Why is residential wiring known as single phase?

[mivey]

Your example is related to a time shift. I agree that we do not have a time shift. A phase shift does not have to mean a time delay. Three-phase generators produce waveforms that all start at exactly the same time but are physically shifted in phase relative to each other.

Rick, in the utility industry we "shift" phases in transformer banks. They do not create a time shift like we would be concerned with in audio, but it is still recognized as a phase "shift" in the electrical world. Call it a phase displacement if it makes you happier.

The shift, displacement, difference, or whatever you want to call it that takes place by using voltages in different directions in the transformer is considered a real physical difference in phase, not just a math difference. That is what my open-wye example demonstrates.

So therein lies the answer to the Original Poster's question. It is called single phase because there is just a single, real, phase angle in the system, even though there may be 2 apparent phase angles.

No. It is because there is one single larger phase in the system; but not meaning it is the only phase present. Two in-phase voltages can be combined to produce a larger single-phase voltage. Two phase-opposed voltages can be combined to produce a larger single-phase voltage.

The way C.P. Steinmetz explained it, if we take the smaller negative phase to be the return circuit of the smaller positive phase, the result is a larger single phase circuit. Steinmetz did not say that the combination of two smaller phases as a larger single-phase meant the smaller phases did not exist. In fact, he referred to the ordinary alternating current system that can be produced by one coil as a two-phase system.

None of the transformer connections we use in the industry to produce physical voltages that differ in phase have a time shift. They are based on real physical phase shifts, not time shifts. So while I agree we do not have a time shift, your time shift technicality really doesn't matter for the topic we are discussing.

 

[Rick Christopherson]

No. It is because there is one single larger phase in the system; but not meaning it is the only phase present. Two in-phase voltages can be combined to produce a larger single-phase voltage. Two phase-opposed voltages can be combined to produce a larger single-phase voltage.

You are arguing mathematics here, and I do not dispute the mathematics.

None of the transformer connections we use in the industry to produce physical voltages that differ in phase have a time shift. They are based on real physical phase shifts, not time shifts. So while I agree we do not have a time shift, your time shift technicality really doesn't matter for the topic we are discussing.

No. Again, you are confusing a mathematical modeling as though it was real. I do not dispute that they are mathematically equivalent, and that is why you can make your parallel connections of your previous example.

As I stated previously, a mathematical phase shift doesn't require a shift in time, but a real phase shift does. My example clearly demonstrates this difference. You agreed with me just a couple posts earlier. I suspect that you are now backpedaling because I put that information to practical use.

 

[rattus]

Well Duh!

Well Duh!

Deleted by user:

 

[mivey]

You are arguing mathematics here, and I do not dispute the mathematics.

I am arguing what our industry recognizes to be a phase shift/difference/displacement by transformer connections even if it is not a time shift. Same as what I have always said.

No. Again, you are confusing a mathematical modeling as though it was real.

Nothing unreal about the transformer example I gave as it is used in the utlity industry to produce voltages that have real phase displacements.

As I stated previously, a mathematical phase shift doesn't require a shift in time, but a real phase shift does.

And I have agreed that as phase shift AS YOU DEFINE IT TO BE WITH A TIME SHIFT is not there. But nobody cares except you because none of the transformer connections we use produce a time shift, but they do produce a phase shift USING THE PHASE SHIFT AS DEFINED BY A PHYSICAL DISPLACEMENT.

My example clearly demonstrates this difference. You agreed with me just a couple posts earlier.

Why don't you go back and read and you will see I agreed there was no time shift.

I suspect that you are now backpedaling because I put that information to practical use.

I agreed that there was no time shift. I also stated that no time shift is required for the phase displacements produced by utility transforemer connections. No backpeddling involved as I am stating the same thing I stated before. Evidently, you read what you wanted to read.

My open-wye example is just as valid now as it was before. The phase displacements produced by my open wye are just as present as they were before.

 

[Besoeker]

Look back at post #963.

Let me repeat it in full.

Yes, they have to be in phase to be paralleled. I don't think that was ever disputed.
But you have already agreed that they are not connected that way for residential wiring.
It's overwhelmingly used as a series connection which results in 120-0-120 with the 120s being mutually displaced by 180 degrees when measured wrt the COMMON neutral.
I would call that different phases.

