single vs. 3 phase

[Rick Christopherson]

A little consistency would be nice. Why is it that you want to call a 120/208 system single-phase, but then you want to call a 120/240 system two-phase?

Stay on subject Rick.

I would say that my response was very much on topic! Unless I have misread these discussions, you are contradicting yourself.

On a system that is mathematically single-phase, you choose to call it two-phase. Conversely, on a system that is inarguably polyphase, you choose to call it single phase. This is not consistent!

You are free to say that this is utilized as single-phase, but you cannot say that this system is single phase. There is not a single mathematical definition of a polyphase system that supports this.

I was observing this discussion from the sidelines, and I really didn't care that much about it, until your last posting. I don't think you want to have me engage in this discussion full time if you want to keep your viewpoint intact.

 

[coulter]

... It is common knowledge that the 208V between any two phases of a 120V wye is sinusoidal.

The sinusoidal issue is easily proven. ...

rattus -
Since it is easy, go head and show us the proof. Please include a derivation of the trig identify (difference of functions) you are going to use, specifically show your derivation for:
sinA - sinB = 2cos(1/2(A + B))sin(1/2(A-B))

I agree Vab is a sine - I just don't think the proof is that easy.

carl

 

[hardworkingstiff]

While you guys are getting over my head with the math now, I must comment that according to Mivey's post on the IEEE definitions, a reference to neutral is required to determine phase.

So, Vab is not the issue, Van as compared to Vbn is the issue. (I think)

 

[rattus]

Bored anyone?

Bored anyone?

The sinusoidal issue can be proven mathematically, but I don't think anyone wants to be bored. It is not hard, but a little tricky.

 

[rattus]

rattus -
Since it is easy, go head and show us the proof. Please include a derivation of the trig identify (difference of functions) you are going to use, specifically show your derivation for:
sinA - sinB = 2cos(1/2(A + B))sin(1/2(A-B))

I agree Vab is a sine - I just don't think the proof is that easy.

carl

Carl,

I could lift a page from my Freshman math book and bore everyone, but it is not necessary to prove something that appears in every mathematical handbook ever printed--the sum and difference formulas that is.

You have the formula, why don't you do it? Show us your stuff. Besides, Quogue is convinced, I think. It is a moot point now.

 

[rattus]

Let's be TRVTHFUL

Let's be TRVTHFUL

On a system that is mathematically single-phase, you choose to call it two-phase. Conversely, on a system that is inarguably polyphase, you choose to call it single phase. This is not consistent!

Rick, be sure of your "facts" before you proceed.

 

[mivey]

A little consistency would be nice. Why is it that you want to call a 120/208 system single-phase, but then you want to call a 120/240 system two-phase?

Uh oh. Now I think Rick may get the retraction he has been looking for. I can't picture an argument that would support both positions. Let's see if rattus can work some magic. :grin:

 

[Rick Christopherson]

Rick, be sure of your "facts" before you proceed.

What facts could I possibly be missing? It is pretty straightforward from an electrical and mathematical standpoint. You used that "tricky" word again. Does that mean we are going to see some more of Rattus' patented rules that defy the physical laws?

Hey, I have an idea, why don't you draw a phasor diagram of the 120/208 system that proves it is single phase.:grin:

 

[rattus]

Well OK:

Well OK:

Uh oh. Now I think Rick may get the retraction he has been looking for. I can't picture an argument that would support both positions. Let's see if rattus can work some magic. :grin:

The magic is that I have never claimed two phases are present in a single-phase system. In fact, I have repeatedly refuted that argument. So Rick owes the retraction.

Furthermore, even if Rick's claim were true, it has nothing to do with this discussion!

 

[rattus]

What facts could I possibly be missing? It is pretty straightforward from an electrical and mathematical standpoint. You used that "tricky" word again. Does that mean we are going to see some more of Rattus' patented rules that defy the physical laws?

Hey, I have an idea, why don't you draw a phasor diagram of the 120/208 system that proves it is single phase.:grin:

Not going to play that game Rick.

 

[winnie]

Rick,

You are going to have to take your argument to the IEEE. A service supplied by two legs of a 208/120 wye is officially _named_ as a single phase service.

It is very clearly polyphase. The physics is that of two legs of a three phase wye service, _very_ different from that of a true single phase service. The official naming only makes sense from the point of view of the sort of loads that would be commonly connected to such a service. Only by specifying custom hardware could I imagine connecting a polyphase _load_ to such a service; realistically only single phase loads will be connected.

