The dots tell us that the waves seen at those points are in phase. They do NOT tell us how to draw our phasors. We can draw them forward or backward as long as we describe them properly with magnitude and phase angle. Some of us choose to draw them tail to tail, PI radians apart. Then we subtract.
Why is residential wiring known as single phase?
- Thread starter TimWA
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The dots tell us that the waves seen at those points are in phase. They do NOT tell us how to draw our phasors. We can draw them forward or backward as long as we describe them properly with magnitude and phase angle. Some of us choose to draw them tail to tail, PI radians apart. Then we subtract.
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If anything, the definitions for phase bolster the case for two phases. Specifically, the clearly stated definition which says in effect that the phase is the argument of the sinusoid describing the wave and that is 'phase =(wt + phi)'.
In this case, phi has been set to zero in the first expression and PI in the second. It is unbelievable that one would claim that a wave and its inverse are of the same phase!
Nowhere does any definition mention the use of identities to come up with a bogus expression for phase. And I mean nowhere, nowhere in the world! Go figure! And, nowhere, nowhere in the world is there anything that allows one to disregard signs in mathematical expressions with the exception of absolute values.
And nowhere in the world is there any textbook which validates this silly notion.
gar
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__dan:
You need an AC circuit analysis course from a major university. But I doubt that time would allow you to do that. So try to learn from what is being presented to you in this thread.
I will review a little.
The dot markings on a transformer schematic are such that each dot is associated with a single coil having two terminals. The phasing defined by the dots is such that the voltage at the dot end of the coil relative to the non-dot end is most positive simultaneous for all coils.
Thus, a normal center tapped coil labeled X1 (non-dot end of X1-X2), X2 (dot end of X1-X2), and X3 (non-dot end of X3-X4), X4 (dot end of X3-X4), has X2 most positive relative to X1 at the same time as X4 is most positive relative to X3. When X2 is connected to X3 to make a center tapped secondary, then the instantaneous sum of the two voltages, vX1X2 and vX3X4 is greater than either individual voltage. There is no need to relate this to core flux, or to that it is even a transformer. It is just two voltage sources with a relationship between them.
These two voltages with the subscripts given are in-phase with each other. Now, if you view these two voltages relative to neutral, meaning the voltages are labeled vX1X2 and vX4X3, then they are 180 degree out of phase. This does not change the total voltage from X1 to X4, but it does change your perspective of the voltages and how they can or can not be used.
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__dan:
You need an AC circuit analysis course from a major university. But I doubt that time would allow you to do that. So try to learn from what is being presented to you in this thread.
I will review a little.
The dot markings on a transformer schematic are such that each dot is associated with a single coil having two terminals. The phasing defined by the dots is such that the voltage at the dot end of the coil relative to the non-dot end is most positive simultaneous for all coils.
Thus, a normal center tapped coil labeled X1 (non-dot end of X1-X2), X2 (dot end of X1-X2), and X3 (non-dot end of X3-X4), X4 (dot end of X3-X4), has X2 most positive relative to X1 at the same time as X4 is most positive relative to X3. When X2 is connected to X3 to make a center tapped secondary, then the instantaneous sum of the two voltages, vX1X2 and vX3X4 is greater than either individual voltage. There is no need to relate this to core flux, or to that it is even a transformer. It is just two voltage sources with a relationship between them.
These two voltages with the subscripts given are in-phase with each other. Now, if you view these two voltages relative to neutral, meaning the voltages are labeled vX1X2 and vX4X3, then they are 180 degree out of phase. This does not change the total voltage from X1 to X4, but it does change your perspective of the voltages and how they can or can not be used.
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And still wrong.
It is hexaphase because there are six phases. All line to neutral and all different.
Vmsin(ωt)
Vmsin(ωt+π/3)
Vmsin(ωt+2π/3)
Vmsin(ωt+π)
Vmsin(ωt+4π/3)
Vmsin(ωt+5π/3)
All different.
The circuit:
The output current and voltage.
This requires a firing pulse every 60 deg - a point you wrongly disputed earlier.
That's six per cycle of the supply.
The fundamental frequency of the output voltage and current is six times the supply frequency.
Hex.......you see?
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Hmmm - Nope; it's still three phase. As I said, earlier you're putting the cart before the horse by making the effect (the down stream effects) rather than the cause (the driving voltages) the definer. The voltages are defined by three phases: (ωt),(ωt+π/3) and(ωt+2π/3) or their equivalents.And still wrong.
It is hexaphase because there are six phases. All line to neutral and all different.
Vmsin(ωt)
Vmsin(ωt+π/3)
Vmsin(ωt+2π/3)
Vmsin(ωt+π)
Vmsin(ωt+4π/3)
Vmsin(ωt+5π/3)
All different.
The circuit:
The output current and voltage.
This requires a firing pulse every 60 deg - a point you wrongly disputed earlier.
That's six per cycle of the supply.
The fundamental frequency of the output voltage and current is six times the supply frequency.
Hex.......you see?
Residential, which what the topic is about, IS the downstream side. Just as the hexaphase arrangement is.
Nope.
The voltages are defined by SIX phases.
Vmsin(ωt)
Vmsin(ωt+π/3)
Vmsin(ωt+2π/3)
Vmsin(ωt+π)
Vmsin(ωt+4π/3)
Vmsin(ωt+5π/3)
Not one of which is equivalent to any other.
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- Professional Electrical Engineer
I'm not going to play "There's a hole in my bucket" with you any more.
Well, I hope I have given you enough information, data, the benefits of decades of practical experience, real circuits, and real pictures of actual kit to help you mend that hole in your bucket.