And, given that we are discussing 0/120/240, the parallel connection is irrelevant to the discussion. You can't get 240V from it.

 

[Besoeker]

All relevant voltage functions for a conventional 120/240V system, however validly determined, measured from whatever reference point, line or neutral, in any direction, or not measured at all, have a mathematically identical phase

Care to explain hexaphase based that argument?

 

[rbalex]

Care to explain hexaphase based that argument?

Why? I thought we're discussing conventional 120/240V systems.

 

[jim dungar]

Jim, are you comfortable working with phasors?

Yes, but why is that important?
You and Mivey, refuse to acknowledge that you are employing double negatives to prove a point and then somehow claiming I am calling your methodology FAKE, IMAGINARY and UNREAL.

I have focused my discussion on the physical connection of transformer windings.
Besoeker emphatically stated that to be in connected in parallel, the windings would need to be 'in-phase', in fact he questioned why it would be a point of discussion. - No phasors were needed to make his statement.

Mivey then posted a graphic that could be summarized as Vleft in parallel with Vright, which means they must be 'in-phase'. His graphic included subscripts such that Vleft = Vbn, Vbn = Van, Vright = Vnb, and Vnb = Van again ergo Vbn = Vnb - again no phasors were involved.

Oh, but Mivey included some arrows on his graphic, to indicate direction from which we could infer they represent phasors, giving Vbn@180? and Vnb@0?, but we already know that Vleft must be 'in-phase' with Vright so Vbn@180? must be 'in-phase' with Vnb@0? - so the phasors have proven that Vbn=-Vnb.

It sure is worthwhile discussing the arbitrary placement of subscripts isn't it. But the subscripts don't change the reality as shown by Mivey's graphic, which is Vbottomleft is 'in-phase' with Vbottomright which is 'in-phase' with Vtopright which is 'in-phase' with Vtopleft. Any other position, means Besoeker is wrong about paralleled connections or Mivey is wrong about his subscript usage or arrow assignment.

And in case you are wondering for transformer windings, my default arbitrary assignment of phasors is odd terminal = head and even terminal =tail. I follow the convention of Head-tail = addition and Head-head or tail-tail = subtraction. So in the case of single phase and deltas my phasors are connected tail to head, and for wyes they are commoned at the tails.

 

[jim dungar]

Let me repeat it in full.


And, given that we are discussing 0/120/240, the parallel connection is irrelevant to the discussion. You can't get 240V from it.

The point was the phase angle of each individual winding is created by the common electomagnetic action of the transformer. Connecting them into a series or parallel arrangement does not change their physical characteristics.

Miveys connection was not a simple 120/240 connection either. But regardless how does that change the issue of paralleling voltages?

Maybe you can disprove it your way - connect Mivey's circuit to your oscilloscope and display the Vleft and Vright voltages.

 

[rattus]

Yes, but why is that important?

Because, all we are doing is writing phasors for the voltages on L1 and L2. That is

V1n = 120Vrms @ 0
V2n = 120Vrms @ PI

We could reverse one or both phasors, but that would let L1 and/or L2 be the references, which we find clumsy.

I see no reason to concern ourselves with the transformer connections because we must assume they are done correctly. Certainly for the OP's question, we can treat the transformer as two ideal sources, with opposing phases when referenced to the neutral.

That's all!

 

[jim dungar]

I see no reason to concern ourselves with the transformer connections....

Yet I have emphatically stated my consistnency in using them because the OP asked about them.

I have been consistent in focusing on the physical connections, and the impression I get from you is that I lack technical understanding of basic power system concepts like phasors.

I stated my arbitrary defaults for assigning directions, which is compaible with the physical connection of delta and wye transfromer windings.

Do you have a consistent method?

 

[rattus]

Yet I have emphatically stated my consistency in using them because the OP asked about them.

I have been consistent in focusing on the physical connections, and the impression I get from you is that I lack technical understanding of basic power system concepts like phasors.

I stated my arbitrary defaults for assigning directions, which is compatible with the physical connection of delta and wye transformer windings.

Do you have a consistent method?

Jim, although a transformer was mentioned, there is no need to discuss the way the terminals are connected. We can use a pair of equivalent sources just as well.

I thought you were comfortable with phasors, but I don't remember you using any phasors in any of your responses.

