Why is residential wiring known as single phase?

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mivey

Senior Member
The reason why this discussion exists and persists is because so many people have heard you (plural) say that the phase shift is real and absolute, when in fact, it is only an apparent phase shift.
I'm 99% sure that you are in fact talking about a time shift. I do not claim there is a time shift nor a phase shift like it. Generators produce multiple phases without having a time shift like you are talking about.

A 3-phase to -2phase or a 2-phase to 3-phase transformer bank produce different phases without a time shift either. In those transformers, an artifact like you are talking about will show up at the same point in time on a different phase.
 

mivey

Senior Member
That is why the noise shows up in both the positive and negative half cycles.
The same effect would take place in the Scott-T transformer and other similar arrangements where the phase angles are different.

Yes, that is an obvious consequence. Which is why it cannot be a "real" phase shift, but instead a "real" inversion that can be viewed as an "apparent" phase shift.
So you are talking about a time shift. I am not claiming a time shift.

I don't contest anyone's usage of an apparent phase shift in evaluating a system. I do contest when it is called a "real" phase shift. This example shows that it is not real, but apparent.
What is not real about the 120? phase displacements becoming 90? phase displacements in a 3-to-2 phase convertor?
 

Rick Christopherson

Senior Member
I'm 99% sure that you are in fact talking about a time shift. I do not claim there is a time shift nor a phase shift like it. Generators produce multiple phases without having a time shift like you are talking about.

A 3-phase to -2phase or a 2-phase to 3-phase transformer bank produce different phases without a time shift either. In those transformers, an artifact like you are talking about will show up at the same point in time on a different phase.
I don't care how you want to view it or define it (I'm not saying that in a snotty way...sorry if it sounds that way). I'm simply contesting that it is not correct to say the apparent phase shift is real. The inversion is real. The phase shift is apparent.
 

Rick Christopherson

Senior Member
The same effect would take place in the Scott-T transformer and other similar arrangements where the phase angles are different.

So you are talking about a time shift. I am not claiming a time shift.

What is not real about the 120? phase displacements becoming 90? phase displacements in a 3-to-2 phase convertor?
But we're not talking about those situations. We're talking about a single phase transformer. I am not saying that a 3-phase transformer does not have real phase shifts, or that even your generator example does not have a real phase shift. I am saying this situation does not have a real phase shift. It comes from an inversion that can appear mathematically as a phase shift if one chooses.
 

mivey

Senior Member
Yes. It was supposed to be:
the fact that the X1->X2 voltage is in phase with the X3->X4 voltage and the fact that the X1->X2 voltage is opposite in phase to the X4->X3 voltage.



Never said you need to change the transfromer to go from Vnb to Vbn,
Well me neither so why is it a topic? One of my arguments is that both voltages exist in the normal fixed-configuration center-tapped transformer.

I guess I missed where I said two independent sources could not be interconnected/ Oh yeah, I have been focusing only on the transformer connections used in millions of installations.
Great so we see the transformer on the right is what we are all familiar with: a single-phase center-tap fed by a single-phase source. One side has said the voltages are in phase. Well that is true for the X1->X2 voltage and the X3->X4 voltage. That is a 0? difference going end-to-end across the windings. We have also referred to this as Van and Vnb having a 0? phase difference: Van in phase with Vnb.

But some have denied there are also voltages in those windings that are not in phase. The purpose for the 2-generator source coming from the left is to show that the X2->X1 voltage and the X3->X4 voltages are not in phase. That is a 180? difference going from end-to-neutral across the windings. We have also referred to this as Van and Vbn having a 180? phase difference: Van phase-opposed to Vbn.

Some have claimed you can't have both voltages and there is only one reality. My graphic illustrates that you can indeed have both and the difference is the reference frame ("end-to-end" vs "end-to-neutral").

Both cases are reality and no physics are violated for both voltage sets to physically exist at the center-tap secondary. That was the purpose of paralleling the two sources across the load. Nothing blows up, no physics are violated, both sets of real voltages exist.

The physics defining the voltage directions on the left and the physics defining the voltage directions on the right use the same rules and yet we wind up with both in-phase and phase-opposed voltages sharing the same space. So "the physics" do not result in only one reality. The reality is that the positive voltage direction is a choice we make and either direction is valid. Nothing about the physics says we have to use one linear direction across both series windings as the positive direction.

You are the one who chooses a voltage directions, so I thought it interesting you would show that the voltage across and the current through a resistive load are not consistent.
I don't see your point. I have not made such a claim. The waveforms are bi-directional and current changes direction every 1/2 cycle. I believe it is the default assignment of a positive direction that is making you think there is an inconsistency.

And I am amazed at how you are insistent that I have tried to 'force a direction' on anyone.
You claim there is only one reality. That one reality tells you the voltages in the center-tapped winding must have a 0? phase difference. I am saying that there also exists a second reality that tells you there are also voltages in the center-tapped secondary that have a 180? phase difference. What makes the difference is the reference frame we choose and that reference frame is a choice, not one that is set by the polarity marks on the transformer.

I have said that the physical construction makes a difference. Real world winding directions are also extremely important in wye, delta, and T connections.
I think that is obvious to everyone here and no one is claiming the physical construction makes no difference. It appears it is the use of that equipment that is being debated.
 

mivey

Senior Member
I don't care how you want to view it or define it (I'm not saying that in a snotty way...sorry if it sounds that way). I'm simply contesting that it is not correct to say the apparent phase shift is real. The inversion is real. The phase shift is apparent.
OK. Then call it a difference in phase and not a phase shift.
 

mivey

Senior Member
But we're not talking about those situations. We're talking about a single phase transformer. I am not saying that a 3-phase transformer does not have real phase shifts, or that even your generator example does not have a real phase shift. I am saying this situation does not have a real phase shift. It comes from an inversion that can appear mathematically as a phase shift if one chooses.
If taking the opposite direction through a transformer is not a change in phase, then how does the open-wye to 4-wire wye use two 120? displaced phases, in combination with their inverses, to create a third phase that is displaced 120? from the original two, thus creating a 3-phase set of voltages?

You have to consider what is normally considered a phase difference. No, the open-wye would not have a time shift but the inversions still result in what is commonly recognized as a phase difference. Perhaps you would be happier if we call it a phase displacement instead of a phase shift?
 
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rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I understand them well enough to know that you can't drop minus signs, and you can't ignore phase angles. Please explain or we will think you are a humbug like the Wizard of Oz.
OK, Go back to your original post #981 and answer four questions:
  1. Do you believe the equation you posted is accurate?
  2. Do you accept gar's trigonometric identity?
  3. Which side of the equation would you like me to manipulate?
  4. What do you believe the phase element of that side to be?
I'm not trying to trap you; you know me better than that.
 

mivey

Senior Member
the open-wye would not have a time shift but the inversions still result in what is commonly recognized as a phase difference.

The reference is to this real-world transformer application:

Open-Wyeto4WWye.jpg


Where we have the following taking place (using cosine for the voltage waveform):

Primary:
Van=2Vcos(ωt+0?)
Vbn=2Vcos(ωt-120?)

Secondary:
VAN=Vcos(ωt+0?)
VBN=Vcos(ωt-120?)
VCN=-Vcos(ωt+0?)-Vcos(ωt-120?)=Vcos(ωt+0?+180?)+Vcos(ωt-120?+180?)=Vcos(ωt+180?)+Vcos(ωt+60?)=Vcos(ωt+120?)

And you will note that the math and the real world both agree.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
120218-2038 EST

I am in stitches as I read this discussion. I just can't stop laughing.

It has also become quite unclear who said what and when, and there are probably at least three different threads intertwined.

For this group of all English speaking persons there is a real language translation problem between them. I don't know how many different definitions are being used but there are many. Agreement is certainly not possible with non-compatible definitions.

.
 

rattus

Senior Member
OK, Go back to your original post #981 and answer four questions:
  1. Do you believe the equation you posted is accurate?
  2. Do you accept gar's trigonometric identity?
  3. Which side of the equation would you like me to manipulate?
  4. What do you believe the phase element of that side to be?
I'm not trying to trap you; you know me better than that.

Do you want the Ruby Red Slippers too? Just tell me how you justify ignoring the phase constant in post 721.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Do you want the Ruby Red Slippers too? Just tell me how you justify ignoring the phase constant in post 721.
I didn't, you just keep trying to change it - like you do when you no longer want to use a definition you originally proposed.

But for the record, I answered your question in post 691.
 
T

T.M.Haja Sahib

Guest
I want to submit that I have given you numerous examples that I believe more than adequately demonstrate my understanding of the differences between AC and DC.
Perhaps you haven't understood them?

I think I shall try again.


Now, what was it you wanted me to prove about my understanding of differences between AC and DC?

I want to submit that you are explaining from the comfort of your own examples about AC and DC which does not convince me at all about your mastery of first principles of Electricity.

Please explain about AC and DC voltages with respect to their numerical values given in post #881.

Considering our web friendship,I offer you one more clue.

The maximum value of DC voltage is either 120V or 240V.This is easily seen from the inspection of the numerical values of voltage given under the head DC.

Now you may proceed further.
 
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Besoeker

Senior Member
Location
UK
I want to submit that you are explaining from the comfort of your own examples about AC and DC which does not convince me at all about your mastery of first principles of Electricity.
I don't have to convince you about my expertise in this field and perhaps I ought to be surprised by your temerity to be judgmental about it. But I'm not.

IPlease explain about AC and DC voltages with respect to their numerical values given in post #881.
I already did.

120Vdc is usually taken to mean mean.
120Vac is usually taken to mean root mean square.


Considering our web friendship,I offer you one more clue.

The maximum? value of DC voltage is either 120V or 240V.This is easily seen from the inspection of the numerical values of voltage given under the head DC.
The value for the voltage for DC is usually taken as a mean. In that sense, talking about a maximum is meaningless unless you are referring to instantaneous values.
And these could be almost anything to give the same mean.

Here's a rectified voltage. I've picked an AC supply voltage to result in Vav i120Vdc.

MeanforTM01.jpg


The maximum value is about 188V.
 
T

T.M.Haja Sahib

Guest
I already did.

120Vdc is usually taken to mean mean.
120Vac is usually taken to mean root mean square.
Hmm.. I requested you to state the differences between AC and DC voltages.You are emphasizing the similarities between the two voltages.I give up.
 
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