Why is residential wiring known as single phase?

[__dan]

It makes no difference where the dot markings are for a two winding single core secondary when performing circuit analysis. You can use any reference frame you want, but you must then use the proper convention to combine the two voltages.

You are free to use Van and Vnb. These phasors would be head-to-tail. 120<0 + 120 <0 = 240<0

You are free to use Van and Vbn. These phasors would be tail-to-tail. 120<0 - 120<180 = 240<0

You are free to use Vbn and Vna. These phasors would be head-to-tail. 120<180 + 120<180 = 240<180

You are free to use Vbn and Van. These phasors would be tail-to-tail. 120<180 - 120<0 = 240<180

It is incorrect to use Van and Vbn (tail-to-tail) and to ADD them together to find the voltage across both windings. The must be subtracted to find the voltage across both windings.

David, Thank you for posting this. At first I did not understand what you were trying to convey, but I see it now.

My disagreement has to do with, the convention does not convey why or what causes the phase shift to appear. Since the cause is both very simple and caused by the observer and not by the transformer, there is a legitimate reason for saying this convention unecessarily adds complexity and does not directly answer the question proposed (is there a phase shift).

The phase shift in this case is caused by the measuring convention and must be subtracted out. This obscures the fact that phase shifts do occur elswhere, for other reasons, caused by the underlying physical reality.

 

[Besoeker]

I apologize for the unkindness. I should have prefaced the "scotoma" statement with - "I believe" too.

No apology required but I do appreciate the gentlemanly manner of the conduct of the discourse. However, you are still wrong about that. Hexaphase isn't all that I do as you might have noted from that other long thread on motor speed control. I introduced hexaphase as a simple (or so I thought) means of demonstrating the point about the number of phases. Anyway, despite being pretty ancient, I do move with the times. In business, you have to.

Back on topic: Basically, to rectify the system voltages and prevent current flow for part of a period. A period for all currents is still 2π even if current isn't measurable or otherwise indicated.

No disagreement with that. In the circuit arrangement shown in post #2125, current for each of the six phases flows for a 60? period in each complete 360? period. But a different 60? period for each of the six phases. Hence hexaphase. Why else would it be called hexaphase? Why else would I need six firing pulses per cycle?

Effectively, you have simply introduced Z ≈ ∞, for part of a period and Z = "whatever your load is" for the rest or Ohms law doesn't apply for the voltage's full period.

I think you have nicely demonstrated that Ohm's law does apply for the full period.

But why do I need to deal with downstream at all?

Because the residential supply (remember the topic of this thread?) IS downstream.
That's precisely where the 120-0-120 comes from.

 

[mivey]

Back on topic: Basically, to rectify the system voltages and prevent current flow for part of a period. A period for all currents is still 2π even if current isn't measurable or otherwise indicated. Effectively, you have simply introduced Z ≈ ∞, for part of a period and Z = "whatever your load is" for the rest or Ohms law doesn't apply for the voltage's full 2π period.

He is only using the positive pulses. That has nothing to do with there being six phases. If Besoeker wanted to use the negative pulses, they are still there.

Look at the following graphic with the six phases. Besoeker is using half of the waves as shown on the top half of the graph. The greyed out part is what he is not using. Just because he does not use them does not mean they aren't there.

 

[jim dungar]

On the subject of positive zero crossing. We usually use it as a reference point for making phase difference measurements because it is a convenient point, but not necessary.

Rattus's postings have been very emphatic that the phase depends on the 'positive going' crossing.

 

[mivey]

Rattus's postings have been very emphatic that the phase depends on the 'positive going' crossing.

I'm pretty sure some of the references I have posted have also used the maximum, or positive peaks, as reference points as well. As long as the same reference point was used for each wave, it makes no difference. There was some mention in some of the references that using the zero crossing might be easier than using the peak.

I don't recall any of them using the minimums, or negative peaks as reference points although there would be nothing wrong with that. The best I recall, the mention of negative or minimums was used when indicating whether the waves were in phase or phase-opposed with a different wave. In those references, a minimum of one wave ocurring at the maximum of a second wave meant they were phase-opposed with a 180? phase difference/displacement/shift.

