Why is residential wiring known as single phase?

[mivey]

I know it has been a lot of posts, but did I miss where someone said the reference must be based on the physical, except for the group talking about the physical connection of an oscilloscope?

Yes, you missed it. That was pfalcon's premise.

Wasn't my premise at all. Mivey would just like it to be my premise. Twas his interpretation.

How else does one interpret what you posted?

For sinusoidal waveforms:
1) Establish a common reference frame for both waves to be tested.
...
For the residential issue, only AB or BA presents a common reference (1). AN, BN, NB, NA exclude other portions of the coil that we wish to test. Therefore those references cannot establish synchronization or phase.

"Exclude other portions of the coil" sure sounds like you are saying the reference frame must be based on the physical. Specifically, it sure reads that you have said that in order for the reference to be valid, the physical portion of the coil containing the reference voltage must overlap the physical portion of the coil containing the voltage to be tested.

Pray tell: how else would you expect this to be interpreted?

 

[mivey]

Yes it can. But it requires additional circuitry to do so.

That does not mean those voltages are not available.

Which is where you and I had arrived on the prior thread. If there is a COMPELLING NEED to know it's single-phase then yes that's exactly what it is.

If we consider only one direction across the coil to be positive and only consider resistive loading, then there is only one phase present in the coil. The configuration is labeled single phase no matter what we discover because that is convention and that is not going to change.

For non-resistive unbalanced loads, there are two different phase currents in the coil. The only way to guarantee there will only be one phase present is to have a two-wire circuit. This uses the technically correct definition of phase, of course.

 

[mivey]

With respect of one end of the circuit to the other end of the circuit, just as with a teeter-totter, the two ends are effectively 180_o out of phase, can be used in that manner, and for all practical purposes may be considered in that manner. Only when being .... retentive is it necessary to acknowledge that at no time are they really displaced but are rather two ends of a single whole piece.

That's where we disagree. We have two non-displaced voltages but we also have two voltages that really are displaced.

The instantaneous direction of forces in the coil under resistive loading conditions is a different issue.

Remember that I can produce a single-phase direction of forces in two series coils using source voltages that are physically displaced by 180? (two 180? displaced voltage phases having their forces in the coils aligned). Then, we can use this as a single-phase source. In that case, the sources and the the use of the voltages from the sources are different.

The sister case is also true where I can use the single-phase source to produce two voltages physically displaced by 180?. The systems of voltage are mirror images of each other. There is nothing that magically makes one of the voltage sets disappear. The simple fact is that both voltage sets are physically there for use and the case of physical displacement is really there. Nothing mysterious about it as it is simply what is physically there.

 

[jim dungar]

... the case of physical displacement is really there

Only if you force me to use the neutral as my reference point. If I make a choose a different analysis the displacement 'disappears'.

 

[mivey]

Only if you force me to use the neutral as my reference point. If I make a choose a different analysis the displacement 'disappears'.

So What? Given the same analogy, if I use the neutral then you would have to say the zero displacement 'disappears'.

In reality, nothing is disappearing. Analysis schamalysis. Both sets of voltages are there for use, we are just not using one of the sets.

 

[jim dungar]

So What? Given the same analogy, if I use the neutral then you would have to say the zero displacement 'disappears'.

Have I ever said anything otherwise?

 

[T.M.Haja Sahib]

TM, here's what we have that you have been trying to tell me how to connect:

Two signal leads each with a ground.
What do you want me to connect to each of the transformer terminals?

Please connect the ground leads to N ,Probe1 to V1 and Probe2 to V2.Use X-Y mode.

What I am trying to convince you is if i1 is the instantaneous current flowing out from terminal V1,the same current i1 is also flowing out from terminal N for equal loads across the secondary so that the total instantaneous current in the neutral is zero.This can only happen when the instantaneous voltages from V1 to N and from N to V2 are in phase.This is what we are going to check now with your scope........

 

[Besoeker]

Please connect the ground leads to N ,Probe1 to V1 and Probe2 to V2.Use X-Y mode.

That is V1n and V2n. As I posted in #713 and exactly as connected for post #404.
Not V1n and Vn2 as you requested in post #700. Do you now see the problem with your requested connection?

