Why is residential wiring known as single phase?

[Besoeker]

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

I came across this definition for polyphase when I was looking for something else:

1. (Engineering / Electrical Engineering) Also multiphase (of an electrical system, circuit, or device) having, generating, or using two or more alternating voltages of the same frequency, the phases of which are cyclically displaced by fractions of a period.

V_an and V_bn are displaced by half a period.
Thus polyphase. Thus not single phase.

 

[mivey]

My my, what busy beavers. Have been out of town for a bit and really thought the thread was going to devolve into an insult stream, but I see it has survived with some real discussion alive. Good responses by gar, besoeker, and rattus to the usual suspects.

The electrician has field condition, the job requirements and the present hardware. He wants to know how to hook "it" up and why, in this case the single phase source and two winding transformer secondary.

Nothing we are discussing will change the day-to-day life of the EC since it is "above and beyond" the understanding needed for day-to-day work.

Saying there is a phase shift to the average person can create FUD, fear, uncertainty, and doubt. The inquiry is focused on relieving this uncertainty, on having an understanding that gives confidence in knowing what is happening and why.

Here is a reality check for you: How does telling the average person that the measuring equipment they are using is lying to them give them confidence and avoid fear, uncertainty, and doubt? The fact is, the equipment is showing you what is actually there. A meter is device measuring the effects of adding a small load, not a device that just makes up something to throw at the display.

In this case the phase shift is caused by a reversal of the leads attached to the windings relative to the winding turn direction, and not by any other cause, like by magic. The reason the reversal of the leads is necessary to cause the phase shift is because the transformer natively does not cause the phase shift, it offers two windings that are exactly matched in winding turn direction and so their outputs are "in phase".

As rattus said in one of the prior posts, he did not reverse any leads because he put them where he wanted them in the first place.

 

[mivey]

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

Batteries are a poor example of what happens in the AC case. How about first pondering the following instead of an equation: I have a flashlight that you can shake back and forth to make it light up. Whether I shake to the left first or to the right first doesn't matter because I will get light either way. Both directions produce positive results.

 

[mivey]

Simple. At the transformer, the winding's turn direction matches and phi 0 = theta 0. This should be obvious because 120(wt + phi) + 120(wt + theta) = 240(wt + phi).

To get phi 0 != theta 0 you have to reverse the polarity of the connection leads relative to the winding's turn direction. The transformer natively offers you two windings that are wound in the same direction.

Irrelevant. The windings from my two transformers on the left side of my generator example also have windings twisting in the same direction, but the voltages are physically 180? displaced from the common Earth point.

The phase reversal on the scope is an artifact of the measuring protocol and not a result of the underlying physical reality.

Wrong. The phase reversal is there because it is what is really there.

If you multiply one of the vectors on the scope by (-1), then it will sum to the correct answer (V1 + V2 = 240 volt), not zero volts. You have been emphatic that the voltages are displaced by 180 deg, which sums to zero. Measuring the actual, the voltages sum to 240.

We can use the potential sums or the potential differences. We are not limited by one method.

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

Yes

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.

You should take the potential difference.

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".

Because in the series direction they are in phase.

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.

That's no excuse. There is plenty of information available outside of a classroom setting. Education should not end when you flip a tassle.

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.

Series additive.

I need to know this because I add and subtract windings to make the L1 L2 voltages that I need.

Then subtract them already and quit just summing them!

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.

Then look at my open-wye example where the both the X1->X2 direction and the X2->X1 direction are present and produce real results.

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.

So? We use addition and subtraction all the time. Consider the 120/208 transformer. We have:

120@60? + 120@0? = 208@30?
or
120@180? + 120@240? = 208@210?
or
120@0? - 120@240? = 208@30?
or
120@240? - 120@0? = 208@210?

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".

You can also subtract. We do it all the time with three-phase voltages. The physical properties of the single-phase transformer make it easy to use addition but that does not change the fact that the voltages in the single-phase transformer do not have to be used all series additive. My open-wye example proves that you can use one half of the winding in one direction and one in the other to produce voltages with displaced phases.

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 ?

What about taking a potential difference do you not understand? It is a basic physics concept.

