240v debate....

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jim dungar

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Location
Wisconsin
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Retired Electrical Engineer - Power Systems
FYI, we have not been discussing a two-wire source. If we have two wire sources it is one thing, but when you have a neutral, you have a three-wire source.

It appears you are saying the current and voltage relationships must change as soon as a neutral conductor (third wire) is added to the circuit and therefore you cannot analyze a 3-wire circuit using the same methodology as a 2-wire one fed from the same (2) sources in series.
 

Rick Christopherson

Senior Member
It is a shame you do not take the time to see that the example was about the single-phase transformers.
Big deal. You make it sound as though you created new phase angles that didn't exist, when all you did was rearrange the secondary coils on your 240? transformer. It doesn't prove your point in any way, and that is why we have blown off your 3-phase example from the beginning.

MiveyTransformer.jpg
What this example does tend to reveal is that you are confusing your vector analysis tools as though they redefine the system. Your vector from x6 to x5 requires a magnitude reversal, but that does not mean that the phase of the coil is reversed, as you suggest below:
The separation between the primary and secondary by a flux allows us to use the secondary voltages like we want.
This is where you go totally astray, because when you resolve your transformer on the basis of the flux, you cannot interject ANY phase difference. This is what I have pointed out previously when you have a common core. The flux not only doesn't give you the flexibility you claim, it actually prohibits it. If you doubt that, go look up your old text books discussing the mutual inductance of a common core. You cannot interject a phase angle.
 

hurk27

Senior Member
I've been thinking of an analogy that would help some understand my view of this single phase circuit that might make sense to others, I just wish I had a way to make a animated graphic of it that would be so much clearer, but I don't have the right programs on this computer so here it goes:

we have a one way street that runs from point A to point B West to East called Winding, at the halfway point is another street that Tee's into Winding from the south called Common and is a two way street, at the bottom of Common it Tee's again, going West is a one way street called Load A, coming from the East east is a one way street called Load B, Load A street is a one way going West and north that returns back to point A of Winding, Load B street is a one way coming from point B on Winding going south then west to the Tee with common.

Now we have our little map we need vehicles, lets call these vehicles Electrons.
Now if I stand at point A looking East down Winding toward point B, I can see all the Electrons going away from me some going all the way to point B and some going as far as Common making a right hand turn to go south, also I can see Electrons coming up Common making a right turn at winding going East to point B then turning back south so from my view all electrons on Winding are travailing from West to East and officer Rick is sitting right there making sure they go in this direction only or there will be a crash.
Now I move to the intersection of Winding and Common, if I look West I have Electrons coming at me and if I look East I have Electrons going away from me, I get confused thinking wow their going two different directions, but I notice officer Rick hasn't pulled anyone over and there isn't any crashes so I move down to point B and look West back up Winding, I'm relived to see that all the Electrons are in fact going only in one direction now I move to common and see that some Electrons are going north and some south and when the Electrons are the same amount passing A point that are passing the B point they have to just bypass Common and travel all the way around the outside of the whole course, but if one extra Electron passes the B point than the A point then a Electron has to turn from load B to Common to relive the extra traffic or if an extra Electron passes point A a car has to turn from Winding onto Common also to relive the extra traffic.

Ok I'm not very good at writing stuff like this but that is my view and like I said depending from which view point I look from if I look from the intersection of Winding and Common the cars can look as if their going in two different directions but in fact they are travailing in the same direction.

If anyone want to simplify this or make a graphic of it go for it.:p
 

mivey

Senior Member
It appears you are saying the current and voltage relationships must change as soon as a neutral conductor (third wire) is added to the circuit and therefore you cannot analyze a 3-wire circuit using the same methodology as a 2-wire one fed from the same (2) sources in series.
That is not what I have said. When a neutral is present, we can now take two voltages from the source (plus the larger voltage, of course). These two smaller voltages can be taken as forces in the same direction, or forces in different directions. There is no MUST about which way you have to do it as the choice of a reference is completely arbitrary.
 

mivey

Senior Member
Big deal. You make it sound as though you created new phase angles that didn't exist, when all you did was rearrange the secondary coils on your 240? transformer. It doesn't prove your point in any way, and that is why we have blown off your 3-phase example from the beginning.
On the contrary, it has been said the the voltages must be in the same direction or they are just math tricks. I have shown the voltages forces used in both directions are real forces that produce real results, not just math tricks.

