Split phase service--one or two?

[Rick Christopherson]

These statements are absolute because they still hold true regardless where your chosen reference point exists. Your statements are true only for a specifically chosen reference point. They are therefore, relative statements.

To follow-up further; for any point, C, in electrical space, your statements that the "voltages are phase opposed" is true, if and only if, A>C>B or A<C<B. For all other reference points C, your statements are false. That is why your statement that the "voltages are phase-opposed" is relative, and not absolute.

The relationships that A>N>B and A<N<B is absolute, because these statements hold true for all reference points C, including when C=N or when C lies outside of A and B.

 

[ggunn]

We know that. But, the voltages in question carry DIFFERENT phase angles, ergo they must be of DIFFERENT phases--just like in three phase.

There is nothing in the definition of phase that even hints that the voltages (or currents) must have a common ancestor.

Whatever. I was just pointing out a difference between split phase and three phase. In split phase you can derive the other waveform or the parent from either one of them, but that is not true of three phase.

Call it whatever you want, but I'm not going to call 240/120 "two phase" when I'm talking to our master electrician and have him look at me like I am an idiot.

 

[rattus]

Whatever. I was just pointing out a difference between split phase and three phase. In split phase you can derive the other waveform or the parent from either one of them, but that is not true of three phase.

Call it whatever you want, but I'm not going to call 240/120 "two phase" when I'm talking to our master electrician and have him look at me like I am an idiot.

No one is asking you to do that. For perhaps the 100th time, the point has been made that we still call it a single phase service even if two phases are present.

 

[ggunn]

No one is asking you to do that. For perhaps the 100th time, the point has been made that we still call it a single phase service even if two phases are present.

So then, what IS the point of all this???

 

[rattus]

So then, what IS the point of all this???

The point is that some members claim that a voltage and its inverse are of the same phase. The gang of four claims that the split phase service splits the single phase into two phases PI radians apart. We see them on the scope, therefore we think they are real.

 

[Rick Christopherson]

We see them on the scope, therefore we think they are real.

I thought "Real" was forbidden from your discussion?

 

[ggunn]

The point is that some members claim that a voltage and its inverse are of the same phase. The gang of four claims that the split phase service splits the single phase into two phases PI radians apart. We see them on the scope, therefore we think they are real.

What practical difference does it make? Tomayto, tomahto.

 

[jim dungar]

No hidden negative has to be present. I can produce these results by spinning the shaft on a generator through a 180? turn.

Swapping the position of a generator shaft is a physical change, swapping reference points is not.

Given any two points X & Y, there is a single voltage difference between them (i.e. V).
You may arbitrarily assign a direction to this single voltage, giving you a single magnitude and a reference direction (i.e. Vyx), but you still only have the single voltage, V.
You may also assign a mathematical equivalency such as Vxy = -Vyx, but you still only have a single voltage V

You can also arbitrarily assign an angle to this single voltage creating a reference phasor (i.e. V@0?), but you still only have a single voltage, V.
You can take the conjugate (colloquially referred to as the inverse) of the phasor (i.e. V@180?), but you still only have a single voltage, V.

You can also arbitrarily assign your phasor angle to your reference direction (i.e. V@180?=Vxy=Vxy@180?), you now have two directions but you still only have a single voltage, V.

If you relate your direction to the angle then, reversing (inverting) the reference direction is different than conjugating (inverting) the angle, but you still only have a single voltage, V.
Vxy@180? invert (opposite) direction yields -Vxy@180?=Vyx@180?
Vxy@180? invert (conjugate) angle yields Vxy@0?
Vxy@180? invert direction and invert angle yields Vyx@0?

 

[jim dungar]

What practical difference does it make?

For one, the series interconnection versus the parallel interconnection of a single phase reconnectable transformer output.
Given terminals X1-X2 and X3-X4, does it make sense to say the (2) 120V voltages are 'out-of-phase' when connected in series but they 'in-phase' when connected in parallel?

 

[rattus]

For one, the series interconnection versus the parallel interconnection of a single phase reconnectable transformer output.
Given terminals X1-X2 and X3-X4, does it make sense to say the (2) 120V voltages are 'out-of-phase' when connected in series but they 'in-phase' when connected in parallel?

Well yes it does make sense, but we are only interested in the 'series' connection. If we want to know the voltages on L1 and on L2 we must specify them as V1n and V2n. We choose 'n' as a reference because it is the logical choice. We do not want the voltages, Vn1 or Vn2.

You must admit that if we define our voltages as V1n and V2n, we see two voltages separated by PI radians. We see them on a scope. That is real enough for me.

Please, no more transformer lectures.