 

[T.M.Haja Sahib]

That is V1n and V2n. As I posted in #713 and exactly as connected for post #404.
Not V1n and Vn2 as you requested in post #700. Do you now see the problem with your requested connection?

If what you says is true,it will show up in the scope X-Y mode display .But are you having X-Y mode facility in your scope or not?

 

[Besoeker]

This can only happen when the instantaneous voltages from V1 to N and from N to V2 are in phase.This is what we are going to check now with your scope........

Really? With probes connected thus?

Please connect the ground leads to N ,Probe1 to V1 and Probe2 to V2

That's from V1 to N and V2 to N.
NOT from V1 to N and from N to V2.

 

[Besoeker]

If what you says is true,it will show up in the scope X-Y mode display .But are you having X-Y mode facility in your scope or not?

I do. What do you expect to see?

 

[T.M.Haja Sahib]

I do. What do you expect to see?

A straight line.Its orientation with respect to axes will be one for zero degree phase difference and another for 180 degree phase difference.

 

[T.M.Haja Sahib]

from V1 to N and V2 to N.
NOT from V1 to N and from N to V2.

It should be possible in your scope to display in X-Y mode the phase difference between V1 to N and V2 to N and also that between V1 to N and N to V2.

If this is not possible in your scope,do not proceed.

Then I have to adopt a different tactic to convince you.......

 

[mivey]

Please connect the ground leads to N ,Probe1 to V1 and Probe2 to V2.Use X-Y mode.

What I am trying to convince you is if i1 is the instantaneous current flowing out from terminal V1,the same current i1 is also flowing out from terminal N for equal loads across the secondary so that the total instantaneous current in the neutral is zero.This can only happen when the instantaneous voltages from V1 to N and from N to V2 are in phase.This is what we are going to check now with your scope........

The problem is that in order to say "in phase" or "phase opposed" we have to establish a positive direction in the winding. You can choose this to be between ungrounded & ungrounded or between grounded & ungrounded. This preference is really the crux of the debate. Some contend that their method is the only valid one. I contend that either choice is valid.

Most people can easily picture the ungrounded-to-ungrounded. It is harder for some to picture the other way as valid because they can't seem to get past the fact that there is one piece of equipment so they think we have to use the same direction all the way through that piece of equipment. That simply is not true as the voltages are the issue, not how they were created.

We can have two pieces of equipment provide two phase-opposed voltages or we can get the same phase-opposed voltages from one piece of equipment. It would never make sense to have the two-piece scenario because it would not be cost effective. We do not see two-phase distribution either anymore because we can accomplish the same thing with a three phase supply. The method of creation is not the concern, it is the voltages we take from the source that is the goal.

With that said, your position that the voltages must be in phase is based on a direction choice. To illustrate how two physically phase-opposed voltages can produce the same voltages we see in a single-phase transformer, please see the following post:

Post #98 from another thread

It should be clear that the direction is a choice we make. Either choice is valid and depending on how we take the voltages, we can take two in-phase voltages from the source or two phase-opposed voltages from the source. Both sets of voltages are valid. It is our choice of direction that is arbitrary, although we often base that choice for convenience or some other reason.

 

[T.M.Haja Sahib]

The problem is that in order to say "in phase" or "phase opposed" we have to establish a positive direction in the winding. You can choose this to be between ungrounded & ungrounded or between grounded & ungrounded. This preference is really the crux of the debate. Some contend that their method is the only valid one. I contend that either choice is valid.

Most people can easily picture the ungrounded-to-ungrounded. It is harder for some to picture the other way as valid because they can't seem to get past the fact that there is one piece of equipment so they think we have to use the same direction all the way through that piece of equipment. That simply is not true as the voltages are the issue, not how they were created.

We can have two pieces of equipment provide two phase-opposed voltages or we can get the same phase-opposed voltages from one piece of equipment. It would never make sense to have the two-piece scenario because it would not be cost effective. We do not see two-phase distribution either anymore because we can accomplish the same thing with a three phase supply. The method of creation is not the concern, it is the voltages we take from the source that is the goal.

