Why is residential wiring known as single phase?

[Rick Christopherson]

Then let's talk about facts. With a transformer, one does not have to have a time shift to have a phase shift.

Well, you immediately jump off on the wrong foot, so there is not much to be said with the remainder. The only reason you can claim that a phase shift does not correspond with a time shift is because it is not truly a phase shift. It is an inversion that can be mathematically represented (if one chooses) as a phase shift if and only if the waveform is periodic and perfectly sinusoidal.

This is not a function of the transformer. This is a function of the waveform entering the transformer. Therefore, your claim that the existence of a center-tapped transformer results in a phase shift, is patently false. It is only the existence of the sinusoidal waveform that may be represented this way.

 

[mivey]

The only reason you can claim that a phase shift does not correspond with a time shift is because it is not truly a phase shift.

Try again:

...
These are the facts:
1) Phase shift without a time shift is in accordance with standard technical definitions of phase shift.
2) Phase shift without a time shift does not match all definitions of phase shift nor does it have to since we have often mutiple definitions for a word or phrase.
3) Phase shift without a time shift is common usage and technical terminology for transformers and other circuitry.
...
It is perfectly fine to have a different preference for definition or for application, but to deny the facts above is illogical and displays denialism.

 

[david luchini]

Likewise, when a poster states that analyzing a circuit can only be performed using their methods, and all other methods are foolish and flat out wrong, that is going to draw the ire of those that do not subscribe to that methodology.

What some respondents in this thread may not realize is that Rattus brought this particular aspect up many times in the past as it relates to summing KVL around a loop. When it was brought to his attention that his vectors did not conform to KVL, his response was that when he encountered tail-to-tail vectors that it meant subtraction. As was demonstrated last night, tail-to-tail is an inappropriate method for signifying subtraction because it is indeterminate.

No offense Rick, but to borrow a phrase...pot, kettle, etc.

You apparently think that only one method can be used, while another method (tail-to-tail) is foolish or flat out wrong.

A -----------> N
+
N -----------> B
=
A -----------+-----------> B

Yes, this diagram is perfectly fine for this example. It shows Van=120<0, Vnb=120<0 and Vab=Van+Vnb = 120<0 + 120<0 = 240<0 (head-to-tail combination)

Yet you reject this diagram, which is also perfectly fine for this example:

A <----------- N
-
N -----------> B
=
A -------------------------> B


It show Vna=120<180, Vnb=120<0 and Vab=Vnb-Vna = 120<0 - 120<180 = 240<0 (tail-to-tail combination).

Both are correct. Either can be used for the system. Why reject one of them?

BTW, only you and pfalcon seem to have trouble grasping phasor combination by subtraction, so I wouldn't say that it was "demonstrated to be inappropriate"...

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

View attachment 6640

"Which vector represents the correct answer, C or D?" is a silly question since you didn't ask which vector you wanted to subtract from which. So the correct answer will obviously be both are correct. D=A-B, and C=B-A.

Just as in the transformer example with tail-to-tail vectors of 120<0 and 120<180, would the correct answer of the combination of the two vectors be 240<0 or 240<180? Both are correct depending on which vector is subtracted from which. 120<0-120<180=240<0 and 120<180-120<0=240<180.

The correct answer cannot be determined until after the subtraction operation has occurred.
Technically all phasors should always have a positive magnitude with their angles being 'inverted' as needed, after all a line cannot truly have a negative length.
Mathematically it makes no difference, so this convention is usually reserved until the final step.

 

[Rick Christopherson]

No offense Rick, but to borrow a phrase...pot, kettle, etc.

No offense David, but your reading comprehension could use some improvement.

Yet you reject this diagram, which is also perfectly fine for this example:

A <----------- N
-
N -----------> B
=
A -------------------------> B

Aside from right now (due to your error), please show where I said this diagram and math is not valid. Please pay more attention. Rattus previously claimed that tail-to-tail vectors automatically signified subtraction, and that is how he could justify his hidden minus sign.

Your eample above is wrong because your resultant is backward from your math: A<------B

 

[Dennis Alwon]

Let's keep it civil. You all are adults -let's not stoop too low

 

[Fulthrotl]

Let's keep it civil. You all are adults -let's not stoop to low

this should clarify everything.... here is the correct relationship between
all phases.

if the photo doesn't appear correct to you, it's cause your monitor is plugged
into a different phase of your single phase system, than the monitor that was
used to make the photo.

please move your monitor from one outlet to another until you find one where
you can view this correctly.

thank you.

 

[Dennis Alwon]

this should clarify everything.... here is the correct relationship between
all phases.

if the photo doesn't appear correct to you, it's cause your monitor is plugged
into a different phase of your single phase system, than the monitor that was
used to make the photo.

please move your monitor from one outlet to another until you find one where
you can view this correctly.

thank you.

