Why is residential wiring known as single phase?

[pfalcon]

... From answers.com and Britannica Concise Encyclopedia
That clearly states that to be in phase a peak has to correspond with a peak and a trough with a trough. Note: crest is the positive peak, and trough is the negative peak.

Note: the use of positive zero crossing as a usual time reference for one wave.

The BCE definition clearly shows the post being stuck on surface wave mechanics.
The Sci-Tech is a much better quote.

So I place the reference lead of my oscilloscope on A (v1) and measure both N and B (v2). I get two synchronous waves with identical phase angle and proportional magnitude. According to the BCE definition and Sci-Tech definition they are both "In phase" and have the same "Phase relationship".

So I place one oscilloscope across A (v1) and N. Then I place another oscilloscope across N and B (v2). I get two IDENTICAL waveforms. By BCE and Sci-Tech they are "In phase" and have the same "Phase relationship".

I am now Sooo happy you've cleared this up Gar. :angel:

Maybe I should move my reference leads to B (v2)? Will that help de-synchronize them? Or are you telling me that by moving your leads around you are somehow controlling the phase angles?

BCE is running two different waves down two different water boxes for their definition. For our purposes it should be ONE water box with a mark halfway down the length called Neutral. It then becomes obvious that it's just one wave traveling as it does in this circuit. And a single wave cannot be out of phase with itself.

Sci-Tech also says that you have to follow the time propagation of the wave "from an arbitrary time origin" and move "in the positive direction". From an electrical standpoint that means:
1) Choose either A (v1) or B (v2) as the "origin" and the other end of the secondary coil as the positive direction.
2) Your reference lead must always be to the "origin" side of the test lead.
For Sci-Tech purposes you cannot use any point in-between as the origin because then you'd be going in the negative direction to test either A or B. That would invalidate the Sci-Tech definition.

 

[jim dungar]

Yes I would based on the way I referenced my currents. I don't see a problem with it.

So, they are out of phase only because you choose to reference them that way. Change your reference and they become in phase. So is one method real and the other just an appearance?

Lets say with your three load example you removed load #1 and load #2 so that only the load from B-N remained. Would you say that the load current "leaves" the source at N and "enters" the source at B. That sounds counter-intuitive to me for a B-N connected load...but it perfectly fine if that is the way you reference the currents.

Yes I would because of the way the transformers are connected. According to ANSI standards for transformer terminal designations; when current enters H1 on the primary, then the secondary current 'leaves' terminal X1 and 'enters' terminal X2.

 

[gar]

120203-1853 EST

At what electrical engineering universities is it being taught that waveforms being "in phase" are defined by coincident zero-crossings with no consideration of the slope at the zero-crossing?

The following does not define "in phase", but it certainly does not define a waveform that is an inversion of another as being "in phase"

"Electronics", by Milliman & Seeley, McGraw-Hill, second edition, 1951. Page 502

An inspection of Fig 17-5 reveals the following extremely significant result: If i_p is a sine wave , then i_p and e_pare exactly 180 deg out of phase with each other. This result follows from the fact that i_p is a maximum, whereas e_pis a minimum at the point 1.

From "The Radio Amateur's Handbook", 1978, page 387

Phase inversion.
...... In this circuit the voltage developed across the emitter resistor of Q1 is equal to, but 180 degrees out of phase ........

.

 

[Rick Christopherson]

So according to these discussions, if you have a resistor in a circuit, and you put one set of scope probes across the resistor from A to B, and the other channel across the resistor from B to A, you will see the same scope representation shown previously. Does this really mean that you have two out-of-phase waveforms across the terminals of that single resistor?

 

[gar]

120203-2113 EST

Rick:

Internal to the scope you do.

The phase inversion is a result of how you chose to amplify the signals. It will require a scope with at least one channel with differential capability. Or a switch on one channel that inverts that channel's signal.

Outside of this forum I have never heard anyone try to define a signal that is 180 deg out of phase with another signal as being in phase with that reference signal. To do so creates an unnecessary ambiguity, and has no good logical basis.

.

 

[jumper]

Cool thread. Off to the races..............