Won't say you are wrong, but my arbitrary default is to use the neutral as a reference except for the 120V legs. That is consistent I think.

 

[jim dungar]

Jim, although a transformer was mentioned, there is no need to discuss the way the terminals are connected. We can use a pair of equivalent sources just as well.

Doesn't equivalent mean almost but not exactly the same?

But regardless, there is no need to use equivalencies when discussing the real connections is possible.

I thought you were comfortable with phasors, but I don't remember you using any phasors in any of your responses.

There has been no need to. The phase relationship between V12 and V34 are established by their physical construction, everything is is simply 'an equivalency'.

Won't say you are wrong, but my arbitrary default is to use the neutral as a reference except for the 120V legs. That is consistent I think.

I find defaulting to neutral points to be too restrictive.
What do you do for phasors in delta connections? What about T connections? How do you relate phasors on the primary side to the secondary side of a transformer?

 

[rattus]

Jim, although a transformer was mentioned, there is no need to discuss the way the terminals are connected. We can use a pair of equivalent sources just as well.

I thought you were comfortable with phasors, but I don't remember you using any phasors in any of your responses.

Won't say you are wrong, but my arbitrary default is to use the neutral as a reference except for V12. That is consistent I think.

corrected an error

 

[rattus]

Doesn't equivalent mean almost but not exactly the same?

But regardless, there is no need to use equivalencies when discussing the real connections is possible.

There has been no need to. The phase relationship between V12 and V34 are established by their physical construction, everything is is simply 'an equivalency'.

I find defaulting to neutral points to be too restrictive.
What do you do for phasors in delta connections? What about T connections? How do you relate phasors on the primary side to the secondary side of a transformer?

Jim, I can answer the OP's question in one sentence:

Because although technically there are two phases (measured in radians, not volts) there is only one transformer, one core.

There are conventions for drawing the phasor diagrams for the delta and wye. But one can reverse all the arrows if one also shifts the phases by PI, or one can reverse just some of the arrows as long as Kirchoff's Voltage Law is satisfied.

I don't think the OP asked about the transformer connections.

 

[rattus]

A Logical Argument:

A Logical Argument:

The mathematical expression for phase is (wt + phi) where phi is defined as the phase constant or phase angle.

The phase constant determines the starting point of the waveform, i.e., sin(wt + PI/4) starts PI/4 radians ahead of t0.

The phase constant cannot be changed. It is part of the expression defining the wave form.

Consider two waveforms with phase constants of 0 and PI.

The phase of the first is (wt); the phase of the second is (wt + PI), they are not equal. One wave starts at 0; the other starts at PI. Nothing can change that.

Therefore, the single phase 120-0-120 system exhibits two phases:

(wt) and (wt + PI)

The OP knew that as well. Any attempt to alter the facts is nonsense.

But, because there is only one transformer, one coil, one generator, this system is known as single phase.

 

[mivey]

You and Mivey, refuse to acknowledge that you are employing double negatives to prove a point and then somehow claiming I am calling your methodology FAKE, IMAGINARY and UNREAL.

Why, Jim. How kind of you to throw me a free ergo. I'll cash that in a minute.

Oh, but Mivey included some arrows on his graphic, to indicate direction from which we could infer they represent phasors, giving Vbn@180? and Vnb@0?, but we already know that Vleft must be 'in-phase' with Vright so Vbn@180? must be 'in-phase' with Vnb@0? - so the phasors have proven that Vbn=-Vnb.

What we do know is that a voltage has direction so to discuss the phase relationship, we pick an arbitrary direction. Vleft and Wright is not clear enough so we must be more clear to discuss the phase relationship so we use arrows and subscripts.

As I pointed out before, a winding has no phase so it is neither "in-phase" or "out of phase" on its own. It is the voltage in the winding that has phase and to compare phase we must pick a direction.

The single-phase paralleled winding has X1->X2 voltage in phase with the X3->X4 voltage. It also has the X2->X1 voltage in phase with the X4->X3 voltage. The X1->X2 voltage is phase-opposed with the X4->X3 voltage, even if they are paralleled. Separating them into a series configuration does not change the relationship of the in-phase voltages or the phase-opposed voltages as they still exists in the series configuration.

