Why is residential wiring known as single phase?
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mivey
Senior Member
I give no thought to whether you will or will not respond. Your participation is your own business and I am OK with whether you do or do not participate. I participate because I want to and I assume you do the same. There is no "you and me".
Myself and others have answered your question but you just did not like the answer I guess. This issue has been discussed many times in previous threads. You make the assumption that when we speak of a phase difference that it means there must be a time shift. The terms "a phase shift" and "a difference in phase" are used interchangeably.
Consider that I can take a single wave and run it through a set of delay circuits to create three 120? displaced waves. I have used this very circuit to get a three-phase set of voltages. In this delay case we have three phases due to a time delay.
In the case of a three-phase generator, you get the three 120? displaced waves from a difference in physical orientation, not a time delay.
In our world, we often create other phases without using delay boxes. The Scott T connection uses physical manipulations to create a 2-phase set of voltages from a 3-phase set and the voltages are "shifted".
I have also shown with the open-wye to 4-wire wye that we use voltages in the halves of a center-tapped winding in opposite directions. This makes use of the fact that the voltages in the winding halves also have a physical 180? displacement and we can use this real phase difference to create real voltages that have other real phase differences.
So the thought that a difference in phase must mean a time delay is just wrong in our world. In some worlds, like audio, that may be correct for certain applications.
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mivey
Senior Member
It can supply either one. And you can use either.
But without another transfomer or something you just can't use them to create a set of voltages to drive a 240 volt load or a load requiring the voltages as a set, like Besoeker's circuit.
You could actually take the two waveforms and run them through isolation transformers to get a set of voltages like you would have with the center-tap secondary.
The equation is perfectly valid. But in one of the earlier posts, someone ignored the signs in order to claim that V1 and V2 are actually in phase. I am asking anyone who knows math better than I to explain it to me.
gar
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In post #981 rattus simply ask how you could remove the - sign from the equation with no other change to the equation.
If I use the identity
sin (a +/- b) = sin a * cos b +/- cos a * sin b and substitute b = 180, then
sin (a +/- 180) = sin a * (-1) +/- cos a * (0) = - sin a
This identity does not remove the - sign. Therefore, I conclude there is no identity that removes the - sign for the 180 deg shift because it would be a contradiction.
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In post #981 rattus simply ask how you could remove the - sign from the equation with no other change to the equation.
I believe someone else said with a trig identity. What identity?
If I use the identity
sin (a +/- b) = sin a * cos b +/- cos a * sin b and substitute b = 180, then
sin (a +/- 180) = sin a * (-1) +/- cos a * (0) = - sin a
This identity does not remove the - sign. Therefore, I conclude there is no identity that removes the - sign for the 180 deg shift because it would be a contradiction.
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Don't yell Rick, you are going to get the thread closed again. You are correct about the noise, but no one cares because we are discussing ideal waveforms. No noise is allowed.
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What an absolutely positively absurd argument; Yeah but if they were connected differently we would get different results.
There are two windings on a common core.
As agreed to be Besoeker, these are real physically defined in-phase windings.
I have repeatedly used the industry standard terminal designations X1-X2&X3-X4. This is the real world.
You then say to change the reference, but I am talking about physical connections, so the only way to change the reference is to rewire the source
You talked about millions of single phase transformer connections, how many of them are connected in your arrangement of X2-X1&X3-X4?
Maybe Besoeker could post the waveforms from your suggested connection, so they can be performed. Of course he won't be able to do this with a center-tapped transformer as its connections are fixed by the manufacturer.
I can guess your rebuttal will still be; but the math can be made to work, just open your eyes to other possibilities.
Over and over, I have not been talking about 'what if', I have been discussing the actual transformer connections found in millions of installations in the real world - just like the OP asked about.
mivey
Senior Member
Absurb if that was actually my argument. Look at the graphic I posted in #847. Both voltages are there and the graphic is not animated to change the connections back and forth. The connections are static.
As I pointed out before, windings in themselves do not have a phase. It is the voltage in the winding that has a phase. To say a winding has a phase you are associating it with a voltage and to do that you must pick a positive direction or you can't compare phases.
