240v debate....

[mivey]

So with your new correction (edit) made, I will return to the response that I was already anticipating that I would need to make. What you have in effect done is placed a new label over the top of the original label and reversed the dot-convention at the same time. If we peel back your label, we will see the original label and dot-convention. It didn't change the original power supply, it only gave it a new label that may lead to confusion (yes, I was planning on pointing out "lead to confusion" before you made your faux paus. That is why I was happy to see your faux paus.).

Maybe we digress. There is no new label over an old label.

I'm saying that the Vs and Vx are my two generator units from post #98. The labels did not change. The wiring did not change. The connections did not change. The load did not change. The only change was a 180? rotation of one winding relative to the other. All of the wiring, polarity marks, labels, etc are the same on both units.

Your two Vs outputs are two of my units but with no rotation difference in the windings. In the two Vs case, one of the generator units would have to be re-wired and re-labeled or the two voltages could not combine to make a double magnitude voltage at the generator output. They would just be two voltages in parallel: smaller voltage but twice the current capacity.

My Vs and Vx outputs are two of my units with a 180? rotation difference in the windings. In the Vs and Vx case, no re-wiring or re-labeling needed and the voltages would combine to make a double magnitude voltage at the generator output. Twice the voltage but 1/2 the current capacity of the paralleled outputs.

 

[Rick Christopherson]

Maybe we digress. There is no new label over an old label.

I'm saying that the Vs and Vx are my two generator units from post #98. The labels did not change. The wiring did not change. The connections did not change. The load did not change. The only change was a 180? rotation of one winding relative to the other. All of the wiring, polarity marks, labels, etc are the same on both units.

I'm short on time, so I can't give this the full attention it needs. I am not directly contesting your generator example. I am only saying that it does not directly apply to what we are discussing. Your example is taking two sources that are physically out of phase and reconnecting them to be in-phase. This discussion is about starting out with two sources that physically are in-phase. Regardless when we start recording t=0, time is time. In one case the time is displaced. In the other is remains equal.

I'll come back to this later when I have more time. (no pun intended).

 

[pfalcon]

Jim Dungar and Mivey are never going to be on the same page unless they get Cowboyjwc to post for one of them.

Spin a rectangle on the right axis and you can make it appear as a square or a line from time to time.

 

[mivey]

I'm short on time, so I can't give this the full attention it needs. I am not directly contesting your generator example.

Well, let's hear it: are you indirectly contesting it?

I am only saying that it does not directly apply to what we are discussing.

Well then, there is no harm in discussing it because if I can't show you later where it applies, then how will that hurt your position?

Your example is taking two sources that are physically out of phase and reconnecting them to be in-phase.

When you get time, show me what "reconnecting" was done. Using "re" implies that there was a connection change.

Consider this:
At the same time, I start two identical, in-phase, frame-grounded generators, both with identical wiring, and use the voltage output from both to feed two identical loads that are grounded at exactly the same point on the load. This is two in-phase sources.

I then stop the generators and they both stop at the exactly the same time. I walk over to one and rotate the shaft 180? degrees. I then re-start the generators at the same time. There is no time shift as the output voltage waveforms start at exactly the same time. There is no "reconnecting" as the connections have not changed. The only difference is I now have two phase-opposed sources.

 

[Besoeker]

It appears we agree on, a single core (i.e. flux path), a single coil, a single current, and a single voltage in phase with the current?

Now, if we add 2 node points only, about 2.5% in from both ends of the transformer winding, we will still have a single current, and a single flux path. Are the three resultant series voltages still in phase with the single current? Why or why not?

If you measure them the same way round wrt to one end or other of the winding.
But that isn't the case where you are looking at a 120-0-120 centre-tapped WRT the centre tap.
Earlier, very much earlier, we had this exchange:
Your post # 60 - That is the whole point. To say they are out phase without including the reference point is technically mis-leading.
My response in post #67: : I did include a reference point. This from my post #49: It's what you would see and do see on an oscilloscope using the the neutral as the common point.
Van abd Vbn are mutually displaced by 180deg.

Do you really dispute that?

 

[cowboyjwc]

Jim Dungar and Mivey are never going to be on the same page unless they get Cowboyjwc to post for one of them.

Spin a rectangle on the right axis and you can make it appear as a square or a line from time to time.

I'll do that yesterday.:lol:

 

[Besoeker]

This discussion is about starting out with two sources that physically are in-phase.

Van and Vbn are not in phase.

Regardless when we start recording t=0, time is time. In one case the time is displaced.

There is no time displacing going on. I don't why you continue to bring that up. Look back at post #22. The waveforms show instantaneous values of the two waveforms. They are clearly in anti-phase. One is not a time displaced version of the other. They are occurring at the same time. There is NO displacing taking place and no means of doing so.

I'll ask you a question I posed before.
Look at this circuit again:

Can you explain why two firing pulses per cycle at 180deg intervals are required if the two sources are physically in phase?

 

[jim dungar]

If you measure them the same way round wrt to one end or other of the winding.
But that isn't the case where you are looking at a 120-0-120 centre-tapped WRT the centre tap.
Earlier, very much earlier, we had this exchange:
Your post # 60 - That is the whole point. To say they are out phase without including the reference point is technically mis-leading.
My response in post #67: : I did include a reference point. This from my post #49: It's what you would see and do see on an oscilloscope using the the neutral as the common point.
Van abd Vbn are mutually displaced by 180deg.

Do you really dispute that?

I am not asking about how you measure things, I am asking about the laws of physics and a coil wound on a single core.

