It is absolutely the case that Van and Vbn are mutually displaced by 180 degrees.
Were it not the case, none of the phase-controlled power electronics I've designed over the past forty years would have worked.
But it did and does.
Why is residential wiring known as single phase?
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Were it not the case, none of the phase-controlled power electronics I've designed over the past forty years would have worked.
But it did and does.
Rick Christopherson
Senior Member
So all of your designs are functional solely because you choose neutral as a test reference? Without that they would...what...blow up? :dunce:
Whatever I, you, or anyone else defines as the reference matters not a jot.
They work despite any logical or illogical choice anyone makes about what point to call the reference.
But, common sense suggests that the common point is chosen for measurements.
If you want to ignore that and pick a different point, fine.
Rick Christopherson
Senior Member
Finally, you get it! :thumbsup:
Good........
You accept that it is absolutely the case that Van and Vbn are mutually displaced by 180 degrees.
Do you then accept that using the one and only common point, the neutral as the logical and obvious choice as a common reference?
If not, why not?
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Not all series connections of transformers use the neutral as a common point.
What about my 2-load electric range example, which is also applicable to a large motor with a small coolant pump.
How about needing to change the methodology when the transformer is tapped but just not at the center.
Then there is the issue of saying 'out of phase voltages combine to a larger number' while 'out of phase currents combined to a smaller number'.
My favorite was the description of how we have two currents entering a single point, with no currents leaving.
All of these can be 'proven correct' through the appropriate application of mathematical principals, however using Vbn is the only one which requires the use of double negatives.
And lets not forget ANSI and IEC transformer terminal designation standards. X1toX2 is either an additive series connection or part of a delta, X1toX1 could be part of a parallel connection or a star/wye.
gar
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Rick:
Your post #234 refers to a pulse. And your argument is that the transformer does not perform a 180 deg phase shift, but rather an inversion.
The concept of a phase angle or shift is based on a sine wave as the signal.
If a transformer, single stage vacuum tube, or RC network is used in a particular manner, then a 180 deg phase shift of a sine wave signal can be obtained.
Instead of a simple sine wave you want use a short pulse as the signal to the transformer and argue that that pulse can not be described as having a 180 deg phase shift because it is a simple inversion of the signal. But the meaning of phase shift is not meant to directly apply to a non sine wave signal.
However, if you have a continuous repetitive pulse, then it can be broken down into its individual sine wave components. And on each of these components the transformer performs the 180 deg phase shift. In an ideal transformer the phase shift is independent of frequency, and the input pulse to the transformer will be reproduced at the output without distortion to the wave shape.
Suppose the RC network referenced above is designed for a 180 deg phase shift at the fundamental frequency of the pulse. That one frequency component will be shifted by 180 degrees. All of the higher frequency components will be shifted more. The end result is that the output of this network is more like a sine wave than the input pulse. This simple circuit with either 3 or 4 stages is the basis of the Hewlett-Packard RC oscillator, that which created the company.
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Rick:
Your post #234 refers to a pulse. And your argument is that the transformer does not perform a 180 deg phase shift, but rather an inversion.
The concept of a phase angle or shift is based on a sine wave as the signal.
If a transformer, single stage vacuum tube, or RC network is used in a particular manner, then a 180 deg phase shift of a sine wave signal can be obtained.
Instead of a simple sine wave you want use a short pulse as the signal to the transformer and argue that that pulse can not be described as having a 180 deg phase shift because it is a simple inversion of the signal. But the meaning of phase shift is not meant to directly apply to a non sine wave signal.
However, if you have a continuous repetitive pulse, then it can be broken down into its individual sine wave components. And on each of these components the transformer performs the 180 deg phase shift. In an ideal transformer the phase shift is independent of frequency, and the input pulse to the transformer will be reproduced at the output without distortion to the wave shape.
Suppose the RC network referenced above is designed for a 180 deg phase shift at the fundamental frequency of the pulse. That one frequency component will be shifted by 180 degrees. All of the higher frequency components will be shifted more. The end result is that the output of this network is more like a sine wave than the input pulse. This simple circuit with either 3 or 4 stages is the basis of the Hewlett-Packard RC oscillator, that which created the company.