 

[mivey]

The windings from my two transformers on the left side of my generator example also have windings twisting in the same direction, but the voltages are physically 180? displaced from the common Earth point.

That is to say: The windings from my two transformers on the left side of my generator example also have windings twisting in the same direction, but the voltages to the common Earth point have a physical 180? phase displacement.

 

[rattus]

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.

Then if I don't use identities, a wave and its inverse would have different phases? Which phase should I use? If I write sin(wt + phi0) = [-sin(wt)]? Should I use the first real one or the fake one. Does

wt + phi0 = wt

How can this be??

I think I will use the same identity to convert back to the original

sin(wt + phi0) = [-sin(wt)] = sin(wt + phi0)

It is simply illogical to make such a claim.

wt is the phase of +sin(wt), NOT -sin(wt)
wt + phi0 is the the phase of sin(wt + phi0)

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.

I would expect better from a Professional Engineer and a moderator. Let's show a little respect.

 

[rbalex]

I came across this definition for polyphase when I was looking for something else:


V_an and V_bn are displaced by half a period.
Thus polyphase. Thus not single phase.

The fact is the periods for V_an and V_bn start and end at the same time. They better for a 120/240V residential system.

In any case, does it somehow alter the fact that any relevant voltage function in the system can be validly written in terms of the same [ωt+φ₀]?

I'm still interested in your response to 1550.

 

[Rick Christopherson]

Then if I don't use identities, a wave and its inverse would have different phases? Which phase should I use? If I write sin(wt + phi0) = [-sin(wt)]? Should I use the first real one or the fake one.

Are you suggesting that the phase shift is what is real and the inversion is only mathematical? You have these reversed, and that is why you refuse to address my example with noise.

 

[gar]

120229-1025 EST

rbalex:

Assumption is we are talking about a periodic function.

If period is defined as the time from a definable point anywhere in the cycle to the next equivalent point in the next cycle, then:

1. The period is invariant no matter where the first point is picked.

2. Two separate waveforms of identical shape, including amplitude, and frequency have the same period.

3. If the equivalent point is used in both waveforms, and that pair of points in both waveforms occurs at the same time, then the waveforms are in-phase.

4. If the equivalent points used in both waveforms do not occur at the same time, then the waveforms are not in-phase.

5. V_AN is not in-phase with V_BN.

6. The periods of V_AN and V_BN do not start at the same time. The zero crossings may coincide, but the slopes at those zero crossings are different in sign and therefore the zero crossings are not equivalent points. One is displaced Pi (180 deg) from the other.

.

 

[rbalex]

Then if I don't use identities, a wave and its inverse would have different phases? No, they aren't "in phase" by your definition, but they still have the same phase. Which phase should I use? If I write sin(wt + phi0) = [-sin(wt)]? When φ₀ = 180? When Should I use the first real one or the fake one. They are both real (Hint: That’s more or less what an identity means)

Does

wt + phi0 = wt

How can this be?? When φ₀ = 0?

I think I will use the same identity to convert back to the original

sin(wt + phi0) = [-sin(wt)] = sin(wt + phi0) Works for me if φ₀ = 180?

It is simply illogical to make such a claim. YES - when you keep trying to change φ₀ indiscriminately.


wt is the phase of +sin(wt), NOT -sin(wt) It is for both when φ₀ = 180? (Now who's ignoring the phase constant)

wt + phi0 is the the phase of sin(wt + phi0) Yes, So?

Does anyone check your math?

I would expect better from a Professional Engineer and a moderator. Let's show a little respect.

Me being a PE gets you nothing one this one; I routinely have to tell people things that they don’t want to hear, even clients. Of course most of them catch on a lot faster.

Respect is an earned commodity.

Nevertheless the complaint about my moderator status may have some validity. I’ll have my fellow moderators check in and see if I’ve been too blunt.

 

[rbalex]

120229-1025 EST

rbalex:

Assumption is we are talking about a periodic function.

If period is defined as the time from a definable point anywhere in the cycle to the next equivalent point in the next cycle, then:

1. The period is invariant no matter where the first point is picked.

2. Two separate waveforms of identical shape, including amplitude, and frequency have the same period.

3. If the equivalent point is used in both waveforms, and that pair of points in both waveforms occurs at the same time, then the waveforms are in-phase.

