Why is residential wiring known as single phase?

[Besoeker]

Yeah, one trigger on the positive half-cycle, and one on the negative half-cycle./QUOTE]
Nope. That's what you do with a dimmer.

Give me a moment....

Here's a basic dimmer circuit:

And the output:

Notice that only ONE phase is involved.

The simple rectifier circuit again:

Notice that now there is another phase involved.

And the output voltage into a slightly inductive load.

Notice also that each SCR is fired on the positive half cycle. They wouldn't conduct otherwise.
Notice also that they conduct at different times of the whole cycle.
Conduction requires forward anode to cathode bias.
Since the conduction periods occur at different times for each SCR, they must each be forward biased at different times during a period of one cycle.
That can't happen unless you have more than one phase.

 

[Rick Christopherson]

Since the conduction periods occur at different times for each SCR, they must each be forward biased at different times during a period of one cycle.
That can't happen unless you have more than one phase.

I'm arguing the distinction between physical and mathematical. Please pardon me for suggesting this if I am wrong, but I am not sure that you even fully comprehend the mathematical portion of the argument (for which I am not even a party to).

You keep repeating that your circuits are not feasible without a phase shift. Mathematically, there is no distinction between a phase shift and an inversion. So your statements are false even from the perspective of those people that support you. They will at least acknowledge that mathematically, a phase shift is equivalent to an inversion. You don't seem to even accept this relationship.

If you can't even acknowledge that mathematically a phase shift and inversion are equal, then this discussion regarding which is real versus mathematical is going to be way over your head.

 

[jim dungar]

Since the conduction periods occur at different times for each SCR, they must each be forward biased at different times during a period of one cycle.
That can't happen unless you have more than one phase.

Your SCR's work because your contains two different voltages, not because it contains two different phases.

One SCR is controlling the voltage Van, and the other controls Vnb.
Or are they on Vna and Vnb? Maybe it is Van and Vbn? It could also be Vna and Vnb? It really depends on your triggering circuit.

 

[rbalex]

The fractional part is 180 degrees. Pi radians.
It is thus not an identical fractional part.
They are thus not in phase by your definition.

Not - so. The "fractional part" is "t/P of the period P." You do realize t/P isn't a constant don't you? t₀ is a constant, so is P; but t/P varies with time. The fractional part t/P of the period P is identical for both functions under discussion at any time t as ? advances relative to the arbitrary origin (t₀).

Just a reminder:

Phase (of a periodic phenomenon ?(t), for a particular value of t) The fractional part t/P of the period P through which ? has advanced relative to an arbitrary origin.
Note: The origin is usually taken at the last previous passage through zero from the negative to the positive direction.

[IEEE Std 100 The IEEE Standard Dictionary of Electrical and Electronic Terms]

The actual definition is underlined. The parenthetic clarifies that the definition applies to periodic phenomena. The ?Note? states a non-mandatory convention.

 

[Besoeker]

Not - so. The "fractional part" is "t/P of the period P." You do realize t/P isn't a constant don't you?

Thus not identical.

 

[rattus]

Your SCR's work because your contains two different voltages, not because it contains two different phases.

One SCR is controlling the voltage Van, and the other controls Vnb.
Or are they on Vna and Vnb? Maybe it is Van and Vbn? It could also be Vna and Vnb? It really depends on your triggering circuit.

But, the two voltages, call them Van and Vbn because we can use the neutral as a common reference, carry two phases, to wit:

Van = 120Vrms*sin(wt)

Vbn = 120Vrms*sin(wt + PI)

Since 'phase' may be defined as the arguments of the sines,
the phases are (wt) and (wt + PI), count them, two.

These two phases, displaced by PI, are necessary for proper operation of the circuit.

However, convention dictates that we call this a single phase system, but a number of people still refer to V1n and V2n as phases.

 

[Besoeker]

Your SCR's work because your contains two different voltages,

Spot on.

 

[rbalex]

Thus not identical.

How so?

