120/240V single or multiphase?

[iMuse97]

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

Five items down

Thank you.

 

[mivey]

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.

I agree that the abstract does not specifically say that (i.e. you MUST) but he does model it as a 2-phase system (his term for a system with 2 line conductors) in the same manner that he models 2-phase primary systems in his book. He clearly has no problem with calling the center-tap secondary a 2 phase system with a 180 degree phase difference. He readily calls a system with two primary conductors and a neutral a two phase system.

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

I'm not really looking into re-hashing old ground but:
The center-tap actually conforms to the pattern of other poly-phase circuits if you label it two-phase. Some prefer to say the true two-phase case doesn't exist.

The 90-degree case should have been called a four-phase system. From IEEE:

two-phase circuit: A polyphase circuit of three, four, or five distinct conductors intended to be so energized that in the steady state the alternating voltages between two selected pairs of terminals of entry, other than the neutral terminal when one exists, have the same periods, are equal in amplitude, and have a phase difference of 90 degrees. When the circuit consists of five conductors, but not otherwise, one of them is a neutral conductor. NOTE?A two-phase circuit as defined here does not conform to the general pattern of polyphase circuits. Actually, a two-phase, four-wire or five-wire circuit could more properly be called a four-phase circuit, but the term two-phase is in common usage. A two-phase three-wire circuit is essentially a special case, as it does not conform to the general pattern of other polyphase circuits.

 

[iwire]

The 90-degree case should have been called a four-phase system.

But it was not. :smile:


I do not really care if we call a 120/240 system 'single phase' or a 'box of rocks' but lets not call it by a name already in use, that leads to confusion.:smile:

Not to mention all the equipment is called single phase and it is already ingrained in many of us.

Can anyone give a short explanation why the industry would be better off if we suddenly called 'single phase' 'two phase'?

 

[mivey]

Can anyone give a short explanation why the industry would be better off if we suddenly called 'single phase' 'two phase'?

So we can debate the merits of changing it to "single phase"? To right past wrongs? To recognize the nature of the system (per the quoted abstract)?

 

[crossman gary]

I like "box of rocks"

 

[Rick Christopherson]

As I have said in the past, it is OK to think of a 120/240 system as having 2 phases, but I believe it to be very wrong to define it as such, because the definition comes solely from the placement of the reference point.

All other polyphase systems exhibit their polyphase characteristics regardless what reference point is chosen. That is, it doesn't matter which node in the system you choose as a reference (i.e. grounded node), angular/time relationships will still exist for all phase relationships.

In the 120/240 system, this relationship is only exhibited when you choose the centerpoint of the system as your reference point, and it vanishes if you choose any other reference point, including a remote reference point not directly attatched to the system.

 

[iwire]

To right past wrongs?

for TRUTH, JUSTICE and the AMERICAN WAY!:grin:

 

[iwire]

As I have said in the past, it is OK to think of a 120/240 system as having 2 phases,

Thanks for your permission to think how we want.:grin::grin::grin::grin:

 

[Rick Christopherson]

The 90-degree case should have been called a four-phase system. From IEEE:

Actually, following that logic, then the 120/240 system would classify as 2-phase.

 

[Rick Christopherson]

Thanks for your permission to think how we want.:grin::grin::grin::grin:

Hey! I never said I gave you permission to think! That's a completely different objective. :grin:

 

[iwire]

I like "box of rocks"

That comes from an co-workers nick name, we called him box of rocks. ('As useful as a box of rocks' etc.) He complained and we said we could not call him a 'bag of hammers' as that would be somewhat useful.:grin:

 

[iwire]

Hey! I never said I gave you permission to think! That's a completely different objective. :grin:

:grin: :grin:

 

[mivey]

All other polyphase systems exhibit their polyphase characteristics regardless what reference point is chosen. That is, it doesn't matter which node in the system you choose as a reference (i.e. grounded node), angular/time relationships will still exist for all phase relationships.

What about the 3-wire network (120/208)?

Actually, following that logic, then the 120/240 system would classify as 2-phase.

Exactly, with the polyphase being defined as a n-phase system when there is a 360/n displacement. I believe Blackburn and Wagner/Evans (I would have to be check to be sure but I think it was those two resources) noted that very thing.

 

[jim dungar]

The Abstract is worthless, as a substantiation of a position. The writer is not consistent in terminology.

The last sentence begins

This paper will describe the modeling and analysis of the single-phase center-tapped transformer

(my emphasis).

 

[Rick Christopherson]

What about the 3-wire network (120/208)?

What about it? That is a polyphase system, and it exhibits this characteristic regardless where the reference point is.

I assume you might be implying that some people consider that to be a single-phase system, correct? For the same reasons that I do not consider the 120/240 to be a 2-phase system, I also do not consider the 120/208 to be a single phase system. This would be a 2-phase system (but not "the" 2-phase system).

 

[weressl]

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


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

[/FONT]

Except we are talking about recognized and standardized systems, not oddities or ancient history.

The above is not part of any Nationally Recognized Standard.

 

[mivey]

What about it? That is a polyphase system, and it exhibits this characteristic regardless where the reference point is.

I assume you might be implying that some people consider that to be a single-phase system, correct? For the same reasons that I do not consider the 120/240 to be a 2-phase system, I also do not consider the 120/208 to be a single phase system. This would be a 2-phase system (but not "the" 2-phase system).

I wasn't real clear on precisely what you meant. I guess you meant by "this characteristic" you mean a non-zero or non 180 degree displacement, or the fact that you can't directly derive a 3-phase system from a 120/240 volt system?

 

[hurk27]

Don't mean to throw another log onto the fire, but what would you call a
4-wire delta between the "A" and "C" phases with the center tap, is this unlike a center tapped 120/240 derive from just one phase of a Polly-phase system? but it does actually have 2 phases?:-?