Why is residential wiring known as single phase?

[rbalex]

Me - Why are Ia and Ib not in phase?
You - They don't need to be.

Sounds like you're agreeing that they are not in phase. If they are not in phase, they are out of phase. If they are out of phase, they are not the same phase. If they are not the same phase, they are different phases. If they are different phases, there must be more than one phase. If there is more than one phase the system cannot reasonably be described as single phase.
QED.

Did you read my response to your follow-up (Post 1221)? I did say the currents don't need to be - I didn't say they weren't; in fact, they probably are. However, the secondary current's behavior isn't what determines whether the transformer secondary voltages have the same characteristic phase and the phase characteristic of transformer secondary voltages isn't dependent on the are measurement technique. If the transformer secondary voltages have the same characteristic phase (which they do - which, in fact, they must) it's quite reasonable to describe the system as single-phase (which it is). QED.

Please review post 888 before we go another round. The definition of phase in that Post was actually supplied by rattus but, for the purposes of this discussion, it is compatible with the IEEE Std. 100 definition above.

 

[Besoeker]

If the current is flowing in the direction of A->N how is that not also in the direction of N->B?

The direction of a non-existent current doesn't seem entirely relevant.
You get two positive half cycles, one from each half of the transformer, at different times. They cannot reasonably be construed as being in phase.

 

[rattus]

Please review post 888 before we go another round. The definition of phase in that Post was actually supplied by rattus but, for the purposes of this discussion, it is compatible with the IEEE Std. 100 definition above.

In fact it came from the A.I.E.E., a forerunner of the I.E.E.E.

 

[jim dungar]

The direction of a non-existent current doesn't seem entirely relevant.

Rattus mentioned the asignment of polarity dots to X1 and X3. For analysis puposes, this means at any one point in time the current is flowing out of X1 (node A) and out of X3 (node N) at the same time. This would mean that based on the direction of current flow and your statement that the voltages and currents are in-phase; then Van must be in-phase with Vnb.

You get two positive half cycles, one from each half of the transformer, at different times.

As I have said repeatedly Vnb=-Vbn. Changing the measuring device connections does not change the actual physical connections.

They cannot reasonably be construed as being in phase.

Looks like we are back to the begining. Which part of my arguement is 'not reasonable'?
Weren't you the one that said V12 can physically be connected in parallel with V34, because they are in-phase?

 

[Besoeker]

I did say the currents don't need to be - I didn't say they weren't; in fact, they probably are.

Given that the rectifier circuit load is resistive, if the currents aren't in phase then the voltages aren't in phase either.

BTW, I already commented on your post #888.

 

[rattus]

SUMMARY OF MY TAKE ON THE MATTER

We are discussing ideal systems, no talk about the real world please. We are discussing voltages and their phases. If one wants to discuss power and energy, one should start a new thread.

We are discussing a split phase system which utilizes a center tapped transformer which provides a second phase*. But we still call the system single phase because it is supplied by a single transformer and generator.

*According to the definition of phase which is measured in radians or degrees, not in volts.

We establish the CT as the common reference, a neutral if you will. We call this node N.

We must be consistent in our measurements, Toward this end we define all voltages relative to N, therefore the voltage on the neutral, Vnn, is always zero. Then, on L1 we see V1n and on L2 we see V2n.

In order to compare V1n to V2n, we must observe them that way. We do NOT observe Vn1 or Vn2!!!

We see that V1n and V2n are separated by 180 degrees or pi radians. V2n NOT Vn2. The phasor diagram shows this graphically. BTW, for those who didn?t know it already, the second subscript means with reference to.

There is no way to change the fact that this separation exists! It is foolish to claim that there is some magic formula, some magic trick, some skullduggery which will somehow make these voltages in phase! It is irresponsible to make this claim,

Although Wikipedia may not be the ultimate reference, I find these two links, previously posted by ?bob? (not rbalex) to the quite informative. You should read them.

http://en.wikipedia.org/wiki/Split-phase_electric_power
http://www.nfphampden.com/xftheory.pdf

 

[Besoeker]

Looks like we are back to the begining. Which part of my arguement is 'not reasonable'?

My half wave rectification of post #1004 would not work if you had only one phase. It needs two.
V_an and V_bn
Two is not single.

 

[jim dungar]

We are discussing ideal systems, no talk about the real world please.

Why does it make a difference?

The whole point of this discussion is the real world. The actual performance of a 120/240V service is what started this thread.