A nice touch of humor....

 

[Fulthrotl]

A nice touch of humor....

a positive post has now unbalanced the neutral on this single phase thread....

can someone please post a negative thread to balance the neutral here?

 

[Fulthrotl]

curious......

curious......

if you are the last one to post on this thread before it's finally put out
of it's misery, do you win a prize or anything?

and does anyone have a betting line on which mod will snap and do
the deed? i'm working up a point spread on bob, private message
me if you wish to place bets....

 

[david luchini]

No offense David, but your reading comprehension could use some improvement.

Aside from right now (due to your error), please show where I said this diagram and math is not valid. Please pay more attention. Rattus previously claimed that tail-to-tail vectors automatically signified subtraction, and that is how he could justify his hidden minus sign.

Your eample above is wrong because your resultant is backward from your math: A<------B

Wow, Rattus was wrong he said because tail-to-tail vectors automatically signify subtraction, but the the vector diagram and math that use subtraction of tail-to-tail vectors is not wrong. Your logic is astounding. Rattus was correct about subtracting tail-to-tail vectors.

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.

So, Rattus' phasor diagram was correct and his phasor math was correct, and his methodology was correct, so why take issue with it? Could it be that it just isn't the method that you would use???? Or could it be that you are so obsessed with this concept of a phantom "hidden minus sign"????

And you are correct, I was in a rush when I posted that diagram. It was posted correctly earlier here...

Vna=120<180 and Vnb=120<0. The phasor diagram is:

A<--------------N-------------->B

The combined phasor is:

A------------------------------->B

A<--------------N-------------->B Vab=Vnb-Vna= 120<0 - 120<180 = 240<0.

 

[Rick Christopherson]

Wow, Rattus was wrong he said because tail-to-tail vectors automatically signify subtraction, but the the vector diagram and math that use subtraction of tail-to-tail vectors is not wrong. Your logic is astounding. Rattus was correct about subtracting tail-to-tail vectors.

David, You don't even know enough about vector math to notice the differences in your own postings, so how can you possibly distinguish one topic from another?

When I said your diagram was correct I did not quote this posting because it is wrong:

Vna: A<--------------N = 120<180
Vnb: N-------------->B = 120<0

The combined phasor would be:

A<--------------N-------------->B

The resultant phasor by combination Vab would be:

A------------------------------->B

I did quote this one, because it is correct (aside from backward):

Yet you reject this diagram, which is also perfectly fine for this example:

A <----------- N
-
N -----------> B
=
A -------------------------> B

If you don't know the difference between the two examples that you show, it is a very good sign that you are in a discussion that is over your head.

 

[jim dungar]

... and the phasor diagrams are similar.

You are incorrect, when you address the physical construction of a single center-tapped winding.
A single center tapped winding is like a delta (phasors are aligned point to tail).

It is only your selection of a reference point that creates the condition of the phasors being point-point or tail-tail.

Because you seem to think you are better at phasors than some, if not most, of us.
Here is are some exercises:

a) Start with the given result of Vab@0?
Vab = |-------------------->

now subtract your voltage of 120@180?
Vbn = <----------|

Could you show us your resulting phasor and the steps it took you to get there?

b) Start with the given result of Vab@0?
Vab = |-------------------->

now subtract your voltage of 120@0?
Van = |---------->

Could you show us your resulting phasor and the steps it took you to get there?

 

[david luchini]

David, You don't even know enough about vector math to notice the differences in your own postings, so how can you possibly distinguish one topic from another?

When I said your diagram was correct I did not quote this posting because it is wrong:I did quote this one, because it is correct (aside from backward):If you don't know the difference between the two examples that you show, it is a very good sign that you are in a discussion that is over your head.

Rick, the discussion is not over my head, but it is clearly over yours.

If I have two phasors Vna=120<180 and Vnb=120<0, and I want to combine them to find the resultant phasor across both, then this is correct:

Vna: A<--------------N = 120<180
Vnb: N-------------->B = 120<0

The combined phasor would be:

A<--------------N-------------->B

The resultant phasor by combination Vab would be:

A------------------------------->B

A<--------------N-------------->B Vab=Vnb-Vna= 120<0 - 120<180 = 240<0. You can see that the resultant phasor has the proper magnitude and angle when properly combined using subtraction of the component phasors based on the tail-to-tail configuration.

The diagram is correct and the result of the combination is correct. For you to suggest that it is wrong indicates that you do not understand anything about vector math.

