Why is residential wiring known as single phase?

[pfalcon]

... There is no "forward" and "backward". Our assignment of these designations is the whole problem. AC is b-directional and there is no "correct" direction. Each voltage can be used with either direction providing providing a positive "push of force". ...

Actually there is direction. At any given instance, the pulse is pushing in one direction only - never in both directions. Using peak and trough; At the 240V peak the push is from one end of the winding uniformly to the other end of the winding. Presuming that A is the instantaneous source then the push is flowing from A through N to B. At the trough then the push is flowing from B through N to A.

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.

 

[pfalcon]

You seem to be equating 2 phase angles to 2-phase service. Van and Vbn carry different phase angles. That does not mean we have a 2-phase source. Neither does the 208V @ 90 in a high leg delta mean we have a 4-phase service.
Whatever, it is nonsense to claim Van and Vbn are not antiphase when the scope traces show clearly that they are. It is more nonsense to claim they merely appear to be so.

You are jousting with windmills.

Are you sure you read my post? Nowhere did I mention 2-phase service, 4-phase service, high leg delta's, or any other such thing. Nor will I. They are irrelevant to the discussion.

An oscilloscope does not actually show phase. It shows the potential difference of the two points relative to the reference. Thereby A & B have a peak potential difference of the distance between the lines. It also shows their relative "direction" at any given instance. Which means the direction the power will flow between the two points at that specific instance of time. That's why properly interpreted you can place the reference ANYWHERE on the secondary winding and get the correct interpretation. Because it will always display a +240 to -240 swing between the two points.

 

[pfalcon]

But in the DC case we have no other phase option so it is not really a good comparison. DC does not change direction like AC.

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 power gets pulled down on a multi-phase generator when one phase is drug down as well. The whole unit is affected.

A multi-phase generator is still a single-source generator. Not the two separate generators I suggested. A multi-phase will also feed back reactance forces and force synchronization just as the residential circuit will. Separate generators separate the reactance and allow the two legs to pull-down independantly as well as de-synchronize.

 

[pfalcon]

Because your membership card has expired. For a nominal fee, I'll get you up to date.

:rotflmao:

 

[topgone]

. . . . . . . . . . .. . . . . . . . . . . . . .
The question on this thread was "Why is residential wiring known as single phase?". The question was undoubtedly asked for the same reason you keep defending, and no one is really questioning. When metered or scoped it appears to be two opposing phases. And when used it works like two opposing phases. So why, when it quacks like a duck and looks like a duck is it not called a duck?
. . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The thread is becoming a back and forth exchange of ideas and perhaps somebody needs to wrap things up and synthesize what has been said all along! I sometimes get to reading seriously that I don't seem to get how the way things are going! Imagine how we can't arrive at a simple understanding of a "single" phase!

On that duck thingy, perhaps it looks like a duck and honks like a duck - - - - - - but it is a gander!:lol::lol:

 

[jim dungar]

... wrap things up and synthesize what has been said all along!

Group 1: single phase 120/240V = (2) out of phase voltages.
Group 2: single phase 120/240V = (2) in phase voltages that can appear to be out of phase when the neutral is chosen as the reference point.
Group 3(?): single phase 120/240V = out of phase voltages and in phase voltages depending on how the load is wired.

Did I grossly misstate any position?

 

[rbalex]

Unless I missed something, you should not have a double "?". You have u ? v = u ? (? 180). I think it should be (modifying your post):

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.

 

[rattus]

The thread is becoming a back and forth exchange of ideas and perhaps somebody needs to wrap things up and synthesize what has been said all along! I sometimes get to reading seriously that I don't seem to get how the way things are going! Imagine how we can't arrive at a simple understanding of a "single" phase!

On that duck thingy, perhaps it looks like a duck and honks like a duck - - - - - - but it is a gander!:lol::lol:

It is 1-phase because the ducks are separated by 180 degrees although the ducks have the same mother. If the ducks were separated by 90 degrees, we could call it 2-phase. And the windmills keep turning, turning, turning,..........

It is still more nonsense to say a scope doesn't indicate phase. We can tell at a glance that V1n and V2n are antiphase or in phase. For other phase angles we can easily calculate the phase angle from the time displacement.

 

[Rick Christopherson]

It is still more nonsense to say a scope doesn't indicate phase.

What's more nonsensical is basing your definition of the world on the viewpoint of a tool. That is the equivalent of saying the world is black and white because you saw a black and white photograph of it.

 

[gar]

120208-2020 EST

Consider the following:

A black box is fed by a single phase source. The box has 4 output terminals, and a continuously adjustable knob with graduations from 0 thru 360.

One pair of terminals has an output voltage of V and a frequency of F.

The first pair of terminals always remains in a fixed phase relationship with the source.