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Yes transfromers can be connected in a manner that does produce a 180? shift, how ever a center-tapped transformer does not. While there are several ways to measure voltage on a 120/240V (center-tapped transformer or a series connection of a re-connectable windings), only one of them shows a shift, the other ways do not. So does a phase shift actually occur? Are we ignoring the physics of a single transformer winding, simply because a measuring method allows us to?
Sure, you can have things connected end to end as well as either end to neutral.
The end to end load would be connected between two hots. Why would it be reasonable to designate one particular hot as a common reference? Common to what?
My reference was to 120-0-120. But the comments would be equally applicable to 180-0-60.
First part:
I don't suppose that you would argue with the point that a transformer wound to give 120-0-120 even if it is two isolated windings connected in series will give 240V end to end.
Second part:
Suppose you load the two 120V supplies, one with a 40 ohm resistor, the other with 60 ohms.
You get this:
This cancelling of the currents in the neutral is one of the merits of a 120-0-120 system
Why does it happen?
Simply because the currents (and voltages) for each load are in anti-phase.
Rick Christopherson
Senior Member
Does this canceling of currents only happen when you are measuring the system with your neutral reference? Why do you keep repeating this? You state it as an "absolute", and that makes this statement incorrect.
No one is trying to force you into changing how you want to reference a system. That is your choice. The reverse is not true, however. You're intolerant of other views, and want to force the rest of the world to conform to your view. But even that isn't my contention. My contention is when you state absolutes, such as the above, when they are not properly absolutes, and are true only when the system is viewed with your methodology.
Rick Christopherson
Senior Member
By the way, currents don't "cancel". That's only a mathematical expression used for analysis. Electrons don't vanish. They don't annihilate one another. (That would be a really big bang. E=mC2, kind of big bang.) They simply flow through other paths. When we say that currents "cancel", what they are really doing is flowing from one phase to the other via the other loads. They bypass the neutral conductor.
gar
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Does a transistor or triode vacuum tube produce a 180 deg phase shift of a sine wave input? With what connection of input and output does this shift occur or not occur?
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Does a transistor or triode vacuum tube produce a 180 deg phase shift of a sine wave input? With what connection of input and output does this shift occur or not occur?
.
Is my first diagram in post #249 incorrect?
If so, care to post a corrected version?
Rick Christopherson
Senior Member
I am not talking about your diagrams. I am talking about the words you use. You make absolute statements that are incorrect when stated as an absolute.
Care to cite any that are incorrect?
Rick Christopherson
Senior Member
Yeah. The one you posted just above.
You have an unlabeled diagram, and made the absolute assertion that the currents and voltages were out of phase and cancel. This absolute statement is untrue for the diagram you have shown without annotation. This statement is true only for your analysis of the diagram, not the diagram itself, and therefore, it should not be stated as an absolute.Second part:
Suppose you load the two 120V supplies, one with a 40 ohm resistor, the other with 60 ohms.
You get this:
This cancelling of the currents in the neutral is one of the merits of a 120-0-120 system
Why does it happen?
Simply because the currents (and voltages) for each load are in anti-phase.
Cancel is a verb and thats exactly what happening,Like you said.That's only a mathematical expression used for analysis.
And when we look at a diagram that usually what most of us look at it for. I think I used the word opposed in my diagrams,but every body knows what is meant by cancel.
Fine.
Post a better diagram that refutes my points.
Rick Christopherson
Senior Member
I agree. I frequently use the expression myself quite frequently. I brought it up only because Besoeker appears to lose sight of that fact that it is simply a tool for easier analysis, and not what is actually happening in a circuit. When he keeps asserting that "the currents can't cancel unless they are anti-phase" suggests that he has displaced what is happening with a circuit with the tools he uses to analyze the circuit. This is what I meant when I brought up (several months ago) that he and others were "redefining" the system based on their tools, not on the actual system.
Rick Christopherson
Senior Member
It is not your diagram that is wrong. It is your points that are wrong because you stated them as absolute. They are true for your analysis of a system, but they are not absolutely true about the system itself.
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