Please show me where I said any of the millions were connected that way. I said the transformer on the right of my graphic is connected the same as the standard residential transformer.
As are the connections on the right side of my graphic.
Based on your responses, my argument would be that you haven't really looked at my graphic and that you are just making assumptions about what is there based on what you want to argue against.
and just like I included in my graphic.
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Being the "someone else" had he said he accepted trig identities; I would have followed up with "Why would you need to? The term "wt" is identically equal to “wt” on both sides of the equation except to folks with a runaway oscilloscope.” Instead he demanded an answer limited to high-school algebra.
But'"a" is identically equal to “a” on both sides of the equation' applies to your math too.
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But, (wt) NE (wt + 180)
Wasn't in HS, wasn't in college algebra, wasn't in college trig, wasn't in analytic geometry, wasn't in calculus, wasn't in DE.... Maybe in the "new math" which I never had.
Still don't see how the minus sign disappears. Maybe it's just "apparent", that is, not really there?
Maybe in Boolean algebra, huh?
I want to submit that I have given you numerous examples that I believe more than adequately demonstrate my understanding of the differences between AC and DC.
Perhaps you haven't understood them?
I think I shall try again.
Here's three phases. They are 400V and equally displaced over 360 degrees.
In short, a typical three phase system.
Here's a six pulse rectifier. A B6U. It's typically what you would have on the input of a variable frequency inverter.
It converts AC to DC. No magic involved. And this is the DC output when fully phased on:
It's DC with some ripple content and I have even included the lowest order harmonic of that ripple.
The mean value of the voltage is shown on the graph. It's 540Vdc.
Derived this way:
Not brilliant resolution. I'm still getting to grips with presenting my equations with the new version of equation editor.
Now, what was it you wanted me to prove about my understanding of differences between AC and DC?
I say it like this:
There are two phases.
Slightly more seriously, how would you account for Ia and Ib being 180 deg apart if there was one phase only?
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Rick Christopherson
Senior Member
No Mivey, you have never answered the question. You've dodged it. I never said anything about a "time shift". The three of you keep saying that the phase shift is "real" not "mathematical".
The question was posed to identify which side of zero the noise anomaly would appear. If it is a physical phase shift, as the three of you keep claiming, then it must appear in the positive half cycle of both secondary waveforms. It can only appear in the negative half cycle if one of them is simply an inversion. Your mathematical equality sin(wt + 180) = -sin(wt) removes the minus sign, so you can't have it in the negative half cycle if it is a phase shift. There is no minus sign if it is a "real" phase shift.
You don't get an argument from me until you claim it is a "real" phase shift, and not an inversion that is mathematically made to appear as a phase shift.
Nevertheless, you have still dodged the question. Which side of zero will you see the noise anomaly? (Rattus has)
Where did I claim that it was a physical phase shift?
Rick Christopherson
Senior Member
So what you are saying when you jump back to saying it is "ideal" is that it is mathematical only and not real. I don't have a problem with you saying there is a mathematical phase shift. I take issue with you saying it is real. If it is a real phase shift, then there is no minus sign that would be necessary to move the noise to the negative half cycle. Your phase shift eliminates the minus sign. So if the noise is appearing in the negative half cycle as you now agree, then the only way to get it there is with an inversion that mathematically appears to be a phase shift. You can't have both.
I didn't say it was ideal.
I didn't say it was a mathematical phase shift.
Then explain how the circuit in post #1004 works.
Rick Christopherson
Senior Member
Where in that post does it say that they are physical?
brother
Senior Member
This got to be the longest post on mike holt forums! I didnt read them all, but I was told that residential is called single phase because the primary side is only using single phase of the 3 phase y system. Im sure someone has already said it, but at what post who knows. Im glad to be part of history now of the longest post on mike holt!
Rick Christopherson
Senior Member
I know you didn't say it was mathematical. That's why I'm taking issue with it. You're claiming its real.
It works by inversion that is mathematically represented as a phase shift. But you're dodging the question.
Rick Christopherson
Senior Member
When you say it is "real," that's physical. When you deny that it is a mathematical equality, that makes it physical. It's not a real phase shift. It is mathematical.
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