It certainly matters where they are generated because if they came from totally separate sources you could connect them together, no matter how they were polarized and the voltages would either buck or boost. but there would be no fire. It is the fact that you are using two halves of a single winding that makes current flow from L1 to L2.
In a 3 phase system they are different independent phases so you can connect them all together (delta)
Getting 120 has nothing to do with how many phases you have. It is still the same phase, just cut in half. If I cut a cookie in half do I have 2 halves of the same cookie or do I suddenly have two cookies?
That is where you are just wrong. It is not 2 sources, it is two ends of one voltage source. Do you understand what a "circuit" means? It is starting to make sense now, why these professors have to come up with such convoluted "models" to explain such a simple concept.
If this was a DC supply, like our two batteries in series, are you still going to say the current suddenly changed directions at the point where they connect?
The problem is you are bring audio thinking into a power scenario.
I would even contend that the audio guy would just call this a push pull amp on one phase. The other stereo channel would be the other phase. (hence "phasing" speakers)
If you mean a center tapped "red leg" delta, 120 degrees, just like any other 3p. They do center tap one of the transformers and ground it there but the phase angles and current flow do not change.
The problem is when using trader_4's parlor trick definition, virtually every residential electrical service installed in the US is in violation of electrical code because the panels are only listed for single-phase service.
So don't blame me when some overzealous code nanny (they're out there) red tags your service...and good luck finding a two-phase panel replacement.
Oh, I almost forgot the most ridiculous argument of all. Since your panel does not meet code, your insurance company can refuse to pay any claim caused by your improper electrical service equipment. You might even have your children confiscated for reckless endangerment of their lives.
Trader's source says: "Distribution engineers have treated the standard "singlephase" distribution transformer connection as single phase because from the primary side of the transformer these connections are single phase and in the case of standard rural distribution single phase line to ground." [I am not "rural" and my distribution is "single phase line to ground".]
Trader's source says that standard practice is that 240/120V systems are single phase.
Trader's source suggests they should be 2 phases. There is no reason to believe anyone but trader agrees.
None of the many people I have met that have worked on 3-phase systems would call 240/120V systems 2 phases. Neither do manufacturers. Just one reason is that it creates confusion with real 2-phase systems. Another reason is it doesn't make sense.
All this has been argued in another long thread.
Trader can, of course, call it whatever he wants. That will alert people familiar with power systems to what he knows.
And I don't remember anyone here who agrees with him, further reinforcing his reputation as a crank.
"Distribution engineers have treated the standard "singlephase" distributio n transformer connection as single phase because from the primary side of t he transformer these connections are single phase and in the case of standa rd rural distribution single phase line to ground. However, with the advent of detailed circuit modeling we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary. Whi ch now brings into focus the reality that standard 120/240 secondary system s are not single phase line to ground systems, instead they are three wire systems with two phases and one ground wires. Further, the standard 120/240 secondary is different from the two phase primary system in that the secon dary phases are separated by 180 degrees instead of three phases separated by 120 degrees. "
He says they have been "treated" as single phase, but that what is actually there are TWO PHASES. And then he proceeded to go through the complex mathematical analysis of it as two phases to show how loading affects the voltages at the transformer. This isn't some random source, it's an electrical engineering professor, with 40 years experience, presenting at a power industry conference of his peers. He's a life fellow of the IEEE and his paper was published in that PEER REVIEWD journal. If it's silly, wrong, then the IEEE would have had it withdrawn.
I'm not arguing what it's commonly called. Like the engineerig prof, I'm telling you what's really there from an electrical engineering perspect ive. I acknowledged that they call it single phase, probably because it originat es from one phase of the 3 phases coming from the power generator. That does not change what there, what you get, when you center tap a transformer ., what you see on a scope. Your silly position is like saying that because the stuff you blow your nose in is called Kleenex or tissues, it isn't really a soft paper product made from trees.
Neither do manufacturers. Just
It makes perfect sense. When you try to deny it, then you wind up like Fretwell, unable to answer simple questions that a high school student or beginning student in circuits 101 would ask. I'll provide those questions at the end, let's see your answers.
Irrelevant of course.
Bud, why do you show up here and start attacking me? I'm comfortable in my knowledge and have no need to attack. Unlike the folks on the other side, I've answered ALL the questions put to me.
