Four-wire delta, phasors, and Kirchoff:
- Thread starter rattus
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- PE (Retired) - Power Systems
Rattus,
You call the voltage Vcg but then you say that really needs to be Vgc in order to solve Kirchoff's Law.
I know I am stretching when I say; before we can apply some standard circuit analysis formulas to your method of describing a 120/240V circuit some modifications need to be made, but it certainly sounds like it.
You call the voltage Vcg but then you say that really needs to be Vgc in order to solve Kirchoff's Law.
I know I am stretching when I say; before we can apply some standard circuit analysis formulas to your method of describing a 120/240V circuit some modifications need to be made, but it certainly sounds like it.
My goodness we are brave sorts. I can feel the wrath of god (oops - mispelled that:roll: ) watching over our shoulders. sigh. Be that as it may:
rattus - Thanks for looking at my sketches. I am pretty sure you got (figured out/understood) my point. Probably the next time this comes up, my response will be a combination of Jim's and mine:
From Jim: Just because you can do a thing doesn't mean you should.
Mine: I prefer the single phase orientation as shown in yum, because when you extend to 240/120 it looks right
From Jim again: And you don't have to move the signs around to get the math to come out.
carl
rattus - Thanks for looking at my sketches. I am pretty sure you got (figured out/understood) my point. Probably the next time this comes up, my response will be a combination of Jim's and mine:
From Jim: Just because you can do a thing doesn't mean you should.
Mine: I prefer the single phase orientation as shown in yum, because when you extend to 240/120 it looks right
From Jim again: And you don't have to move the signs around to get the math to come out.
carl
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
I like the yummy drawing. 
It makes perfect sense to me.
I also say that the entire discussion is much ado about nothing. :roll:
It makes perfect sense to me.I also say that the entire discussion is much ado about nothing. :roll:
Basic stuff:
Basic stuff:
Jim, no stretch at all. Ages ago, we learned to sum voltages along a string of phasors. A voltage rise from one node to another is added. A voltage drop from node to node is subtracted. That is, if we travel from phasor tail to phasor head, we add that phasor. If we travel from phasor head to phasor tail, we subtract that phasor. As we all know, the sum around a closed phasor loop must be zero, and that is true for either method.
In short, Vcg is 120 @ 180 for either method which is the point I have been trying to make. You of course will do it your way, and that is perfectly valid, but it is not the only way.
Basic stuff:
jim dungar said:
Jim, no stretch at all. Ages ago, we learned to sum voltages along a string of phasors. A voltage rise from one node to another is added. A voltage drop from node to node is subtracted. That is, if we travel from phasor tail to phasor head, we add that phasor. If we travel from phasor head to phasor tail, we subtract that phasor. As we all know, the sum around a closed phasor loop must be zero, and that is true for either method.
In short, Vcg is 120 @ 180 for either method which is the point I have been trying to make. You of course will do it your way, and that is perfectly valid, but it is not the only way.
Rick Christopherson
Senior Member
This is just too funny. And I thought it was going to be a boring afternoon. :grin:
Lest we have a thread closed before we can properly discuss this, can we please promise to keep this civil without personal attacks? Rattus, if you don't like what I have to say, then please attack the information instead of the messenger. OK?
I haven't looked through all of the numbers in the table, but the very first thing that jumped out at me was the statement, "Note that Vcg must be negated because its arrow is backwards so to speak."
This is the issue I had the first time around. When you acknowledge that you need to negate this phasor's magnitude, it means that either the phasor is improperly defined, or it violates Kirchoff's law regarding summation. Regardless which of these two alternatives you choose is immaterial, but it should be raising red flags that you have misplaced the minus sign somewhere.
Adding phasors and adding vectors is the same, in the sense that you place them tip-to-tail, yet you have shown two phasors being added that are tail-to-tail, which is by definition, subtractive.
Phasors are not arbitrarily assigned based on a changing point of reference. They are mathematically defined from the voltage function (in this example) for which they represent. I would have to do some reading on this, but it has something to do with Euler's Identity, which frankly, I don't remember a thing about.
Lest we have a thread closed before we can properly discuss this, can we please promise to keep this civil without personal attacks? Rattus, if you don't like what I have to say, then please attack the information instead of the messenger. OK?