4. If the equivalent points used in both waveforms do not occur at the same time, then the waveforms are not in-phase.

5. V_AN is not in-phase with V_BN.

6. The periods of V_AN and V_BN do not start at the same time. The zero crossings may coincide, but the slopes at those zero crossings are different in sign and therefore the zero crossings are not equivalent points. One is displaced Pi (180 deg) from the other.

.

If you have followed the rest of the argument, I have already accepted they are not "in phase"; nevertheless they have the same phase; i.e., every relevant voltage function may be written using the same phase.

 

[ronaldrc]

Batteries are a poor example of what happens in the AC case. How about first pondering the following instead of an equation: I have a flashlight that you can shake back and forth to make it light up. Whether I shake to the left first or to the right first doesn't matter because I will get light either way. Both directions produce positive results.

Thanks for the response mevy

I do know that, thats the way diodes work.

I know I wouldn't understand your equation anyway.

Oh, I keep forgetting theres no such thing as a neg. potential.

 

[rattus]

Phase constants:

Phase constants:

rbalex's identity only holds for a separation of 180 degrees. Let us consider phase constants of 0 and 179 degrees. Now let the second phase constant be 180 degrees. Am I to believe that the phase constant suddenly goes to 0??

Sounds like a discontinuity to me.

 

[Rick Christopherson]

rbalex's identity only holds for a separation of 180 degrees.

Yes, but it is the same identity that you use to get your phase shift from an inversion. So if you deny his identity, you have to first deny your own usage of it.

 

[rbalex]

rbalex's identity only holds for a separation of 180 degrees. Let us consider phase constants of 0 and 179 degrees. Now let the second phase constant be 180 degrees. Am I to believe that the phase constant suddenly goes to 0??

Sounds like a discontinuity to me.

Are you really that thick?

First, “rbalex's identity only holds for a separation of 180 degrees” is the only identity relevant to this discussion as it applies to conventional 120/240V systems.

But, if you want to use other phase constants you will need to use the full identity:

sin(u ? v) = sin (u)cos (v) ? cos(u)sin(v)

The only discontinuity is your ability to follow an argument.

 

[__dan]

Irrelevant. The windings from my two transformers on the left side of my generator example also have windings twisting in the same direction, but the voltages are physically 180? displaced from the common Earth point.

Yes, move the test leads from a device that does not support your premise to one that does. That has been the arguement, moving the leads has been creating the effect you have been claiming.

Wrong. The phase reversal is there because it is what is really there..

The phase reversal is there because you have reversed the leads relative to the winding's turn direction. If you maintain consistency of lead connection arrangement with winding turn direction, the phase reversal magically disappears.

We can use the potential sums or the potential differences. We are not limited by one method...

Yes, just give me your cell number and I'll call you to tell me when I should subtract when adding and when I should add when adding.

You should take the potential difference...

Because in the series direction they are in phase.

This is where we agree. There is no need to claim the phases are reversed when it is the measuring method that has reversed. In fact, the transformer windings are in series, in phase, and this fact is fixed and determined at the time of manufacturing. This series, in phase, arrangement does not change, although the connections to the taps provided may change.

What about taking a potential difference do you not understand? It is a basic physics concept.

I do not understand why I must subtract the voltage vector supplied by you when I physically add windings in series and the real voltage actually adds. Can you explain this ?

Nothing we are discussing will change the day-to-day life of the EC since it is "above and beyond" the understanding needed for day-to-day work.

Day to day EC's have been making this inquiry repeatedly, is there one phase or more than one. And your response, do you want to say that the need to understand this is "above and beyond".

Here is a reality check for you: How does telling the average person that the measuring equipment they are using is lying to them give them confidence and avoid fear, uncertainty, and doubt? The fact is, the equipment is showing you what is actually there. A meter is device measuring the effects of adding a small load, not a device that just makes up something to throw at the display.