 

[Rick Christopherson]

We choose 'n' as a reference because it is the logical choice.

Actually, it is not a logical choice, because this is a 120/240 volt system, and your 240 volt loads do not share this common reference point.

 

[rattus]

Actually, it is not a logical choice, because this is a 120/240 volt system, and your 240 volt loads do not share this common reference point.

Actually it is, because we are discussing V1n and V2n ONLY!

 

[Rick Christopherson]

Actually it is, because we are discussing V1n and V2n ONLY!

Oh. Another limitation. Will there be anything left once you are done adding limitations?

 

[jim dungar]

Please, no more transformer lectures.

The previous thread asked specifically about transformer outputs, so I tried to keep my focus on that condition.

You seem to still be in the process of defining conditions for this thread.

 

[ggunn]

Well yes it does make sense, but we are only interested in the 'series' connection. If we want to know the voltages on L1 and on L2 we must specify them as V1n and V2n. We choose 'n' as a reference because it is the logical choice. We do not want the voltages, Vn1 or Vn2.

You must admit that if we define our voltages as V1n and V2n, we see two voltages separated by PI radians. We see them on a scope. That is real enough for me.

That's not what I see. I see a sine wave and its inverse.

 

[rattus]

That's not what I see. I see a sine wave and its inverse.

[-sin(wt)] = sin(wt +/- PI)

Check it out.

 

[rattus]

The previous thread asked specifically about transformer outputs, so I tried to keep my focus on that condition.

You seem to still be in the process of defining conditions for this thread.

Jim, I think most of us understand basic transformer theory.

Yes, I will define conditions for my postings to be sure everyone understands what I am saying.

 

[gar]

120404-0814 EDT

In my post numbered 4 I asked the question ---
"What does electron flow have to do with the phase difference of two waveforms?"

Your response was

Because electron flow is absolute and cannot be altered by changing reference points. ----

This does not answer my question.

.

 

[ggunn]

[-sin(wt)] = sin(wt +/- PI)

Check it out.

Of course I know that mathematically they are equivalent. I know that if you invert a pure sine wave or if you shift it by an odd multiple of pi it looks the same. Duh. But phase shifting only works for the special case of a pure sine wave while inverting the waveform works for the general case. Any waveform, any frequency or combination of frequencies. The math as you present it is a simplistic model that predicts what the waveforms look like, and it breaks down if you feed it anything more complex than a simple sine wave. Yeah, I know, all you want to talk about is a simple sine wave and for that restricted case it works. That's OK by me. No skin off my nose.

But I don't think that there is any doubt in anyone's mind that what is physically happening in our all too familiar center tapped transformer is an inversion, not a time based phase shift (i.e., delay). I use this same type of transformer (though much smaller, of course) all the time in my audio work to generate a balanced (complementary) signal from an unbalanced one. If you look at those waveforms you will see that no amount of phase shift will produce the complement of a complex waveform. Still, in audio many folks who should know better erroneously refer to an inversion of an audio signal as generating a signal which is "180 degrees out of phase". Whatcha gonna do? We all know what it means even if it is technically incorrect. But I digress...

I know that mathematically it makes no difference whatsoever whether you use -sin(wt) or sin(wt+PI) (or sin(wt+3PI) or sin(wt+(10^31+1)PI), for that matter) to represent the complementary waveform in the case of a pure sine wave, but -sin(wt) describes more accurately what is physically happening in the transformer.

 

[Rick Christopherson]

120404-0814 EDT

In my post numbered 4 I asked the question ---
"What does electron flow have to do with the phase difference of two waveforms?"

That's because it has been stated so many times in these discussions that the phase shift is real; The phase shift is not an inversion; The phase shift is not mathematical; The phase shift is not the result of a double-negative. And then to make everything work out and look pretty, the current has to be shifted too.

It's the same reason why they scurried into the shadows over the noise analogy. It reveals that the phase shift is apparent and mathematical, and not physical. Two cross sections cut in each of the windings will show that the electrons are flowing in the same direction, regardless of their chosen points of reference.

We used to think that the Earth was the center of the Universe. This meant that stars and galaxies had to be spinning around us at incomprehensible speeds. Speeds that had to exceed the speed of light. We now know this to be false. We now know this to be a mathematical perspective that does not conform with the physical universe and the laws of the universe. Thankfully, someone was smart enough to figure this out several hundred years ago, even though they were under great pressure from the older-folk of the time to keep thinking of things in the same manner that they considered true for millennia.

Mathematically, the Earth can be modeled as the center of the universe. But thankfully, more intelligent minds prevailed, and we have come to realize that this is only a mathematical perspective that does not hold true for absolute perspectives. If only.......:dunce: