Why is residential wiring known as single phase?

[gar]

120209-0959 EST

For clarification of what an is an oscilloscope I will describe a typical CRT (cathode ray tube) of the electrostatic deflection type.

The CRT has a more or less flat face coated with a phosphor that glows when and where an electron beam hits the screen. Internal to the tube there is a vacuum, thus nothing to obstruct electrons, an electron beam generator, and two sets of deflection plates perpendicular to each other.

The electron beam generator produces a very small diameter electron beam that is pointed toward the center of the screen. There are components in the electron beam generator to focus the beam to a small spot at the screen. Also there is a grid that can adjust the intensity of the beam and therefore the intensity of the spot on the screen. Thus, far there is just one small spot on the screen.

An electron beam passing thru an electrostatic field or magnetic field has its direction changed in proportion to that field intensity. Thus, if the beam is passed thru an adjustable electrostatic field (electric field, like in a capacitor), then the spot on the screen can be moved. If two sets of deflection plates are located inside the tube, but orientated so their electric fields are perpendicular to each other, then the spot on the screen can be positioned anywhere within some rectangular region on the screen.

With no amplifiers to confuse the issue we apply a sine wave from a single voltage source simultaneously to both sets of deflection plates the result is a Lissajous figure of a single straight line at 45 deg to horizontal. If the phasing of the signal to one set of plates is inverted (phase shift of 180 deg), then the angle of the straight line changes by 90 deg.

If the phasing of the two signals is 90 deg, then the result is a circle. Any other phase relationship produces an ellipse.

Next instead of placing a sine wave on the x-axis (typically horizontal) a linear sawtooth waveform is applied. Suppose its frequency is about 10 Hz, and not synchronized to anything, then in a linear fashion relative to time the beam moves from a point on the left side of the screen to a point on the right side in 1/10 second, and then immediately jumps back to the left side. Scopes are generally designed for increasing time going from left to right. What you see is a straight line of uniform brightness that is vertically in the middle of the screen.

Now apply to the y-axis (vertical) plates another signal. Make this signal a sawtooth of about 30 Hz. Now you see a sawtooth waveform on the on the screen of about 3 peaks and probably slowly drifting across the screen.

Change the horizontal sweep generator to one that can be synchronized to some other signal. This means make the starting point of its sweep start at a controlled point in time based on an external signal. Let that signal be the signal applied to the vertical axis and use the very rapid change of voltage of the y-axis sawtooth signal to be the trigger point. Now there will be exactly 3 saw teeth displayed on the screen without drift sideways.

Add a time delay from the trigger signal to when horizontal deflection starts and you can adjust the displayed starting point of the left side to any point on the vertical saw tooth.

Make the y-axis input a sine wave and the displayed waveform can start at any desired phase angle of the sine wave.

Thus, in the use of an oscilloscope to relate the phase of one signal to another it is important know what is the synchronizing signal and keep this a constant.

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[Rick Christopherson]

....then V1n and V2n are as Bes says antiphase. They don't just appear to be so, they are.

As long as you stated this while I was writing the above posting, I will expand on this further. The difference between Vn1 and V1n is an inversion. One of the two was the result of a polarity change by reversing the designation or test probe. We use a mathematical expression to say that sin(x) = -sin(x+180), but this expression is true only with a mathematically symmetrical function.

An "inversion" is true for any electrical waveform, but the "phase shift" is true only for most waveforms. It is therefore incorrect to say they are out of phase.

 

[jim dungar]

No, we are not saying N must be used. We are saying that it is convenient and logical to do so...

Are you saying my methodology is not logical or convenient?

I understand how circuits can be analyzed, and yet I have never found the need to use words like 'antiphase'. I do not need to explain how; 'out of phase voltages add' but 'out of phase currents subtract'. I do not need to change my math when a neutral conductor is not used by my load. I do not need to talk about positive and negative currents 'entering' a single 2-wire node. I do not choose to 'gloss over' the physics of the circuit, simply because the test equipment I choose to use is limited in its connections.

Imagine 2 windings connected in series X1->X2+Y1->Y2, or they are connected in series X1->X2+Y2<-Y1. Would the traces on Besoeker's two channel oscilloscope be sufficient to tell which connection is which?

 

[jim dungar]

Group 4 (me apparently): phase is not an electrical phenomenon; it is an applied mathematics concept. As long as the derived voltage functions [V(t)] with respect to time have the same phase value [φ(t) = ?t + φ₀], the functions are "in phase." They may not be in synchronism (all values the same at all times) but they are ?in phase.?

