120/240V single or multiphase?

[weressl]

We had this discussion a while ago and it wasn't the first time.

Will this IEEE paper at least offer some reasoned path to choose?



Abstract

—Distribution engineers have treated the standard “single-phase” 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. 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, which now brings into focus the reality that standard 120-/240-V secondary systems are not single-phase line-to ground systems, but they are three-wire systems with two phases and one ground wire. Furthermore, the standard 120-/240-V secondary system is different from the two-phase primary system in that the secondary phases are separated by 180◦ instead of three phases separated by 120◦. What all of this means is that analysis software and methods must now deal with an electrical system requiring a different set of algorithms than those used to model and analyze the primary system. This paper will describe the modeling and analysis of the single-phase center-tapped transformer serving 120- and 240-V single-phase loads from a three-wire secondary.​

 

[iwire]

I will comply when I can buy "two phase" 120/240 panels.:grin:

 

[StephenSDH]

You can buy a 2 phase panel, but its really 4-phase:smile:.

 

[dbuckley]

Mods - bury it quickly

 

[jim dungar]

Will this IEEE paper at least offer some reasoned path to choose?

Is this a published IEEE white paper or simply a proposal?

 

[dbuckley]

The paper is:

Center-Tapped Transformer and 120-/240-V Secondary Models
Kersting, W.H.;
IEEE Transactions on Industry Applications,
Volume 45, Issue 2, March-april 2009 Page(s):575 - 581
Digital Object Identifier 10.1109/TIA.2009.2013590

I've just had a quick read.

The focus of the paper is as described in the last line of the abstract: "This paper will describe the modeling and analysis of the single-phase center-tapped transformer serving 120V and 240V single-phase loads from a three-wire secondary".

What the paper develops is a model for a single phase centre tapped transformer and three wire triplex cable. The issue under examination is the voltage delivered to the customer, which in the cases examined in the paper showed that customers would not necessarily get the expected voltage.

No-where in the paper does it suggest that the single phase centre tapped 120/120 supply is a two phase supply.

 

[weressl]

The paper is:


I've just had a quick read.

The focus of the paper is as described in the last line of the abstract: "This paper will describe the modeling and analysis of the single-phase center-tapped transformer serving 120V and 240V single-phase loads from a three-wire secondary".

What the paper develops is a model for a single phase centre tapped transformer and three wire triplex cable. The issue under examination is the voltage delivered to the customer, which in the cases examined in the paper showed that customers would not necessarily get the expected voltage.

No-where in the paper does it suggest that the single phase centre tapped 120/120 supply is a two phase supply.

Really?!

<<Abstract

?Distribution engineers have treated the standard ?single-phase? 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. 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, which now brings into focus the reality that standard 120-/240-V secondary systems are not single-phase line-to ground systems, but they are three-wire systems with two phases and one ground wire. Furthermore, the standard 120-/240-V secondary system is different from the two-phase primary system in that the secondary phases are separated by 180◦ instead of three phases separated by 120◦. What all of this means is that analysis software and methods must now deal with an electrical system requiring a different set of algorithms than those used to model and analyze the primary system. This paper will describe the modeling and analysis of the single-phase center-tapped transformer serving 120- and 240-V single-phase loads from a three-wire secondary.>>

The abstract does so by specifically calling out two phases and using plural form.​

 

[mivey]

No-where in the paper does it suggest that the single phase centre tapped 120/120 supply is a two phase supply.

Really?!

dbuckley is correct. It does not suggest...it just plain out states it. :grin:

 

[jim dungar]

Really?!

The abstract does so by specifically calling out two phases and using plural form.​

An abstract is not part of the paper.
Does the paper actually refer to the 120/240 3-wire system as 2-phase, or is it simply referring to the number of phase [conductors] involved in the system?
How does the paper address the point raised in the abstract that "these [primary] connections are single phase" but there are "secondary phases"; does the paper say or imply that the transformer converts single-phase into 'poly-phase'?

 

[weressl]

An abstract is not part of the paper.
Does the paper actually refer to the 120/240 3-wire system as 2-phase, or is it simply referring to the number of phase [conductors] involved in the system?
How does the paper address the point raised in the abstract that "these [primary] connections are single phase" but there are "secondary phases"; does the paper say or imply that the transformer converts single-phase into 'poly-phase'?

Tha Abstract IS part of a paper. It is the summary of the paper.

The paper does NOT address the issue, the usage of the two phase and plural form demonstrates the authors position that it should not be looked upon as a single phase system - which creeps in form the commonly used mistaken reference to is as a 'single phase' sytem - and demonstrates what effect this simple misconstruance of a word can have on system studies. His point is that UNTIL it is recognized and studied as a two phase system the problem he highlights is not appearent.

 

[Besoeker]

Hmmm....
I suppose you could look it as two phases 180 deg apart as opposed to a three phase system with three phases 120 deg apart.
But there are at least a couple of significant differences.