 

[rattus]

Rattus mentioned the asignment of polarity dots to X1 and X3. For analysis puposes, this means at any one point in time the current is flowing out of X1 (node A) and out of X3 (node N) at the same time. This would mean that based on the direction of current flow and your statement that the voltages and currents are in-phase; then Van must be in-phase with Vnb.

As I have said repeatedly Vnb=-Vbn. Changing the measuring device connections does not change the actual physical connections.

Looks like we are back to the begining. Which part of my arguement is 'not reasonable'?
Weren't you the one that said V12 can physically be connected in parallel with V34, because they are in-phase?

Yes, Jim, but that makes V43 out of phase with V12. We must measure all voltages with respect to a common reference, in this case the common junction between X2 and X3. We are concerned with the voltages at X1 and X4. They must be out of phase for the full wave rectifier to function properly.

 

[jim dungar]

We must measure all voltages with respect to a common reference,....

Where is that written?
I thought measurements needed to be consistent and repeatable.

Oh, that's right. Your oscilloscope is limited in its capabilities.
This sounds like, "if the only tool you own is a hammer, then everything looks like a nail."

 

[Besoeker]

The actual performance of a 120/240V service is what started this thread.

I think calling it 120/240 is a but misleading although I may have an inkling of why you do so.

The usual arrangement of the transformers in question is two 120V secondary windings. There is no 240V winding.
The 240V comes from connecting the two 120V windings in series thus providing a 120V-0-120V supply.
The series is the only connection that gives 240V.

 

[jim dungar]

I think calling it 120/240 is a but misleading although I may have an inkling of why you do so.

120/240 is the IEEE/ANSI recognized methodology. It better not be misleading.

 

[gar]

120223-1022 EST

On "synchronous" and its meaning. There are references that equate "synchronous" and "in-phase" as being identical. I do not hold to this definition. My definition is more like two or more items move together in time, but may have a constant phase difference.

The following definition supports my usage.

Computing Dictionary

synchronous definition
operating system, communications
1. Two or more processes that depend upon the occurrences of specific events such as common timing signals.
2. Occurring at the same time or at the same rate or with a regular or predictable time relationship or sequence.
Opposite: asynchronous.
(1996-04-11)

Consider a synchronous motor. At zero torque load the shaft angle is "in-phase" with the rotating magnetic field. As torque load is increased the mechanical position of the shaft moves away from being "in-phase" with the rotating field, and lags the field in time. If torque is applied to the shaft, now the motor becomes a generator, and the mechanical shaft position leads the magnetic field. The shaft is synchronous to the field, but has different relative phase angles as a function of torque. So only under no load conditions is the shaft "in-phase" with the field. Note: in the real world one has to apply a small amount of torque to the shaft to get at exactly the "in-phase conditions. This is because energy has to be supplied to overcome the motor's losses, and create an actual no-load condition.

For those that don't like oscilloscopes consider synchronizing the the horizontal sweep. With modern scopes I can sync almost anywhere I choose on a periodic waveform. This can be at an arbitrary phase angle to some reference point on the waveform, such as the positive zero crossing of a sine wave, and I can make the sine wave look like a cosine wave or an inverted sine wave, or any arbitrary shift.

.

 

[rbalex]

120222-2254 EST

Assuming an original voltage source is a sine wave. This source feeds either one or two ideal transformers. If it is a single transformer, then it has two identical secondaries. If it is two transformers, then the two transformers are identical.

By my definition of "in-phase" in this circuit you can parallel two secondaries with no appreciable circulating current resulting. Any other phase relationship will cause circulating current. In particular a 180 degree phase shift, inversion if you want to call it that, will cause a maximum and very large circulating current. Any non-"in-phase" relationship is an "out-of-phase" condition.

Can you connect the two outer ends of a center tapped transformer together and have essentially no circulating current, or do you get big sparks? No sparks and the coils are "in-phase". No meters, no scopes, just a simple experiment.

The sources I have previously referenced would support my use of "in-phase".

Tried to quickly go back to some other references provided by others. Did not get very far.

Post 1084 on p 28 does not define "in-phase".

Post #13 on p 1 is an incorrect description. Two voltages differing by 180 degrees produce a large voltage difference, not 0 volts. A zero phase difference and equal magnitudes would produce a zero voltage difference.

Two coherent monochromatic light waves at a point and with a phase displacement of 0 degrees produce a bright spot or band, displaced by 180 degrees and the result is a dark band. Interferometry. How a diffraction grating works.

