a circuit on each winding if it wished.

Looking at a STAR (WYE), one end of each phase (winding) is connected
to a common point.. This common point does not need to be used but is in
some cases.

The point is, there are 3 individual windings that are out of phase
with each other. Makes it 3 phase...

In the case of residential, the CT will give you 2 phases of 180
degree's when you only need 115 volt circuits how ever, because the
transformer here is really only a single winding with a CT, when you
need full voltage for 230 appliances, that circuit ends up being
a single phase.. How ever, most appliances like that also have the
CT/Neutrual so it can use half of that to operate the control electronics.

Some people call it split phase, only because you are taking a single
phase and splitting it in the middle. But that does give you a 2 phase
source if you to use the CT as the common for both.. It would be the
same as 2 transformers with their secondaries joined on one side only to
form a CT.

Remember "Split Phase" only means a single winding with a CT it,
hence, you have split the phase in half!

Now here's a tricky one.. Just think of the 3 phase system with a CT
in each winding. Now we're talking ! :)

Jamie
 
W

William Sommerwerck

Jan 1, 1970
0
If there were two electrically isolated windings, with opposite polarity,
you would clearly have two phases. (I think.)

But the center tap gives them a common neutral. So are they still separate
phases? I'm inclined to say yes, because in a conventional three-phase
system, loads can be attached to individual phases, or across two phases for
a higher voltage. And these are considered multi-phase systems.
 
P

PeterD

Jan 1, 1970
0
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!
 
J

Jeffrey Angus

Jan 1, 1970
0
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!

Ding! We have a winner.

Thank you peter.

Jeff
 
F

Fred McKenzie

Jan 1, 1970
0
William Sommerwerck said:
If there were two electrically isolated windings, with opposite polarity,
you would clearly have two phases. (I think.)

Reminds me of the story of two carpenters. One says, "Half of my nails
have the head on the wrong end." His partner responds, "You dummy,
those are for the other side of the house!"
 
P

PeterD

Jan 1, 1970
0
Reminds me of the story of two carpenters. One says, "Half of my nails
have the head on the wrong end." His partner responds, "You dummy,
those are for the other side of the house!"

And the other carpenters doing the other side of the house: "Damn, I
just cut this board too short." His partner replies, "Simple, just
turn it around and cut somemore off the other end..."
 
D

David Nebenzahl

Jan 1, 1970
0
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?


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.
 
J

Jeffrey Angus

Jan 1, 1970
0
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
 
P

Phil Allison

Jan 1, 1970
0
"Jeffrey Angus"
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.

** Totally irrelevant how the 2-phase is derived.

That there is a center tap allowing for 120/120 or 240 loads is
immaterial. It's STILL single phase.

** Pedantic nonsense.

There are two AC waves that differ only in phase and if both "phases" are
loaded equally, the neutral current is zero.

So it is completely analogous to 3-phase power.

The 90 degree system is just an obsolete odd ball only a moronic pedant
would even mention.




..... Phil
 
D

David Nebenzahl

Jan 1, 1970
0
"Jeffrey Angus"

** Totally irrelevant how the 2-phase is derived.


** Pedantic nonsense.

There are two AC waves that differ only in phase and if both "phases" are
loaded equally, the neutral current is zero.

So it is completely analogous to 3-phase power.

The 90 degree system is just an obsolete odd ball only a moronic pedant
would even mention.

I have to say I totally agree with Phil here. Especially the reference
to "true" 2-phase power brought up in this argument (the one over on
a.h.r), meaning that totally antiquated and obsolete system.

Those with which I disagree seem to think that just because the two
phases aren't somehow manufactured separately, by two different windings
of a generator or some such, that the center-tapped xfmr can't possibly
supply two separate phases, when it so clearly does just that.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.
 
D

David Nebenzahl

Jan 1, 1970
0
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.

Keep in mind the premise of my original question. Remember I pointed out
that 120-0-120 current supplied by a center-tapped transformer is *not*
called "2-phase" by those in the electrical power industry, but that it
is, in fact, 2-phase power. Do you disagree that there are actually two
separate phases of power present at the secondary of the transformer?

Regardless of what they call it ...


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.
 
J

Jeffrey Angus

Jan 1, 1970
0
Keep in mind the premise of my original question. Remember I pointed out
that 120-0-120 current supplied by a center-tapped transformer is *not*
called "2-phase" by those in the electrical power industry, but that it
is, in fact, 2-phase power. Do you disagree that there are actually two
separate phases of power present at the secondary of the transformer?

Regardless of what they call it ...

Nope, single phase.

The definition of "more than one" phase is a difference
of something other than 0 or 180 degrees.

With either 2-Phase (the old 90 degree system) or 3-phase
(current 120 degree system) the phases can NOT be generated
with a simple transformer. They are generated by multiple
alternators mounted on a common shaft.

With a single transformer, and a center tap, you have two
voltages, in phase, that add together.

It's single phase.

Jeff
 
J

Jamie

Jan 1, 1970
0
Jeffrey said:
Ding! We have a winner.

Thank you peter.

Jeff

having a CT in a winding gives you 2 phases, 180 apart..

Calling it split phase is just a method of doing it.

Lets look at it this way..

Take a control xfomer..

If I was to wire the secondary as

X1, X2+X3, X4;

X2 and X3 being the CT, I now have a source that has 2 secondaries
(2 windings) that can give me 180 degree shift via the CT. This gives
me 2 phases..Why? because they are not in phase with each other.. It
does not matter if they are only 1 degree off from each other.. They
would be two difference phases, because we are using the CT as the
common point. Same as, if you were to use the STAR Center of a WYE
transformer as the common point, this would give you 3 phases which
we all know are 120 degrees different from each one. The analogy isn't
any different if you had the pole pig which is just a single winding
with a CT in it on the secondary side for your common. Other wise known
as a split phase because can treat that as a single phase to get the
full voltage or split phase to get half voltage with 180 shifts.(2 phases)


Now, take that same xformer I have above there and....

X2, X1+X3, X4;

What do you get? You get two different power points sharing a CT but
in phase with each other. And yes, I've seen this done before to avoid
over voltage through grounds if the neutral was ever lifted for some
reason. This basically is only one phase and does not allow you to
use them for double voltage. In fact, you'll get no voltage between X2
and X4.


Oh well.

Jamie
 
J

Jamie

Jan 1, 1970
0
Jeffrey said:
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
 
D

David Nebenzahl

Jan 1, 1970
0
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?

Excellent question. I await answers.

So far, we have two objections to a center-tapped transformer giving two
phases, both very doubtful:

1. Not two phase because the "source" (i.e., the other side of the xfmr)
is single phase.

2. Not two phase because two phases that are 180° are not actually two
phases (?!?!?!).


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.
 
P

Phil Allison

Jan 1, 1970
0
"Jeffrey Angus"
Nope, single phase.

The definition of "more than one" phase is a difference
of something other than 0 or 180 degrees.


** Who's " definition " is that ????

I wonder ........



...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Bob AZ"

( snip tedious drivel)

But in no case, with the information presented here, is there any
method or device utilized to give any additional phases. One or two or
more. The hot legs are simply the same phase, transformed as needed,
added within the transformer, with the resultant two hot legs, 180
degrees out of phase with each other.


** A really beautiful example of "double think" if I ever saw one.


Three phase distribution starts with a generator with 3 sets of
windings that is distributed as three phase and utuilzed as needed.

** And if it had only 2 windings instead of 3 ??

Two AC waves would be produced simultaneously, remaining always 180 degrees
apart in phase and be completely * indistinguishable * from any other means
of creating the same situation.



...... Phil
 
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