Are the two functions discussed periodic?
Do they have the same period P?
Do they have the same origin arbitrary, t₀?
Do they have the same the same t/P as they advance from t₀?

 

[mivey]

How so?

Are the two functions discussed periodic?
Do they have the same period P?
Do they have the same origin arbitrary, t₀?
Do they have the same the same t/P as they advance from t₀?

As has been pointed out to you many times, you are mis-applying the definition to compare phase. The many references that have been posted, and the examples and explanations given show that to be an improper application. Using your method, you can say any number of waves have the same phase.

{Begin music}
There must be

50 waves that we can cover:

According to you:

To get the same phase, Hayes
You can sub in a minus, Linus
You can ignore the degree, Lee
Just listen to me

We say:

Get your references handy, Andy
Then read the texts, Rex
And check out the facts, Jack
Then it's easy to see:

With a common bus, Gus
And a voltage either side, Clyde
There is a shift, Cliff
And two voltages there be

 

[rattus]

Question time:

Question time:

How so?

Are the two functions discussed periodic?
Do they have the same period P?
Do they have the same origin arbitrary, t₀?
Do they have the same the same t/P as they advance from t₀?

Perhaps rbalex can answer questions for a change. Just one though.

In describing Bes's hexaphase circuit, there are six equations, six sine waves, six phase constants, six phases.

Perhaps you can tell us why you ignore these simple facts?

 

[mivey]

When you have to "condition" your answer to "limit it" to a specific field in electrical systems, it is a pretty good indication that it is not a fully true statement.

It is not limited to power systems. Even in audio sometimes, the physical inversion are called phase shifts.

Power systems is only a small portion of the electrical field. When something applies to one field but not others, then is it a sign that it is merely a convention, and not a fact. My background in electrical systems is not limited to power systems, but runs the full gamut of all electrical systems.

I suspect most of us older guys have extensive backgrounds and experience. If you have done it all, then you should have heard this terminology before and realize that it applies to multiple fields.

And that is a physical inversion, by its definition, not a time shift or phase shift.

Resources that cross many electrical fields do not agree. I've posted some in #1744 and #2224 including some of these I think:

"Engineering Circuit Analysis", William Hayt:

The name single phase arises because the voltages Ean and Enb, being equal, must have the same phase angle. From another viewpoint however, the voltages between the outer wires and the central wire, which is usually referred to as the neutral, are exactly 180? out of phase. That is, Ean = -Ebn and Ean + Ebn = 0. In a following section we shall see that balanced polyphase systems are characterized by possessing a set of voltages of equal magnitude whose (phasor) sum is zero. From this viewpoint, then, the single-phase three-wire system is really a balanced two-phase system. "two-phase", however, is a term that is traditionally reserved for something quite different, as we shall see in the following section.

"Center-Tapped Transformer and 120-/240-V Secondary Models", William H. Kersting:

Distribution engineers have treated the standard ?single-phase? distribution transformer connection as single phase because, from the primary side of the transformer, these connections are single phase and, in the case of standard rural distribution, single phase line to ground. However, with the advent of detailed circuit modeling, we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary, which now brings into focus the reality that standard 120-/240-V secondary systems are not single-phase line-to-ground systems, but they are three-wire systems with two phases and one ground wire. Furthermore, the standard 120-/240-V secondary system is different from the two-phase primary system in that the secondary phases are separated by 180? instead of three phases separated by 120?.

"Handbook for Electrical Engineers", Harold Pender:

Strictly, the so-called single-phase system is a star-connected two-phase system, since the currents from the two terminals are in opposite directions at any instant, the current leaving by one and entering by the other. However, in practice the name two-phase system is used for a system supplied from a generator or other source of e.m.f. having two windings in which are developed two e.m.f.'s differing in phase by 90?; i.e., a two-phase system is in reality two distinct single-phase systems each with two terminals.