Mac presents graphs.

David does math.

Mivey explains well.

Gar presents solid arguments.

I am but a simple guy who twists wire nuts.....but I choose sides here, I can easily relate to their view. It is what I learned in school and I understand it.

And Rob Alexander keeps it real for both sides.:thumbsup:

I am done, one post and out. I am satisfied on this issue.:bye:

 

[Besoeker]

So, they are out of phase only because you choose to reference them that way.

V_an and V_bn are in anti-phase with reference to the neutral.
It makes complete sense to use the neutral as the reference. It is, after all, THE common point of a 120-0-120 system.
To get the two 120V sources to appear to be in phase, you'd have to use two different reference points. For me, that seems a bit perverse. But isn't that what you're suggesting?

Here's a picture of the power supply section of a PCB (amazing some of the stuff lurking in the bowels of my computer):

It produces ?24V unregulated and ?12V unregulated. If you measure between T66 (red lead) and T71, your meter would display -12V. You could, of course, measure from T71 (red lead) and your meter would display +12V. But wouldn't consider T71 to be the same voltage as T64. And that, it seems to me, to be the equivalent of viewing the two halves of the 120-0-120 winding as being in phase.

Here's another picture, again part of a PCB.

The 50-0-50 winding is used to time two SCR firing pulses 180deg apart. The two halves of the winding have to be 180deg apart, not in phase, for this to work - the circuitry following the transformers identical and use the same common zero as the transformer.
Single phase?
Not in my opinion.

 

[jim dungar]

It is, after all, THE common point of a 120-0-120 system.
To get the two 120V sources to appear to be in phase, you'd have to use two different reference points. For me, that seems a bit perverse. But isn't that what you're suggesting?

First I have consistenly said your choice of reference is exactley that, a choice.
I have been saying it is possible to consider the physics of the transformer and to follow industry standard terminal designations. But, you call this perverse.

Not in my opinion.

That is the core of the problem, every time someone wants to use Vnb, you tell them it is not 'allowed' and is even illogical, when in reality it is just an opinion.

I have tried to point out how it is pefectly allowable (having current enter and leave a node) and logically (i.e. consistently use a transformer winding's X1 terminal as the reference). But then someone jumps in and says, it is much better to simply insert a double negative into the math, maybe just because it fits the limitations of their measuring equipment.

When I program 3-phase electronic protection relays, it is imperative that I pay attention to how the circuit is wired. ANSI standards treat the system as if the current always leaves the X1 terminal, while in the IEC world sometimes the current enters X1 and sometimes it leaves (depending on if the circuit is a main or a feeder). If it is done different, the relay thinks the 'phase rotation' is reversed.

 

[Besoeker]

First I have consistenly said your choice of reference is exactley that, a choice.

But an entirely sensible choice of reference given that the centre-tap or connection between the two windings in a 120-0-120 system is only common point.

 

[Rick Christopherson]

The 50-0-50 winding is used to time two SCR firing pulses 180deg apart. The two halves of the winding have to be 180deg apart, not in phase, for this to work - the circuitry following the transformers identical and use the same common zero as the transformer.

Here's where you go wrong. You define the system by the manner you have "chosen" to measure it, and you set that definition as though it was absolute. The two windings appear out of phase only because you have chosen to measure it that way. Does this mean the system doesn't work when you are not measuring it?

How you chose to examine a system is your choice. Redefining the system based on that choice is wrong. It's fine when you're working alone in your basement, but is very poor engineering when you have to collaborate with others.

By the way, regardless of choice, it is incorrect to say the two windings are out of phase. Only your two chosen voltage references are out of phase. That's the difference between redefining the system versus choosing how you wish to measure it.

 

[Besoeker]

Here's where you go wrong. You define the system by the manner you have "chosen" to measure it, and you set that definition as though it was absolute.

Regardless of how I measure it, the diagrams in post #227 are real circuits in operation in hundreds of applications.
The second circuit I presented produces two SCR firing pulses at 180deg intervals.
That requires the two halves of the winding to be mutually displaced by 180deg wrt to the zero. Were it not so, the circuit wouldn't produce the required outputs.
But it does.
Regardless of how I or anyone else wishes measures it, it works.

