And the tap in the middle creates two 120V voltage sources that are 180 deg out of phase with each other with respect to the neutral. That's the whole point of the tap. If you feel otherwise, show us your circuit model where you don't use TWO 120V voltage sources. I've given you that request several times now. And it doesn't matter if those voltage sources are from a transformer, a generator, or synthesized electronically from a battery. All I need to tell an electrica l engineer is I'm giving you two ideal voltage sources, 60 hz, 180 deg out of phase, with a shared common return. That's all you need to know to analyze and use what's there. It doesn't matter how or what it was generated from. Do you disagree with that?
That is simply not true, no matter how many times you repeat it. This is one winding, continuously wound in the same direction, with current flowing in the same direction, transformer or generator and tapping the middle does not change that. I don't care how many professors need to complicate this simple concept to get it through the heads of dumber students.
With a disconnected (or nonexistent) center tap, you'd have 240V single phase. The difference from 2 different phases is that you changed the point of reference.
The same way, if you were in between the cities of Dallas and Fort Worth (Texas), the cities are in 2 different directions. If you're in Atlanta Georgia they're in the same direction.
There are 2 possibilities right away. That is where you actually need to understand the distribution systems used in the US. I would need to determine what kind of system I was looking at. Simply poking around with a meter or even a scope, is not going to give you that answer unless you understand that. Single phase and a corner grounded delta will look pretty much exactly alike, just having strange voltages (typically 480/240 for the delta, 120/240 for our old friend the center tapped single phase). Both have 2 ungrounded conductors and one white. They will appear the same, single phase. A center tapped delta will look a lot like 2 phase if you have a scope with a grounded common (the only ones we had back on the olden days), again you need to spot the "wild" 208v leg to figure that out because it will look like it is 90 degrees out. The other two look just like single phase. You will also have 4 conductors (one white) so that does not apply to your question The idea that you will simply see a 120 degree phase shift and say that is 3 phase only works on a wye but that will be 4 conductors too (one white). The red herring Trader can't get over, 2 phase, will have 4 ungrounded conductors and may or may not have a 5th grounded conductor (white) but it is not a neutral, nor is the one on the corner delta above.
They are all perfectly legitimate questions that any first week circuits 101 student should be able to answer. And you don't answer them in series, you go part way into the example and then you start talking about transformers when there are no transformers in the simple problem and you bail.
Engineers can answer simple theoretical circuit questions. This is a bizarre position, that only that which has been built can be analyzed and explained.
Two phases requires four ungrounded conductors according to whom, exactly? I can have three phase with only three! And that exists, right? So in what universe is it that I can't have two phases with less than four? You really should just stop already. Of course I can have two phases, 90 deg apart, with two hots and a shared neutral. I simply take two windings on the same shaft, separated by 90 deg, tie one end of each together into a common neutral. This is really basic stuff.
A unique singularity in the world of electrical engineering? That indeed is your parlor trick! You told us that 3 phases exists with phases at 0, 120, 240. Yes? I have to check, because above you say that two phases can't exist without 4 conductors, so that would imply that 3 phase requires more than 4 conductors. But previously you just told us that I can have:
3 phase 0, 120, 240
3 phase 0, 179, 240
but if I dare to move that winding one more degree to 0, 180, 240 Poof! now it's single phase? Are you sure that's your position? In my world, the real world, you still have 3 phases. If you have those 3 windings, connect one end of each to a shared neutral, you still have a 3 phase power source, nothing magically disappeared.
And are you really, really sure you want to be on record that I can't have two phases without four conductors? Maybe some of the other "experts" here will weigh in on those two interesting positions.
I addressed it in the other post. As I said, this is the first time you've insisted that one can't have two phases without 4 conductors. You said that was the old 90 deg two phase system. I said OK, we can morph that one step at a time. First step, instead of using two wires, lets use a shared neutral, make it 3 wires. There isn't anything radical in that, is there? Just connect one end of each winding to a common return/neutral. For a couple days, you didn't object. You have two windings, separated by 90 deg on one shaft, two hots, one neutral. Very simple. But now I understand you're insisting that one can't have two phase without four conductors. Are you sure that's your position of record? It seems very odd, since we have 3 phase all over the place with just 3 conductors that it now takes 4 conductors to get two phase. You might want to rethink that one.
So, your position is that I can take a 3 phase power source, with three windings, one at 0, one at 120, one at 240 and it's 3 phase. And if I move the 120 one to 179, it's still 3 phase. If I move it to 181 it's still 3 phase. But if I move it to 180, Poof, it's no longer a phase? Where did it go? If I hook up a scope, I can see it when it's at 179, yes? I can see it at 181, yes? It delivers power at all those phases, yes? But if I move the winding one degree, it's no longer there? You might want to rethink that one. What happens on the scope? It's gone? There would be your parlor trick. Electrical engineering isn't built on parlor tricks. Just because it's 180 and the inverse of the one at 0 doesn't mean it;s gone. And just for arguments sake, I'm not clear on what all disappeared because we had 3 phase and now you say it's single phase? Did it kill off the phase at 240 too?
I already let you have generators and your theory still falls apart.
Engineers live in a theoretical world. Ever see one wire a house? It is zip cord and flying splices because that works on paper.
The people who wire the grid.
