Why is residential wiring known as single phase?

[ronaldrc]

I just changed the batteries in my led flash lite a while ago turned the dag gone thing on and guess
what? The thing wouldn't work. I took the batteries out and just happen to notice one battery was
turned around backwards, yelp turned 180 degrees physically from the other one. Since we started in the electrical field with batteries this is probably where the term originated. I bet you money one experimenter turn to the other one and said there is whats wrong you have one battery turned 180 degrees around from the other one. I just wish he could read this thread. I bet he had no idea what confusion he had just started.

I have a good friend that?s an Engineer and I might want to tell him about this,

So could one of you write me an equation to fit my predicament? Please

Is this really what this long discussion is all about? You all call it a phase reversal some even a phase shift I call it opposite polarity.

Don't get me wrong I do enjoy checking every hour or so just to see if anyone is in agreement with anyone else, so please don't stop

 

[rbalex]

Of course V_msin ωt = -V_msin (ωt+π)
...
But not terribly illuminating in the context of a three wire system where V_an = V_m Sin(ωt) and V_bn = V_m Sin(ωt+π)
NOT - V_msin (ωt+π)

AND V_bn = -V_m Sin(ωt)

GASP some how that damned ωt ended up being the same argument for both valid equivalent functions.

 

[Besoeker]

Do you believe the periods for the driving voltages aren't 2π?

No. And I have never claimed that to be so. In fact I have given equations, drawings, diagrams,and real life pictures that clearly demonstrate that to be the case.

Because if they aren't Mr. Ohm needs a serious talking to.

Given that Mr Ohm had not a lot to do with alternating currents that's an irrelevant comment.

 

[Besoeker]

AND V_bn = -V_m Sin(ωt)

Care to rethink that?

 

[rbalex]

Care to rethink that?

Not particularly, Your the one that said, "Of course V_msin ωt = -V_msin (ωt+π)." Doesn't that mean -V_msin ωt = V_msin (ωt+π) also?

 

[rbalex]

No. And I have never claimed that to be so. In fact I have given equations, drawings, diagrams,and real life pictures that clearly demonstrate that to be the case.

Given that Mr Ohm had not a lot to do with alternating currents that's an irrelevant comment.

So we can agree the voltage functions' periods are 2Π and we can quit trying to climb the Grand Tetons because they aren't relevant to the system voltages of a residential 120/240V single-phase system?

Edit Add: Or would you care to say Ohm's law doesn't apply to AC circuits altogether?

 

[Besoeker]

Not particularly, Your the one that said, "Of course V_msin ωt = -V_msin (ωt+π)." Doesn't that mean -V_msin ωt = V_msin (ωt+π) also?

But not
V_bn = -V_m Sin(ωt)

 

[Besoeker]

So we can agree the voltage functions periods are 2Π and we can quit trying to climb the Grand Tetons because they aren't relevant to the system voltages of a single-phase system?

Fine.
But the 120-0-120 isn't a single phase system.

 

[rbalex]

Fine.
But the 120-0-120 isn't a single phase system.

Sure it is. There?s only one phase in the system. Any relevant voltage function can be validly written in terms of [ωt+φ₀]

 

[rbalex]

But not
V_bn = -V_m Sin(ωt)

Really?
V_bn = V_m Sin(ωt+π)
Doesn’t that mean
V_bn = -V_m Sin(ωt)?

 

[rattus]

AND V_bn = -V_m Sin(ωt)

GASP some how that damned ωt ended up being the same argument for both valid equivalent functions.

By using a well known trig identity, rbalex has shown that a sine wave, shifted by PI, is equivalent to its inverse, but we already knew that. He then erroneously claims that the phase is (wt) not (wt + PI). We have already been around this block Bob. We're not buying it.

sin(wt + PI) = -sin(wt)

Actually, I think Kerchner and Corcoran's treatment of phase is a bit confusing. Maybe that is why I struggled with the course in 1956. But after reading it several times, it really says that phase must include the phase angle. That is,

phase = (wt + phi0)
phase = (wt) only if phi0 = 0

We knew that too.

