Why is residential wiring known as single phase?

[gar]

120319-1448 EDT

Jim:

To Besoeker you commented

There is no progess unless you are finally admitting that the two halves of a single centertapped winding are IDENTICAL.
The number of voltage you derive are immaterial. The directions you arbitrarily assign are immaterial.

Van=-Vna=Vnb=-Vbn: It really is just about the equalities.

Van = 1 wave
Vbn = 1 wave
Vna = 1wave
Vnb = 1 wave

Not really sure what you were saying in that statement. So I commented

Anyone that is really familiar with circuit analysis will not classify V_AN and V_BN of a center tapped secondary as being "in-phase".

I my opinion in this thread there are those that are saying, at least, that these two voltages are the "same phase". Are "in phase" and "same phase" different or not, and if so, then how? Your direction of argument seems to put you on the side of V_AN and V_BN being of the "same phase".

Why did you come back with this response

Please tell me who said it was.
You cannot connect terminal A to N or B to N without sparks either.

It is amazing how many posts have resulted from arguing points I have never made.

What does "A to N or B to N" have to do with my comment? These are simply two wire single voltage sources. A to B is from two voltage sources connected in series. Quite a different circuit.

Then you came back again with your comment on identities. How are V_AN and V_BN identities? If you are not considering these as identities, then why bring up identities?

Further in a newer post I believe I see you saying that there can not be a phase difference between the primary and secondary of a single phase transformer.

Draw the "equivalent circuit" of a single primary transformer winding and a single secondary winding. What references would you cite, to have Vsec be of a different phase than Vprimary? Why does IEEE/ANSI waste space in their 'standards' describing the relationship between X1 and H1 terminals?

This is nonsense no matter what your reference is, and how you interpret the reference. I can get either a zero or 180 degree phase shift from the input voltage to the output voltage of a single phase transformer with two isolated coils. If this was not possible you could not have both "buck" and "boost" applications.

.

 

[pfalcon]

Back from vacation. Really wish I could have stayed there. Bet you're feeling I should have stayed there too

I'm gonna step on Rattus' phasors again.

Phasors are originally supposed to be drawn in stacked formations. From an origin for the first, from the head of the first for the second. From the head of the second for the third and so on. The resultant is then from the origin to the last head. All addition. No subtraction. A + B + C = R

Or if you're trying to find a component you draw the resultant R from the origin and stack the known parts (A + B + ?) allowing you to subtract the parts from the resultant. R - (A + B) = C

You don't automatically subtract when you place all the components at the origin. You subtract from a resultant to get a component. You always add components. And they always end up with their tails together when you shift them to the origin for visual convenience.

Rattus is subtracting a component from a component which violates phasor math. It's 240<0 - 120<0 = 120<0 if you want to subtract. I mean think about it guys. You don't say 2 - 2 = 4. And don't tell me 2 - (-2) = 4 because phasors aren't ever negative. Moving the second phasor's origin from 120<0 backward to 0<0 is a phase shift itself of (120<180). So rattus is drawing (120<180 + 120<180) and dropping the shift.

 

[Besoeker]

There is no progess unless you are finally admitting that the two halves of a single centertapped winding are IDENTICAL.

Well, you've accepted that there are two waves. Thus, even based on your own posts there more than one.

A single center-tapped winding has 2 physically identical windings. Every mathematical manipulation must result in indentical results.

If they were identical results, why does this circuit

require two non-identical firing pulses per cycle? Non identical in terms of phase displacement to produce this:

As I put it a few posts back:

Why otherwise would the circuit require two firing pulses per cycle?
Care to explain away that little inconvenient truth?

Same question.
Care to explain away that little inconvenient truth?

 

[jim dungar]

Why did you come back with this response What does "A to N or B to N" have to do with my comment? These are simply two wire single voltage sources. A to B is from two voltage sources connected in series. Quite a different circuit.

Vab, Van, and Vbn are all voltages across two different terminals of a single transformer winding. There is no reason to analyze any one 'two wire voltage' differently than any other.

