single vs. 3 phase

[hardworkingstiff]

Only Mivey

Only Mivey

Only Mivey has posted a definition (that he says is IEEE and I have no reason to doubt) of a single-phase service. Others have posted how they think a single-phase should be looked at but I've not seen a definition other than what Mivey posted.

Does anyone have a definition different than Mivey?

Come on, Rattus? Jim Dungar? Jon? Q? Crossman? etc etc.

 

[crossman]

I see no reason to argue with the IEEE definition of "single phase".

 

[engy]

I see no reason to argue with the IEEE definition of "single phase".

Who is?


...so energized that, in steady state, the alternating voltages between any two terminals of entry have
the same period and are in phase or in phase opposition....

 

[coulter]

IEEE std-141 references NEMA C84.1, which says:

American National Standard for Electric Power Systems and Equipment ? Voltage Ratings (60 Hertz), Nema C84.1 ? 2006,

Table 1, Note d (applicable to 208Y/120):
(d) A modification of this three-phase, four-wire system is available as a 120/208Y-volt service for singlephase, three-wire, open-wye applications.

Annex A, Principal transformer connections to supply the system voltages of table 1:
(d) Single-phase services and single-phase loads may be supplied from single-phase systems or from three-phase systems. They are connected phase-to-phase when supplied from three-phase, three-wire systems and either phase-to-phase or phase-to-neutral from three-phase, four-wire systems.

I do very little residential (DIY only) and even less commercial (office space connected to industrial) so I don't have an opinion. However, "singlephase, three-wire, open-wye", seems sort of a mouthful for common usage.

carl

 

[winnie]

So you find it easy to say that the voltages in a single phase MWBC are out of phase and therefore combine to equal a higher voltage, and the currents are out of phase but they combine to equal zero? Or have I misrepresented your description?

I cannot figure how you use this to describe phase conversion from single to three phase

I prefer to say that the currents from the various branches that add on the neutral are out of phase. This lets me use the same description for both single phase and three phase MWBC, and also leads simply to the calculation of neutral current when only two of three phases are present.

For single phase to three phase conversion, I prefer the 0 and 180 degree representation because it just seems to fit better with the fact that the resulting three phase power will have a 120 degree phase difference (ideally, only approximated in practise, and that 120 degree difference is measured relative to the three phase neutral, which may only be virtual, is not grounded, and is not used in a circuit.

-Jon

 

[jim dungar]

Only Mivey has posted a definition (that he says is IEEE and I have no reason to doubt) of a single-phase service. Others have posted how they think a single-phase should be looked at but I've not seen a definition other than what Mivey posted.

Does anyone have a definition different than Mivey?

Come on, Rattus? Jim Dungar? Jon? Q? Crossman? etc etc.

I have previously been quoted as supplying the references to the IEEE Red book which refers to ANSI C84.1-1989.

I have never been able to find an "official" interpretation of single phase, that is why I use the concept of the number of L-L voltages.

Can anyone cite a source that says the (2) Vl-n of a 3-w single phase service cannot be out of phase when referencing the "n" point, or that in a balanced MWBC the common current must equal zero?

In a wye connected transformer the windings are connected with the polarity dots away from the neutral point. This arrangement means that all of the phasors have their tails at the center and are pointing out. So even if you only use (2) of the phasors (i.e. an open wye) you still end up with one L-L voltage.

However in a (2) winding transformer the windings are connected with the polarity dots in series. I say this arrangement means that both the current and voltage phasors should also in series (i.e. connected head to tail). Rattus and others, say the direction of the voltage phasors should not be consistent with the construction of the transformer and they should be connected tail to tail just like in the "open wye".

So if you believe the concept that single phase 120/240 allows for 180?out of phase voltages, then you must also accept the fact that 120/208 open wye is also a valid single phase system.

 

[coulter]

I have previously been quoted as supplying the references to the IEEE Red book which refers to ANSI C84.1-1989. ...

Whoops - didn't see that Jim had already posted an excerpt from C84.1

carl

 

[rattus]

What original question are you quoting?

How does a typical residential utility transformer work?
From bretheiling, 11/3/2007

I am not saying that V1n and V2n are not opposite. I am saying who cares. The only practical reason I can see for describing a 180? difference is to validate an oscilloscope voltage tracing.

Good question. I care, the OP cares, and you must care because you responded to the OP's question, and I am claiming your response was incorrect.