 

[rattus]

Rattus's postings have been very emphatic that the phase depends on the 'positive going' crossing.

Sorry to leave that impression, but I was emphasizing the fact that similar points on the curves must be compared for waves to be 'in phase' or 'of the same phase'.

Could have used negative going crossings, peaks, or troughs.

 

[rbalex]

No apology required but I do appreciate the gentlemanly manner of the conduct of the discourse. However, you are still wrong about that. Hexaphase isn't all that I do as you might have noted from that other long thread on motor speed control. I introduced hexaphase as a simple (or so I thought) means of demonstrating the point about the number of phases. Anyway, despite being pretty ancient, I do move with the times. In business, you have to.

...

If you happened to have read Post 132, you would note I said, 'The real question is not why residential voltages are called “single phase” but why Y-connected secondaries of three winding transformers aren’t described as “six-phase”.' It is actually "three-phase wye" and your "hexaphase" that are the "conventional" descriptions if the line-to-line voltages aren't considered.

As you have used your hexaphase system, there is one 2π period where all voltages as functions of time, having a common t₀, may be validly expressed in terms reduced to arguments of ωt, ωt+π/3 and ωt+2π/3 or three "phases." That is, the period and t₀ are the same, but the phase constants differ. The definition of phase that you accepted was “phase (of a periodic phenomenon ƒ(t), for a particular value of t) The fractional part t/P of the period P through which ƒ has advanced relative to an arbitrary origin.” Since t is the only independent variable, the only "arbitrary origin" available is t₀ and it must be common to all functions and there is no reference to displacements.

...
No disagreement with that. In the circuit arrangement shown in post #2125, current for each of the six phases flows for a 60? period in each complete 360? period. But a different 60? period for each of the six phases. Hence hexaphase. Why else would it be called hexaphase? Why else would I need six firing pulses per cycle?

...

It appears to me that you have equated a "peak” with phase. Peaks are displacement sensitive, phase isn't. The period for all currents must still be the same 2π from the same origin t₀ even if they are blocked for 5/6 of the period.

I think you have nicely demonstrated that Ohm's law does apply for the full period.
...

Thank you. Back in the "single-phase" branch of the discussion, it appeared to me that you believed the i_a and i_b only had periods of π displaced by π; but their periods must both be 2π.; i.e., if they both have the same t_0, they have the same period and thus the same phase. And they must have the same t₀ and the same period if they are driven by a conventional 120/240V system.

Because the residential supply (remember the topic of this thread?) IS downstream.
That's precisely where the 120-0-120 comes from.

The residential supply system is at the secondary terminals of the supply transformer; it isn't downstream of anything and isn't defined by anything it feeds.

 

[mivey]

It appears to me that you have equated a "peak” with phase.

If he was doing that, then he would be calling the waves shown in #2143 12-phase because there are 12 peaks if we count the positive and negative peaks separately.

The period for all phases must be the same 2π since time is the only independent variable.

The six phases in #2143 all have the same period and angular frequency but different phases.

if they both have the same t_0, they have the same period and thus the same phase. And they must have the same t₀ and the same period if they are driven by a conventional 120/240V system.

Three phase generators create three waves with the same t₀ and same period but they differ in phase.

The residential supply system is at the secondary terminals of the supply transformer; it isn't downstream of anything and isn't defined by anything it feeds.

A 240/120 transformer can supply a 2-wire or a 3-wire residence so it matters there. A high-leg delta bank can feed a 3-phase panel or a single-phase panel so it matters there also. Besoeker's transformer can feed three-phase loads or six-phase loads so it matters there also. A center-tap winding can supply loads needing in-phase voltages or phase-opposed voltages so it matters there also.

The fact that we have a larger single-phase voltage does not mean that we can't have smaller phase-opposed voltages. These smaller phase-opposed voltages co-exist with the larger voltage and also co-exist with the smaller in-phase voltages. It is a simple fact that these voltages are there to be taken for use downstream.

