Why is residential wiring known as single phase?

[Besoeker]

You are a marvelous engineer.

But, according to you, I do not understand the difference between a DC voltage and AC voltage.
It that were true, I'd not be fit to be called an engineer. Let alone marvelous. Yet, that's the charge you are laying at my door.
From anyone with reasonable knowledge and experience of electrical circuits, I'd have been chagrined to have been so charged.
In this case, I just found it amusing.

I have provided ample information including real life oscilloscope measurements that support my point that V_an and V_bn are mutually displaced by 180 degrees or pi radians if you prefer that measure. Using N as the reference point is entirely logical since that's the common point in residential supplies.

So, how about you now reciprocate with your measurements that show it to be different in any way shape or form.
As my late uncle was fond of saying, your move son.

 

[pfalcon]

Since in an AC circuit the current alternates direction, the choice of Positive or Negative is arbitrary but should remain constant for the system being analyzed.

Once I picked it, I do not change it.

Except you're never picking "it". You're picking "them". You select TWO reference frames. One for NA and one for NB. One for voltage in the direction of power and current; and one for voltage in the direction opposed to power and current. Two separate reference frames with different definitions of "positive" and "negative". Then you compare and scope them as though they were only measured on the first reference frame.

It just looked that way. My apologies for any mistakes about that and for not being clear enough.
You can have 4 reference frames:
1) Positive away from one end
2) Positive towards one end
3) Positive away from neutral
4) Positive towards neutral

The system is the secondary coil and its behaviour.
Cases 1) and 2) each maintain a constant reference frame for measurements within the system.
Cases 3) and 4) use separate, opposed reference frames for measurements within the system.

That the frames for 3) and 4) are separate, opposed reference frames explains why the traces appear so be in opposition on the scope. The scope is limited to displaying the waves in terms of one frame or the other, never both at the same time. The effect is the inversion of the unreferenced frame relative to the reference frame.

 

[rattus]

Com'on - even mivey didn't disagree with that one - it fundamental algebra. Where does "peak" show up in the definition of phase you provided - it isn't even implied.

"When i and e are in phase: If the current i reaches its maximum positive value at the same instant at which the emf e reaches its maximum positive value, the current is said to be in phase with the emf."
[Tang,Alternating Current Circuits, International, 1960]

I think we can reasonably interpret maximum positive value as a peak, and we can reasonably replace i with e. Clearly, V1 and V2 being inverses of each other cannot reach their maximum positive values at the same time. Therefore, the two waves can never be in phase.

 

[rbalex]

"When i and e are in phase: If the current i reaches its maximum positive value at the same instant at which the emf e reaches its maximum positive value, the current is said to be in phase with the emf."
[Tang,Alternating Current Circuits, International, 1960]

I think we can reasonably interpret maximum positive value as a peak, and we can reasonably replace i with e. Clearly, V1 and V2 being inverses of each other cannot reach their maximum positive values at the same time. Therefore, the two waves can never be in phase.

Again, you're using descriptions, not definitions;i.e., tell me what phases ARE not what they DO.

 

[jim dungar]

Look again. On the right is a single-phase source on the two-wire primary side of the transformer. This powers the center-tapped secondary to the left. This center-tapped secondary is paralleled with the source from the left. The left and right sources parallel feed the resistive load.

How is this connection related to the 120/240 center tapped secondary that started this discussion?

A single answer for what? I thought above you said you were not stuck on there being only one answer.

Do you not realize what you are calling the "real world" is a relative concept?

It never occurred to me, that the actual physical connections of transformer windings were not important. I am pretty sure that Besoeker is very concerned about the real world connections of his rectifier circuits.

Given the two transformer windings you mentioned much earlier, X1-X2 and X3-X4, will all of these possible connections provide the same oscilloscope display?
X1-X2&X3-X4
X1-X2&X4-X3
X2-X1&X3-X4
X2-X1&X4-X3
Will Besoeker's rectifier circuits work equally well on all of these connections, without modifications?

Do you not see that two voltages that are physically created to have a 180? phase difference can exist across the same center-tapped secondary windings on a transformer that has a single-phase source on the two-wire primary side? Does that not help you see that what you are calling the "real world" is based on relative reference frames?