You might, theoretically be able to have it but it doesn't exist in the power distribution system. I live in the real world. I am not sure what planet you are on.
Perhaps you should just look at the geometry of the way these are generated in the real world. I don't know what might be possible in the lab.
I understand reality is a foreign planet to you but this is a diagram of a 3phase "Scott Tee" making 2 phase. (drawn by a power engineer, not a college geek)
You can duct tape a funnel on the nose of a horse and call it a unicorn but that does not make it so.
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Look at the diagram on the bottom. You will see that needs 4 wires. If you make it a Tee or an Ell, you will end up with 3 phase. In fact that was how they made 3 phase when they had 2 phase distribution, well up into the 20th century. It was still in my IBM physical planning manuals in 1990. Same transformer, just wired the other way. I am sorry if I keep coming back to transformers but that is what electrical distribution uses. Don't blame me, blame Tesla and Westinghouse.
No actually when you get to "181" you are 3 phase with opposite rotation and it becomes a 179 phase shift. The reality is that might technically be 3 phase but I am not even sure it is sustainable.
When you reach 180 degrees "poof" it does disappear. That is when a triangle becomes a line with no phase angle. That is elementary school geometry How many degrees are there in a triangle? any triangle? Don't even try to say this isn't the geometry of triangles when your white paper is loaded with trig symbols. Trig is the science of triangles.
I already showed you how you can create the illusion of 2 phase from a
3 phase red leg delta on a scope,. You just need to hang the common on the center tap. Your 3 phase motors are still happily spinning away but you will look at your scope and swear there are only 2 phases.
I don't know why you can't accept the opinion of someone with 50 years in the business who has actually done this shit (30 years in computer hardware and 20 years as an inspector) and you rely on something you googled up and a misconception you can't seem to shake..
Yes, you're right and that's what he said and I acknowledged way back. I just put two wires in the latest formulation of the questions that I posed by mistake. The old 90 was two phase, 90 deg, on four wires. I used that as a starting point because that's what Frewell says was a two phase implementation. So the problem I posed is where I morph that into 240/120 service, one step at a time. Looks like we're stuck on step one, Fretwell says if I have those two windings that are 90 apart share a common neutral return, it's no longer two phase, that two phase has to have 4 wires. Which of course is bizarre. Why would two phases require 4 wires, when we have 3 phase all over the place with with just 3?
Exactly. They try to treat the center tap as a mere curiosity, when it's purpose is to create two 120V voltage sources that are 180 deg out of phase with each other with respect to it. And it becomes the NEUTRAL, the SYSTEM reference point. I've asked many times for someone to draw a circuit diagram that models that circuit without using two 120V voltage sources that are either 180 out of phase or of opposite polarity, which is the same thing. They won't because it can't be done.
Nonsense Fretwell. He asked a general question, not one specific to any distribution system. You're given three conductors from an unknown source, one identified as the neutral. Could be from anything, directly from a generator or synthesized electronically from a DC battery. How would you determine what the phase relationships are?
In my world, the answer is a scope will give you the answer. That's because the same rules of electricity apply universally. The electrons don't care if they were created from a generator, a transformer or an electronic box that synthesizes them from a battery. It's the voltages, the phase relationship and the ampacity, that's all that matters. And when you do that with the 240/120 service, you have two 120V voltage sources that are 180 deg out of phase with each other.
Single phase and a corner
Sigh.
Nonsense. I take a generator with two windings on a single shaft. They are at a phase difference of N degrees on the shaft. I tie one end of each winding to the other, creating one common return/neutral. I now have 3 wires and TWO phases. It really is that simple. If you make N=90, you have the old 90 deg two phase implemented over 3 wires instead of two. What do you claim I have there on those two hots? If it's not two phases, what is it?
My theory falls apart? Your latest bizarre position is that if I take two windings and put them on a single shaft generator, N deg apart, connect one end of each winding to one end of the other and making that a common return/neutral, that I don't have two phases over 3 wires. THAT is where the failure is. To claim that there are not two phases there is absurd.
As is your claim that if I take a 3 phase generator and rotate the 120 winding to 179 or 181 it's still 3 phases, but if I dare rotate it to 180, then it becomes a one phase system. (I presume 181 is still OK, you said 179 was, so it seems 181 would be OK by your methods too) And I'm really concerned about that poor 240 phase conductor. Did it get whacked too? If it's now single phase, what happened to that poor fellow?
In my world they live in both the theoretical and real world. Just look around you.
Ever see one wire a house? It
Is that the new fallback position? Maxwell's equations no longer apply? It's all determined by the guys who do the wiring?
Just because that's one way of getting two phases to power something doesn't mean it's the only way.
I did actually leave out something, that the 2 non-grounded conductors carry the same voltage at the same frequency.
That and a voltmeter is all you need. There's no need to bring in extraneous information, like power distribution systems.
If the 2 conductors carry the same phase, the voltage changes (AC) are in step, so at any time they have the same voltage on them. The difference is 0V and that is what you measure. No need for any of that complex stuff, like where those conductors came from. It works the same if you have 2 synchronized electronic inverters with a DC supply.
BTW, 240V is NOT the same as 0V.
Also, I remember someone talking about synchronizing generators by putting a light bulb between the outputs. Same phase: no light.
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