With that said, your position that the voltages must be in phase is based on a direction choice. To illustrate how two physically phase-opposed voltages can produce the same voltages we see in a single-phase transformer, please see the following post:

Post #98 from another thread

It should be clear that the direction is a choice we make. Either choice is valid and depending on how we take the voltages, we can take two in-phase voltages from the source or two phase-opposed voltages from the source. Both sets of voltages are valid. It is our choice of direction that is arbitrary, although we often base that choice for convenience or some other reason.

Beautiful mind.
Please note for all measurement purposes,phase by itself is meaningless.Only the phase difference counts.You propose a 'direction' to fix it.But comparing the phase of a sinusoidal with another one is more appropriate for the present discussion.Accordingly I did it in post#747.Also note that the instantaneous currents in the hot conductors are in the opposite directions.This means the instantaneous current in the 'top terminal'and the instantaneous current flowing out of neutral terminal are in the same direction.

 

[Besoeker]

A straight line.Its orientation with respect to axes will be one for zero degree phase difference and another for 180 degree phase difference.

And what orientation would they be respectively?

 

[mivey]

Also note that the instantaneous currents in the hot conductors are in the opposite directions.This means the instantaneous current in the 'top terminal'and the instantaneous current flowing out of neutral terminal are in the same direction.

If we ignore the source impedance, the feeder impedance, and assume the load is purely resistive, then the currents in both halves of the winding are flowing in the same direction at any instant. This is not always the case.

To be technically correct,"phase" indicates the position on the waveform. With a two wire circuit, there can only be one phase. It would not matter if the load were resistive, reactive, or otherwise because the current leaving one terminal would be exactly the current entering the other terminal. Thus we can only have one phase present on a two wire circuit. FWIW, most of the circuits fed by a center-tapped transformer are two-wire circuits. Some just share a conductor. We usually have 240 volt, two-wire, single-phase loads and 120 volt, two-wire, single-phase loads. The 120 volt loads are usually dispersed and are fed by two different single-phase 120 voltages. That is why we say it is a single-phase supply.

But that same source can be a supplier of two 120 volt sources that have a 180? displacement as well. It is a mirror image of the scenario I just linked to in the other thread. There I had two 180? displaced voltages working in-phase in one direction across both windings. We would call what appears across both windings to be single-phase. But the two phase-opposed voltages did not go away. They are still there and are just as real as they ever were. The mirror image would take that single-phase source and use it to extract back out the two 180? displaced voltages. It is just a physical fact that the 0? displaced voltages and the 180? displaced voltages share the same physical space and we can use either set of voltages.

Looking at the instantaneous values will not change the fact that both sets of voltages are there. I don't believe anyone here is saying for the general case that the currents in the windings are not in synch. What my links shows is that is not the issue because we can also have two phase-oppsed voltages produce currents that are in synch and still not lose the 180? relationship. In reality, the AC source is bi-directional and can produce a positive force in either direction. Our assignment of a positive direction is what muddies the water.

So:
1) In general, the currents in the windings are in synch (in one direction across both windings).
2) The currents are not in synch for every circuit (the currents in the winding halves are not always in the same direction across both windings).
3) Two voltages with a 0? displacement or two voltages with a 180? displaced are available to be taken from the transformer because they map to the same physical space.
4) AC in itself does not have a positive direction and assigning a positive direction is a choice we make.

 

[Besoeker]

It should be possible in your scope to display in X-Y mode the phase difference between V1 to N and V2 to N and also that between V1 to N and N to V2.

Referring to my diagram in post #733 tell me how you think I need to connect the probes in each of the cases you have given.

 

[T.M.Haja Sahib]

If we ignore the source impedance, the feeder impedance, and assume the load is purely resistive, then the currents in both halves of the winding are flowing in the same direction at any instant. This is not always the case.

Kindly give (illustrated ) evidence for your statement in bold letters above.It has truly educational value.

 

[T.M.Haja Sahib]

Referring to my diagram in post #733 tell me how you think I need to connect the probes in each of the cases you have given.

First you please check the continuity between the grounds of two probes connected to the scope in the X-Y mode.Does the continuity exist?