Go outside and look at a single-phase utility transformer (I am sure you can find one someplace) is it connected like your graphic? Have you ever seen a 120/240V premises wiring system supplied by a transformer connected per your graphic?

 

[rbalex]

"When i and e are in phase: If the current i reaches its maximum positive value at the same instant at which the emf e reaches its maximum positive value, the current is said to be in phase with the emf."
[Tang,Alternating Current Circuits, International, 1960]

I think we can reasonably interpret maximum positive value as a peak, and we can reasonably replace i with e. Clearly, V1 and V2 being inverses of each other cannot reach their maximum positive values at the same time. Therefore, the two waves can never be in phase.

Come to think of it, using your new description as a definition, says I can ignore period as well as zero crossing.

 

[mivey]

Except you're never picking "it". You're picking "them". You select TWO reference frames. One for NA and one for NB. One for voltage in the direction of power and current; and one for voltage in the direction opposed to power and current.

If you are going to bring power direction into it, get the facts straight. The real power flows towards the load DOWN BOTH WIRES. An easy way to think of it is to think of the two wires like a wave guide. So if you want to be persnickity about the direction of power, it is actually leaving X1 and leaving X4, not entering X4 and leaving X1.

Two separate reference frames with different definitions of "positive" and "negative". Then you compare and scope them as though they were only measured on the first reference frame.

Using the neutral is actually using only one reference point for the voltages ("n" for both Van and Vbn). The other way actually is the one with two reference points ("n" for Van and "b" for Vnb).

The system is the secondary coil and its behaviour.
Cases 1) and 2) each maintain a constant reference frame for measurements within the system.
Cases 3) and 4) use separate, opposed reference frames for measurements within the system.

Again, you must understand relative reference frames to understand why those statements are incorrect.

 

[rattus]

Come to think of it, using your new description as a definition, says I can ignore period as well as zero crossing.

Of course the periods are the same. Wouldn't make sense if it were otherwise.

If I didn't know better, I would think you are just stalling to avoid the question: "How can two sinusoids which are inverse of each other be in phase"?

 

[mivey]

How is this connection related to the 120/240 center tapped secondary that started this discussion?

Because the question concerns the voltages across the center-tapped winding.

It never occurred to me, that the actual physical connections of transformer windings were not important. I am pretty sure that Besoeker is very concerned about the real world connections of his rectifier circuits.

You can keep quoting it like that over and over and I can keep telling you that I do not say the physical connections are not important. Quoting it over and over won't change the fact that I did not say it.

Given the two transformer windings you mentioned much earlier, X1-X2 and X3-X4, will all of these possible connections provide the same oscilloscope display?
X1-X2&X3-X4
X1-X2&X4-X3
X2-X1&X3-X4
X2-X1&X4-X3
Will Besoeker's rectifier circuits work equally well on all of these connections, without modifications?

Besoeker's circuit requires the 120/240 equivalent connections.

Go outside and look at a single-phase utility transformer (I am sure you can find one someplace) is it connected like your graphic? Have you ever seen a 120/240V premises wiring system supplied by a transformer connected per your graphic?

With dual feeds? No. With a single-phase transformer like I have on the right? Millions.

 

[rbalex]

Of course the periods are the same. Wouldn't make sense if it were otherwise.

That's not what the description you used said or even implied. It just said they have to reach a maximum at the same time to be "in-phase". That could apply to any number of random "periods." Even functions with no periods at all could meet that discription; e.g., parabolas. Periods being the same is something you imposed on the description.

If I didn't know better, I would think you are just stalling to avoid the question: "How can two sinusoids which are inverse of each other be in phase"?

I answered that one in Post 888; you just don't like it-apparently because I don't need an oscilloscope to understand what "single-phase" properly means is as it applies to conventional 120/240V systems. I don't have an oscilloscope and haven't used one for years - but I still know what phase means.

 

[Besoeker]

Given the two transformer windings you mentioned much earlier, X1-X2 and X3-X4, will all of these possible connections provide the same oscilloscope display?
X1-X2&X3-X4
X1-X2&X4-X3
X2-X1&X3-X4
X2-X1&X4-X3

Which of those arrangements do you usually see in residential wiring?