"Handbook for Sound Engineers", Glen Ballou:

25.11.19 The Two-Integrator Loop
This, for better or worse, and a variety of reasons, is by far and away the most popular filter topology used in parametric equalizers. Three inverting amplifiers connected in a loop, as shown in Fig. 25-65, seem a perfectly worthless circuit and, as such, it is. It's there to demonstrate (assuming perfect op amps) that it is a perfectly stable arrangement. Each stage inverts (180? phase shift), so the first amplifier section receives a perfectly out-of-phase (invert, revert, invert) feedback, canceling any tendency within the loop to drift or wobble. Removing 180? phase shift would result in perfect in-phase positive feedback; the result is an oscillator, of unknown frequency determined predominantly by the combined propagation times of the amplifiers.

"Techniques of Circuit Analysis", Carter/Richardson
On forming polyphase sources from voltage sources separated by phase angle differences:

...two voltage phasors in opposition-that is, with a phase difference of 180 degrees; a single-phase transformer with a center-tapped secondary winding would be such a source.

"Alternating Curent Machines", Sheldon:

If the zero ordinates of the two curves coincide, but the positive maximum of one coincides with the negative maximum of the other, as in Fig. 11, then Φ = 180? and the curves are in opposite phase.

"M-I-C-K-E-Wye", Richard P. Bingham, Dranetz-BMI:

A "delta" circuit looks like the delta symbol, which is an equal-sided triangle. There are numerous variations of the delta circuit, such as: grounded deltas (one corner of the triangle is connected to a grounded conductor); open-leg delta (only two elements instead of three are used); or, crazy-leg (where one leg is center-tapped to produce two voltages that 180 degrees out of phase from each other).

"Navy Electricity and Electronics Training Series-Module 8?Introduction to Amplifiers-NAVEDTRA 14180 pg 1-7":

One way in which a phase splitter can be made is to use a center-tapped transformer. As you may remember from your study of transformers, when the transformer secondary winding is center-tapped, two equal amplitude signals are produced. These signals will be 180? out of phase with each other. So a transformer with a center-tapped secondary fulfills the definition of a phase splitter.

"Photovoltaic Power Systems and The National Electrical Code", Sandia National Laboratories:

In a utility connected system or with a 120/240-volt stacked pair of inverters, where the 120 /240-volt power consists of two 120-volt lines that are 180 degrees out of phase, the currents in the common neutral in the multiwire branch circuit are limited to the difference currents from any unbalanced load. If the loads on each of the separate branch circuits were equal, then the currents in the common neutral would be zero.

RF/Microwave Circuits lecture on baluns by Dr. Charles Baylis, Ph.D, of USF:

Baluns are commonly made using the center-tapped transformer below...{illustrates a X1->X2 primary winding and a X3->X4+X5->X6 center-tapped secondary winding}...The center tap (nodes 4,5) is grounded. This provides a 180-degree phase difference between nodes 3 and 6.

When observing that the four-phase system also had opposing pairs of E and -E as well as jE and -jE, C.P. Steinmetz noted that the four e.m.fs of the quadrature system were in pairs opposite to each other and:

...Hence can be produced by two coils in quadrature with each other, analogous as the two-phase system, or ordinary alternating current system, can be produced by one coil.

"Differential VNA Measurements...", James R. Andrews, Ph.D, IEEE Fellow, of SPL:

Figure 2 shows another example of a BALUN. In this case the balanced secondary consists of two identical windings that are connected as a center-tapped secondary. The center tap is usually then connected to the common ground. Coax connectors might now be used for all three terminals. Note that the black dots are polarity indicators for the various transformer windings. With the arrangement shown in Figure 2, one of the secondary outputs is "in-phase" with the input and is thus labeled as the (+), or Non-Inverting output. The other secondary output is "out-of-phase" with the input and is thus labeled as the (-), or Inverting output. There is a 180 degree phase difference between the (+) and (-) outputs.

Andrei Grebennikov in "High Frequency Electronics" on Combiners and Couplers:

The main requirements to baluns are to provide an accurate 180-degree phase shift over required frequency bandwidth, with minimum loss and equal balanced impedances.
...
A wire-wound transformer with a simplified equivalent schematic, shown in Figure 13(a), provides an excellent broadband balun covering in commercial applications frequencies from low kHz to beyond 2 GHz. They are usually realized with a center-tapped winding that provides a short circuit to even-mode (common-mode) signals while having no effect on the differential (odd-mode) signal.