The second pair of terminals has a voltage and frequency identical to the first pair of terminals, but the phase difference between the two output voltages is continuously adjustable from 0 thru 360 with the knob.

Are these outputs two phases or a single phase? And why?

.

 

[topgone]

Group 1: single phase 120/240V = (2) out of phase voltages.
Group 2: single phase 120/240V = (2) in phase voltages that can appear to be out of phase when the neutral is chosen as the reference point.
Group 3(?): single phase 120/240V = out of phase voltages and in phase voltages depending on how the load is wired.

Did I grossly misstate any position?

That's kinda easier to follow. Thanks.

 

[ronaldrc]

I've got to put my last two cents in.

Viewing this thread you would never think it. But this forum is the most informative conversations I have ever
conversed with, not all but most have forgotten more than I will ever know.

I how ever would have like to have had three more opinions all three could have steered me in another direction.

Those where Bennie Palmer,Electric Edd and Larry Fine. By far three of the most knowledgible.

I think they all would have been in, group no. Two with myself.

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

Just my opinion:Ronald

 

[rattus]

120208-2020 EST

Consider the following:

A black box is fed by a single phase source. The box has 4 output terminals, and a continuously adjustable knob with graduations from 0 thru 360.

One pair of terminals has an output voltage of V and a frequency of F.

The first pair of terminals always remains in a fixed phase relationship with the source.

The second pair of terminals has a voltage and frequency identical to the first pair of terminals, but the phase difference between the two output voltages is continuously adjustable from 0 thru 360 with the knob.

Are these outputs two phases or a single phase? And why?

.

Presuming the outputs are stiff enough, one could obtain a true 2-phase system at 90 degrees, either four wire or three wire. One could then increase the separation to 180 degrees and obtain a 3-wire V/2V system.

The first case is 2-phase because it can drive 2-phase loads, namely motors.

The second is 1-phase because the 180 degree phase shift cannot drive any polyphase loads.

Any other phase separation is undefined.

 

[Besoeker]

N would still be common to node A and node B

Sloppy.
N would still be the common for node A and node B

 

[Besoeker]

What's more nonsensical is basing your definition of the world on the viewpoint of a tool.

If you wanted to connect a three phase motor to a supply and direction of rotation was important you might want to use a phase rotation meter. Would you accept what it told you?
I routinely deal with power electronics where correct phase rotation is required for proper functioning of the equipment. I use an oscilloscope to check phase rotation and the relative timing of trigger pulses.
Nonsensical?

 

[pfalcon]

It is still more nonsense to say a scope doesn't indicate phase.

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.

It's not showing phase, it's showing differential voltage to your current reference point and the instantaneous direction of power flow relative to that point. Which is why, when you set it up on A or B it's all in sync and flowing in the same direction. The phase isn't reversing even though it appears to have reversed. You're presuming your scope provides more information than it does.

This is not to say it cannot be used to measure phase. But you've got to understand what you're really connected to rather than what you want to see.

 

[rattus]

Why, to the source neutral reference that Besoeker and Rattus seem to insist must be used.

No, we are not saying N must be used. We are saying that it is convenient and logical to do so, then V1n and V2n are as Bes says antiphase. They don't just appear to be so, they are. After all, V1n and V2n are what is seen on the bus bars in a residential panel.

 

[rattus]

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?

 

[rbalex]

Group 1: single phase 120/240V = (2) out of phase voltages.
Group 2: single phase 120/240V = (2) in phase voltages that can appear to be out of phase when the neutral is chosen as the reference point.
Group 3(?): single phase 120/240V = out of phase voltages and in phase voltages depending on how the load is wired.

Did I grossly misstate any position?

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.”

 

[Rick Christopherson]

If you wanted to connect a three phase motor to a supply and direction of rotation was important you might want to use a phase rotation meter. Would you accept what it told you?
I routinely deal with power electronics where correct phase rotation is required for proper functioning of the equipment. I use an oscilloscope to check phase rotation and the relative timing of trigger pulses.
Nonsensical?

What you said in this posting is related to "observing" the system. What you have stated in the other postings is related to "defining" the system. When you use a "relative observation" and mistakenly use it to create an "absolute definition", it changes the system. An absolute definition must be true regardless who is observing it and from what perspective it is being observed. Saying V1 and V2 are 180 degrees out of phase with respect to N, is a relative observation of the system. Saying the two windings are out of phase is an absolute definition, but is only true from one perspective, and therefore, false as an absolute.

Taking that farther, the same is true with the voltage designations. It is OK to say V_an and V_bn appear to be out of phase, but it is not correct to say V_an and V_bn are out of phase. The distinction is because the statement is not true for every case. The proper way to state this is that V_an and V_bn are inverse, and a mathematical transformation allows us to view them as 180 degrees out of phase.

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.