Why is residential wiring known as single phase?

[jim dungar]

No Jim, even rbalex agrees that inverses cannot be in phase. It just shows that one expression is just as real as the other.

Besoeker said the voltages must be 'in-phase' in order to be paralleled.
Mivey posted a graphic of Vleft being connected in parallel with Vright.
Ergo, per Besoeker, they must be in-phase.
This gives us Vleft=Vright as opposed to -Vright.

Gar and Rattus jump in and say 'you fool - don't you see' we changed the direction of the arbitrarily assigned arrows, therefore what you see is Vleft@180? and Vright@0? which means they are inverses.
Ooops, now we have Vleft=-Vright: which totally contradicts what Besoeker said and Mivey drew.

Ahhh they say, but we can deal that, we will also assign subscripts that point in opposite directions, just like our arrows: Vleft=Vbn and Vright=Vnb. Now we have inverted our opposites, thus we subtract Vbn instead of adding Vnb because we are smart enough to know about double negatives.

So we are left with a "real" connection of (2) sets of [two voltages in parallel] connected in additive series and a "real" arbitrary assignment of voltage directions.
One is an actual physicality.
One is an actual mathematical manipulation.

 

[Besoeker]

Not if they start and finish at the same time.

They do start and finish at the same time. But go in opposite directions.

Edit Add: What they actually have is a mutual amplitude displacement of 180deg

So you're expressing amplitude as a phase displacement??
Novel way of looking at it.

 

[Besoeker]

Besoeker said the voltages must be 'in-phase' in order to be paralleled.

Not entirely what I said, JD.

 

[Besoeker]

Every relevant voltage function however validly determined in a conventional 120/240V system, either initially or replaced by identiities, can be written in terms of the same phase.

In a three phase system, L₁, L₂, and L₃, I can write L₂ and L₃ in terms of L₁. That doesn't make them the same phase.

 

[rbalex]

They do start and finish at the same time. But go in opposite directions...

Yes - So how does that alter application of the definition of phase unless time runs backwards?

...So you're expressing amplitude as a phase displacement??
Novel way of looking at it.

No - I've said fairly consistently that amplitude and polarity aren't relevant to determing phase. They may be relevant to determining "in phase." The only direction phase is interested in is time - not motion.

 

[Besoeker]

That would be a real phase shift. No argument there.

But nothing actually gets phase shifted. Wasn't that a point you made a while back to support your assertions?

 

[Rick Christopherson]

But nothing actually gets phase shifted. Wasn't that a point you made a while back to support your assertions?

No, that is not a direct interpretation of my assertion. In the example that I later realized he (Mivey) was referring to, there is both a physical (real) and apparent (mathematical) phase shift. That is why it was a poor example.

If it is not clear what the difference is between a real and apparent phase shift, then please refer to my graphical example in post #1654. It has your name in that post, so it is directed equally at you.

 

[K8MHZ]

Does anyone know what the longest thread in MH's forum's history is? This thread has more posts than 50 percent of the MH forum user populace.

The question of 'why is it?' has morphed into 'why should it?' vs. 'why shouldn't it?' What amazes me is the length that some of you will go to in order to support your views. I find it commendable.

Boring and trite, but nonetheless commendable.

Now I know why the NEC is the size of a telephone book and growing faster than Jake on Two and a half Men.

:lol:

 

[rattus]

This was the defintion you supplied:



You do understand the conjunction or does not mean both, right? Nevertheless, assuming t₀ is the same for all functions and the periods are identical, (and they better be for a conventional 120/240V system) then the "fractional part of a period through which time or the associated time angle wt has advanced from an arbitrary reference" is identical for all phases. If "the associated time angle" (not the associated phase angle) ever has a negative value, you're up for a Nobel Prize in physics for discovering how to make time run backwards.

Yes, i have the option of measuring the fractional part of the period as t/T OR wt/wT. The fraction turns out to be the same, that's all.

Surely you know that you can measure positive or negative time relative to t0.

Refer to the excerpt from Kerchner and Corcoran which is attached. Look at fig. 5. At t = 0 , the angle has advanced by theta, that is the phase is theta at that instant. Actually, fig. 5 shows theta to be 1/12 of a period. For a given sine function, theta cannot be changed. It is the phi0 of the phase expression.



