Why is residential wiring known as single phase?

[rattus]

One diode is connected V_an anode to cathode in series with the load. The other diode is connected V_bn anode to cathode in series with the load.
That's how it is. No effective about it.
It requires the 180deg displacement to make it work.
Two voltages displaced by 180 deg cannot be in phase.
They are thus different phases. So, more than one phase.

Found the diagram, post #1004?

This is the classic full-wave rectifier circuit using SCRs.

Node a is X1,

Common/neutral is the junction between X2 and X3.

Node b is X4.

Polarity dots could be added to nodes X1 and X3.

The rectifiers conduct at 180 degree intervals to minimize ripple.

Van and Vbn are in antiphase.

Did I get it right Bes?

 

[Besoeker]

Where do I find the schematic for said rectifier circuit? Sounds like a full wave rectifier to me.

I'm sure I have posted this a few times already:

 

[rattus]

OK, Let's try this - the big hand is on ... oh yeah, you use a digital watch, you won't understand. (I apologize right now - I don't know what came over me)

Seriously, you acknowledge the frequency is the same ? that?s a start. Speaking of starting, while it may be a wild assumption, I believe you would probably agree the phasors started rotating at the same time. That means their periods are identical. It also means the characteristic phase of the voltage functions they inscribe can BOTH be written based on either (wt + 0) or (wt + 180) or (wt - 180) or (wt + 360) or (wt - 360) or, guess what, any other (ωt + Φ₀) or (ωt - Φ₀) you choose; i.e., the phases are also identical.

No, the phase of one is (wt), the phase of the other is (wt + 180), they are not identical.

 

[Besoeker]

Found the diagram, post #1004?

This is the classic full-wave rectifier circuit using SCRs.

Node a is X1,

Common/neutral is the junction between X2 and X3.

Node b is X4.

Polarity dots could be added to nodes X1 and X3.

The rectifiers conduct at 180 degree intervals to minimize ripple.

Van and Vbn are in antiphase.

Did I get it right Bes?

Pretty much in my opinion.

Full wave for me is this/;

 

[rbalex]

No, the phase of one is (wt), the phase of the other is (wt + 180), they are not identical.

I guess I'll have to let gar explain how trig identities work.

 

[rattus]

Pretty much in my opinion.

Full wave for me is this/;

We call that a full wave bridge.

 

[jim dungar]

Polarity dots could be added to nodes X1 and X3.

You are assigning something based on the physical construction of the windings.
Aren't polarity dots used for assinging direction to current flow during analysis?
Isn't it standard practice to install the dots based on the physical construction of the transformer (i.e. current into H1 yields current out of X1)?

The rectifiers conduct at 180 degree intervals to minimize ripple.

Yes, one diode conductors as current flows from point A towards point B and the other diode conducts when current flows from B towards A.

Van and Vbn are in antiphase.

More than a thousand post, and we are right back to Vnb = -Vbn


You stated that given the physical connection of winding X1-X2 joined with winding X3-X4, that current flows out of X1 at the same time it is flowing out of X3 (as evidenced by your polarity dots). This means the current is flowing from A towards N at the same time it is flowing from N towards B; sure sounds like Van is in phase with Vnb based on resistive loading.

You then apply some basic math (i.e. swap the reference points), and get Vbn = -Vnb, Now you can use Van and Vbn and say they are 180? opposed.
Physically nothing has changed, so isn't the current still flowing out of X1 and X3, based on your assigned polarity dots? This sounds like the currents are still in-phase with each other

I am sure that Besoeker's half-wave rectifier uses currents and voltages that are relatively in-phase with each other.

 

[Rick Christopherson]

Mathematics is an important tool for engineering.
I had a lecturer who put this very succinctly.
You have an electrical problem that requires calculation. Three stages.

Understand the problem and express it in mathematical terms.
Solve the mathematical problem.
Interpret the results.

Mathematics is an important tool. However, some of you are confusing your tools with the definition of the system. For example, with transistors not operating in their saturation limits, we use a "small signal equivalent circuit" to represent that transistor for analysis.

Does this mean that we have physically replaced the transistor with several other discrete components in the circuit? No!! It is a tool that we use for analysis. The model fails when we hit saturation, because it is just that, a model.

You guys are confusing the tools that you use for analysis with the physical system. I am not contesting your tools. I am contesting that you are using your tools to define the system. It is not a 2-way path.

That's why your tools and models fail when you put a noise artifact in the positive peak of the primary and don't see it on the positive peaks of the secondary. You all know this, but you are being dishonest with your arguments by ignoring it.

 

[rattus]

I guess I'll have to let gar explain how trig identities work.

\

Don't count on gar. How do you equate (wt) and (wt + 180)? You can't drop negative signs, you can't ignore the FACT that one wave is displaced from the other by a half period. You can't ignore the FACT that the voltages are in antiphase, if they were in phase, Besoeker's full wave rectifier circuit would be only half wave. It is what it is, and you can't change that.

Don't count on identities either. They are useful, but there is nothing hard about them. FYI, I took trig before you were in diapers. Made an A in it too, honors course at that. So knock off the condescending remarks.

 

[weressl]

There are two ways to handle this.

For me I just accept 'because we do'

The other way takes 600 forum posts.


Good luck!

Yep, this and the ground prong position....