I guess I don't see this as fundamentally different than group 2.
I was trying to summarize.:ashamed1:

 

[rattus]

Edit: I didn't see Rattus' posting while I was typing, but he did this very thing. He claims that they are out of phase, when in reality, they only appear out of phase due to a mathematical equality that is true only for symmetrical waves.

Of course pure sinusoids are symmetrical, and phase angles only apply to pure sinusoids. Should I say instead the fundamental frequencies are out of phase? Do we say the phase angle of V1n appears to be zero?

We all know that a pure sinusoid is practically non-existent, but when analyzing a circuit we assume that the waves are pure. To do otherwise would greatly complicate circuit analysis.

To focus on such trivia is silly.

 

[mivey]

What if we had 2-loads but the common conductor was X1?

Then the 120 volt output would be in phase with the 240 volt output.

Are you saying they cannot be in-phase?

Of course they can be in phase.

The point I was trying to illustrate is that X1->X2 is not just a mirror image of X4->X3. They are separate waveforms and the direction of positive force can be separately taken either with a 0? displacement or a 180?displacement.

T.M seemed to be going down a path of reversing a 2-wire source and plotting the waveform along with the original waveform. That is strictly making a mirror image. In that case, there is only one current through the source and thus can be only one phase.

 

[mivey]

Actually there is direction. At any given instance, the pulse is pushing in one direction only - never in both directions.

And I have never said otherwise for most cases. I get what you are saying and I have agreed that two sources physically displaced by 180? will have their forces acting in synch (in phase, if you will). But you do realize that the forces in Besoeker's circuit only push in opposite directions for the winding halves? That should make it clear that the forces do not have to be used as positive forces in the same direction.

The correct reading on the oscilloscope is the distance between the curves yields the magnitude (peaking at |240V|) and the relative position of the lines at any given instance yields the polarity aka direction of the power flow.

Polarity and power flow direction are not the same thing. Also, polarity is an indicator of relative directions at a given instant in time but is not an indicator of what direction must be positive.

 

[Rick Christopherson]

To focus on such trivia is silly.

No it is not trivial. You have made a conscious effort to make the statement (requoted below) many times. If it has to have qualifiers, then it is not true as an absolute statement. Saying V1n=-Vn1 does not require any qualifiers for it to be true for all cases. It is an absolute statement. Saying V1n<0=Vn1<180 requires qualifiers to limit it to symmetrical waves. It is therefore not an absolute statement. (more below...)

They don't just appear to be so, they are.

When you state this, you turn the statement into an absolute. That is an incorrect statement because it requires qualifiers for it to be true.

 

[rattus]

Are you saying my methodology is not logical or convenient?

I understand how circuits can be analyzed, and yet I have never found the need to use words like 'antiphase'. I do not need to explain how; 'out of phase voltages add' but 'out of phase currents subtract'. I do not need to change my math when a neutral conductor is not used by my load. I do not need to talk about positive and negative currents 'entering' a single 2-wire node. I do not choose to 'gloss over' the physics of the circuit, simply because the test equipment I choose to use is limited in its connections.

Imagine 2 windings connected in series X1->X2+Y1->Y2, or they are connected in series X1->X2+Y2<-Y1. Would the traces on Besoeker's two channel oscilloscope be sufficient to tell which connection is which?

Didn't say a word about your methodology. As the old song says, "I did it my way", and you will no doubt.

Well yes. Using the tie point as a reference, the first case yields waveforms which are out of phase while the second set of waveforms are in phase. But you could use just a voltmeter. The first connection yields a voltage which is the sum of the two output voltages; the second yields the difference.

 

[mivey]

The DC case I gave is is a great comparison. It's the instantaneous description of the AC circuit when it's at peak. You can even build one and play around with it. Then when you want to see a different snapshot you can change the overall voltage or polarity. And if you were REALLY good a building things you could put the power adjustments on the circuit and generate your own imitation AC circuit by cycling the voltage.

The example you gave is a poor comparison. To even make it remotely workable you have to oscillate the battery directions at regular intervals. Without that, the idea of a phase difference does not exist for the DC example.

A multi-phase generator is still a single-source generator. Not the two separate generators I suggested.

Even the remaining two-phase stuff do not use that set up anymore so how is that relevant? All of it comes from multi-phase generators. In my previous postings, I have shown my 180? displaced generators being coupled through a common shaft.

 

[jim dungar]

The point I was trying to illustrate is that X1->X2 is not just a mirror image of X4->X3.

Yes they are from a center-tapped transformer. Yes they are for 99.99%(?) of commercially available transformers with re-connectable secondaries, built to ANSI/IEEE standards. And absolutely, it is possible that they may not be.