There's at least two posters here in this thread that agree. Plus the electrical engineering professor. Where are you authorities that explain why he's wrong?
OK, since you called my qualifications and knowledge into question, class is in session.
Test question one:
Define N phase power?
Test question two:
According to Fretwell, two phase power existed 100 years ago, and it was over two wires, 90 degrees phase difference. Suppose I run it over 3 wires instead, with a shared neutral, make it 120V. So, you have a generator supplying 120V, two coils, one shared neutral. Would there still be two phases there? (I believe Fretwell said yes) Your answer?
So now, I run that from the generator into a house, we have three wires,
120V, two phases. If I change the phase difference to 179 degrees instead of 90 by rotating one coil, are there still two phases? Yes or no?
Now I rotate it to 180 phase difference. Are there still two phases, yes or no?
And the final step above is absolutely IDENTICAL to what you have coming into the house with 240/120. The electrons are behaving exactly the same. If you disagree, explain how it's different.
Fretwell can't make it through the above, answer every question, because it's clear he's cornered and the truth is obvious.
Problem number 3
I take 3 phase power with a neutral into a house. One phase is at zero, one is at 120, one is at 240, correct?
Now I rotate one coil so that instead of 120, it's at 179. Are there still three phases?
Now I rotate it one degree more, to 180. Are there still 3 phases, yes or no?
Now take away the 240 phase. How many phases now? If it's not two, explain why.
And if it is two, then again, it's ELECTRICALLY IDENTICAL TO 240/120 servic e. IF you believe it's electrically different, explain why.
Problem number 4:
Draw the basic circuit model of 240/120 service. My model uses TWO voltage sources, with a shared neutral. One is 120V sin(wt), the other 120V sin(wt+180) or of alternate polarity connection, if you like. That is the only way to model that circuit, because that is what is there. When you center tap it, you now have TWO voltage sources. Which by the way is exactly what the professor is saying, you have two sources, 180 out of phase with each other. Tell us your alternate model.
Note that none of the others here can make it through answering those simple, very basic questions, because their arguments fall apart, they are making it up as they go. Half way through, they cut it apart, stop answering, and start talking about transformers. What's on that service doesn't matter where it came from, whether it's a transformer or sy nthesized electronically from a battery. I defined N phase power and gave a clear explanation that's consistent with what a first semester electrical engineering student knows. I can and have answered all those simple student questions consistent with electrical engineering. Can you?
There are 3 conductors, so how can it possibly be all flowing in the same direction? It would pile up in the house.
You have to look
He actually said that the sum of the currents at a node is zero. Which does translate into the fact that all the current entering the house has to leave the house. Which of course is yet another red herring, IDK what your point is here. That is true if there is one phase, two phases, N phases.
Ridiculous. It's not a random spot, it's the SYSTEM ground, it's reference point. I can and have defined N phase power and it's completely defined by the number of voltage sources, their amperage and phase relationship to each other. It matters not a wit if it's generated by a transformer, by a generator, or again, synthesized electronically from a DC battery. If I synthesized 3 phase from a battery, is it DC?
Simply the fact
IDK where you got that from.
If we assume current flows negative to
Current doesn't have to be flowing in L2 at all, if all you have is a 120V load on L1, the current in L2 is ZERO. And all of the above has nothing to do with the fact that those two transformer coils are separate 120V voltage sources that are 180 deg out of phase or connected in alternate polarity, which is exactly the same thing. You could have
100 amps flowing in one half, zero amps flowing in the other.
Go see my reply to Bud and take the simple quiz at the end. See if you can make it through one step at a time, answer every question. Youy can't because you're quickly caught up in contradictions. When you apply electrical engineering uniformly, there are no contradictions.
Ridiculous. The behavior of that 240/120 3 wire power service is defined by the voltages and phase relationships. Same with any power source. Where it comes form matters not a wit. You have TWO 120V voltage sources sharing a common neutral, 180 deg out of phase with each other, or connected in reverse polarity if you like. THAT is what's there. It;s all you need to know. It could come from a nuclear power plant, a transformer, or be synthesized electronically. IT doesn't even have to exist at all, we can analyze it using ideal voltage sources. If you disagree, give us your circuit model, the professor and I gave you ours, from elec engineering circuits 101.