And why is that I am complicating things by not agreeing with using your method, yet you are not complicating things by not agreeing with me that the method you use has a limited purpose?

Because you are talking all around the issue without admitting that the OP's question was correctly phrased.

Case in point: The applicability of this method is general, but that has nothing to do with the issue. That is complicating the issue.

Jim, all you have to do is agree that V1n and V2n are out of phase by 180 degrees without bringing in your personal preferences. You have almost done that, but not quite.

 

[engy]

Rattus and others, say the direction of the voltage phasors should not be consistent with the construction of the transformer and they should be connected tail to tail just like in the "open wye".

I don't think anyone is saying it HAS TO be one way or the other.
Are you saying it has to be your way?
Both ways are correct ( if you mind your p's and q's)

The dare I say "correct way" (maybe "traditional" is better) is V1n,Vn2, but V1n,V2n COULD be used.........right?

 

[engy]

Would be a shame if we couldn't hit 200...

 

[rattus]

Engy has got it!

Engy has got it!

I don't think anyone is saying it HAS TO be one way or the other.
Are you saying it has to be your way?
Both ways are correct ( if you mind your p's and q's)

Then dare I say "correct way" (maybe "traditional" is better) is V1n,Vn2, but V1n,V2n COULD be used.........right?

Yes, of course. But, we have different views of convention. I prefer to think of the CT/neutral/ground reference as conventional. After all, we do that with a wye; why not with the split-phase? The results are the same.

The only incorrect thing I see is telling the OP he is incorrect when in fact he is correct. That is the crux of the matter.

 

[rattus]

Door prize, booby prize?

Door prize, booby prize?

Would be a shame if we couldn't hit 200...

Does the 200th poster get a prize, or does he get kicked off the Forum?

 

[jim dungar]

How does a typical residential utility transformer work?
From bretheiling, 11/3/2007

I answered the question in Post #1 of this discussion dated March of 2008. I didn't realize you had gone back to last year.

Jim, all you have to do is agree that V1n and V2n are out of phase by 180 degrees without bringing in your personal preferences. You have almost done that, but not quite.

Please remind me when I have said they were not.

I have consistently said "Just because you can, doesn't mean you should". You are right this is a personal preference.

For example post #146

A problem I see with your method of describing a 180? voltage difference, is it is not easily applicable to other power system analyzes as we have seen when describing the voltages and current flow in a single 2-wire circuit. It only works for voltages. You admit that your model is not applicable to describe magnetic flux, but it would be if the voltages were in the same direction

Where did I say the method was wrong.

...and I am claiming your response was incorrect.

You have finally admitted that If I don't agree with you I am wrong.

I wish you would provide at least one reason why I am incorrect for modeling the voltages in the same manner as I do the currents and magnetic fluxes which is based on the real world connection of the voltage sources.

edited to make quotations work

 

[gpedens]

single phase vs 3 phase

single phase vs 3 phase

Rattus would you believe V12 = V1n + (- V2n) = 240V or V12=V1n + Vn2 = 240 for a single 240 volt winding center tapped at n? Both equations say the same thing. 1 is positive with respect to 2 and n, 2 is negative with respect to 1 and n. Kirchoffs law says the sum of the voltages around a loop are 0. V1n + Vn2 + V21 = 0 or V1n + Vn2 = -V21 or V1n + Vn2 = V12. By your method V1n +(- V2n) + (- V12) = 0 or V1n - V2n = -(-V12) or V1n - V2n = V12. In your case you are not really subtracting but you are adding a negative value. I prefer to call the positive end the head of the mule and the negative end the tail. When voltage is induced in the winding 1 to 2 at some instant in time if 1 goes positive then the other end 2 will go negative with respect to 1. Since n is in the middle it will be negative to 1 but positive to 2. The terminal "n" is not really neutral or 0, it is simply in the middle. By saying that V1n and V2n are 180 out of phase to me you are implying that 1 and 2 both go positive with respect to n. Do a "kick" test with a battery on the winding and you will see that that is not the case. Even your equation V12 = V1n + (- V2n) = 240V shows me 2 is the negative end of V12 and V2n. Its only one winding or 2 halves) on one core, only one voltage is induced. We choose to split it for convience.