Then different sine waves would carry different values for phi0.

Oh yes, two waves are said to be in phase if their POSITIVE peaks occur at the same instant in time. Polarity is important. I challenge anyone to prove otherwise.

Then a wave can NOT be in phase with its inverse.

 

[gar]

120228-2108 EST

__dan:

Relative to post 1531. Your circuit analysis is wrong.

V_AB is not equal to V_AN + V_BN

If the sum was zero then you could connect A to B with no sparks, but you will get sparks. Find a good book on circuit analysis and study it.

In the normal center tapped transformer providing 120-0-120 you add V_AN to V_NB to get the voltage from A to B. Start with A and advance toward B and use the same sense for subscripts to add the voltages.

.

 

[gar]

120228-2127 EST

__dan:

Relative to your post 1535. You misunderstood the meaning of the waveforms on the scope. There are two independent waveforms on the screen. Channel A and channel B. One could be the sine wave V_AN, and the other any other waveform of a related sub harmonic, or harmonic, or combination thereof. The waveforms are not added, subtracted, multiplied, or in any other way related to each other than by how the second waveform is created. And it could even be a random signal for that matter.

What you can tell from the scope description I provided is that in one case the second signal was an inversion of the first signal.

.

 

[rbalex]

By using a well known trig identity,

So why do you keep trying to exclude trig identities?

Then a wave can NOT be in phase with its inverse.

So? I accepted your definition of "in phase;" however, the functions still have the same identical phase. In fact, every valid voltage function 120V or 240V may be written in terms of the same identical phase - a single-phase.

 

[rattus]

So why do you keep trying to exclude trig identities?

So? I accepted your definition of "in phase;" however, the functions still have the same identical phase. In fact, every valid voltage function 120V or 240V may be written in terms of the same identical phase - a single-phase.

Because there is no need for a trig identity to answer the OP's question, and you used the identity improperly.

So you now agree that inverses cannot be in phase?

You continue to ignore the phase constant which is part of the phase definition.

The phase constant is so called because it is the constant part of the phase expression--(wt + phi0). It is also called the phase angle.

And another perhaps informal definition of phase says the two waves are in phase if their phases are equal. Since wt is always equal to wt, that means that two waves are in phase only if the phase constants are equal. That is clearly not the case in a split phase system.

 

[Rick Christopherson]

Because there is no need for a trig identity to answer the OP's question, and you used the identity improperly.

This makes no sense. You used the same trig identity to create your phase shift from inversion, and then you say that he can't reverse it?

 

[__dan]

120228-2108 EST


In the normal center tapped transformer providing 120-0-120 you add V_AN to V_NB to get the voltage from A to B. Start with A and advance toward B and use the same sense for subscripts to add the voltages.

.

Yes, the transformer offers you two voltages,V_an and V_nb which sum to 240 volt. Theses voltages, are they in phase ???

The voltages on the scope which show a 180 deg displacement, or multiplication by (-1), or a lead reversal, these voltages sum to zero. However, when I measure the voltage sum at the transformer, I do not get zero, I get 240.

As you have said previously, the scope is limited in what it can show because the scope common is tied to the power supply ground, which is at the center of the transformer winding. If the scope common were tied to the end of the winding and measured the sum of the series connections, the sum would show each and every winding is "in phase". In fact, that is the actual condition.

The phase shift occurs due to the connections to the transformer and not by the transformer itself.

 

[rattus]

Yes, the transformer offers you two voltages,V_an and V_nb which sum to 240 volt. Theses voltages, are they in phase ???

The voltages on the scope which show a 180 deg displacement, or multiplication by (-1), or a lead reversal, these voltages sum to zero. However, when I measure the voltage sum at the transformer, I do not get zero, I get 240.

As you have said previously, the scope is limited in what it can show because the scope common is tied to the power supply ground, which is at the center of the transformer winding. If the scope common were tied to the end of the winding and measured the sum of the series connections, the sum would show each and every winding is "in phase". In fact, that is the actual condition.