 

[Rick Christopherson]

It is not limited to power systems. Even in audio sometimes, the physical inversion are called phase shifts.

The argument is not about what something may or may not be "called" by convention. The argument is about what it physically is. It is a physical inversion that may be mathematically transformed into a phase shift. However, even that mathematical transformation is available only for periodic functions. If it was a physical phase shift, it would apply to all signals, not just the periodic ones.

 

[rattus]

Perhaps rbalex can answer questions for a change. Just one though.

In describing Bes's hexaphase circuit, there are six equations, six sine waves, six phase constants, six phases.

Perhaps you can tell us why you ignore these simple facts?

And, if you ignore this simple question, it will be further proof that you have been stonewalling us which we have suspected all along.

BTW, signs do matter; they are relevant!

 

[rattus]

The argument is not about what something may or may not be "called" by convention. The argument is about what it physically is. It is a physical inversion that may be mathematically transformed into a phase shift. However, even that mathematical transformation is available only for periodic functions. If it was a physical phase shift, it would apply to all signals, not just the periodic ones.

Does anyone really care? Other than Rick that is.

 

[mivey]

The argument is not about what something may or may not be "called" by convention. The argument is about what it physically is.

One argument is over what we have when we take voltages from different terminals and in different winding directions.

It is a physical inversion that may be mathematically transformed into a phase shift. However, even that mathematical transformation is available only for periodic functions.

It is the phase shift we get from transformers, which is the main topic of discussion.

If it was a physical phase shift, it would apply to all signals, not just the periodic ones.

When we start talking about "the full gamut of all electrical systems", then we can worry about time shifts. But for this thread, we are talking about transformers and the shifts we have with them. The conventions of all members of "the full gamut of electrical systems" is not of real importance in this discussion.

Other than the 180? inductive shift, the shifts we get from the transformer are all the results of physical changes we make by taking voltages from different terminals and in different winding directions, not shifts caused by time delays.

Some have said that taking a voltage in a different winding direction does not make a phase change. The evidence contradicts that saying because it is done all the time with transformers. I have, as have others, provided many examples of where this is routinely done.


In addition, there is the other argument about the application of the definition of phase. One side takes a definition applicable to a single wave and extrapolates it to apply to comparing multiple waves to say similar waves that start at the same time have the same phase. The other side looks at how the rest of the industry applies the definition when comparing the phase of waves and uses that application instead.

 

[Rick Christopherson]

When we start talking about "the full gamut of all electrical systems", then we can worry about time shifts. But for this thread, we are talking about transformers and the shifts we have with them. The conventions of all members of "the full gamut of electrical systems" is not of real importance in this discussion.

Then why do you continually insist on using words like "real" and "physical" if you are not willing to defend them? You chose those words for a reason and you accentuated them repeatedly for a reason. You did so because you were attempting to make a false point, and then you choose not to defend that point when called out on it. That is dishonest.

 

[Rick Christopherson]

And, if you ignore this simple question, it will be further proof that you have been stonewalling us which we have suspected all along.

 

[jim dungar]

Spot on.

Different, but 'in phase' voltages.

 

[jim dungar]

I suspect most of us older guys have extensive backgrounds and experience.

You because you are old does not make you correct.
Utilities references are notorious for using the single word 'phase' when in context it is clear that they are addressing 'conductors'.

I have only been dealing with waves for about 40yrs, I am comfortable with a mathematical inversion being the same phase as the original and yet also acknowledge there is difference between an inversion and an opposing phase.

A single waveform is a single wave form, regardless how you manipulate its magnitude.

 

[rattus]

Different, but 'in phase' voltages.

Now Jim, how can two sines be 'in phase' with different phase constants? Different phase angles? We are of course talking about Van and Vbn, which are out of phase by PI radians.