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Whether you believe it or not; I do respect it. But your experience isn't my standard. I still believe you are putting the effect before the cause and it is caused by "the benefits of decades of practical experience." You have a scotoma that won't let you see past your experience.
gar
Senior Member
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- EE
120312-1803 EST
In "Electrical Circuits and Machinery", Hehre (Columbia University) and Harness (University of Southern California), John Wiley, 1942. Page 269 shows two circuits for transforming three-phase to six-phase. One circuit is classified as "diametrical or double Y", and the other as "double-delta".
Also Chapter 1 discusses a 180 degree phase shift in relation to reflection of one curve to the other, and this one is not a sine wave, but the magnetizing current to a transformer. 180 degree shift here essentially is being related to an equivalent time shift.
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In "Electrical Circuits and Machinery", Hehre (Columbia University) and Harness (University of Southern California), John Wiley, 1942. Page 269 shows two circuits for transforming three-phase to six-phase. One circuit is classified as "diametrical or double Y", and the other as "double-delta".
Also Chapter 1 discusses a 180 degree phase shift in relation to reflection of one curve to the other, and this one is not a sine wave, but the magnetizing current to a transformer. 180 degree shift here essentially is being related to an equivalent time shift.
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A tad unkind if I may say so.
An ad hominem with no basis whatsoever in fact.
A Chinese proverb comes to mind:
Back on topic.
Why do I need six firing pulses per cycle for hexaphase if it is glorified three phase.
Well, if Bes had only three phases, what would he do with those three extra rectifiers? According to definition #2 I believe, phase is the argument of the sinusoid associated with that phase. Nowhere does the definition say that inverses don't count as phases. They all look pretty much alike to me. BTW, which is the real phase and which is the unreal phase?
rbalex is still clinging to his cockamamie notion that inverses are of the same phase despite ample proof that it is wrong.
rbalex is still clinging to his cockamamie notion that inverses are of the same phase despite ample proof that it is wrong.
6-phase rectifier
6-phase rectifier
In the book, Alternating Current Machines, a '6-phase rectifier' is described. It is powered from a 3-phase source. Pretty much like Bes's rectifier except it uses a mercury pool. I suppose you could call it 'hexaphase', although the authors called it a '6-phase rectifier'. Let's see 'hexa' means 'six' and vice-versa right?
I guess they didn't know their trig, although the book is full of phasor diagrams. Don't know how they managed!
6-phase rectifier
In the book, Alternating Current Machines, a '6-phase rectifier' is described. It is powered from a 3-phase source. Pretty much like Bes's rectifier except it uses a mercury pool. I suppose you could call it 'hexaphase', although the authors called it a '6-phase rectifier'. Let's see 'hexa' means 'six' and vice-versa right?
I guess they didn't know their trig, although the book is full of phasor diagrams. Don't know how they managed!
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More references.
http://www.electronics-tutorials.ws/accircuits/phase-difference.html
The author does not say it is a requirement that phase be defined as the 'positive going' zero crossing. Instead he says it is a common practice and then provides some conversion equalities.
-sin(wt) = sin(wt+/-180)
-sin(wt)=sin(-wt)
http://www.electronics-tutorials.ws/accircuits/phase-difference.html
The author does not say it is a requirement that phase be defined as the 'positive going' zero crossing. Instead he says it is a common practice and then provides some conversion equalities.
-sin(wt) = sin(wt+/-180)
-sin(wt)=sin(-wt)
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- Professional Electrical Engineer
I apologize for the unkindness. I should have prefaced the "scotoma" statement with - "I believe" too.
Back on topic: Basically, to rectify the system voltages and prevent current flow for part of a period. A period for all currents is still 2π even if current isn't measurable or otherwise indicated. Effectively, you have simply introduced Z ≈ ∞, for part of a period and Z = "whatever your load is" for the rest or Ohms law doesn't apply for the voltage's full 2π period.
But why do I need to deal with downstream at all? We agreed some time ago the downstream doesn't generate the system voltage functions. How you use the voltages downstream is apart from what they are within the driving system. You might use the driving voltages for any number of things - that's where your ingenuity and experience comes in. And I doubt those would change whether you agreed with me about phase or not. The system is simply not defined by how you use the voltages downstream, the system is what the system is.
Obviously being useful to you is both important and relevant and I've never denied that to either you or anyone else; but it doesn't alter the characteristics of the driving system voltages.
I believe all that to be correct Jim, and it just bolsters our case that 'phase' of V2 should be taken from sin(wt + PI).
Phase difference has been described I believe as simply the difference in the phases of two waves. That is, the phase difference between V1n and V2n is,
wt +/- PI - wt = +/- PI
If the phases of the two waves are equal, then the phase difference would be,
wt - wt = 0
which is clearly not the case. Therefore the phase of V2n cannot be the same as that of V1n.
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
120312-2249 EST
Jim:
Your reference is good and skimming it it looks accurate. It is says what we have been saying. I do not know what your equation - sin wt = sin (-wt) is supposed to mean or represent. It is time going in reverse. What was the point?
On the subject of positive zero crossing. We usually use it as a reference point for making phase difference measurements because it is a convenient point, but not necessary. If it is used, then one does not have to toss in a normalizing constant to adjust amplitude to get a common reference point.
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Jim:
Your reference is good and skimming it it looks accurate. It is says what we have been saying. I do not know what your equation - sin wt = sin (-wt) is supposed to mean or represent. It is time going in reverse. What was the point?
On the subject of positive zero crossing. We usually use it as a reference point for making phase difference measurements because it is a convenient point, but not necessary. If it is used, then one does not have to toss in a normalizing constant to adjust amplitude to get a common reference point.
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