Why is residential wiring known as single phase?

[rattus]

Which definition was that? The "shell game - switch thing around indiscriminately " version or the "Just cause rattus sez so." version?

The informal definitions which are easier to understand:

"The argument of the sinusoid describing the wave", or

"The angular position of a wave."

 

[pfalcon]

To be in phase, waves must meet these criteria:
They must of course be of the same frequency.
They must start at the same time. That is their phase constants must be equal providing that both waves are expressed as sines (or cosines)
If their phase constants are equal, the phases of both waves are equal.

Givens

If the waves are NOT in phase, their phase constants differ, therefore their phases are NOT equal.
Then it follows that out of phase waves cannot carry equal phases.
Then a wave and its inverse cannot be of the same phase.
Specifically V1n and V2n CANNOT carry the same phase.
Therefore it is UNTRUE that all waveforms in an ideal split phase system carry the same phase.

Definition dependent.

You operate under the definition "Since I can measure different phase constants therefore they are different phases." Which is a common and acceptable definition for field work.
But as the voltage between V2 and N can be measured as 120<0 or 120<180 depending on which way you measure, are they really two different phases? Or just a point of observation?

 

[jim dungar]

Others make the claim that phase is the same for all voltages in an ideal system although the phase constants are clearly different.

I have not seen this claimed as a generality.
I have seen the claim that for the specific single phase transformer we have been discussing that there is only one phase constant.

I believe that you, Mivey and Besoeker have all agreed: Vbn=-Vnb.
Didn't Rbalex effectively write: sin(wt+180) = -sin(wt)?

How much math substitution and phasor rotation is needed before you acknowledge that one side of this specific equality equation can always be reduced to effectively sin(wt)?

 

[rattus]

But as the voltage between V2 and N can be measured as 120<0 or 120<180 depending on which way you measure, are they really two different phases? Or just a point of observation?

Yes, they are. However you observe them, the phases of the two waves are always 180 degrees apart. You could let the phase of one be (wt -90), then the other would be (wt + 90).

 

[rattus]

I have not seen this claimed as a generality.
I have seen the claim that for the specific single phase transformer we have been discussing that there is only one phase constant.

I believe that you, Mivey and Besoeker have all agreed: Vbn=-Vnb.
Didn't Rbalex effectively write: sin(wt+180) = -sin(wt)?

Yes he did misuse a trig identity to discard the phase constant, in this case 180 degrees. All this identity does is show that a sine wave, shifted by PI, is equivalent to its inverse.

Yes (wt) is the phase of PLUS sin(wt) which starts at 0, but it is not the phase of MINUS sin(wt) which starts at PI.

phase = (wt + phi) in simple terms! phi is set to 0 for one wave and 180 for its inverse, that's all.

 

[rattus]

Yes - So?

You have carried phi0 along in your 3-phase expressions instead of setting phi0 to 0, 120, and 240 for the three voltage waves. That is pointless.

Perhaps we should say phi1, phi2, and phi3. Makes sense.

 

[rbalex]

You have carried phi0 along in your 3-phase expressions instead of setting phi0 to 0, 120, and 240 for the three voltage waves. That is pointless.

Perhaps we should say phi1, phi2, and phi3. Makes sense.

Yes - So?

 

[rbalex]

The informal definitions which are easier to understand:

"The argument of the sinusoid describing the wave", or

"The angular position of a wave."

So it WAS the ol' switcheroo - You can go back to the "ignore with a clear conscience" corner.

 

[gar]

120307-1027 EST

pfalcon:

Can you put a shorting bar between leg A and leg B of a single phase transformer with a center tapped secondary while voltage is applied to the primary, and have near zero current flow in the shorting bar?

If there is significant current, then the voltages are not in-phase. For those that want to argue something about voltage level note that the center tapped secondary implies nearly equal voltage magnitudes on either side of the center tap.

.

 

[rattus]

So it WAS the ol' switcheroo - You can go back to the "ignore with a clear conscience" corner.

Yes, because they are all equivalent.

I like,

(wt + phi) is called the phase best! University of Tennessee.........

 

[pfalcon]

But as the voltage between V2 and N can be measured as 120<0 or 120<180 depending on which way you measure, are they really two different phases? Or just a point of observation?

Yes, they are. However you observe them, the phases of the two waves are always 180 degrees apart. You could let the phase of one be (wt -90), then the other would be (wt + 90).

And as you see, this is why you can't resolve your equations with Rbalex. V2 - N is a two wire circuit. There can only be one thing there. Hence it is a single phase system to one group. But it can be measured in two different directions. V_2n or V_n2 yielding two opposing sine waves which by a different definition are also called phases.