 

[rbalex]

If he was doing that, then he would be calling the waves shown in #2143 12-phase because there are 12 peaks if we count the positive and negative peaks separately.

The six phases in #2143 all have the same period and angular frequency but different phases.

Three phase generators create three waves with the same t₀ and same period but they differ in phase.

A 240/120 transformer can supply a 2-wire or a 3-wire residence so it matters there. A high-leg delta bank can feed a 3-phase panel or a single-phase panel so it matters there also. Besoeker's transformer can feed three-phase loads or six-phase loads so it matters there also. A center-tap winding can supply loads needing in-phase voltages or phase-opposed voltages so it matters there also.

The fact that we have a larger single-phase voltage does not mean that we can't have smaller phase-opposed voltages. These smaller phase-opposed voltages co-exist with the larger voltage and also co-exist with the smaller in-phase voltages. It is a simple fact that these voltages are there to be taken for use downstream.

I clarified some of my points before you posted.

So - how about letting Bes answer for himself, he's fully competent.

 

[rattus]

Sorry to leave that impression, but I was emphasizing the fact that similar points on the curves must be compared for waves to be 'in phase' or 'of the same phase'.

Could have used negative going crossings, peaks, or troughs.

Or for that matter, similar points must be compared when measuring 'phase shift'.

 

[mivey]

I clarified some of my points before you posted.

I see that. Almost an hour later than your original post. Why do you keep doing that? Do you not agree with the forum time limits for changing posts? I understand the mods would have a need to do this for special cases but you seem to do it just for regular posts.

 

[mivey]

So - how about letting Bes answer for himself, he's fully competent.

No doubt. He might be eating supper so we'll just have to wait to see what he has to say.

 

[david luchini]

My disagreement has to do with, the convention does not convey why or what causes the phase shift to appear. Since the cause is both very simple and caused by the observer and not by the transformer, there is a legitimate reason for saying this convention unecessarily adds complexity and does not directly answer the question proposed (is there a phase shift).

Personally, I do not find Subtraction to be very complex. I was not addressing phase shift, I was addressing your mathematical error that caused you to conclude that two voltage phasors with the same magnitude (120V) with phase angles 180 degrees apart would lead to zero volts at the output of the transformer, rather than 240V.

The phase shift in this case is caused by the measuring convention and must be subtracted out. This obscures the fact that phase shifts do occur elswhere, for other reasons, caused by the underlying physical reality.

There is no need to "subtract out" anything with this measuring convention. Just use the proper phasor combination method, as Jim pointed out. The phasor combinations work the same on single phase, two phase, three phase, six phase, etc. systems without having to adjust your methodology.

For instance, think of a 3 phase system with voltage phasors Van=120<0, Vbn=120<-120, Vcn=<120, where you want to find the voltage at the output between A and B. Van and Vbn phasors are connected tail-to-tail, so subtraction must be used for the phasor combination. Vab = Van-Vbn = 120<0 - 120<-120 = 208<30.

If we had tried to add the Van and Vbn phasors which are 120 degrees apart, we would get only 120V across A and B. That is clearly incorrect. Using the proper phasor combination convention will provide the correct answer for any system with any number of phases.

 

[rbalex]

I see that. Almost an hour later than your original post. Why do you keep doing that? Do you not agree with the forum time limits for changing posts? I understand the mods would have a need to do this for special cases but you seem to do it just for regular posts.

I have always acknowleged I've done it or note the reason. Sometimes I respond a bit to quickly and later spot statements that those of you that mine for intentional misunderstanding rather than the genuine argument will jump on.

 

[mivey]

Personally, I do not find Subtraction to be very complex.

Thanks for the laugh.

 

[mivey]

I have always acknowleged I've done it or note the reason.

So that makes ignoring the limit ok? Acknowledgment is automatic as the software stamps the change or do the mods have to add the stamp?

Sometimes I respond a bit to quickly and later spot statements that those of you that mine for intentional misunderstanding rather than the genuine argument will jump on.

Sure, I understand exactly what you mean as I often face the same thing on the other side of the argument. I understand it might be a little tough to play by the rules when you don't have to but why wouldn't you?