On the side topic of the 'phase difference' in a 120/240V single phase system, Rattus never claimed that there were two different phases, or that such a system was a 'two phase' system. He simply claimed that the two different output terminals could be reasonably described as having a 180 degree phase difference. I agree with him on that point; a 180 degree phase difference is a useful description, and doesn't make a polyphase system.


Rattus,

You say in post #75 that only single phase loads can be driven by such a system. I disagree. While it is true that most common uses of such a system would be single phase loads (either line-neutral or line-line), I claim that one could design a polyphase load that would use the phase difference present in a 120/208 "single phase" system. For example, I could design a motor that functions with two supply legs, 120 degrees apart at 120V 60Hz.

-Jon

 

[mivey]

The magic is that I have never claimed two phases are present in a single-phase system. In fact, I have repeatedly refuted that argument. So Rick owes the retraction.

Quote from Mr. Whiplash of The Good 'ol Boy's Club: "Curses! Foiled again!" :grin:

Furthermore, even if Rick's claim were true, it has nothing to do with this discussion!

We did start off by discussing "2 phase" 120/240 but I think the 120/208 case is in the same spirit of the original question.

 

[rattus]

Sure Winnie:

Sure Winnie:

Rattus,

You say in post #75 that only single phase loads can be driven by such a system. I disagree. While it is true that most common uses of such a system would be single phase loads (either line-neutral or line-line), I claim that one could design a polyphase load that would use the phase difference present in a 120/208 "single phase" system. For example, I could design a motor that functions with two supply legs, 120 degrees apart at 120V 60Hz.

-Jon

Sure, such a motor could be designed, and a real 2-phase motor would likely run. I am only claiming this service is meant to drive single-phase loads, and in practice this is the case except for a few experimenters here and there.

 

[rattus]

We did start off by discussing "2 phase" 120/240 but I think the 120/208 case is in the same spirit of the original question.

I didn't claim that did I? If I did, I was asleep.

 

[quogueelectric]

http://www.udel.edu/idsardi/sinewave/sinewave.html Nice little wave generator applet.

 

[mivey]

I didn't claim that did I? If I did, I was asleep.

Not here. That was the OP's question. I assumed Rick was talking about something you said in another thread somewhere that was also discussing 120/240.

 

[crossman]

I claim that one could design a polyphase load that would use the phase difference present in a 120/208 "single phase" system. For example, I could design a motor that functions with two supply legs, 120 degrees apart at 120V 60Hz.

When you say "two supply legs" do you mean two conductors? We would really need three current-carrying conductors, right?

 

[Rick Christopherson]

You are going to have to take your argument to the IEEE. A service supplied by two legs of a 208/120 wye is officially _named_ as a single phase service.

Naming it as single phase is completely different from defining it as single phase. Unless I misread some of the discussions above (and I could have), some of these discussions were attempting to justify the "single phase" name by defining the system as single phase.

He simply claimed that the two different output terminals could be reasonably described as having a 180 degree phase difference.

I absolutely do not contest a "description" of a system. However, Rattus goes beyond just "Names" and "Descriptions", and tries to redefine the systems to meet his names and descriptions. He seems to have a problem differentiating a name versus a definition, or a reference versus an absolute.

 

[coulter]

...You have the formula, why don't you do it? ...

Cause I wasn't the one that said it was easy - you were

...I could lift a page from my Freshman math book and bore everyone, but it is not necessary to prove something that appears in every mathematical handbook ever printed--the sum and difference formulas that is. ...

I don't know rattus, this one feels necessary. Go ahead and bore us. I'll make it easy for you, just scan your page and cite the reference.

edit: and complete the rest of the proof.

... Besides, Quogue is convinced, I think. It is a moot point now.

Q -
I really think this proof would help understanding. Don't you think rattus should show us?

carl

 

[Rick Christopherson]

I am only claiming this service is meant to drive single-phase loads, and in practice this is the case except for a few experimenters here and there.

I used to deal with portable power distributions systems that were sourced from 3-phase, wye configured generators, but the loads (in many cases) were exclusively single phase, 120 volt. So by your rationale, does this mean that I really had a single-phase generator just because the load was single phase?

By the way, wasn't there a recent discussion where a set of condominiums were powered with a 120/208 "single phase" system? And wasn't part of this discussion asking about 4-wire (with ground) cooking ranges on that system? Wouldn't that cooking range, as a whole device, constitute a load that utilized both phase conductors and neutral?