Why is residential wiring known as single phase?

[Rick Christopherson]

Relative to the question of whether a phase shift is from a time delay or some other means, such as two mechanically linked alternators, it is not possible to know what is the source (a time delay line, two alternators, transformer secondaries, etc.) because a steady-state condition is assumed and this means you need to think mod X. Where mod X is in whatever set of units you use, for example 360 or 2*Pi, etc.

My post wasn't about where the delay comes from. It was that for time-varying expressions, a phase shift is a time shift. What that means is that the zero crossings (or any other chosen reference) of the functions are occurring at separate points in time. Mivey claimed that some phase shifts (as it applies to this discussion) do not involve a time displacement of the zero crossings, and I asked him to provide an example.

For any periodic AC signal, there will be two zero crossings per period: a positive-going and a negative-going. For this reason, even a 180 degree phase shift still has a time shift, because you compare the same points, not just their absolute values=0. Conversely, if there isn't a time-shift, then there isn't a phase shift. In this case, it is only an apparent phase shift that comes about from an inversion of the function.

 

[rattus]

Amazing, simply amazing, he just keeps on going!

Amazing, simply amazing, he just keeps on going!

Looooong ago I explained to Bes why your misinterpretation of my position is in error. (It wasn't the time, he tried to introduce "hexiphase" into the discussion.) While the voltage functions of a conventional two-phase system may have the same t₀ and period, the functions don't have an identical phase.

Using a "conventional two-phase" system, and a common t₀ and period, you still will not be able to resolve the arguments to less than ([ωt + φ₀]) and ([ωt + φ₀]+ 90?) or their equivalent inverses. Likewise for conventional three-phase delta systems with a common t₀ and period, the arguments cannot be resolved to less than ([ωt + φ₀]), ([ωt + φ₀]+ 120?) and ([ωt + φ₀]+ 240?) or their equivalent inverses. However you don't introduce EVERY equivalent inverse into the argument mix to create new mythical phases which is what the "'2-phases' in a single-phase system" advocates are attermpting to do.

My earlier response to you was limited to the logical application of the definition of phase to a conventional 120/240V system where all valid voltage functions have the same t_0. That is, the arguments of every valid function can be reduced to ([ωt + φ₀]) OR its equivalent inverse -([ωt + φ₀]+180?), but you DON'T get to write them indiscriminatey in terms of BOTH - THAT is what introduces the myth.

Four of us are telling you that you are wrong, and you respond with more snake oil.

Trig identities are just that, they are identical functions in every way; they cannot have different phases. While it is true that (wt) is the phase of sin(wt), it is not the phase of -sin(wt). And, there is no reason to 'reduce' sin(wt + PI) in the first place.

It is quite simple, the phases are (wt) and (wt + PI), and you have not produced one reference to support your position. Until you do we will have to believe the myth is yours. Very unprofessional!

 

[Besoeker]

Why? I thought we're discussing conventional 120/240V systems.

It's relevance is that the same 120-0-120 (or whatever voltage) arrangement is used.
All connected like six spokes of a wheel.

Here's a piccy:

Arrangement A is the usual residential arrangement. The one you want to call single phase.
Depicted in blue.

Arrangement B shows that exactly. Plus the exactly same arrangement from the other two of the three phases.

Yet it is a hexaphase arrangement. Hex. Six.
Working backwards from that, how do you get from six to one?

 

[mivey]

I don't understand where you can be coming up with this idea that a phase shift can exist without a time shift. That is exactly what a phase shift is! You shift the starting reference of one signal from another, and since our expressions for voltage are time-based, this is a time shift. (yes, in my previous posting I left the door open for your apparent phase shift that was actually an inversion.)

I am also quite perplexed about what you could possibly mean by a physical displacement as your phase shift. Sorry for the snarky comment, but does that mean you're going to move the wires some distance and call it a phase shift?

As it relates to the customary time-varying electrical expressions we use, please provide an example where a phase-shift is not a time shift. If the 180 degree shift is the only example you can come up with, that's because it is not a real phase-shift, as I have been saying. Do you have any situation that applies to this discussion where a phase shift is not a time shift?