See, there you go again. Instead of sticking to the example, it's off to the wilderness. I can explain to a student why you can't parallel any two outlets, they are 180 deg out of phase. If they were 120V and in phase, you could parallel them.
In general, that's true.
It is
It's not just one voltage source when you cut it in half, it's TWO. And they are tied together 180 deg out of phase, or with opposite polarity if you like.
Do cookies have polarity and phase?
I've asked you about 6 times now to give you your basic circuit model that uses just one source to get 240/120. I've given you mine, the same as the professor, the same as any first semester EE would. It's TWO
120V voltage sources tied together, sharing the neutral, one 180 deg out of phase with the other or connected with opposite polarity.
If it;s so simple, where is your model? Where, BTW is your definition of N phase? How can you be arguing about what something is, when you can't even define it? And note the definition doesn't rely on transformers, generators, batteries or anything else.
that come off the pole into your house that are 180 deg apart and/or oppos ite polarity and in his mind these are ONE phase because he knows they were both derived from ONE phase of the 3 phase grid system and one is just inv erted polarity of the other.
that are 180 deg apart and says, these are two sine waves that are 180 deg phase so it is TWO phases.
You know, I kind of saw that coming. Mako said "signal" and I let it go. I didn't want to be overly critical or accused of nitpicking and I thought he has it about right. But it isn't an issue of from a signal prospective. It's basic electrical engineering circuit analysis 101.
You seem to think that there is one way of doing circuit analysis for power circuits and another for audio circuits. It's all one and the same thing. I gave you my circuit model using two 120V voltage sources that are either 180 deg out of phase with each other or connected with opposite polarity, same thing. That is your 240/120 service and it could come from a transformer, be synthesized from a battery, or just exist on a piece of paper. It doesn't matter, it defines what's there and it's all you need to know.
The audio guy would hook up his scope ground to the ground on his audio system and take a look at the phase relationships. When you do that in your house, connect the scope ground to the house neutral/ground, what do you see? TWO 120V voltage sources that are 180 deg out of phase with each other. That explains why you can't randomly parallel any two receptacles. It explains how you get 240V from one hot to the other. I don't need to go outside, look for a transformer, talk about ends of transformers. It doesn't matter if that service came from a synthesized source powered by a car battery. What's there is what defines what you have. Knowing what I just stated, and how many amps I am allowed, is all I need to know to design with it, to use it.
Don't you think the circuit goes all the way back to the transformer? At any given moment all of the current is flowing the same way in the transformer secondary and exactly the same amount of current is flowing in the house. Say it starts in L1 of the transformer, it is flowing towards L2. Any unbalanced current will be flowing in the neutral but it is still flowing towards L2. If the unbalance favors the L1 side it goes out on the neutral but it is still flowing the same way in the transformer.
If the balance on both ungrounded conductors is equal, there is zero current in the neutral.
It is certainly a random spot, you can ground the system in at least 3 places.
When it gets back to the transformer it is still flowing towards L2
A system with "n" number of separate phases coming at different angular displacements and coming from separate windings in a Separately Derived Source or a Utility. That does not include simply tapping a single phase transformer tho because there is only one phase at the source.
Since you are not properly describing how 2 phase works, the question is bogus. There are 2 separate windings with primaries at different phase relationships (90 degrees). You can derive 2p from a 2p generator (the way it was done originally) and also from a 3 phase source in some retrofit installations. You can't get there from single phase ... period.
I can't get through a question when the initial supposition is bullshit. Find out a little more about 2 phase and get back to me,.
To start with, there is no way to get to 179 but as soon as you get to
180, and both windings are in phase (current flowing in the same direction in both secondaries at the same time), you have a single phase that doubles the voltage. If they are out of phase, voltage is zero. They buck each other. You can see that in a GFCI.
Yes it is exactly the same as your house, single phase.
I am not sure how you get to two sources when there is only one secondary winding, no matter where you tap it.
OK lets try this one more time. At my utility I decided to ground one end of the secondary (L1) instead of the center tap. (like most of the civilized world according to Bod) I still center tap the transformer and have 3 buses in my service panel. (lets ignore how you would need to do overcurrent for now but the answer is a split bus panel).