I haven't looked through all of the numbers in the table, but the very first thing that jumped out at me was the statement, "Note that Vcg must be negated because its arrow is backwards so to speak."
This is the issue I had the first time around. When you acknowledge that you need to negate this phasor's magnitude, it means that either the phasor is improperly defined, or it violates Kirchoff's law regarding summation. Regardless which of these two alternatives you choose is immaterial, but it should be raising red flags that you have misplaced the minus sign somewhere.
Adding phasors and adding vectors is the same, in the sense that you place them tip-to-tail, yet you have shown two phasors being added that are tail-to-tail, which is by definition, subtractive.
Phasors are not arbitrarily assigned based on a changing point of reference. They are mathematically defined from the voltage function (in this example) for which they represent. I would have to do some reading on this, but it has something to do with Euler's Identity, which frankly, I don't remember a thing about.
Not so:
Not so:
First, one sums up the real and imaginary components algebraicly as you yourself have quoted Kirchoff. For that matter, some negative components must be present in order for the sum to be zero. This is basic; one adds voltage rises; one subtracts voltage drops.
Second, one cannot negate a magnitude. One can negate the components of the phasor. For example, in the expression,
Vm*cos(wt);
Vm is always positive, but cos(wt) alternates between + and -.
Third, one can define phasors either way. More basic stuff. Perfectly legal. You must give us a reference which proves otherwise.
Not so:
Rick Christopherson said:
First, one sums up the real and imaginary components algebraicly as you yourself have quoted Kirchoff. For that matter, some negative components must be present in order for the sum to be zero. This is basic; one adds voltage rises; one subtracts voltage drops.
Second, one cannot negate a magnitude. One can negate the components of the phasor. For example, in the expression,
Vm*cos(wt);
Vm is always positive, but cos(wt) alternates between + and -.
Third, one can define phasors either way. More basic stuff. Perfectly legal. You must give us a reference which proves otherwise.
Last edited:
Trvth
Trvth
Larry, it is about TRVTH. I am trying to show that, contrary to popular opinion, the voltage on the two single phase legs can be described as 180 degrees out of phase.
I am also trying to demonstrate that Kirchoff's voltage law is satisfied with yumm or yuck.
Either way, the sum around the loop is ZERO.
Trvth
LarryFine said:I like the yummy drawing.
I also say that the entire discussion is much ado about nothing. :roll:
Larry, it is about TRVTH. I am trying to show that, contrary to popular opinion, the voltage on the two single phase legs can be described as 180 degrees out of phase.
I am also trying to demonstrate that Kirchoff's voltage law is satisfied with yumm or yuck.
Either way, the sum around the loop is ZERO.
mivey
Senior Member
Snickers and Bugles
Snickers and Bugles
Maybe we should refrain from using the term out of phase. I have come to understand that there are some who take this to mean a time delay (like in the audio sense), which is not even under consideration as far as I understand. Use phase difference or maybe even better reference angle or phasor angle. I think we are going to find it is a matter of terminology. Maybe we are getting hung up on the word instead of what we mean by the word.
I don't think external references are going to help either as we are talking about the terminology WE use. I think it has been said before that we could probably find some external reference that uses whatever terminology we are familiar with. I mean, after all, we aren't just making this up as we go along. I think both sides know what they are talking about but the question is, do they know what the other is trying to say?
Suppose we were from different countries with different language and terminology and were trying to solve real world problems. Would we get hung up on the language or try to break through to understand what the other was saying?
I suspect we are not going to find an incorrect application of theory by either side. Chalk up those differences in terminology on the board and come up with a common terminology, like Snicker bars and Bugles (which I'm currently eating), we are probably going to say the same thing. If we are arguing over language, who cares?
Snickers and Bugles
rattus said:
Maybe we should refrain from using the term out of phase. I have come to understand that there are some who take this to mean a time delay (like in the audio sense), which is not even under consideration as far as I understand. Use phase difference or maybe even better reference angle or phasor angle. I think we are going to find it is a matter of terminology. Maybe we are getting hung up on the word instead of what we mean by the word.