First, there is a time shift from the primary to secondary that is an artifact of induction physics where the flux is not in phase with the voltage. We usually compensate for that by swapping the polarity or winding direction to have the primary and secondary in phase. So from the get-go, we are using a winding reversal to negate a real 180? phase shift.

So just on that, you could throw out the notion that a winding reversal does not give you a phase shift. However, we tend to ignore that phase shift so let's continue with some transformer phase shift references you can read that are talking about the phase shift caused by the physical voltage directions:

http://www.ece.msstate.edu/~donohoe/ece3414three_phase_transformers.pdf

The wye-delta and delta-wye configurations of three-phase transformers result in 30? phase shifts between the primary and secondary line-to-line voltages.

http://basler.com/downloads/3phXfmrs.pdf

Most engineers have some familiarity with two commonly known delta connections that give either a +30? or - 30? phase shift of positive sequence voltages and currents...The paper will review the variety of possible winding configuration and give examples of the nomenclature that is used with them and how these various phase shifts are created.

http://nptel.iitm.ac.in/courses/Web...l Technology/pdf/L-26(TB)(ET) ((EE)NPTEL).pdf

In the example shown, the phase shift of secondary winding is +30? with respect to the corresponding primary winding...
Considering the same example, if the primary delta connection had been made by connecting A2B1, B2C1 and C2A1, this would have resulted in a phase displacement of 30? clockwise(lagging) on the secondary side, i.e. the 1 o?clock position. This type of connection is termed asDy1 (Or Dyn1)

Westinghouse Distribution Transformer Guide:

2. Angular Displacement (Phase Shift)
For standard three-phase connections the phase-to-neutral voltage on the primary side either leads that on the secondary by 30? or is in phase with the phase-to-neutral voltage on the secondary side.
...
The delta wye and wye delta connections produce the 30? phase shift.

These are just a few examples from an untold number available.

In my open-wye to 4-wire wye, some of the voltages are:

Some linear voltages:
X1->X2 + X3->X4 = V@0? + V@0? = 2V@0?
X4->X3 + X2->X1 = V@180? + V@180? = 2V@180?

Some three-phase voltages:
X3->X4 = V@0?
X7->X8 = V@240?
X2->X1 + X6->X5 = V@180? + V@60? = V@120?

you will note that we have both the X1->X2 = V@0? and X2->X1 = V@180? voltages have physical phase displacments that produce voltages with physical phase displacements.


I can provide more examples but you should get the concept by now.


Another thing concerning time vs. phase:

A phase shift and a time shift go hand in hand but it really does depend on your reference frame. For example, in a three-phase generator all of the voltages start at the same time so they all have the same t₀. But from a different reference frame, we could consider the time that they peak. In that frame, the time of the positive peak (t_peak) will be different for the voltages. With the three-phase generator, we produce a shift by a physical shift, just like I did for the voltages on the left side of my generator example.

Using the winding voltages in different ways does not produce a real time shift for t₀ in one reference frame. But if we look at the positive peak times (t_peak) for those voltages, they do occur at different times.

The other way to get a shift is to actually delay the waveform. You could do this using delay boxes. I have a delay cascade circuit that I use on my workbench to get a 3-phase set of voltages from a single-phase source. The time shift due to flux lag from the primary to secondary side of the transformer is another example of a time delay.

This actual time delay appears to be the shift you are thinking about, but is not the phase shift we normally talk about when discussing transformer phase shifts. Outside of the shift from the flux delay (which we routinely ignore), the transformers do not have that kind of time shift.

 

[Besoeker]

The point was the phase angle of each individual winding is created by the common electomagnetic action of the transformer.

The post was, and I hope still is, about residential supplies.
The customary 120-0-120 service.

 

[Rick Christopherson]

And, there is no reason to 'reduce' sin(wt + PI) in the first place.

Why not? You added the (wt + pi) when you transformed the negative sign in the original expression, so why is it illogical for someone else to not put it in, or to take out out?

 

[mivey]

I apologize if my use of the word winding was confusing to you.
...
then either of you should be refuting it, not obfuscating it.