 

[jim dungar]

Which of those arrangements do you usually see in residential wiring?

It would be X1-X2&X3-X4.

The typical wiring diagrams would be:
120V 2-wire
connect X1&X3
connect X2&X4
Connect load X1-X3&X2-X4

240V 2-wire
connect X3&X2
Connect load to X1 & X4

12-/240 3-wire
connect X3&X2
Connect load to X1 & X4
Junction X3-X2 may be used as the neutral.

 

[Besoeker]

It would be X1-X2&X3-X4.

The typical wiring diagrams would be:
120V 2-wire
connect X1&X3
connect X2&X4
Connect load X1-X3&X2-X4

240V 2-wire
connect X3&X2
Connect load to X1 & X4

12-/240 3-wire
connect X3&X2
Connect load to X1 & X4
Junction X3-X2 may be used as the neutral.

But X1-X2&X3-X4 is overwhelmingly the most commonly used for residential?

 

[jim dungar]

Because the question concerns the voltages across the center-tapped winding.

No, the OP question concerns the voltage outputs of an actual center-tapped transformer, not of some 'black box' source.

You can keep quoting it like that over and over and I can keep telling you that I do not say the physical connections are not important. Quoting it over and over won't change the fact that I did not say it.

Then what did you mean when you said:

...the "real world" is a relative concept

What is your 'real world' and how does it differ from my 'actual physical connections'?

Besoeker's circuit requires the 120/240 equivalent connections.

Which one are they? Can Besoeker use the scope to determine which ones they are?
Your answer infers the actual connections affect the output.

With dual feeds? No. With a single-phase transformer like I have on the right? Millions.

So, it appears there is an actual industry accepted 'right way' to make a center tapped connection.

 

[charlie b]

We interrupt this discussion to bring you a special news bulletin. Although I have avoided (much as I would have avoided the plague) any participation in this thread, and indeed have not made any attempt to read it (fully expecting it to amount to nothing more than an argument along the lines of “The grass is green” followed by “No you are wrong, the sky is blue”), I would like to mention that this thread has long since taken over the record for the longest in the history of this forum. The previous record was set about 75 months ago, with a final post count of 782. If anyone is totally bored, and in search of new distractions, you may find the previous record holder here:
http://forums.mikeholt.com/showthread.php?t=58998&highlight=big+oops

We now return you to your regularly scheduled discussion.

 

[rbalex]

... ?The grass is green? followed by ?No you are wrong, the sky is blue?...

No Fair!!! I already used that analogy in Post #545

 

[Rick Christopherson]

Using the neutral is actually using only one reference point for the voltages ("n" for both Van and Vbn). The other way actually is the one with two reference points ("n" for Van and "b" for Vnb).

Ummm, doesn't it take 2 reference points to determine any voltage? I would tend to think so. So regardless how you examine the system, you still have 3 reference points: A, B, & N

 

[charlie b]

No Fair!!! I already used that analogy in Post #545

But I would not have known that, for as I said, I have not been reading this thread. :happysad: But just quickly checking your post 545, I see that you used the green-blue differently than the version from my copyrighted green-blue argument (i.e., you left off the "no you are wrong" part). :happyyes:

 

[jumper]

ot i know, but i cannot resist.

I see trees that are green
Red roses too
I watch them bloom
For me and for you
And I think to myself
What a wonderful world.

I see skies of blue
Clouds of white
Bright blessed days
Dark sacred nights
And I think to myself
What a wonderful world.

The colors of a rainbow
So pretty in the sky
Are also on the faces
Of people going by
I see friends shaking hands
Sayin how do you do
Theyre really sayin
I love you.

 

[jim dungar]

But X1-X2&X3-X4 is overwhelmingly the most commonly used for residential?

Absolutely, when there are two windings on a single core, which is common for customer owned transformers. Utility transformers are usually center-tapped single winding units.

Did you notice these windings can be connected either in parallel or in series?
If the parallel connection is X1-X2 and X3-x4, doesn't that mean winding X1-X2 and winding X3-X4 are 'in phase' with each other based on this specific construction?