Everything works exactly the same except I have the neutral (centertap) bus at 120 above ground and L2 is 240v above ground. Nothing in your house will notice the difference if you are not using the EGC (ground) for a current carrying conductor (a violation of
Of course it does, where the transformer acts as two 120v voltage sources. But I don't need a transformer to define N phase power. Still waiting for your definition of that. How can you be here arguing about what something is, but can't define it? My engineering world everything is defined and consistently applied. I could replace that transformer with any two voltage sources that are 120V sine waves, that share a common neutral, that are 180 out of phase and the power going to the house would be exactly the same.
The unbalanced part never goes into the second half of the coil.
If the unbalance favors
I agree with that. And it's flowing through two voltage sources, (the two halves of the secondary) that with the center tap, are of opposite polarity, which is the same thing as 180 deg out of phase.
Sure, that's the special case, not the general case.
That's beyond absurd. The ground is the REFERENCE POINT for your SYSTEM. It was deliberately chosen by the folks who set up this power SYSTEM, not by me. So, it's the logical place to connect the ground reference of your oscilloscope to analyze what's there. It's not a parlor trick, some trick spot, that I selected.
No, it's not. If I just have a 120V load on the L1 side, I could cut out and remove the other half of the transformer secondary, the L2 side. There is no current flow in it. Current is flowing in one half of the secondary only.
You haven't taken your simple circuits 101 quiz yet:
Test question one:
Define N phase power?
Test question two:
According to Fretwell, two phase power existed 100 years ago, and it was over two wires, 90 degrees phase difference. Suppose I run it over 3 wires instead, with a shared neutral, make it 120V. So, you have a generator supplying 120V, two coils, one shared neutral. Would there still be two phases there? (I believe Fretwell said yes) Your answer?
So now, I run that from the generator into a house, we have three wires,
120V, two phases. If I change the phase difference to 179 degrees instead of 90 by rotating one coil, are there still two phases? Yes or no?
Now I rotate it to 180 phase difference. Are there still two phases, yes or no? If you disagree, explain how it's different.
(My answer is yes and the final step above makes it absolutely IDENTICAL to what you have coming into the house with 240/120. The electrons are behaving exactly the same. )
Problem number 3
I take 3 phase power with a neutral into a house. One phase is at zero, one is at 120, one is at 240, correct? I can see them on a scope, yes?
Now I rotate one coil so that instead of 120, it's at 179. Are there still three phases?
Now I rotate it one degree more, to 180. Are there still 3 phases, yes or no?
Now take away the 240 phase. How many phases now? If it's not two, explain why.
And if it is two, then again, it's ELECTRICALLY IDENTICAL TO 240/120 service. IF you believe it's electrically different, explain why and how it matters in terms of the behavior of the electrons in the service conductors.
Problem number 4:
Draw the basic circuit model of 240/120 service. My model uses TWO voltage sources, with a shared neutral. One is 120V sin(wt), the other 120V sin(wt+180) or of alternate polarity connection, if you like. That is the only way to model that circuit, because that is what is there. When you center tap it, you now have TWO voltage sources. Which by the way is exactly what the professor is saying, you have two sources, 180 out of phase with each other, that's how you treat it. Do you agree with that? If not, tell us your alternate model.
Problem number 4:
Someone asks why they can't randomly parallel any two receptacles in a house. My answer is, because you have two 120V voltage sources that are 180 deg out of phase with each other or of alternate polarity if you like. If they were of the same phase or polarity, you could parallel them. Your answer?
I can and have answered all those simple student questions consistent with electrical engineering, one after the other, without wandering off into the wilderness. Can you?
-phase generators are built on a single shaft) so that you get two 120VAC o utputs that are 180 degrees out of phase. Would it be reasonable to call th is two-phase power?
t of the transformer is single phase as well. I don't have a two-phas e generator on my utility pole.
Yes, because your neutral is still connected to the center tap. So, inside the house you will still see two hots at 120V with respect to the neutral, one 180 deg out of phase with the other, or of alternate polarity if you like. Hook up a scope, connecting the scope ground reference to the neutral. The SYSTEM neutral, not some parlor trick point that I've been accused of using. What do you see? Two hots,
120v, 180 out of phase. I can do the same with 3 phase, run it into the house. I'd see one sine wave at 0 deg, one at 120 deg, one at 240 deg, correct? Rotate the 120 deg coil to 180, what do you see now? It's a sine wave at 180, correct? Are there still 3 phases there or did one just disappear? Now remove the 240 phase conductor. Three minus one is TWO. And what you have left is exactly identical to 240/120 service. Two hots, 180 deg out of phase with each other.