What you fail to admit is that both voltages really exist because you keep saying there are only in-phase voltages. Ergo, you think the phase-opposed voltages are not real. Again, thanks for the ergo freebie.

It sure is worthwhile discussing the arbitrary placement of subscripts isn't it. But the subscripts don't change the reality as shown by Mivey's graphic, which is Vbottomleft is 'in-phase' with Vbottomright which is 'in-phase' with Vtopright which is 'in-phase' with Vtopleft. Any other position, means Besoeker is wrong about paralleled connections or Mivey is wrong about his subscript usage or arrow assignment.

No, it means that the single-phase paralleled winding has the X1->X2 voltage in phase with the X3->X4 voltage. It also has the X2->X1 voltage in phase with the X4->X3 voltage. It also means the X1->X2 voltage is phase-opposed with the X4->X3 voltage.

Before you repeat your "double-negative" stuff, note that my generator example shows that both voltages do really exist. The voltages from the generator are physically defined, not just mathematically defined by a double negative.

And in case you are wondering for transformer windings, my default arbitrary assignment of phasors is odd terminal = head and even terminal =tail. I follow the convention of Head-tail = addition and Head-head or tail-tail = subtraction. So in the case of single phase and deltas my phasors are connected tail to head, and for wyes they are commoned at the tails.

Good. Then you should have no trouble confirming using my generator example that both 0? and 180? voltages are really present in the center-tap windings.

The point was the phase angle of each individual winding is created by the common electomagnetic action of the transformer. Connecting them into a series or parallel arrangement does not change their physical characteristics.

Really? Again with the ergo gift? You claim that you do not deny the existence of the voltages but deep down in your heart you really only think they are physically real in one arrangement. You are missing the fact that in the parallel cases, we still have that the X1->X2 voltage is phase-opposed with the X4->X3 voltage.

Yet I have emphatically stated my consistnency in using them because the OP asked about them.

I have been consistent in focusing on the physical connections, and the impression I get from you is that I lack technical understanding of basic power system concepts like phasors.

I stated my arbitrary defaults for assigning directions, which is compaible with the physical connection of delta and wye transfromer windings.

Do you have a consistent method?

Why do you resist saying there is also a star connection with the center-tap?

There has been no need to. The phase relationship between V12 and V34 are established by their physical construction, everything is is simply 'an equivalency'.

And the X1->X2 voltage is phase-opposed with the X4->X3 voltage. The physical construction does not change that. You do not recognize the X4->X3 to be a physical voltage. Ergo, you think it is a not-real equivalent.

 

[jim dungar]

You do not recognize the X4->X3 to be a physical voltage. Ergo, you think it is a not-real equivalent.

You have no idea what I recognize or do not.

I have never raised the issue of something being 'not-real'.

Any more blatant misrepresentation of what I have said or what I do recognize, will cause me to start acting like a moderator and not a participant.

 

[jim dungar]

Why do you resist saying there is also a star connection with the center-tap?

Wow, it appears you really do not read what I post.

I said a center tap has more in common with a delta connection than it does with a star.
Physically the connection of the windings in a star and a center tap is an Xeven connected to an Xodd, but a wye connection has an Xeven connected to an Xeven.

Yes there are other possible connections, but the OP asked about residential services. And in a true center-tap we do not have the individual center Xeven and Xodd terminals because they are actually the same point.

 

[mivey]

You have no idea what I recognize or do not.

I have never raised the issue of something being 'not-real'.

Then by this:

The point was the phase angle of each individual winding is created by the common electomagnetic action of the transformer. Connecting them into a series or parallel arrangement does not change their physical characteristics.

You are agreeing that there are both in-phase and phase-opposed voltages in the winding? If so, why the insistence that "the windings" are in phase when we really know that we are discussing the voltages in the windings? If you agree that both voltages exist, then you agree that by saying "the windings are in phase" that you really only mean that a select set of the voltages are in phase?

Any more blatant misrepresentation of what I have said or what I do recognize, will cause me to start acting like a moderator and not a participant.

Then practice what you preach first and stop getting upset when someone responds in kind:

You and Mivey, refuse to acknowledge that you are employing double negatives...

Any other position, means Besoeker is wrong about paralleled connections or Mivey is wrong about his subscript usage or arrow assignment.