 

[rattus]

Personally, I do not find Subtraction to be very complex.

Well it scared me in the 3rd grade, or was it the 2nd? Oh Heck, who cares?

 

[mivey]

Well it scared me in the 3rd grade, or was it the 2nd? Oh Heck, who cares?

I've seen cuneiform. Who wouldn't be intimidated?

 

[rbalex]

So that makes ignoring the limit ok? Acknowledgment is automatic as the software stamps the change or do the mods have to add the stamp?

I will try to be more careful in the future. I believe the stamp is automatic. Usually the edits without comment were just to correct spelling or grammar. When there was a substantive change I usually add an "edit add" statement or acknowledge it in an immediate response as I did with you.

Sure, I understand exactly what you mean as I often face the same thing on the other side of the argument. I understand it might be a little tough to play by the rules when you don't have to but why wouldn't you?

This is why I attempt to inquire (Are you saying...?) rather than declarative (You are saying...) It permits the other person to correct misimpressions, if necessary. As I said I'll try to be more careful in the future; but I don't believe I've ever intentionally misunderstood anything - nor tried to misdirect the discussion. The only time I've spoken "outside" the OP, was when a "two-phase" advocate inquired about how my interpretation of phase applied to three-phase systems.

 

[__dan]

Personally, I do not find Subtraction to be very complex. I was not addressing phase shift, I was addressing your mathematical error that caused you to conclude that two voltage phasors with the same magnitude (120V) with phase angles 180 degrees apart would lead to zero volts at the output of the transformer, rather than 240V.



There is no need to "subtract out" anything with this measuring convention. Just use the proper phasor combination method, as Jim pointed out. The phasor combinations work the same on single phase, two phase, three phase, six phase, etc. systems without having to adjust your methodology.

For instance, think of a 3 phase system with voltage phasors Van=120<0, Vbn=120<-120, Vcn=<120, where you want to find the voltage at the output between A and B. Van and Vbn phasors are connected tail-to-tail, so subtraction must be used for the phasor combination. Vab = Van-Vbn = 120<0 - 120<-120 = 208<30.

If we had tried to add the Van and Vbn phasors which are 120 degrees apart, we would get only 120V across A and B. That is clearly incorrect. Using the proper phasor combination convention will provide the correct answer for any system with any number of phases.

I had been feeling like I was the one bringing rocks to the quarry. I see your point, the measuring convention takes the phasor measurements tail to tail. The tail to tail convention shows one of the phasors has a phase reversal and the phasor sum of tail to tail phasors is subtraction and cancels this out.

Subraction is not complex. Try taking chocolate away from a three year old and see what happens. Try adding a second piece of chocolate to the first one. Comprehension time may be ~ 3 seconds. Try the double negative notation system and see how many years it takes to achieve comprehension. It is conveying insight and understanding that is complex.

Do you see my arguement that usually the notation systems are chosen to convey insight, understanding, and describe an underlying physical reality. In the windings themselves, there are a lot of weird and magical things that could be going on. It would be easy to claim, by magic. That's how I see the question. What is really giong on physically. Is there a phase shift.

In the three phase case yes there is a phase shift internally in the transformer. In the single phase case, no, there is not a phase shift internally in the transformer. There are two windings that are the same and matched in every actual physical characteristic. 240 is created from 120 by connecting two of these in series, adding a second winding to the circuit.

Do you see my arguement that pounding the table on the phase shift obscures the actual physical reality. The phase shift is created by the arrangement of the leads connected to the transformer and not by the transformer itself. The phasor measuring convention does not convey this essential information and the phase shift crowd relies on omitting this essential informaton.

The phasor convention makes the single phase case appear to be similar in character to the three phase case, when it is not. For three phase there is a phase shift and this is shown by the measurments. For single phase there is no phase shift, however a phase shift, the special case of reversing the leads = 180 deg, can create a 180 deg phase shift. The crowd claims there is a phase shift (implying it is internal to, or caused by, the transformer) and not that they created the phase shift external to the transformer by how the leads are attached.

It is obfuscation.