May I ask a question about the single vs two phase stuff

[LarryFine]

So the only 240/120V with or without neutral is incapable of producing a rotating magnetic field by itself and so must be a single phase system.

That's always been my take.

Two lines from a wye supply with the neutral can supply two transformers and create an open delta, but two lines alone are definitely a single-phase source.

 

[Besoeker]

That's always been my take.

Two lines from a wye supply with the neutral can supply two transformers and create an open delta, but two lines alone are definitely a single-phase source.

The 120-0-120 arrangement is two lines phase displaced by 180° plus a neutral.
I think we can all agree on that.

 

[GoldDigger]

The 120-0-120 arrangement is two lines phase displaced by 180° plus a neutral.
I think we can all agree on that.

Actually, I am afraid we can't. :happysad:
Some say that 120-0-120 has two line to neutral voltages, of which one is the negative of the other. Others say that it has two line to neutral voltages offset in phase by 180 degrees. The two are equivalent for pure sine waves and ones with symmetry about the 90 degree time point. But if the basic waveform is sufficiently far from ideal (a sawtooth wave is a good example to look at) the two descriptions (negative versus 180 degree phase shift) are not identical.












[/B] equivalent.

 

[LarryFine]

The 120-0-120 arrangement is two lines phase displaced by 180° plus a neutral.
I think we can all agree on that.

I agree that we can't. The only application of 180 degrees is to refer to instantaneous polarity, and that's only because of the choice to use the center tap as a stationary reference point. There is no displacement.

Added: If viewed on a dual-channel o-scope, the two waves might appear displaced in time, but the fact is they rise and fall in sync in opposite directions from zero simultaneously; thus, it's a matter of polarity.


You really need to find and read that incredibly long thread we did.

 

[Besoeker]

Actually, I am afraid we can't. :happysad:
Some say that 120-0-120 has two line to neutral voltages, of which one is the negative of the other. Others say that it has two line to neutral voltages offset in phase by 180 degrees. The two are equivalent for pure sine waves and ones with symmetry about the 90 degree time point. But if the basic waveform is sufficiently far from ideal (a sawtooth wave is a good example to look at) the two descriptions (negative versus 180 degree phase shift) are not identical.
[/B] equivalent.

Yes. Two. Displaced in phase.
i.e. not the same phase.

 

[jaggedben]

The 120-0-120 arrangement is two lines phase displaced by 180° plus a neutral.
I think we can all agree on that.

I wonder if you will get anyone to agree with that.

The two hot legs brought by themselves without the neutral have a voltage which isn't displaced from anything.

 

[ggunn]

The 120-0-120 arrangement is two lines phase displaced by 180° plus a neutral.
I think we can all agree on that.

You're new around here, aren't ya'?

(I know you aren't)

 

[jaggedben]

So the only 240/120V with or without neutral is incapable of producing a rotating magnetic field by itself and so must be a single phase system.

...

Think about it: The 3-wire quadrature two-phase we get from a transformer bank is just the 120/208 system shifted from 120d to 90d. We could also call 120/208 two-phase except that the name has already been taken by the quadrature two-phase system.

Here we are (finally?) getting back to what the OP was actually asking about. How can 120/240 be considered more than one phase if it is incapable of producing a rotational field? If that's what single phase means (no rotational field) then 120/240 is single phase. But I doubt that we can get Boeseker to agree that that's the meaning.

To that point, Mivey, you're exactly correct that the three wire quadrature two-phase is qualitatively similar to the 120/208 3-wire system. But I don't agree that the latter is not called 'two-phase' because the name is already taken. After, all, a lot of utilities call it 'single phase' and that name was already taken, too. Which just proves that people have been using disparate conventions for too long, and this will never get resolved. At least not in a free society. I concede the point on that.

 

[Besoeker]

I wonder if you will get anyone to agree with that.

The two hot legs brought by themselves without the neutral have a voltage which isn't displaced from anything.

But that wouldn't be 120-0-120, would it..................