I'm really not sure if it is Jim the participant or Jim the moderator who is expecting a response. I'll just refuse to respond in kind so we don't punish the rest of the group with snipey exchanges.

 

[iaov]

O scope

O scope

If said sparky is working on a 120/240 volt single phase system and thinks he is working with 2 phases, he doesn't know his subject very well.

It's known as single phase because that is what it is. Just because there are two voltages, doesn't mean there are two phases.

Connect two car batteries in series. You will have both 12 and 24 volts. Does that make DC 'two phase'?

If you (or anyone) insists that 120/240 single phase is actually two phase, please, I would like to see both phases on an oscilloscope.

If you look at both legs you will see two wave forms 180 degrees out of phase. These are two phases and to call this single phase is not correct. However the term single phase seems to be "grandfathered" in. Perhaps the term " single transformer winding would be more accurate. In industry where most 120/208 is derived from three phase wye connected transformers it is still called single phase.:roll:

 

[Rick Christopherson]

So just on that, you could throw out the notion that a winding reversal does not give you a phase shift.

Yes, even though there is a phase shift from the primary to the secondary, that is not what we are discussing, nor is it justification to claim there is a physical phase shift within the center-tapped secondary winding. You made the original statement, and now you are avoiding it. When can you have a phase shift that is not a time shift.

Your example of how all three phases in a 3-phase system have the same t₀ is foolish. Of course they all have the same t₀, but their zero crossings are shifted in time. This is the time shift. This is the reason why there is a phase constant added to each expression, so we can reference them to the same time-variable while having unique instantaneous values.

 

[rattus]

It's relevance is that the same 120-0-120 (or whatever voltage) arrangement is used.
All connected like six spokes of a wheel.

Here's a piccy:

Arrangement A is the usual residential arrangement. The one you want to call single phase.
Depicted in blue.

Arrangement B shows that exactly. Plus the exactly same arrangement from the other two of the three phases.

Yet it is a hexaphase arrangement. Hex. Six.
Working backwards from that, how do you get from six to one?

Yes, someone has seen fit to apply the term hexaphase to this arrangement. Clearly there are six phase angles present. A four phase system has also been described.

It seems that in general, rbalex would have us apply his trig identity to every phase shift anywhere. Now that just boggles my mind!

 

[mivey]

However you don't introduce EVERY equivalent inverse into the argument mix to create new mythical phases which is what the "'2-phases' in a single-phase system" advocates are attermpting to do.
...
but you DON'T get to write them indiscriminatey in terms of BOTH - THAT is what introduces the myth.

Not a myth to C.P. Steinmetz. He did not say that the combination of two smaller phases as a larger single-phase meant the smaller phases did not exist. He referred to the ordinary alternating current system that can be produced by one coil as a two-phase system.

In case you don't recall, he was one of the founding fathers of electricity and an AC guru:

http://edisontechcenter.org/CharlesProteusSteinmetz.html

 

[mivey]

These are two phases and to call this single phase is not correct.

As a label it is correct, just not a complete description of the system. If we take the negative phase to be the return of the positive phase, we have one larger single-phase circuit as a result. That is why it is called single-phase.

But it is not completely descriptive because the fact that we have a larger single-phase result does not mean the smaller phases have disappeared or do not exist.

 

[rattus]

Why not? You added the (wt + pi) when you transformed the negative sign in the original expression, so why is it illogical for someone else to not put it in, or to take out out?

Because -sin(wt) = sin(wt + PI), the original form. I was emphasizing the fact that the phase of -sin(wt) is not (wt) but (wt + PI).

Why why mess with an expression which is correct in the first place? If you think otherwise, give us a reference.

 

[mivey]

Yes, even though there is a phase shift from the primary to the secondary, that is not what we are discussing, nor is it justification to claim there is a physical phase shift within the center-tapped secondary winding. You made the original statement, and now you are avoiding it. When can you have a phase shift that is not a time shift.

How is my response avoiding your question? I directly answered it.

Your example of how all three phases in a 3-phase system have the same t₀ is foolish. Of course they all have the same t₀, but their zero crossings are shifted in time. This is the time shift. This is the reason why there is a phase constant added to each expression, so we can reference them to the same time-variable while having unique instantaneous values.