 

[Besoeker]

So according to these discussions, if you have a resistor in a circuit, and you put one set of scope probes across the resistor from A to B, and the other channel across the resistor from B to A, you will see the same scope representation shown previously. Does this really mean that you have two out-of-phase waveforms across the terminals of that single resistor?

You'd just knacker the the average scope if you did that.

 

[rattus]

SIMPLY PUT

SIMPLY PUT

If one defines V1n and V2n relative to N, then they ARE out of phase by 180 degrees; they do not just appear to be so!

If one swaps the leads on V2n say, one measures Vn2 which IS in phase with V1n, but Vn2 is a DIFFERENT voltage albeit of the same magnitude.

There is no justification in claiming there is only one way to measure a voltage, and this has nothing to do with the fact that the voltages are provided by the same xfrmer.

 

[Rick Christopherson]

If one defines V1n and V2n relative to N, then they ARE out of phase by 180 degrees; they do not just appear to be so!

No. Technically that is a polarity reversal. We say it is "equivalent" to a 180 degree phase shift, but it is not the same. I brought this up months ago, and not a single one of you guys would touch it. It is only true when you have an electrical wave that is purely symmetrical about 180 degrees. The sine function is mathematically symmetrical, but electrical waves are not pure mathematical sine waves. The example I gave several months ago was a mechanical tick (noise) in a generator that repeats every 360 degrees or longer. It breaks symmetry and reveals that your 180 degree shift is actually a polarity reversal.

 

[rattus]

No. Technically that is a polarity reversal. We say it is "equivalent" to a 180 degree phase shift, but it is not the same. I brought this up months ago, and not a single one of you guys would touch it. It is only true when you have an electrical wave that is purely symmetrical about 180 degrees. The sine function is mathematically symmetrical, but electrical waves are not pure mathematical sine waves. The example I gave several months ago was a mechanical tick (noise) in a generator that repeats every 360 degrees or longer. It breaks symmetry and reveals that your 180 degree shift is actually a polarity reversal.

We are of course discussing an ideal sinusoid. It would be near impossible to obtain an absolutely pure sinusoid. So, we need not distinguish between a phase shift and an inversion.

 

[Rick Christopherson]

I'm not contesting the principles. I am contesting the absolute statements that some people have made in this discussion. If it carries conditions, then it should not be stated as an absolute. Reversing test probes is a polarity change. Assigning a phase angle to a polarity change is a mathematical equivalence, but it is not an absolute.

 

[rattus]

Nit Picking!

Nit Picking!

I'm not contesting the principles. I am contesting the absolute statements that some people have made in this discussion. If it carries conditions, then it should not be stated as an absolute. Reversing test probes is a polarity change. Assigning a phase angle to a polarity change is a mathematical equivalence, but it is not an absolute.

Whenever we discuss phase angles, we know that the ideal case (or the fundamental) is assumed. There is no need to qualify things further.

 

[Rick Christopherson]

I am not contesting your assumption. I am contesting your absolute statement. Don't state absolutes if they have conditions. It wasn't simply a matter that you "lightly misspoke". You emphatically stated it as an unequivocal absolute.

 

[jim dungar]

There is no justification in claiming there is only one way to measure a voltage...

Yet that is just what Besoeker appears to be claiming.
How did he put it? Oh yeah, choosing to not use the neutral is 'perverse'.


And really, we don't need to get into the whole Vbn = -Vnb, because I am pretty sure no one has said otherwise.

Face North, Put the car in drive and go forward or face South, put it in reverse and go backwards: different choices that still result in a single real/actual direction of North.

 

[Besoeker]

Yet that is just what Besoeker appears to be claiming.
How did he put it? Oh yeah, choosing to not use the neutral is 'perverse'.

That's not claiming that you can't.
Just that makes no sense NOT to use the ONE single common point of a 120-0-120 system as the reference for the measurement of the voltages. You seem to be suggesting that using two different reference points for the measurements is fine. That's what I'm suggesting is perverse. Mais, chacun ? son go?t.....