 

[Besoeker]

Here we are (finally?) getting back to what the OP was actually asking about. How can 120/240 be considered more than one phase if it is incapable of producing a rotational field? If that's what single phase means (no rotational field) then 120/240 is single phase. But I doubt that we can get Boeseker to agree that that's the meaning.

With respect, the capability of producing a rotational field is not of relevance. I designed multi-phase high current rectifiers. No rotation involved.

 

[jaggedben]

With respect, the capability of producing a rotational field is not of relevance. I designed multi-phase high current rectifiers. No rotation involved.

Lol, that's just your opinion, and has been literally debated since posts 4 and 5 of this thread. And just because it's not relevant to one application doesn't mean it's not relevant too all.

 

[ggunn]

With respect, the capability of producing a rotational field is not of relevance. I designed multi-phase high current rectifiers. No rotation involved.

As the song says, "tomayto, tomahto, potayto, potahto, let's call the whole thing off".

 

[mivey]

Here we are (finally?) getting back to what the OP was actually asking about. How can 120/240 be considered more than one phase if it is incapable of producing a rotational field? If that's what single phase means (no rotational field) then 120/240 is single phase. But I doubt that we can get Boeseker to agree that that's the meaning.

You would not get a lot to agree with that. There are different definitions as well. Rotation is okay but not everything and every application. There are other applications of phase than just the simple way to turn a motor.

To that point, Mivey, you're exactly correct that the three wire quadrature two-phase is qualitatively similar to the 120/208 3-wire system. But I don't agree that the latter is not called 'two-phase' because the name is already taken. After, all, a lot of utilities call it 'single phase' and that name was already taken, too. Which just proves that people have been using disparate conventions for too long, and this will never get resolved. At least not in a free society. I concede the point on that.

Exactly. There are too many names, too many definitions, too many applications to reach a one size fits all resolution. That's why I say each definition is ok with me in its own right. I have no problem understanding the physics behind both sides and I know both exist.

 

[mivey]

Lol, that's just your opinion, and has been literally debated since posts 4 and 5 of this thread. And just because it's not relevant to one application doesn't mean it's not relevant too all.

or just because it is relevant to one application does not mean it must be relevant to all.

 

[Besoeker]

Lol, that's just your opinion, and has been literally debated since posts 4 and 5 of this thread. And just because it's not relevant to one application doesn't mean it's not relevant too all.

Let me remind you of your comment:

How can 120/240 be considered more than one phase if it is incapable of producing a rotational field?

My hexaphase rectifiers were static.

 

[GoldDigger]

Let me remind you of your comment:


My hexaphase rectifiers were static.

The statement was "capable of producing a rotational field", not "currently being used to produce a rotational field."

 

[Besoeker]

The statement was "capable of producing a rotational field", not "currently being used to produce a rotational field."

How can 120/240 be considered more than one phase if it is incapable of producing a rotational field?
On the basis of that assertion............well I'm sure you can interpret it as you wish.
In my opinion it is simply incorrect speculation.

 

[jaggedben]

For the record, it's no skin off my back if you don't want a rotational field to be a defining characteristic of multiple phases. It was not a statement of my personal opinion. I was just reminding everyone that some people think that defines single vs. multiple phases. Go back and look at post #4. The comment about Boeseker agreeing was tongue-in-cheek: look at post #5.

I would comment that it is of about as much interest and practical important as any other characteristic one could choose. And then I will give up. Again.

 

[Besoeker]

Been fun......

 

[Carultch]

How can 120/240 be considered more than one phase if it is incapable of producing a rotational field?
On the basis of that assertion............well I'm sure you can interpret it as you wish.
In my opinion it is simply incorrect speculation.

Because V1-to-N is a sine wave, and V2-to-N is a sine wave. The essential difference between the voltage functions, can be seen as a shift in time. A shift in time between periodic functions, is called a phase shift. That's why one might see it as two phases, even though it is instead generated by mirroring the first sine wave around the V=0 axis, instead of shifting it by 180 degrees along the time axis.