Take your artifact analysis and apply it to my open-wye to 4-wire wye example. You will find the same type shift you get in the center-tap transformer.

Take your artifact analysis and apply it to a Scott-T transformer. You will find the same type shift you get in the center-tap transformer.

 

[jim dungar]

The post was, and I hope still is, about residential supplies.
The customary 120-0-120 service.

I have been trying to stay on target.

But, in post #1744, Mivey raises the issue of the phase relationship between the primary and secondaries of a 3-phase transformer. This goes along with how I have been saying that the two secondary reconnectable windings X1-X2 and X3-4, or two halves of a single center-tapped winding, have a relationship with each other and the primary winding H1-H2, based on the real physical construction of the actual transformer.

 

[Rick Christopherson]

Because -sin(wt) = sin(wt + PI), the original form. I was emphasizing the fact that the phase of -sin(wt) is not (wt) but (wt + PI).

Why why mess with an expression which is correct in the first place? If you think otherwise, give us a reference.

That's incorrect Rattus. The phase of -sin(wt) is (wt). You have used a mathematical operation to transform the phase to be shifted, and then deny that this is what you did.

Yes, the expression is mathematically correct, right up until the point you call it "Real". Then it becomes a false statement.

You keep insisting on saying this, but then instead of defending it or providing a reference yourself, you dodge the question by saying it is not important to the discussion.

 

[Rick Christopherson]

How is my response avoiding your question? I directly answered it.

No you didn't. You previously stated that a phase shift does not have to be a time shift, and you have yet to provide an example where this is the case.

Take your artifact analysis and apply it to my open-wye to 4-wire wye example. You will find the same type shift you get in the center-tap transformer.

If it shows the same thing, then why do you insist on ignoring the original question in favor of a convoluted example that contains both real and apparent phase shifts? That's a rhetorical question, because we both know the answer. You want to do this for deceptive reasons, because it convolutes the answer needlessly.

 

[mivey]

I have been trying to stay on target.

But, in post #1744, Mivey raises the issue of the phase relationship between the primary and secondaries of a 3-phase transformer. This goes along with how I have been saying that the two secondary reconnectable windings X1-X2 and X3-4, or two halves of a single center-tapped winding, have a relationship with each other and the primary winding H1-H2, based on the real physical construction of the actual transformer.

Sure they do. I don't think any of us deny that.

H1-H2 is in phase with X1-X2
H1-H2 is in phase with X3-X4
H1-H2 is in phase with X1-X4

H1-H2 is phase-opposed with X2-X1
H1-H2 is phase-opposed with X4-X3
H1-H2 is phase-opposed with X4-X1

X1-X2 is phase-opposed with X2-X1
X1-X2 is phase-opposed with X4-X3
X1-X2 is phase-opposed with X4-X1

X3-X4 is phase-opposed with X2-X1
X3-X4 is phase-opposed with X4-X3
X3-X4 is phase-opposed with X4-X1

etc.

As far as I can tell, we all agree.

None of the connections we have proposed can change those relationships because they are based on the physics of the transformer and we would have to re-wind the transformer to change them. I don't remember anyone doing that.

The fact that we can safetly connect X1 to X3 and X2 to X4 does not change the fact that X1-X2 is phase-opposed with X4-X3.

What have we said that you think is any different?

 

[mivey]

No you didn't. You previously stated that a phase shift does not have to be a time shift, and you have yet to provide an example where this is the case.

Of course I provided an example. More than one.

If it shows the same thing, then why do you insist on ignoring the original question in favor of a convoluted example that contains both real and apparent phase shifts? That's a rhetorical question, because we both know the answer. You want to do this for deceptive reasons, because it convolutes the answer needlessly.

Rick, I'm really trying to answer your question as clearly as I can. I'll continue trying if you stay civil. If you want to hurl insults, then you can just talk to yourself.

 

[Rick Christopherson]

Rick, I'm really trying to answer your question as clearly as I can.

If you are truly trying to answer the question, then why do you keep reverting to poly-phase systems, when this discussion is about a single-phase system?