 

[Besoeker]

I am not asking about how you measure things,

But how it is measured it is central to the discussion.
Van and Vbn are mutually displaced by 180deg.
Do you dispute that?

 

[jim dungar]

But how it is measured it is central to the discussion.
Van and Vbn are mutually displaced by 180deg.
Do you dispute that?

Do you dispute that Van and Vnb are in phase?

You insist on talking about results based on how you look at something (i.e. measuring based on an arbitrary reference that you chose to use).

I keep asking about the voltages across a single winding which are the result of physics and the 'way transformers work'.
Do you dispute the construction of a single core transformer impacts the 'polarity dot' location of its output winding?

 

[Besoeker]

You insist on talking about results based on how you look at something (i.e. measuring based on an arbitrary reference that you chose to use).

Nothing arbitrary about it. It's how things work in real life.
We, and mostly I, design and manufacture systems that use centre-tapped windings. Sometimes single-phase but mostly three phase.Sometimes simple and sometimes not.

Here's one we did for a 40kA system:

It is 24-pulse. From just a three phase supply.

And a picture of one limb of the transformer of a 20kA system. Without that 180deg displacement...

 

[Besoeker]

And a pic...

 

[Rick Christopherson]

I'll ask you a question I posed before.
Look at this circuit again:

Can you explain why two firing pulses per cycle at 180deg intervals are required if the two sources are physically in phase?

And I will point out again, that your circuit, as drawn, is wrong. Did you miss that posting (#377)? You labeled your nodes, and therefore, the voltage from A to B is zero volts.

What you have created with this diagram is what I previously showed on the right-hand side with two opposing batteries.

 

[jim dungar]

Nothing arbitrary about it.

So, it appears I cannot choose to say Van+Vnb=Vab, instead I must say Van-Vbn = Vab

It's how things work in real life.

Again I am discussing the real life of a single winding transformer.
Based on the resistive load, from earlier, and the agreed upon single current what dictates the actual relationship between the flux of the core and the voltage between any two points on the winding; physical laws or how things are viewed (i.e. measured)?

 

[Rick Christopherson]

Well then, there is no harm in discussing it because if I can't show you later where it applies, then how will that hurt your position?

Mivey,
I think you are confusing me for a discussion you have had with someone else in the past. I am not contesting the phases of your generator example, nor am I saying that it is not possible. It is entirely possible. But it doesn't model what is happening in a single-core, center-tapped transformer, which is what this discussion is about. Just because you can come up with an example that uses voltage sources that are physically out of phase, does not mean that it models what is happening in the center-tapped transformer that we are discussing here.

I am OK with discussing this topic, and I suspect that you and I would already be in agreement on it. However, discussing it in this thread would simply add greater confusion to a topic that apparently already has quite a bit of confusion surrounding it.

 

[hurk27]

Can you explain why two firing pulses per cycle at 180deg intervals are required if the two sources are physically in phase?

Simple this is no different then a full wave bridge using a center tapped transformer:

Node A: At 90? Ia is positive N is negative so SCR1 is forward biased and can fire.

Node B: At 270? Ib is positive and N is negative so SCR2 is forward biased and can fire

these two fire points will give you a 120 volt DC pulse at 120hz to the load.

If Node B was 180? out of phase with Node A then both SCR's would be forward biased at the same time at the 90? point and reversed biased at the 270? point and instead of 120hz DC pulse you would only have 60hz DC pulse at twice the amperage.

At 90? Ia is positive N will be negative and Ib will be negative with N positive referenced to Ib.
with A 180? out of phase:
At 90? Ia is positive N is negative, Ib is positive with N Negative in reference to Ib.

Just because the two SCR's are forward biased at 180? apart is not because the source is 180? out of phase but because they are in-phase.

 

[mivey]

Mivey,
I think you are confusing me for a discussion you have had with someone else in the past. I am not contesting the phases of your generator example, nor am I saying that it is not possible. It is entirely possible. But it doesn't model what is happening in a single-core, center-tapped transformer, which is what this discussion is about. Just because you can come up with an example that uses voltage sources that are physically out of phase, does not mean that it models what is happening in the center-tapped transformer that we are discussing here.

I understand that it is a different setup. And that, oddly enough, is a point that I would like to use later. But I just wanted to be sure we agreed on the "other setup" first.

I am OK with discussing this topic, and I suspect that you and I would already be in agreement on it.

I was thinking so as well until you said: "Your example is taking two sources that are physically out of phase and reconnecting them to be in-phase." I do not understand why you said that if we are in agreement on the two phase-opposed sources. Nothing had to be re-connected.

What is a fact is that the voltage force during the "reverse" portion of one source's output is actually already in phase with the voltage force during the "forward" portion of the other source output. Since they are already "see-sawing", to use the phrase from an earlier post, no "re"connection has to be made.

Agreed?

While I do not agree with your time statement, I think it is a minor issue at the moment since it mostly hinges on definitions that I do not feel like debating at the moment.

 

[jumper]

This analogy is probably the simplest way to try to understand how flux in a coil wound in a given direction induces voltage. One point needs to be made; it is a two way street, but with only one car(flux)!

I can live with that. I am a simple guy and I can only state it as I see it.

Thank you Lazlo.:thumbsup: I appreciate your imput. :happyyes:

 

[mivey]

Simple ... Just because the two SCR's are forward biased at 180? apart is not because the source is 180? out of phase but because they are in-phase.

Congratulations. You got all that exactly backwards. :slaphead:

 

[jumper]

I'll do that yesterday.:lol:

Haven't you been eaten by a Morlock by now?