You really do need to read my posts instead of reading 'into' them. I am focused on a single center-tapped winding.
I did not say there could never be a 'phase' difference between a primary and a secondary.

A single center-tapped winding is not two isolated 'outputs' it is a single voltage, Vab, cut into two equal pieces.
I am adamant about not addressing other transformer connections, except for the occasional tangential touch.

Focus on the OP.
A standard residential 120/240V connection.

 

[jim dungar]

Residential wiring is known as single phase because that's what we call it.

Actually the OP effectively asked if the two voltages were 'in-phase' or 'opposite phase'.

Believe it or not this discussion is not on why it is called what it is called, but rather what it really is.

 

[Rick Christopherson]

Rattus is subtracting a component from a component which violates phasor math.

Yeah, I noticed this several weeks ago, but it wasn't worth commenting on at the time. There is no such thing as "tail-to-tail" vector subtraction, because doing so does not signify the direction of the resultant. Vector subtraction is always performed by taking the inverse vector and then adding them. Without this, the graphical answer is indeterminate because the direction cannot be determined.

 

[Besoeker]

Focus on the OP.
A standard residential 120/240V connection.

And it gives two phase displaced 120V supplies.
Two is not single.

 

[Besoeker]

Believe it or not this discussion is not on why it is called what it is called, but rather what it really is.

Anti-phase would seem as good a description as any since there is more than one phase and two-phase is a description commonly used for orthogonal systems.

 

[jim dungar]

Well, you've accepted that there are two waves. Thus, even based on your own posts there more than one.

As two independent voltages there are two waves.Don't believe I have evera said differently.
As two related voltages there is no phase difference. Van=Vnb=-Vbn=-Vna.

Your circuit works because of the way you have it wired not because there is a phase difference. No inconvient truth anywhere.
You placement of the components creates and apparent shift due to the inversion.

Now how about the oscilloscope tracings of Mivey's circuit showing 120@0? in parallel with -120@180??

 

[Rick Christopherson]

If they were identical results, why does this circuit............require two non-identical firing pulses per cycle? Non identical in terms of phase displacement to produce this:

You keep bringing this circuit up, and it takes every ounce of personal control I have to not lash out and call you an idiot for doing so. Doing it once, is an oversight. Continually doing it, well that posses a challenge to politeness.

You present this circuit as though it becomes functional only because you analyze it a certain way. Therefore, all other methods of analysis cause this circuit to fail. That's not the way circuits work.

As was stated earlier "Every mathematical manipulation must result in indentical results." So for you to claim that your circuit functions solely because you have chosen to analyze it using a phase shift is short-sighted and logically flawed. The circuit doesn't function solely because you analyze it based on a central reference point. It will continue to function just the same regardless which point(s) you choose for your analysis.

 

[david luchini]

Back from vacation. Really wish I could have stayed there. Bet you're feeling I should have stayed there too

I'm gonna step on Rattus' phasors again.

Rattus is subtracting a component from a component which violates phasor math. It's 240<0 - 120<0 = 120<0 if you want to subtract. I mean think about it guys. You don't say 2 - 2 = 4. And don't tell me 2 - (-2) = 4 because phasors aren't ever negative. Moving the second phasor's origin from 120<0 backward to 0<0 is a phase shift itself of (120<180). So rattus is drawing (120<180 + 120<180) and dropping the shift.

I'm asking again....please read Jim's refresher course on phasor math in post #1999:

Maybe you need to read up on phasors just like your advice to anyone who disagrees with you.

In a tail-to-point configuration we ADD the phasors together.
In a tail-to-tail or a point-point configuration we SUBTRACT them.

Rattus' phasor diagram is correct the way he drew it...

What say we make a phasor diagram for this problem?

120Vrms @ PI <----------0---------->120Vrms @ 0

He drew two phasors (both positive) connected tail-to-tail. As Jim points out, tail-to-tail phasors would be combined by subtraction:

120@0 - 120@PI = 240@0.