Where is the reference?

 

[jim dungar]

Not entirely what I said, JD.

Look back at post #963.

...
Yes, they have to be in phase to be paralleled. I don't think that was ever disputed.
....

 

[rbalex]

...No - I've said fairly consistently that amplitude and polarity aren't relevant to determing phase. They may be relevant to determining "in phase." The only direction phase is interested in is time - not motion.

Come to think of it phase is an element of amplitude for voltages of convential 120/240V systems. Amplitude just isn't an element of phase.

 

[rbalex]

Yes, i have the option of measuring the fractional part of the period as t/T OR wt/wT. The fraction turns out to be the same, that's all.

Surely you know that you can measure positive or negative time relative to t0.

Refer to the excerpt from Kerchner and Corcoran which is attached. Look at fig. 5. At t = 0 , the angle has advanced by theta, that is the phase is theta at that instant. Actually, fig. 5 shows theta to be 1/12 of a period. For a given sine function, theta cannot be changed. It is the phi0 of the phase expression.

Where is the reference?

But you don't have the option of indiscriminately substituting the associated phase angle" with the associated time angle, which is what you are doing now, just as you did with ϕ₀ = 0 or 180? in the past. Figure 5 is discussing the phase angle, not the time angle.

Frankly, with your history, a reference would just confuse you more.

 

[rattus]

But you don't have the option of indiscriminately substituting the associated phase angle" with the associated time angle, which is what you are doing now, just as you did with ϕ₀ = 0 or 180? in the past. Figure 5 is discussing the phase angle, not the time angle.

Frankly, with your history, a reference would just confuse you more.

I have the freedom to assign any value I wish to the phase angles. No one is changing the time angle, I presume you mean wt?

phase = (wt + phi0), I set phi0 to 0 for one wave, phi0 to PI for the other. Perfectly legal.

Well, confuse me then! One expects references from a PE/moderator instead of insults. Very unprofessional.

 

[rbalex]

I have the freedom to assign any value I wish to the phase angles. No actually you don't; you get to assign an arbitary t₀. No one is changing the time angle, I presume you mean wt? You tried to misdirect the discussion from phase to phase angle. As usual, you can't seem to recognize subtle differences.

phase = (wt + phi0), I set phi0 to 0 for one wave, phi0 to PI for the other. Fine, and if t₀ is the same for both, then the phase will be the same for both.

Well, confuse me then! I don't need to; you already are.

One expects references from a PE/moderator instead of insults.

One does not expect insults from a PE who is also a moderator.

I've already given you my PE perspective, and the concensus of the other moderators is that I've been rather mild. And where I believe I've been over the top, I've apologized.

 

[rattus]

I've already given you my PE perspective, and the concensus of the other moderators is that I've been rather mild. And where I believe I've been over the top, I've apologized.

But they are not the same. phi0 = 0 and 180 for the two waves. If they are the same, then the waves are in phase.

I believes all members are to be treated with respect. Apparently not.

I guess this means we won't see any references, nor we will understand why when we have a valid expression for phase, why we can't use it as is? Why do we have to 'reduce' it in the first place? I am so confused.

 

[gar]

120302-2124 EST

I may have found an indirect definition of what rbalex is using for his argument that "same phase" implies that a center tapped transformer is single phase.

From: http://en.wikipedia.org/wiki/Phase_(waves)

Phase in sinusoidal functions or in waves has two different, but closely related meanings. One is the initial angle of a sinusoidal function at its origin and is sometimes called phase offset. Another usage is the fraction of the wave cycle which has elapsed relative to the origin.[1]

Formula

The phase of an oscillation or wave refers to a sinusoidal function such as the following:

first is cos
second is sin

where , , and are constant parameters called the amplitude, frequency, and phase of the sinusoid. These functions are periodic with period , and they are identical except for a displacement of along the axis. The term phase can refer to several different things:

It can refer to a specified reference, such as , in which case we would say the phase of is , and the phase of is .
It can refer to , in which case we would say and have the same phase but are relative to their own specific references.
In the context of communication waveforms, the time-variant angle or its modulo value, is referred to as instantaneous phase, often just phase.

All the details do not copy so you have to go to the source.