Let's try another example. Let's say I had a vector A= 1<135 and a vector B=1<45, and I drew both of these vectors starting at a common origin. (Imagine this A<--------------N-------------->B, with A and B both turned "upwards" 45 degrees.) Now lets say I wanted to know the vector resulting across A to B. I would solve for AB by subtracting A from B. AB=B-A=1<45 - 1<135 = 1.414<0

Now lets say I wanted to know the vector resulting across B to A. I would solve for BA by subtracting B from A. BA=A-B= 1<135 - 1<45 = 1.414<180.

Now draw and measure a vector from A to B and from B to A. You will find the magnitude and angles of these drawn vectors are AB=1.414<0 and BA=1.414<180. For reference, see post #2373 for a diagram of these vectors.

It is interesting that the phasor "diagram" that you think is correct is not even a phasor diagram at all. It is a mathematical expression using vectors - Vector NB minus Vector NA equals Vector AB. The one I drew was as a response to pfalcon's "diagram" that you were so enamored with. The correct phasor diagram for Vector NB minus Vector NA equals Vector AB is the one that you think is incorrect. I would suggest that you study up on vectors.

 

[rattus]

You are incorrect, when you address the physical construction of a single center-tapped winding.
A single center tapped winding is like a delta (phasors are aligned point to tail).

There is no rule dictating a delta. I prefer the wye.

It is only your selection of a reference point that creates the condition of the phasors being point-point or tail-tail.

One is free to point his phasor arrows in one of two ways, regardless of the reference.

Because you seem to think you are better at phasors than some, if not most, of us.
Here is are some exercises:

a) Start with the given result of Vab@0?
Vab = |-------------------->

now subtract your voltage of 120@180?
Vbn = <----------|

Could you show us your resulting phasor and the steps it took you to get there?

b) Start with the given result of Vab@0?
Vab = |-------------------->

now subtract your voltage of 120@0?
Van = |---------->

Could you show us your resulting phasor and the steps it took you to get there?

Why don't I just show you how I obtain Vab?

Vab = Van - Vbn, all phasors

Van = 120Vrms @ 0
Vbn = 120Vrms @ PI

Vab = 120Vrms[cos(0) + jsin(0) -cos(PI) -jsin(PI)]

Vab = 120Vrms[+1 -(-1)] = 240Vrms

One can find the same result without a diagram:

Vab = Van - Vbn; potential difference is what we do in general

I might add that the values of Van and Vbn are unaffected by the way the phasor diagram is drawn.

Now we could end this silly discussion if you would just explain to us why you think Vab and Vbn are of the same phase even though they carry different phase constants. No tricks now.

BTW, Vab@0 is incorrect because Vab is a phasor in its own right. You are hanging an extra angle on a phasor.

 

[jim dungar]

There is no rule dictating a delta. I prefer the wye.

I acknowledge your freedom to do so, but that does not make it the correct method. The physical construction of a delta and wye are difference, the difference is important. Denying the physical reality is not good engineering.

Why don't I just show you how I obtain Vab?

NO.

You are ducking a simple valid question

As I have said before, the mathematics must work in all permutations regardless of the arbitrary assignment of direction.

Answer the subtraction questions I asked.
Show us your phasor diagrams.

Or if you are not as comfortable with phasors as you claim, then go ahead and use rectangular coordinates.
Vab -Van = Vw = 2V@0? - V@0? = V@X = 2V(cos0 +jsin0) - V(cos0+jsin0) = V(cosX+jsinX)
and
Vab -Vbn = Vz= 2V@0? - V@180? = V@Y = 2V(cos0 +jsin0) - V(cosPI+jsinPI) = V(cosY+jsinY)

 

[rattus]

I acknowledge your freedom to do so, but that does not make it the correct method. The physical construction of a delta and wye are difference, the difference is important. Denying the physical reality is not good engineering.

There is no correct method. As long as the correct result is obtained, anything goes, but I prefer tail to tail because the resulting diagram is balanced as is a wye diagram. No one is denying the physical reality, three coils are tied to the neutral in one case, two coils in the other.

NO.

You are ducking a simple valid question

As I have said before, the mathematics must work in all permutations regardless of the arbitrary assignment of direction.

Answer the subtraction questions I asked.
Show us your phasor diagrams.

Or if you are not as comfortable with phasors as you claim, then go ahead and use rectangular coordinates.
Vab -Van = Vw = 2V@0? - V@0? = V@X = 2V(cos0 +jsin0) - V(cos0+jsin0) = V(cosX+jsinX)
and
Vab -Vbn = Vz= 2V@0? - V@180? = V@Y = 2V(cos0 +jsin0) - V(cosPI+jsinPI) = V(cosY+jsinY)

I find your attitude condescending. I don't think I have boasted of being a phasor expert, and I don't feel compelled to defend myself. I don't wish to spend a lot of time on a silly exercise. I posted a simple phasor diagram, correct in every detail, and you and a couple of self-styled experts are tearing it apart. Why?