The phasor diagram is correct and the phasor math is correct. I don't see what you are taking issue with.


P.S. Hope you had a good vacation. Counting down to mine in a month. Can't wait.

 

[Rick Christopherson]

Rattus' phasor diagram is correct the way he drew it...



He drew two phasors (both positive) connected tail-to-tail. As Jim points out, tail-to-tail phasors would be combined by subtraction:

120@0 - 120@PI = 240@0.

The phasor diagram is correct and the phasor math is correct. I don't see what you are taking issue with.

No it is not correct, because the resultant phasor is indeterminate. It could be pointing to the right, or to the left. That's why tail-to-tail is never used for vector subtraction. It's a pipe dream that Rattus dreamed up.

 

[Rick Christopherson]

No it is not correct, because the resultant phasor is indeterminate. It could be pointing to the right, or to the left. That's why tail-to-tail is never used for vector subtraction. It's a pipe dream that Rattus dreamed up.

So here is your tail-to-tail vector problem. Which vector represents the correct answer, C or D?

 

[ggunn]

Actually the OP effectively asked if the two voltages were 'in-phase' or 'opposite phase'.

Believe it or not this discussion is not on why it is called what it is called, but rather what it really is.

You are kidding, right? Does anyone disagree on what the waveforms Van and Vbn look like? Does anyone disagree that Van and Vbn give you 120VAC and Vab gives you 240VAC? That's what it really is. The rest of it is just bickering over semantics and frames of reference, neither of which are absolute.

 

[ggunn]

So here is your tail-to-tail vector problem. Which vector represents the correct answer, C or D?

View attachment 6640

Neither. Assuming both vectors are 1 unit long in the directions of X=Y and X=-Y, the resultant of those two vectors is sqrt(2) units long on the Y axis, if I remember my high school physics correctly. It's been a while, though.

 

[Besoeker]

Your circuit works because of the way you have it wired

Which is just the same way as residential 120-0-120.
The SCRs don't change that.
Now if it's just one phase why does it require two firing pulses per cycle?

 

[Rick Christopherson]

Neither. Assuming both vectors are 1 unit long, the resultant of those two vectors is sqrt(2) long in the +Y direction, if I remember my high school physics correctly. It's been a while, though.

Then I strongly suggest you go back to school. Because what you just said would result in a zero answer for Rattus' example. You did in fact ADD the two vectors I showed by sliding one across the other and made them tip-to-tail!

 

[ggunn]

Then I strongly suggest you go back to school. Because what you just said would result in a zero answer for Rattus' example. You did in fact ADD the two vectors I showed by sliding one across the other and made them tip-to-tail!

Going back to school is not an option at my advanced age, thank you very much. I thought that what you wanted to do was add the vectors. Subtracting B from A would, I believe, result in D. I guess one thing I never learned to do was to read the problem completely.

 

[Rick Christopherson]

Going back to school is not an option at my advanced age, thank you very much. I thought that what you wanted to do was add the vectors. Subtracting B from A would, I believe, result in D. I guess one thing I never learned to do was to read the problem completely.

Yes. You actually understood how vectors work, which was the whole point in the first place. You performed the proper vector addition. It is Ratuss' "Voodoo Vectors" that don't follow proper vector math that I was pointing out.

Sorry for the response. You accidentally stepped into the middle of Rattus' "voodoo math" without realizing it.

 

[rattus]

No it is not correct, because the resultant phasor is indeterminate. It could be pointing to the right, or to the left. That's why tail-to-tail is never used for vector subtraction. It's a pipe dream that Rattus dreamed up.

Maybe you could demonstrate by telling us how we get 208V from a 120V wye? Do we reverse one of the phasor arrows, no we can't do that because that would amount to subtraction!

Adding or subtracting as the case may be yields a phasor (complex number) with the correct magnitude and phase angle. It is nonsense to claim otherwise.

BTW, how are you coming on proving that a sine and its inverse are of the same phase? Frankly, I don't know how to do it.