The truth is that the voltages can be used as forces in either direction. They can also be used as forces in directions other than forward and reverse if they have a reference elsewhere, like the new voltage force that was defined by having a reference not on the original winding. A voltage is defined by its reference.

What this example does tend to reveal is that you are confusing your vector analysis tools as though they redefine the system.
I think the issue is becoming clear that you are confusing circuit polarity with voltage direction and they are not the same thing.

Your vector from x6 to x5 requires a magnitude reversal, but that does not mean that the phase of the coil is reversed, as you suggest below:
This is where you go totally astray, because when you resolve your transformer on the basis of the flux, you cannot interject ANY phase difference. This is what I have pointed out previously when you have a common core. The flux not only doesn't give you the flexibility you claim, it actually prohibits it. If you doubt that, go look up your old text books discussing the mutual inductance of a common core. You cannot interject a phase angle.
The flux in both halves of the winding will not always be the same. The current at X1 is not always the same as the current at X4. But that is not the point. The point is that the way we take the voltages is not completely defined by the way they were created.
 

Besoeker

Senior Member
Location
UK
I suspect it is because he can't. I find it incredible that a EE would deny that the voltages are displaced by 180?. That fact is used in so many places in our field it just boggles the mind.
Like I said before, there are two possible explanations. I was going with the more benign of the two. It has become increasingly difficult to do so.


Here is a quote from your side of the pond from Prof. G.W. Carter of the University of Leeds in his 1972 "Techniques of Circuit Analysis" (I hit the color button on my scanner for the second page but did not feel like re-doing it):
[/QUOTE]
Appreciated, thank you. Fig 3.17(a) is the arrangement we use for Hexaphase rectifiers. The transformer primary is three-phase delta and the three corresponding secondary windings centre-tapped. Each such winding gives two voltages displaced by 180deg. The three secondary windings thus result in six phase displaced outputs evenly spaced at 60deg intervals. Not possible without the 180deg displacement from each centre-tapped winding. Just like.......well,I don't need to spell it out for your benefit.
 

Besoeker

Senior Member
Location
UK
I do.

Because when two nodes that are in-phase and each has a load applied share a common wire the current flow will be both directions in this common wire, and when this current is equal they will cancel each other, this is the only point where you will have two currents 180? out of phase, and it is not because the source is out of phase
Sources, not source.
Do you not accept that, for a resistive load, the voltage and current are in phase with each other?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
There is no MUST about which way you have to do it as the choice of a reference is completely arbitrary.
I thought it must be a requirement, as every time I bring up a circuit that does not have a load neutral connection, you always respond with an answer that is based on a neutral reference point.

Why do you not answer my questions about a simple 2-wire loop of 2 resistors in series (no neutral conductor), first fed by one source, and then by two sources in series?
After all, these are a real world circuits, the single source is typical of a British residential supply and the second source is when a US 120/240V center tapped transformers looses its neutral connection.
 

Rick Christopherson

Senior Member
The flux in both halves of the winding will not always be the same. The current at X1 is not always the same as the current at X4. But that is not the point. The point is that the way we take the voltages is not completely defined by the way they were created.
I find it very disingenuous that we were discussing how the flux in a transformer cannot allow you to change a phase angle, but your response that says the flux will vary in the core, changes the topic from angle to magnitude without notice. In my opinion, this is deliberately deceptive in an attempt to "win" a discussion. It is one of the reasons why my respect for you has diminished from when I first joined this forum.

So let's stay on the topic. Both you and Besoeker are saying that the 180? phase angle is real and absolute. With a common-core, single-phase, center-tapped transformer whose flux is driven by the primary source, how can you interject a phase angle between the two halves of the center-tapped coil? What part of the mutual inductance permits you to do this?

I am not sure if you are taking the same stance as Besoeker, but he is emphatically stating that this isn't simply due to a chosen point of view, but that it is absolute. If it's absolute, then it should be traceable back to Faraday's Law and the flux equations for a transformer.
 

mivey

Senior Member
I thought it must be a requirement, as every time I bring up a circuit that does not have a load neutral connection, you always respond with an answer that is based on a neutral reference point.