 

[rattus]

120307-1027 EST

pfalcon:

Can you put a shorting bar between leg A and leg B of a single phase transformer with a center tapped secondary while voltage is applied to the primary, and have near zero current flow in the shorting bar?

If there is significant current, then the voltages are not in-phase. For those that want to argue something about voltage level note that the center tapped secondary implies nearly equal voltage magnitudes on either side of the center tap.

.

Actually, if we assume an ideal system, the voltages would be absolutely equal, and for purposes of discussion we can do make that assumption.

 

[rattus]

Shocking!

Shocking!

I have been shocked by 120V; I have been shocked by 240V. If I must be shocked I prefer 120V.

 

[pfalcon]

pfalcon:
Can you put a shorting bar between leg A and leg B of a single phase transformer with a center tapped secondary while voltage is applied to the primary, and have near zero current flow in the shorting bar?
If there is significant current, then the voltages are not in-phase. For those that want to argue something about voltage level note that the center tapped secondary implies nearly equal voltage magnitudes on either side of the center tap.

Gar,
You need a literacy check. Look over the following closely. Better yet, follow it back for more detail.

Phase 1: The phase generated by the induction field that gives single-phase it's name.
Phase 2: The individual voltage readings that can be measured.
Phase 3: The individual current readings that can be measured.

Phase is an overloaded word just as the word duck is (duck beneath, also the water fowl). Therefore depending on which usage the poster is discussing may generate 1, 2, 4, 6, or infinite phases. All are legitimate answers depending on the usage in play. But only one usage gives the system it's name.

Your example states your position that you won't depart from (2) for a definition. Fine. Good. Congratulations. And (2) has nothing to do with the OP.

 

[pfalcon]

I have been shocked by 120V; I have been shocked by 240V. If I must be shocked I prefer 120V.

I would prefer by an old biker chick at Sturgis.

 

[rbalex]

And as you see, this is why you can't resolve your equations with Rbalex. V2 - N is a two wire circuit. There can only be one thing there. Hence it is a single phase system to one group. But it can be measured in two different directions. V_2n or V_n2 yielding two opposing sine waves which by a different definition are also called phases.

And on top of that:

sin(wt + 90) = -sin(wt-90) Or
sin(wt - 90) = -sin(wt+90)

Pick one from the left and one from the right and you have your two "phases" which may or may not include the mythical phase, depending on which ones you choose; however the system may still be be described in terms of one phase, either (NOT both) sin(wt + 90) OR sin (wt - 90), or for that matter (wt + 90) or (wt - 90).

 

[rbalex]

120307-1027 EST

pfalcon:

Can you put a shorting bar between leg A and leg B of a single phase transformer with a center tapped secondary while voltage is applied to the primary, and have near zero current flow in the shorting bar?

If there is significant current, then the voltages are not in-phase. For those that want to argue something about voltage level note that the center tapped secondary implies nearly equal voltage magnitudes on either side of the center tap.

.

Actually gar, I wouldn't put a shorting bar across the line terminals even if there wasn't a center tap - or between line and neutral if there was.

 

[rattus]

And on top of that:

sin(wt + 90) = -sin(wt-90) Or
sin(wt - 90) = -sin(wt+90)

Pick one from the left and one from the right and you have your two "phases" which may or may not include the mythical phase, depending on which ones you choose; however the system may still be be described in terms of one phase, either (NOT both) sin(wt + 90) OR sin (wt - 90), or for that matter (wt + 90) or (wt - 90).

Nonsense. There are TWO phases present, nothing mythical about it. We have long agreed though that the TWO phases are obtained by center tapping the transformer--the split phase system--and this system is known as a single phase system.

All voltages in the split phase system do not carry the same phase. In other words, the phase of

sin(wt + phi) is NOT wt except for the trivial case!

And, we CANNOT dump phi with tricky trig!

 

[jim dungar]

phase = (wt + phi) in simple terms! phi is set to 0 for one wave and 180 for its inverse, that's all.

Vbn=-Vnb

sin(wt+180)=-sin(wt+0): no dropped phis

So do you mean that -sin(wt+0) is not equal to -sin (wt)?

Or do you mean that -sin(wt+0) is not equal to sin(wt-180)?

 

[gar]

120307-1120 EST

If leg A to neutral and leg B to neutral were "in-phase" and of equal magnitude, then you could put the shorting bar between them. That is what you do when you parallel generators. But if they are not "in-phase" then there will be a large current, and obviously you would not short those terminals together.

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