I don't think external references are going to help either as we are talking about the terminology WE use. I think it has been said before that we could probably find some external reference that uses whatever terminology we are familiar with. I mean, after all, we aren't just making this up as we go along. I think both sides know what they are talking about but the question is, do they know what the other is trying to say?
Suppose we were from different countries with different language and terminology and were trying to solve real world problems. Would we get hung up on the language or try to break through to understand what the other was saying?
I suspect we are not going to find an incorrect application of theory by either side. Chalk up those differences in terminology on the board and come up with a common terminology, like Snicker bars and Bugles (which I'm currently eating), we are probably going to say the same thing. If we are arguing over language, who cares?
mivey
Senior Member
Rick, how is KVL being violated? If it is a matter of how we define terms, I would not consider that violating a law. I see violating a law as mis-application of real theory like saying transient analysis is the same as steady-state analysis (as long as we both agree on what is meant by transient and steady state).
Let's come up with some Klingon terms with some definitions we can agree on and then see if we have any differences. (Klingon? Have I just raised the nerd flag?)
[edit KVL not VKL]
Let's come up with some Klingon terms with some definitions we can agree on and then see if we have any differences. (Klingon? Have I just raised the nerd flag?)
[edit KVL not VKL]
quogueelectric
Senior Member
- Location
- new york
Well everyone knows that the centertap neutral is to reduce the shock hazard to human life right??
quogueelectric
Senior Member
- Location
- new york
Not unless you are in the tubrattus said:
quogueelectric
Senior Member
- Location
- new york
They must have messed with B+rattus said:
quogueelectric
Senior Member
- Location
- new york
So you think nm cable is dangerous to those not having electrical knowledge?rattus said:
Rick Christopherson
Senior Member
The problem with Rattus' example is that he forgot to negate the negative that he created with his 180 degree phase shift. He drew his phasor with the 180 degree direction, but then did not account for this in the magnitude of the phasor. As he stated previously (he and I both agree on this), you cannot have a negative magnitude with a phasor (at least not when properly used).
V(t) = V Sin(ωt) = -V Sin(ωt + 180)
However, what Rattus drew is equivalent to:
V(t) = V Sin(ωt) ≠ +V Sin(ωt + 180)
(Just in case the symbol does not show up for some browsers, there is a not-equal sign in the above equation.)
He compensated for this by subtracting the voltage when he performed Kirchoff's summation, which is contradictory to Kirchoff's "summation".
If he draws the phasor going right-to-left (in the example drawing), then he must give it a negative magnitude. The phasor he drew is not equivalent to the voltage source it is representing.
The most important thing about phasors, is that they do not change when you change your point of reference.
V(t) = V Sin(ωt) = -V Sin(ωt + 180)
However, what Rattus drew is equivalent to:
V(t) = V Sin(ωt) ≠ +V Sin(ωt + 180)
(Just in case the symbol does not show up for some browsers, there is a not-equal sign in the above equation.)
He compensated for this by subtracting the voltage when he performed Kirchoff's summation, which is contradictory to Kirchoff's "summation".
If he draws the phasor going right-to-left (in the example drawing), then he must give it a negative magnitude. The phasor he drew is not equivalent to the voltage source it is representing.
The most important thing about phasors, is that they do not change when you change your point of reference.
Rick Christopherson
Senior Member
quogueelectric, with all due respect, I would like to try to keep this discussion civil and on topic. Can we address your questions in a separate thread?quogueelectric said:
Mivey -mivey said:
I don't understand. out of phase <> time delay <> phase difference <> phasor angle difference <> reference angle difference
where I use the symbol <> to mean equavalence (not equality)
All of these are the same thing. One uses what ever term fits the math you are using. So "out of phase" = "time delay (like in the audio sense)" is exactly true.
180 deg oop = 8 1/3ms delay for 60 hz.
I'm thinking this is not news to you, its all stuff you know. So I'm puzzled
I'm lost again. We are engineers, not scientists doing original research. Everything we do is covered by a code, standard, recomended practice. External references are what we live by.mivey said:
My recommendations are to use the standard language. Use recognized codes, standards, recomended practices.
We don't have a secret society. Why would we even consider making up a new language?
carl
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