It's not a matter of opinion. It's a fact to anyone that's passed circuits 101. That's why I can apply circuits 101 and answer all those questions and you and Fretwell can't.
So, the guy who came in attacking, claiming to be an expert, can't answer the simple electrical engineering circuits 101 questions I posed. I can and did. Nuff said. And if you bothered to read my first post on the issue, I clearly said that while there are two phases there, it's not how it's referred to in the industry. Following that logic, you can only talk about the stuff you blow your nose in as Kleenex or tissues, that to analyze it, describe what it really is, as a soft paper product made from trees, isn't allowed. The IEEE Fellow knows what's there. I know what;s there. And we can answer these simple questions that a beginning student could ask a teacher. You can't. Thanks for playing.
Test question one:
Define N phase power?
Test question two:
According to Fretwell, two phase power existed 100 years ago, and it was over two wires, 90 degrees phase difference. Suppose I run it over 3 wires instead, with a shared neutral, make it 120V. So, you have a generator supplying 120V, two coils, one shared neutral. Would there still be two phases there? (I believe Fretwell said yes) Your answer?
So now, I run that from the generator into a house, we have three wires,
120V, two phases. If I change the phase difference to 179 degrees instead of 90 by rotating one coil, are there still two phases? Yes or no?
Now I rotate it to 180 phase difference. Are there still two phases, yes or no? If you disagree, explain how it's different.
(My answer is yes and the final step above makes it absolutely IDENTICAL to what you have coming into the house with 240/120. The electrons are behaving exactly the same. )
Problem number 3
I take 3 phase power with a neutral into a house. One phase is at zero, one is at 120, one is at 240, correct? I can see them on a scope, yes?
Now I rotate one coil so that instead of 120, it's at 179. Are there still three phases?
Now I rotate it one degree more, to 180. Are there still 3 phases, yes or no?
Now take away the 240 phase. How many phases now? If it's not two, explain why.
And if it is two, then again, it's ELECTRICALLY IDENTICAL TO 240/120 service. IF you believe it's electrically different, explain why and how it matters in terms of the behavior of the electrons in the service conductors.
Problem number 4:
Draw the basic circuit model of 240/120 service. My model uses TWO voltage sources, with a shared neutral. One is 120V sin(wt), the other 120V sin(wt+180) or of alternate polarity connection, if you like. That is the only way to model that circuit, because that is what is there. When you center tap it, you now have TWO voltage sources. Which by the way is exactly what the professor is saying, you have two sources, 180 out of phase with each other, that's how you treat it. Do you agree with that? If not, tell us your alternate model.
Problem number 4:
Someone asks why they can't randomly parallel any two receptacles in a house. My answer is, because you have two 120V voltage sources that are 180 deg out of phase with each other or of alternate polarity if you like. If they were of the same phase or polarity, you could parallel them. Your answer?
But you can't even do your parlor trick now because the ground on the scope would be connected to 120v and kaboom. Who cares what the signal looks like there anyway? This is quite clearly a single phase source that is 120 and 240 above ground yet it is wired exactly the same way. The only thing I did was move where I land the MBJ. It is just easier to see that in any given instant current is flowing anywhere in the circuit in exactly the same direction. If I don't use the center tap to supply 120v loads towards L2 it is actually not a bad way to do things because it would allow single pole breakers everywhere, That will be important when they expand GFCI/AFCI to the 240v circuits, I could draw how you would hook up an existing panel that way if you haven't figured it out by now. At the end of the day, landing the neutral on the center tap was just an arbitrary decision by Westinghouse to allay some of the fears of his "killer" AC.
If you connect them together and they are in phase now, you just created a single phase. In a series circuit (source) that actually works, you always connect the positive to the negative and you create a single source. Take the 9v batteries you were talking about earlier. You said it was
2 sources when I snapped two together in series. Thanks for confirming what I said because to use your theory, there are actually 12 sources now because you need 6 cells to get 9v. You just can't easily get to the 6 in the can. It does not change the fact that once they are all in series you have to treat them as one source, whether you can measure each cell or not.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.