Although this at least has some technical merit as one need to look at the transformer for what it is: a generator without moving parts. Thus it generates opposing phase voltages.:lol:

 

[mivey]

Fundamentally, you are just resorting to Post 2...."Yeah, we call it that; but it really isn't"

Because that is just the way it is. The labels are set by convention. The questions arise because the labels don't always match the physical. As I have said before, I'm not proposing we change the labels, just that we understand why they are what they are and that they are not comprehensive system descriptions. They are just labels.

For the record you are still equating synchronism with phase.

For the record, I'm using "in-phase" the same way the rest of our industry uses it.

As far as I can tell, I haven't seen either of them jump to defend your statement. I doubt gar would say identities aren't relevant; he may not like the application, but they are valid. mivey might agree with you; but he's had several opportunities to say so.

rattus does not need me to defend him as he is a big boy. You are misinterpreting what he is saying and he can point that out on his own. However, I will say that I have noticed you trying to spin what he is saying, much like you do with me.

As for me, my position is that your whole approach is wrong and your are trying to re-define some math terms to make your idea fit. That is not necessary as there is a legitimate way to state what you are trying to say without butchering the math in the process. I believe I have made that clear in many prior posts but I've stated it again since you brought it up.

 

[mivey]

With your own logic in play, try and prove it.

Try? I have already said a two-wire circuit is single-phase by default. Single-phase is a single voltage or current in a circuit. With a two wire source, only one voltage is applied to the circuit and there can be only one current (the current leaving one terminal is the same current entering the other).

That would be an opinion. I can wire circuits to make use of both the forward phase and the reverse phase. I can get six phases out of it with a neutral.

Sure, both voltage options are available, but you would have two separate circuits, not two voltages applied to the same circuit. However, as I gave in a prior example, you could separate the flux using two isolation transformers and get two voltages with a 180? difference that could be applied to the same circuit at the same time. Hmmmm, separate fluxes from a single source...sound familiar?

 

[mivey]

The fact is there was a reason for calling it "single-phase" that predates oscilloscopes.

Yeah, the reason predates the oscilloscope by about 30 years. The idea was that two smaller AC forces can combined in a series-additive manner to produce one larger force. Although we could get one larger force, it did not mean the smaller forces were gone.

The use of the term "single-phase" for the larger combined force does not negate the fact that we can also obtain two phase-opposed forces from the same output.

 

[mivey]

But it's still only a single voltage gradient with a center tap.

A voltage gradient has a direction component; basic physics tells us that. You saying "a single voltage gradient" is the same as saying there is only the one linear direction. A voltage gradient can also mean the voltage as directed away from a test charge and does not have to be one linear direction. Think of the voltage gradient above Earth: it does not have to be all in one linear direction.

 

[mivey]

Combining two available forces from a center-tapped transformer produces a larger resultant force in most circuit applications when the two forces are in phase, in series. These combined forces will act as one combined larger series force so we call it single-phase. A more descriptive label would be "series additive single-phase".

The use of the term "single-phase" does not negate the fact that we can also obtain two phase-opposed forces from the same output. This use is in the same manner that we use poly-phase forces as individual forces with a phase difference and not as one combined series force. The circuits that utilize two 180? phase-opposed forces are relatively few in number as compared to the circuits that result in one series additive combined force. Since the transformer can supply both series additive single-phase forces as well as the phase-differentiated forces it is a source for both but is labeled by the most common use.

The label is not that it is a pure single-phase system as it is that the two smaller phases combined result in a larger single phase. Considering one phase to be the return of the other (possible since they are opposing pairs) equates the combination to a larger single-phase system, but it is still a system containing two smaller phases. Both systems can be produced by one center-tapped winding, in the same manner that the quadrature, or four-phase system, can be produced by two center-tapped windings.

As for a labeling rule:
Only voltage phases will be considered for labeling purposes, and multiple phases that can be paralleled or that are opposing pairs will be counted as one phase in total.

 

[rbalex]

\

Don't count on gar. How do you equate (wt) and (wt + 180)? You can't drop negative signs, you can't ignore the FACT that one wave is displaced from the other by a half period. You can't ignore the FACT that the voltages are in antiphase, if they were in phase, Besoeker's full wave rectifier circuit would be only half wave. It is what it is, and you can't change that.

Don't count on identities either. They are useful, but there is nothing hard about them. FYI, I took trig before you were in diapers. Made an A in it too, honors course at that. So knock off the condescending remarks.

Let me get this straight - are you saying that the voltage functions of the phasors can't be written as equivalent functions using either (wt) or (wt + 180)?

Do you really want to commit to the statement,"Don't count on identities either. They are useful, but there is nothing hard about them."?

 

[Besoeker]

Yes, one diode conductors as current flows from point A towards point B and the other diode conducts when current flows from B towards A.
I am sure that Besoeker's half-wave rectifier uses currents and voltages that are relatively in-phase with each other.

Not so.
One diode conducts from Va to N when Va is positive wrt N.
The other diode Vb to N when Vb is positive wrt N.

These two conduction periods occur at different points in time thus are not in phase.
I wouldn't call that relatively in-phase.
I'd call it anti-phase.

 

[Besoeker]

Mathematics is an important tool. However, some of you are confusing your tools with the definition of the system. For example, with transistors not operating in their saturation limits, we use a "small signal equivalent circuit" to represent that transistor for analysis.

I've provided actual circuits. Things that work in real life.
Not equivalents.

 

[Rick Christopherson]

I've provided actual circuits. Things that work in real life.
Not equivalents.

Thank you for quoting me out of context. I appreciate that.

 

[Besoeker]

i.e., the phases are also identical.

If the phases were identical the circuit in post #1004 wouldn't work.
But it does.