.

Gar,

If I have missed a formal definition you posted, I since sincerely apologize.

However, by the various definitions of phase I have referred to, none of them mention transformers or measurement techniques; they all define phase in terms of mathematical concepts. None of them mention amplitude or polarity in the root definition. You’re correct that post 1084 doesn’t define “in-phase” but it does define phase. I find it curious that you balk at saying two voltages, however they are derived, that obviously have the same characteristic phase aren’t “in-phase.”

Since you have offered your definition of “in-phase,” I offered mine in post 888. I distinguish between “in-phase” and “in-sync.” Your experiment is a marvelous example of two voltages that are “in-phase” but aren’t “in-sync.” Simple, elegant, no measurement instruments necessary. Thanks.

Edit add: I was writing this when you made your last post, I appreciate you posted definiton of synchronous that are compatible with Post 888 - even if it had to come from a "computing" source. Thanks again.

 

[rattus]

Why does it make a difference?

The whole point of this discussion is the real world. The actual performance of a 120/240V service is what started this thread.

Because it clutters up the thread with extraneous side arguments.

No, performance is not the issue. The question was and is still, "Why is residential service called single phase?"

 

[rattus]

Where is that written?
I thought measurements needed to be consistent and repeatable.

Oh, that's right. Your oscilloscope is limited in its capabilities.
This sounds like, "if the only tool you own is a hammer, then everything looks like a nail."

Just good practice Jim. Perhaps I should say, "insofar as possible"?

How can you understand a full wave rectifier circuit if V1 and V2 are defined relative to different references?

I don't even own an oscilloscope.

 

[jim dungar]

Because it clutters up the thread with extraneous side arguments.

No, performance is not the issue. The question was and is still, "Why is residential service called single phase?"

You need to go back and read the very first post, it clearly says "same utility transformer (ie. one winding)".

 

[rattus]

You need to go back and read the very first post, it clearly says "same utility transformer (ie. one winding)".

Doesn't matter Jim. We know that it is a center tapped winding which is effectively two windings. Since we know that, we can represent the two voltages as two sources with the voltages defined relative to the neutral. No need to concern ourselves with the X's and H's anymore.

The point is that by defining the voltages relative to N, we see a phase separation of 180 degrees. That is technically two phases, but we call the service single phase for reasons already posted--many times.

In the rectifier circuit, it is then obvious that current flows alternately in one loop and then the other. That is, CW in one loop, and CCW in the other

 

[rbalex]

From a "non-computer" source:

IEEE Std 100 The IEEE Standard Dictionary of Electrical and Electronic Terms:

synchronism: The state where connected alternating-current systems, machines, or a combination operate at the same frequency and where the phase angle displacement between voltages in them are constant, or vary about a steady and stable average value. See also: asynchronous machine.
(PE) [9], 1344-1995
Original Sources:​

1. (PE)[9] - IEEE Power Engineering Society Committee on Rotating Machinery.​
2. 1344-1995 - IEEE Std 1344-1995. IEEE Standard for Synchrophasors for Power Systems. The synchronizing input and the data output for phasor measurements made by substation computer systems is discussed. Processes involved in computing phasors from sampled data, data-to-phasor conversions, and formats for timing inputs and phasor data output from a Phasor Measurement Unit (PMU) are also addressed.​

I confess I grieved that the definition didn't essentially demand the same amplitude or polarity, but I must post it for the sake of professionalism. On the other hand, my practical examples in Post 888 distinguishing "in-phase" and "in-sync", which are informal terms to start with, are consistent with both formal definitions of phase and synchronism.

I also doubt anyone would directly “connect” two “… alternating-current systems, machines, or a combination ...”, however the voltages were derived, that didn't have the same amplitude and polarity as well as phase (well, maybe if one was dead). Furthermore, the OP limits the discussion to REAL 120/240V residential transformers where amplitude and polarity of the voltages aren't essential elements of the definition of phase or single-phase.

 

[Fulthrotl]

Sorry but the concept of 2-phase was settled somewhere in the first 20 or so posts. Lets stay on topic.

Seriously, we have been wrestling with a center tapped transformer output being; (2) voltages in-phase or (2) voltages out-of phase.

ah.... god forbid we stray from the topic, now that i know what it is.... ;-)

*fulthrotl makes note.... topic is picking flychit out of pepper: a brief treatise*

off to work... ya all have fun now, and don't damage that carpal tunnel....