 

[rattus]

Rattus would you believe V12 = V1n + (- V2n) = 240V or V12=V1n + Vn2 = 240 for a single 240 volt winding center tapped at n? Both equations say the same thing. 1 is positive with respect to 2 and n, 2 is negative with respect to 1 and n. Kirchoffs law says the sum of the voltages around a loop are 0. V1n + Vn2 + V21 = 0 or V1n + Vn2 = -V21 or V1n + Vn2 = V12. By your method V1n +(- V2n) + (- V12) = 0 or V1n - V2n = -(-V12) or V1n - V2n = V12. In your case you are not really subtracting but you are adding a negative value. I prefer to call the positive end the head of the mule and the negative end the tail. When voltage is induced in the winding 1 to 2 at some instant in time if 1 goes positive then the other end 2 will go negative with respect to 1. Since n is in the middle it will be negative to 1 but positive to 2. The terminal "n" is not really neutral or 0, it is simply in the middle. By saying that V1n and V2n are 180 out of phase to me you are implying that 1 and 2 both go positive with respect to n. Do a "kick" test with a battery on the winding and you will see that that is not the case. Even your equation V12 = V1n + (- V2n) = 240V shows me 2 is the negative end of V12 and V2n. Its only one winding or 2 halves) on one core, only one voltage is induced. We choose to split it for convience.

I know all that, except that adding another tap creates a second voltage, and we can define each voltage in one of two ways. If we define each voltage relative to the CT, then the phase difference is 180 degrees. That is a very basic fact. What I don't understand is the notion that a common core makes any difference as to one's choice of reference. That is all it is, the choice of reference. The voltages could come from separate separate transformers, separate generators, or a black box for that matter.

Furthermore, L1 and L2 are circuit nodes, not windings. It is very logical to define the voltage on these nodes relative to the CT. However no one is claiming a lock on the TRVTH. I am just claiming that the OP on a distant thread was correct when he referred to V1n and V2n being out of phase by 180 degrees.

 

[jim dungar]

However no one is claiming a lock on the TRVTH. I am just claiming that the OP on a distant thread was correct when he referred to V1n and V2n being out of phase by 180 degrees.

But you do claim a lock on the truth, why else would you say that I am incorrect?

and I am claiming your response was incorrect.

You have said you want to use the 120/240 neutral as your voltage reference point because that is what you do with a 208Y/120 system.

I want to designate my 120/240 voltages and current based on the real word connection and operation of transformers just like I do with 208Y/120. But you don't approve of my disagreeing with you

Jim, all you have to do is agree that V1n and V2n are out of phase by 180 degrees without bringing in your personal preferences.

Maybe it is time for me to leave.

 

[rattus]

But you do claim a lock on the truth, why else would you say that I am incorrect?

Jim, if you deny that v1n and V2n are out of phase, you are incorrect. That is all I am saying.

You have said you want to use the 120/240 neutral as your voltage reference point because that is what you do with a 208Y/120 system.

No Jim, I am merely comparing the two systems to illustrate the commonality of the method.

I want to designate my 120/240 voltages and current based on the real word connection and operation of transformers just like I do with 208Y/120. But you don't approve of my disagreeing with you

Jim, that is not the question. The only question is,

"Is it permissible to use the CT/neutral/ground node as a reference?"

I say yes; others have said yes. You won't say yes or no. Just say one or the other so we can get on with it. Then we will know if we disagree. I am not sure.

 

[Rick Christopherson]

Jim, all you have to do is agree that V1n and V2n are out of phase by 180 degrees without bringing in your personal preferences. You have almost done that, but not quite.

Rattus, you are even stating this as though it was an absolute, and not just your personal preference. You prefer to think of these voltages as being 180 degrees out of phase with each other, but others, including myself, would prefer to think of V2n as -120 volts with the same phase angle as V1n. Mathematically both methods are the same, but the minus sign is more consistent with reversing the polarity of your oscilloscope leads.

 

[rattus]

Not at all:

Not at all:

Rattus, you are even stating this as though it was an absolute, and not just your personal preference. You prefer to think of these voltages as being 180 degrees out of phase with each other, but others, including myself, would prefer to think of V2n as -120 volts with the same phase angle as V1n. Mathematically both methods are the same, but the minus sign is more consistent with reversing the polarity of your oscilloscope leads.

One is free to do this anyway he wishes, not absolute at all.

Clearly V2n can be described as 120 @ 180. A purist would use that terminology, that is, magnitude and phase angle.

 

[Rick Christopherson]

A purist would use that terminology, that is, magnitude and phase angle.

No, a purist wouldn't be reversing it in the first place. A purist would prefer to keep their current and voltage with the same sense.