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

[jumper]

if we had a gun in this thread, we could at least put it out of it's misery.

I am not allowed to play with guns. Makes people nervous for some reason...

 

[jaggedben]

the slope must be of the same sign
they are not

Well, that's one choice of the meaning of "in phase". Another choice is not to require that.

The definitions of "phase" and "in phase" obviously should be a consensus choice. But if I were in charge, then in the context of sine waves of a fixed frequency, I would define a phase as a one-dimensional vector space of such functions. That would correspond to the usual usage of single phase, two phase, and three phase systems (with the exception of calling two hots and a neutral from a 3 phase wye system "single phase").

Cheers, Wayne

if you don't require that they are out of phase

Circular reasoning there Ingenieur.

My question is where does this get defined in the text books, or is it not defined? Is there any use in having a strict meaning of 'in phase' other than settling discussions like this? i.e. is it just academic?

Seems we have engineers on both sides of the question here.

 

[jaggedben]

I don't think this has been mentioned yet...

Seems like industry nomenclature and the NEC follows the Line-to-Line voltages only.

120/240 = 1 waveform line to line
120/208 = 1 waveform line to line
Three phase any voltage, wye, high leg or not = 3 waveforms

Two phase - bit of an outlier because I understand it wasn't always done this way, but seems to have started out 4 wire, 4 lines = 2 waveforms

To those saying a 120/240 service is two phases, I'd like to ask: how many phases is a high-leg delta?

 

[jumper]

To those saying a 120/240 service is two phases, I'd like to ask: how many phases is a high-leg delta?

How many do you want to it be?

Lotta different signals could be produced and analyzed from that supply, depending on reference.....

 

[jaggedben]

How many do you want to it be?

Three.

 

[jumper]

Three.

You do not see six? or more?

 

[__dan]

120 / 208, delta to Y. One (or two) phase(s) loaded per residence around here is called a network connection. Don't know what the utility calls it. But they have some old ones installed in the city. 120 / 208, X1 X2 N, three conductors.

Three phase delta connected supply side, H1 H2 H2, three wire (three or four conductor, if EGC). Phase voltages are H1H2, H2H3, H1H3. Three independent variables at the supply. Any phase voltage can vary independently but the utility likes to keep the same relationship between them "stiff".

Load side X1 X2 X3, voltages are bound to the turns ratio of the transformer and the primary side voltages, H1H2, H2H3, H1H3.

Now drop any one leg at the primary. Primary side voltages across the winding become x 0 0.

Only one phase will remain with a voltage that will power a winding. Now the transformer is in its single phase condition.

Load side voltages are 120 0 0 on the three conductors. It can be single phased, but the complaints will not stop until more than one phase is available at the primary.

120/ 240 Single Phase, only one winding needs a phase voltage at the primary. Single phasing is its normal condition.

 

[jaggedben]

You do not see six? or more?

I see more than three voltage waveforms, but not more than three electrical 'phases'.

 

[LarryFine]

Now drop any one leg at the primary. Primary side voltages across the winding become x 0 0.

Only one phase will remain with a voltage that will power a winding. Now the transformer is in its single phase condition.

Load side voltages are 120 0 0 on the three conductors. It can be single phased, but the complaints will not stop until more than one phase is available at the primary.

Dan, wouldn't the other two primaries now be connected in series across the two still-hot primary phases, i.e., in parallel with the still-fully-energized primary? Wouldn't they now each see half of their original line-to-line voltage, and create two 60-volt sources? Of course, there would no longer be a phase difference, but wouldn't there now be 120, 60, 60?

 

[LarryFine]

To those saying a 120/240 service is two phases, I'd like to ask: how many phases is a high-leg delta?

Good question. The 2-ph guys would insist on keeping the 'scope - probe on the neutral, and see A-N as -180 deg., B-N as (I'm not sure; 120? 0?), and C-N as +180 deg.

I would connect it A-B, B-C, and C-A, and see three equal and in-sequence phases.

 

[LarryFine]

By the way, I just got off the phone with my E.E. friend, and we spoke at length about this topic. He immediately said that this is a polarity matter, not a phase matter. I explained the insistence of the 'scope - probe on the neutral, and he agreed it's a choice of measurement method. (Forget earthing the neutral for the moment.) Swapping 'scope leads changes polarity, not phase angle.

He asked, if it's a matter of phase (meaning claiming it's two phases), "What would be the sequence?"


This is from my E.E. friend:
For those of us who would like a new challenge (part of which is suffering through the 51 minutes), see if you can find the flaw in the professor's logic (I did):

http://forums.mikeholt.com/showthread.php?t=192966&p=1934769#post1934769

 

[jumper]

I see more than three voltage waveforms, but not more than three electrical 'phases'.

Define phase. Last time I checked it was a mathematical expression.

Phase angle between conductors perhaps...

 

[jumper]

By the way, I just got off the phone with my E.E. friend, and we spoke at length about this topic. He immediately said that this is a polarity matter, not a phase matter. I explained the insistence of the 'scope - probe on the neutral, and he agreed it's a choice of measurement method. (Forget earthing the neutral for the moment.) Swapping 'scope leads changes polarity, not phase angle.

Our assigned reference, the neutral, designates the polarity we give it for analysis. We take our phase angle from that reference point.

 

[jumper]

Good question. The 2-ph guys would insist on keeping the 'scope - probe on the neutral, and see A-N as -180 deg., B-N as (I'm not sure; 120? 0?), and C-N as +180 deg.

I would connect it A-B, B-C, and C-A, and see three equal and in-sequence phases.

No, we view each part individually here. Three phase and single phase. Six signals.

More if needed...

 

[LarryFine]

Our assigned reference, the neutral, designates the polarity we give it for analysis.

Aha! You said polarity!

We take our phase angle from that reference point.

Which, in a 1ph system, merely resembles two opposing phase angles.

 

[LarryFine]

Three phase and single phase. Six signals.

Please define the six.

 

[jumper]

Aha! You said polarity!


Which, in a 1ph system, merely resembles two opposing phase angles.

Only an assigned polarity for reference. Gotta make a choice.

It resembles the waveforms I based my model on. Where I stood in the road watching traffic. Perspective/reference.

 

[jumper]

Please define the six.

AB, BC, CA
An, Cn, CA in reference to An and Cn.

 

[jaggedben]

Define phase.

That's what I'm trying to get you engineers to do! Seems it's not simple, no one can just quote a book.

Last time I checked it was a mathematical expression.

Phase angle between conductors perhaps...

Seems like it's a concept that emerges from some math and some other stuff, and it's genuinely fuzzy around the edges.

 

[jaggedben]

Our assigned reference, the neutral, designates the polarity we give it for analysis. We take our phase angle from that reference point.

And if there's no neutral?