But what about my question? I have asked it previously and you have consistently ignored it. Can't you answer it?

 

[jim dungar]

There is no correct method.

did not say they was.

I don't think I have boasted of being a phasor expert, and I don't feel compelled to defend myself.

I have not claimed you boasted anything. I simply said you have given the impression that you feel you understand phasors better than others in this thread. I also gave you an option to use the polar coordinate method you have already demonstrated.

I don't wish to spend a lot of time on a silly exercise.

Why is it silly, Working on the premise of a single winding the voltage could be called Vab. That winding is then cut in half, so your analysis methodology should be capable of starting with a large voltage and subtracting a smaller one. In fact with the phasors I have posted I would think you could do it simply by using 'cut and paste'. But don't worry about, I am sure someone else will eventually attempt to answer it.

I posted a simple phasor diagram, correct in every detail, and you and a couple of self-styled experts are tearing it apart. Why?

Again I get teh impression you do not read what I post. David regularly uses my post where I defended your method of subtracting phasors when they are joined tail to tail.

But what about my question? I have asked it previously and you have consistently ignored it. Can't you answer it?

At the risk of offending you I need to play dumb, and ask which of one your questions concerning this single center-tapped winding, have I not answered?
Remember I have tried very hard not to get off on to tangential discussion of other waveforms and other phase or voltage relationships. The best guess I can make is it the question you have consistently asked about an inverse waveform, which I have repeatedly answered with an equality based on cutting a single winding into two dnetical halves.

 

[rattus]

did not say they was.

You certainly implied that the delta method was the correct method.

I have not claimed you boasted anything. I simply said you have given the impression that you feel you understand phasors better than others in this thread. I also gave you an option to use the polar coordinate method you have already demonstrated.

Why is it silly, Working on the premise of a single winding the voltage could be called Vab. That winding is then cut in half, so your analysis methodology should be capable of starting with a large voltage and subtracting a smaller one. In fact with the phasors I have posted I would think you could do it simply by using 'cut and paste'. But don't worry about, I am sure someone else will eventually attempt to answer it.

It is silly because I have already demonstrated my expertise, such as it is.

Again I get teh impression you do not read what I post. David regularly uses my post where I defended your method of subtracting phasors when they are joined tail to tail.

Yes, I read them.

At the risk of offending you I need to play dumb, and ask which of one your questions concerning this single center-tapped winding, have I not answered?
Remember I have tried very hard not to get off on to tangential discussion of other waveforms and other phase or voltage relationships. The best guess I can make is it the question you have consistently asked about an inverse waveform, which I have repeatedly answered with an equality based on cutting a single winding into two dnetical halves.

But the question is about an inequality:

Why do you claim that Van and Vbn are of the same phase even though their phase constants are different? They are NOT the same waveform.

or

Why do you think sin(wt) is of the same phase as [-sin(wt)] even though their phase constants are different? They are NOT the same waveform either.

A straight answer please.

 

[Rick Christopherson]

The diagram is correct and the result of the combination is correct. For you to suggest that it is wrong indicates that you do not understand anything about vector math.

Vna: A<--------------N = 120<180
Vnb: N-------------->B = 120<0

The combined phasor would be:

A<--------------N-------------->B

The resultant phasor by combination Vab would be:

A------------------------------->B

If you understood vectors as well as you thought you did, you would see that your combined phasors and resultant phasors would both equal zero, as you have drawn them. Vector math didn't start out in the electrical field, and it is universal to many of the sciences. The error of what you have drawn above might be more evident to you if you were to consider these vectors to represent physical forces acting on the body "N". Force A and Force B are acting in opposition on body N, and the net result of the forces on N would be zero.

Electrical system do not use vector math any differently than any other field. The fact that you have incorrectly applied vector mathematics is because you have become complacent with your skills.

 

[rattus]

If you understood vectors as well as you thought you did, you would see that your combined phasors and resultant phasors would both equal zero, as you have drawn them. Vector math didn't start out in the electrical field, and it is universal to many of the sciences. The error of what you have drawn above might be more evident to you if you were to consider these vectors to represent physical forces acting on the body "N". Force A and Force B are acting in opposition on body N, and the net result of the forces on N would be zero.

If they were "vectors" say forces, they would cancel, but they are not "vectors", they are phasors representing a voltage magnitude (always positive) and phase angle. The rules are different. You subtract one potential from the other to get the potential DIFFERENCE--phasorially that is.

Good reason to use the term "phasor" instead of "vector".