Here is a reality check for you: The last time the average person saw a phase shift, they were watching Star Trek or Stargate where stepping through the door that causes the phase shift would land them in an alternate parallel dimension, usually a punisment or hell dimension. The random phase shift is something to be afraid of. Considering that this is how the majority of the audience is trained, do you really want them to just blindly and obediently accept there is a phase shift at the transformer without conveying the fact that the phase shift is caused by how the load is connected to the transformer and not by the transformer itself. It is smoke and mirrors.

As rattus said in one of the prior posts, he did not reverse any leads because he put them where he wanted them in the first place.

rattus maintains there is a phase shift and placed the leads where he could show his predetermined conclusion. However, the voltages he displays sum to zero while the actual voltages sum to 240. Yes, I know, I should subtract when I am adding. Can I have your pager number to call you when it's time to subtract when I am adding?

 

[rattus]

Yes, move the test leads from a device that does not support your premise to one that does. That has been the arguement, moving the leads has been creating the effect you have been claiming.




The phase reversal is there because you have reversed the leads relative to the winding's turn direction. If you maintain consistency of lead connection arrangement with winding turn direction, the phase reversal magically disappears.



Yes, just give me your cell number and I'll call you to tell me when I should subtract when adding and when I should add when adding.






This is where we agree. There is no need to claim the phases are reversed when it is the measuring method that has reversed. In fact, the transformer windings are in series, in phase, and this fact is fixed and determined at the time of manufacturing. This series, in phase, arrangement does not change, although the connections to the taps provided may change.



I do not understand why I must subtract the voltage vector supplied by you when I physically add windings in series and the real voltage actually adds. Can you explain this ?



Day to day EC's have been making this inquiry repeatedly, is there one phase or more than one. And your response, do you want to say that the need to understand this is "above and beyond".



Here is a reality check for you: The last time the average person saw a phase shift, they were watching Star Trek or Stargate where stepping through the door that causes the phase shift would land them in an alternate parallel dimension, usually a punisment or hell dimension. The random phase shift is something to be afraid of. Considering that this is how the majority of the audience is trained, do you really want them to just blindly and obediently accept there is a phase shift at the transformer without conveying the fact that the phase shift is caused by how the load is connected to the transformer and not by the transformer itself. It is smoke and mirrors.



rattus maintains there is a phase shift and placed the leads where he could show his predetermined conclusion. However, the voltages he displays sum to zero while the actual voltages sum to 240. Yes, I know, I should subtract when I am adding. Can I have your pager number to call you when it's time to subtract when I am adding?

__dan,

You don't need to to call anyone. If the phasor arrows are connected tail to tail, you SUBTRACT. If the phasor arrows are connected head to tail, you add, phasorially that is.

It is just a different view of things--different but just as valid.

Consider a three phase wye. How do you get 208 volts out of that? Let's add 120 @ 0 to 120 @ - 120.

120 + j0 +120[cos(-120) + jsin(-120)]

=120 - 60 - j104 = 60 - j104 NE 208

Now let's subtract:

120 - 120[cos(-120) + jsin(-120)]

= 120 + 60 + j104

= 180 + j104 = 208Vrms @ 30

If I made any typos, I am sure to hear about them.

 

[Besoeker]

The fact is the periods for V_an and V_bn start and end at the same time.

But going in opposite directions. That cannot reasonably be construed as the same phase.

I'm still interested in your response to 1550.

Brainfart on my part. Happens.

 

[rattus]

Are you really that thick?

First, ?rbalex's identity only holds for a separation of 180 degrees? is the only identity relevant to this discussion as it applies to conventional 120/240V systems.

But, if you want to use other phase constants you will need to use the full identity:

sin(u ? v) = sin (u)cos (v) ? cos(u)sin(v)

The only discontinuity is your ability to follow an argument.

Well, what is the phase for

sin(wt + 179)??

 

[rbalex]

But going in opposite directions. That cannot reasonably be construed as the same phase.

Sure it can unless you are applying "opposite directions" to time.

I have already accepted the wave forms are not "in phase", but I assert there is a difference between "in phase" and "same phase" since every relevant system voltage function can be validly written in terms of a common identical phase; i.e., the "same phase." Direction is not an essential element of the definition of phase assuming time is unidirectional. Direction (polarity) may apply to "in phase."

...Brainfart on my part. Happens.

:thumbsup: Don't I know it.