But it does not make a difference using my methodology. When I do my analysis, negative voltages and negative currents, tell me I have made some incorrect assumptions in regards to assigning directions.

 

[mivey]

Did I grossly misstate any position?

Probably close enough, but the underlying problem is as you noted a while back: the term "phase" is not being used the same way across the board.

 

[mivey]

I thinkt you missed something. I'm not sure what. But even if I did, it would still ultimately resolve to ?V_max sin (t + φ) [2]

BTW thanks for not ignoring it altogether.

I looked back through and my notes were correct. The problem is that you have moved part of the phase component and let it reside outside the sinusoidal expression (i.e., the negative sign).

Clearly, the original expression [2] Vmax sin (t + φ) is not the same as what I will call your revised expression [2] Vmax sin (t + φ ? 180?).

You can't conclude that the original [2] shifted by 180? degrees is just one equivalent expression ?Vmax sin (t + φ). What you really have is expression [2] shifted by 180? is -[2], like we would expect.

Vmax sin (t + φ) does not equal Vmax sin (t + φ ? 180?)
Vmax sin (t + φ ? 180?) does not equal ?Vmax sin (t + φ)

I think you got caught in a round-a-bout.

 

[rbalex]

I guess I don't see this as fundamentally different than group 2.
I was trying to summarize.:ashamed1:

My point from several earlier posts is, mathematically, the reference can be entirely arbitrary. The only significant factors are period and origin (which doesn't necessarily need to be a zero crossing) with respect to the question raised in the OP. The polarity, magnitude, neutral reference poiints, zero-crossings, etc. are very convienient analysis tools and certainly need to be observed with respect to circuit design but they are not essential in determining phase.

 

[mivey]

I don't know how anyone can understand basic electrical circuitry and know a little about transformers and not be in group #two.

Because there is a little more to it than basic electrical circuitry. Group #2 is correct in one respect in that the forces in the transformer are physically acting in the same direction for normal loads. But that view is limited in scope and does not give a complete picture. I do agree with part of what they are saying, and I understand why they hold to that view, but I also see that there is a broader picture not covered by the standard labels.

 

[rattus]

No it is not trivial. You have made a conscious effort to make the statement (requoted below) many times. If it has to have qualifiers, then it is not true as an absolute statement. Saying V1n=-Vn1 does not require any qualifiers for it to be true for all cases. It is an absolute statement. Saying V1n<0=Vn1<180 requires qualifiers to limit it to symmetrical waves. It is therefore not an absolute statement. (more below...)

When you state this, you turn the statement into an absolute. That is an incorrect statement because it requires qualifiers for it to be true.

Any competent engineer knows we are dealing with ideal waveforms. No need to qualify, no need to clutter up the language with trivia, no need to be pedantic about it or should I say nit-picking? And, who cares? Just a few nit-pickers. Silly and a waste of time.

 

[mivey]

Group 4 (me apparently): phase is not an electrical phenomenon; it is an applied mathematics concept.

And is the basis for the only technically correct use of the term "phase". The rest is essentially slang and is the source of much confusion.

 

[Rick Christopherson]

Any competent engineer knows we are dealing with ideal waveforms. No need to qualify, no need to clutter up the language with trivia, no need to be pedantic about it or should I say nit-picking? And, who cares? Just a few nit-pickers. Silly and a waste of time.

It's not nitpicking. You made a very specific and absolute statement, and it goes to the core of this discussion.

If it is just nitpicking, then you would have no problem retracting the statement, correct?

 

[jim dungar]

Probably close enough, but the underlying problem is as you noted a while back: the term "phase" is not being used the same way across the board.

Following the reasoning of the NEC, is there really a reason to define words that are commonly used.:roll:

For the vast majority of the time, there is no problem. But we need to understand the phraseology we use is rarely absolute, therefore when a question arises, we should switch to using very specific phraseology, maybe even including a definition or reference, and make no assumption the other person is 'speaking the same language'. Of course once we are back on familiar ground, we can go back to our old habits.

The one thing I wish was taught with more emphasis is that; adjectives are important.

 

[pfalcon]

Move your scope's reference point off the half mark (neutral) and show me your new scope graph. Then you can try your best to explain how the segment between your new reference and your old reference magically reversed phase. It doesn't, it can't, but that's what your scope will show.

Why would I want to do something stupid like that?

And why do you call it stupid? Unless of course you already know what you'll see and don't want to acknowledge it. And that would be that your definition of phase has nothing to do with electricity, just your eyeballs.