The phase shift occurs due to the connections to the transformer and not by the transformer itself.

___dan,

You probably learned that the voltages on the center tapped secondary add to create 240V. That is correct. It is also correct to use only the neutral as a reference to see the opposing phases. Then you must SUBTRACT, not add,one from the other to get the POTENTIAL DIFFERENCE. These voltages are real, they are what is on L1 and L2; that is what we want to know. You need to know complex arithmetic and phasors to fully comprehend this. But if you don't know, that doesn't make you a bad person.

As you know you can measure any voltage in two ways. Both voltages are real. No one voltage is more real than another.

 

[rbalex]

Because there is no need for a trig identity to answer the OP's question, and you used the identity improperly.

So you now agree that inverses cannot be in phase?

You continue to ignore the phase constant which is part of the phase definition.

The phase constant is so called because it is the constant part of the phase expression--(wt + phi0). It is also called the phase angle.

And another perhaps informal definition of phase says the two waves are in phase if their phases are equal. Since wt is always equal to wt, that means that two waves are in phase only if the phase constants are equal. That is clearly not the case in a split phase system.

Trig identities show that any relevant voltage in the system can be written in terms of the same phase. You may have had the mechanics of trig down, but it appears you didn?t actually comprehend what you were doing when you dealt with identities; in other words, I used identities properly.

I accepted your definition of ?in phase?; but inverses have the same phase as their primary functions through identities. Your reading comprehension skills appear to be lacking too since you can?t seem to differentiate between ?same phase? and ?in phase? any more than you were able to initially see the distinction between phase and phasor until it was explained to you.

I simply used the same implied phase constant, φ₀ =0, as Bes. So it seems your cognition is also poor. BTW, this is very close to a false assertion, but I?ll chalk it up to your poor comprehension.

The phase constant establishes what the phase is when t = 0, not "because it is the constant part of the phase expression." So you demonstrate you're having problems with algebra comprehension too.

I don?t care to deal with any more informal definitions ? even if I may happen to agree with some of them and you just don?t understand how to apply them properly.

 

[__dan]

___dan,

You probably learned that the voltages on the center tapped secondary add to create 240V. That is correct. It is also correct to use only the neutral as a reference to see the opposing phases. Then you must SUBTRACT, not add,one from the other to get the POTENTIAL DIFFERENCE. These voltages are real, they are what is on L1 and L2; that is what we want to know. You need to know complex arithmetic and phasors to fully comprehend this. But if you don't know, that doesn't make you a bad person.

As you know you can measure any voltage in two ways. Both voltages are real. No one voltage is more real than another.

I have no need to say so but I have had tons of calculus, complex math circuit courses, signals and systems, electromagnetic fields and waves. The university I went to did not have a power program, so the electromechanical energy conversion course had no vector math, everything was sin(wt+phi) and e^j*omega*t.

What I want to know is if the phase shift is caused by the transformer internally, and the answer is no, the windings on the same core are matched and in phase. I need to know this because I add and subtract windings to make the L1 L2 voltages that I need.

I need a paradigm of understanding I am comfortable with because it represents and accurately describes the underlying physical reality that it is my job to hook up and make work.

The two winding 120 0 120 transformer. Each winding is in series to add to 240 volt. I am adding windings and adding voltages. In your paradigm, adding the windings to yield 240 volt, you say I must SUBTRACT the voltage representations provided by you. Listen to yourself, the physical operation is to add the windings in series and you say to make the math work I have to SUBTRACT the voltage vector.

The notation is selected to make the underlying physical reality easier to understand. It is an abstract construct useful only if it aids understanding. To add windings in series I want a notation which represents the underlying physical reality, adding windings = adding voltage vectors, therefore, to make the math work (and represent the physical fact) the windings are in phase and "add".

The voltages on the scope, when I add them their sum is zero. When I measure the added sum at the transformer I get 240 volts. Can you explain this POTENTIAL DIFFERENCE ?