One sentence has the world pair "same phase" and I believe this seems to correlate with what rbalex is saying. If you have two functions of time (t) with the same argument, then they are of the same phase.
Let:
f1(t) = sin (wt), and
f2(t) = sin (wt + 180) and this is also equal to - sin (wt),

Thus,
f1(t) = sin (wt), and
f2(t) = - sin (wt).
So the arguments of f1(t) and f2(t) can be written to be of the same phase because wt is the argument of both.

From here rbalex seems to classify "same phase" as meaning "single phase" even through there are two out-of-phase voltages. Why is it logical with this definition of "same phase" to conclude that it implies a single phase?

Now consider the two functions:
f1(t) = sin (wt), and
f2(t) = sin (wt + 90) = cos (wt),
So again f1(t) and f2(t) can be written so as to be classified as of the same phase, because the arguments are the same, and by the above logic of same meaning single we have a single phase system. But, I believe everyone here thinks this is a 90 degree two phase system.

Am I getting to the root of the problem?

.

 

[rattus]

120302-2124 EST

I may have found an indirect definition of what rbalex is using for his argument that "same phase" implies that a center tapped transformer is single phase.

From: http://en.wikipedia.org/wiki/Phase_(waves)

All the details do not copy so you have to go to the source.

One sentence has the word pair "same phase" and I believe this seems to correlate with what rbalex is saying. If you have two functions of time (t) with the same argument, then they are of the same phase.
Let:
f1(t) = sin (wt), and
f2(t) = sin (wt + 180) and this is also equal to - sin (wt),

Thus,
f1(t) = sin (wt), and
f2(t) = - sin (wt).
So the arguments of f1(t) and f2(t) can be written to be of the same phase because wt is the argument of both.

From here rbalex seems to classify "same phase" as meaning "single phase" even through there are two out-of-phase voltages. Why is it logical with this definition of "same phase" to conclude that it implies a single phase?

Now consider the two functions:
f1(t) = sin (wt), and
f2(t) = sin (wt + 90) = cos (wt),
So again f1(t) and f2(t) can be written so as to be classified as of the same phase, because the arguments are the same, and by the above logic of same meaning single we have a single phase system. But, I believe everyone here thinks this is a 90 degree two phase system.

Am I getting to the root of the problem?

.

gar, I found the same entry, but when we consider -sin(wt) we must consider the negative sign which is an operator if you will that shifts the wave 180 degrees back to sin(wt + 180).

I contend that (wt + 180) is the phase, it can't be (wt) as well. Plus no one to my knowledge has found any reference which supports this notion. In my several decades, I have never heard of it.

My burning question though is "Why do we need to 'reduce' sin(wt + 180) in the first place??

 

[mivey]

If the phase shift is real, then the output will not be inverted, but shifted by 1/2T (half period).

So you are talking about a time shift. I thought before you said you were not talking about a time shift. I agree there is no time shift.

 

[mivey]

Besoeker said the voltages must be 'in-phase' in order to be paralleled.
Mivey posted a graphic of Vleft being connected in parallel with Vright.
...
Ooops, now we have Vleft=-Vright: which totally contradicts what Besoeker said and Mivey drew.
...

Perhaps some terminal numbers will help you understand that what I drew is the same as what was said. I'll add them.

But to explain:

We have X1 and X0 terminals from the generator side (single-bushing transformers) and X1, X2, X3, and X4 terminals on the center tap transformer on the right. For one parallel set we have the following connections:
X1-X1
X0-X2

and for the other paralleled voltages we have these connections:
X0-X3
X1-X4

The directions are those given by using the "industry standard blah blah blah" terminal directions that you love so much.

So we are left with a "real" connection of (2) sets of [two voltages in parallel] connected in additive series and a "real" arbitrary assignment of voltage directions.
One is an actual physicality.
One is an actual mathematical manipulation.

There you go again, yet you want to protest when I say 'ergo' you make claims of "real" and "not real".

 

[mivey]

Not entirely what I said, JD.

I think JD is playing games and pretending he did not get what you said. I'm pretty sure he gets it.

It has been explained many times through discussions, graphs, and circuit diagrams that with phase-opposed voltages in the winding we are saying the positive of one waveform is in phase with the negative of the other. Those are the waveforms from the left side of my generator example.