For 120-0-120 the two phases are generally used on just single phase loads at either 120V or 240V. There are few loads that I know of that utilise the two phase attribute. A rectifier bridge circuit employing just two diodes instead of the usual four maybe?
By contrast, three phase is commonly used to supply three phase loads.

The two phases are derived from the winding on one core. The voltages can only be in phase or anti-phase with the primary. You can't introduce any kind of vector displacement.
For three-phase, you have windings on three cores. You can mix and match different configurations and tappings to get any vector displaced output.

I would thus contend that it it a bit of a stretch to consider 120-0-120 as having two phases.

 

[mivey]

Hmmm....
I suppose you could look it as two phases 180 deg apart as opposed to a three phase system with three phases 120 deg apart.

And you would not be the first. As the other threads will show, this has been done in the past and present history of our industry. And it has been done by industry leaders, not just hacks. But, its use seems to lead to confusion at times, certainly to debate.

Back to the paper:

I did find it interesting that the writer felt it was important enough to include in the abstract, but did not feel it was important enough to elaborate on. I did read through his book that he referenced but found no mention of the center-tap/180 degree/two phase concept (it is possible that I missed it). Perhaps one of the other references he mentions covers this idea but I'm not sure at this point. In his book, he did make extensive use of the term "two phase" when referencing a "V" phase distribution system.

 

[jim dungar]

His point is that UNTIL it is recognized and studied as a two phase system the problem he highlights is not appearent.

Again I do not see this position in the Abstract. I see the abstract as simply saying that the methodology for studying a 2-wire (line-ground) primary cannot be used on a 3-wire (2 lines to ground) secondary.

The abstract seems to consist of mixed terminology. According to your first post.

...are not single-phase line-to ground systems, but they are three-wire systems ...

. I take the next statement of

two phases with one ground wire

to be a reference to the number of conductors where the word 'phases' could be substituted with the word 'line'.

 

[iMuse97]

The problem I see with calling a 120/240 three wire system a 2Phase system is that at any given point in time the "2 phases" are oriented in one direction, whereas when we discuss any other 2 phases, at any given point in time there is the variation in vector orientation.

Isn't this precisely the reason we've been calling 120/240 a single phase system? I'm sure there are differences operationally between these two systems (as the paper points out, supposedly), but as J Dungar notes above, calling a 120/240 three wire system a 2phase system may cause a different sort of terminology problem.

By the way, am I missing something or are we only being blessed with the abstract of this paper at this time? I looked around for the full document, but failed to turn it up.

 

[weressl]

Hmmm....
I suppose you could look it as two phases 180 deg apart as opposed to a three phase system with three phases 120 deg apart.
But there are at least a couple of significant differences.

For 120-0-120 the two phases are generally used on just single phase loads at either 120V or 240V. There are few loads that I know of that utilise the two phase attribute. A rectifier bridge circuit employing just two diodes instead of the usual four maybe?
By contrast, three phase is commonly used to supply three phase loads.

The two phases are derived from the winding on one core. The voltages can only be in phase or anti-phase with the primary. You can't introduce any kind of vector displacement.
For three-phase, you have windings on three cores. You can mix and match different configurations and tappings to get any vector displaced output.

I would thus contend that it it a bit of a stretch to consider 120-0-120 as having two phases.

One of the characteristic of phases as vectors having an angular displacement in relation to each other.

 

[weressl]

Back to the paper:

I did find it interesting that the writer felt it was important enough to include in the abstract, but did not feel it was important enough to elaborate on. I did read through his book that he referenced but found no mention of the center-tap/180 degree/two phase concept (it is possible that I missed it). Perhaps one of the other references he mentions covers this idea but I'm not sure at this point. In his book, he did make extensive use of the term "two phase" when referencing a "V" phase distribution system.

It was not the subject, but the basic premise of the resultant investigation.

 

[iwire]

The problem I see with calling a 120/240 three wire system a 2Phase system is that at any given point in time the "2 phases" are oriented in one direction, whereas when we discuss any other 2 phases, at any given point in time there is the variation in vector orientation.

The problem I see is there is already another system that is called two phase.


[FONT=Verdana, Arial, Helvetica][/FONT][FONT=Verdana, Arial, Helvetica]2 Phase Power Systems

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[charlie b]

Will this IEEE paper at least offer some reasoned path to choose?

I doubt it.

 

[iMuse97]

The problem I see is there is already another system that is called two phase.


[FONT=Verdana, Arial, Helvetica][/FONT][FONT=Verdana, Arial, Helvetica]2 Phase Power Systems

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... Which I was saying in a sort of roundabout way, by means of description, but you said in one short sentence.

 

[mivey]

By the way, am I missing something or are we only being blessed with the abstract of this paper at this time? I looked around for the full document, but failed to turn it up.

http://ieeexplore.ieee.org/xpl/tocr...241&isYear=2009&count=48&page=0&ResultStart=0

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