Why do you not answer my questions about a simple 2-wire loop of 2 resistors in series (no neutral conductor), first fed by one source, and then by two sources in series?
After all, these are a real world circuits, the single source is typical of a British residential supply and the second source is when a US 120/240V center tapped transformers looses its neutral connection.
Stay away from a 2-wire circuit. We have been focusing on the 2 voltages 'found' in a 120/240V 3-wire system derived from a center tapped transformer.
 

mivey

Senior Member
I find it very disingenuous that we were discussing how the flux in a transformer cannot allow you to change a phase angle, but your response that says the flux will vary in the core, changes the topic from angle to magnitude without notice. In my opinion, this is deliberately deceptive in an attempt to "win" a discussion. It is one of the reasons why my respect for you has diminished from when I first joined this forum.
Why would you think your respect is important to anyone? It isn't to me. But don't take that personal, as I don't consider my respect for anyone makes them anything either. I'm just another person in this world and don't feel like I am "owed" anything. There is only One who's respect really amounts to anything in the long run.

What I would like to see from you is a discussion without you having to be such a drama queen about
every
little
thing.

The drama and insults don't add any credibility to what you are saying. Just stick to the discussion and it will help it go much smoother.

So let's stay on the topic. Both you and Besoeker are saying that the 180? phase angle is real and absolute. With a common-core, single-phase, center-tapped transformer whose flux is driven by the primary source, how can you interject a phase angle between the two halves of the center-tapped coil?
Because the choice of a reference is arbitrary.

What part of the mutual inductance permits you to do this?
What part prevents it? The choice of a reference is arbitrary.

I am not sure if you are taking the same stance as Besoeker, but he is emphatically stating that this isn't simply due to a chosen point of view, but that it is absolute. If it's absolute, then it should be traceable back to Faraday's Law and the flux equations for a transformer.
It is, and there is nothing in those that specifies a reference point. The choice of a reference is arbitrary.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Stay away from a 2-wire circuit. We have been focusing on the 2 voltages 'found' in a 120/240V 3-wire system derived from a center tapped transformer.
One of my questions is exactly that source, just without a neutral conductor.

Are you saying the number of conductors in the circuit, affects how you would solve a circuit fed by a center tapped transformer?



I am asking for a solution for two simple circuits one from the US and one from the UK. Hopefully any methodology used would provide similar results in regards to the phase angles of voltages and currents.

With the established baseline of the current and voltage relationships in sources and loads and a methodology for determining them, I hoped to move into a slightly more complex circuit similar to that in an electric stove, 1 load connected L-L and a second load connected L-N on the center tapped transformer. Finally, using our common methodology, we should be able to move to your open-wye and even an open delta, which I would start again using a simple 2-wire loop even though the source has a neutral point.
 

mivey

Senior Member
Are you saying the number of conductors in the circuit, affects how you would solve a circuit fed by a center tapped transformer?
It might, depending on the analysis method used.

Are you saying your choice of voltage directions for your analysis are the only real voltage directions and that all others then become math tricks?
 

pfalcon

Senior Member
Location
Indiana
Oh yeah, if I want to tell you have a nice day-I can.:p

Left 4 Dead 2 said:
Bill: Why are you always so happy? Louis: Bein' positive is how I got where I am today! Bill: What? About ta die in a brick factory? I got here too and I got to complain the whole way!

To do circuit analysis you have to choose a direction to do your math. In this circuit that means measuring your voltage from B to N and N to A. You can't swap your directions and go N to B then N to A. So the two voltages must remain in phase. B-N-A is simply a voltage divider.

From a physical point of view this is like looking at a see-saw. The board is always straight (in-phase) no matter which end is up.

The 180 degree shift/phase problem is apparent but not actual. Like taking that see-saw and trying to find a way to lock the motion of the two ends in sync so they go up and down together. Not happening. But measuring from the center tap the ends appear to be 180 degrees out of sync. So from a pragmatic viewpoint, any attempt to tie A-B will have the same result as though they were 180 out.
 
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