single vs. 3 phase

[winnie]

I'm not sure about the 2-phase 4-wire system. There has to be a common reference point if you are going to tie two separate 2-wire systems together.

I don't believe that this is true.

I believe that in the history of '2 phase' systems, all of the following were used:
2 phases with common end points, requiring 3 conductors (the 'L' shape that you mention)
2 phases with common center taps, requiring 5 conductors (the 'X' that you mention)
2 entirely electrically isolated phases, requiring 4 conductors. The only thing relating the two phases was the fact that they were produced on the same rotating machine, and thus had a definite phase relationship.

With two 90-degree displaced coils, you could also have a reference point that was the midpoint of the coils and create a 4-phase system. The 4-phase system was "X" shaped and could have a neutral wire (the 5th wire) coming from the center of the "X". This was the same as joining two 180 degree displaced "L" systems at the corner of the "L".

My understanding is that a system with 4 legs 90 degrees apart is called a 2 phase system, in the same way that 2 legs 180 degrees apart is called a single phase system.

One reference that I've read, describing 'high phase order' motor systems, and dated from the '70s, came up with an interesting naming scheme. Motor coils which were electrically 180 degrees apart 'hemi-phases'...so under this naming scheme a normal 3 phase motor would also be a 6 'hemi phase' motor, and a conventional center tapped system would have 2 hemi-phases. I've never seen this naming convention used anywhere else, so I guess the language didn't catch on.

Each phase of a system has 2 phase angles associated with it. A 3 phase 7 wire system (if such were ever built) would have 6 legs, but would still be a 3 phase system.

The 2 phase angles associated with each phase are _not_ equivalent; imagine synching a generator to the grid and throwing the switch when the phase difference was _exactly_ 180 degrees (Not in answer to Mivey's post; just a general statement out to this discussion).

-Jon

 

[Rick Christopherson]

Mrs. Mitchell, Can Rattus come out and play?

Mrs. Mitchell, Can Rattus come out and play?

Well, to use your own words, if you can't defend your position then mine must be proven by default. This is the only TRVTH.
Case Closed.

 

[winnie]

Rattus' failure to convince Rick that a particular statement is true does not make that statement false.

Rick, you have made the statement that electrically, inversion is not the equivalent of a 180 degree phase shift. You have also made the statement that _mathematically_ they are the same.

I believe that it falls to you to explain the limitations of the mathematics. What makes it incorrect to apply this well known mathematical identity to this case?

-Jon

 

[winnie]

It is improper to assign phase angles to non-sinusoidal waveforms. You may do so with the individual harmonics, but not the waveform as a whole.

Phase angles are regularly and properly applied to many non-sinusoidal waveforms.

For example, a quadrature encoder is described as having two outputs 90 degrees out of phase. These outputs are square waves.

-Jon

 

[winnie]

If you want to play the math versus electrical card, then you prove that the two signals are electrically out of phase. For this to be true, then there needs to be a time-shift, which there is not. You can show that they are mathematically out of phase, but that is not the same as being electrically out of phase. So I challenge you--prove this electrically.

Why _must_ there be a time shift for there to be a phase difference?

-Jon

 

[Rick Christopherson]

Rattus' failure to convince Rick that a particular statement is true does not make that statement false.

I know that. Of course it doesn't prove anything, but how many times have you seen Rattus say that same thing to other people on this forum. What goes around comes around. :smile:

Rick, you have made the statement that electrically, inversion is not the equivalent of a 180 degree phase shift. You have also made the statement that _mathematically_ they are the same.

I believe that it falls to you to explain the limitations of the mathematics. What makes it incorrect to apply this well known mathematical identity to this case?

-Jon

It was not my intention to argue whether the term "phase shift" was inappropriate, but it was the direct result of Rattus claiming that my argument was true only mathematically, and his argument was based electrically. The TRVTH is the opposite. Electrically, it is more proper to say the two voltages are inverses, because their relationship was derived by reversing the polarity of the test probes. Mathematically, both answers are correct.

What I take issue with is that Rattus has claimed that referring to the voltages as "inverse" is incorrect. His argument for this rationale was flawed, and he backed himself into a corner with it. He put himself into this corner by his own choice and his own mistakes. I just choose to not let him wiggle his way out of it again.

Why _must_ there be a time shift for there to be a phase difference?

-Jon

Because that is what a phase shift is defined as. See the following excerpt:

 

[mivey]

I don't believe that this is true...2 entirely electrically isolated phases, requiring 4 conductors. The only thing relating the two phases was the fact that they were produced on the same rotating machine, and thus had a definite phase relationship.

It sounds like they might be tied on the primary side somehow? With no binding relationship, I would think it would be like taking just one terminal of a battery, there is no relationship to make it functional. In your example, the common machine defined the relationship but would this 4-wire float around with unbalanced loads? I'm not sure what they did with this animal. If they just fed motors, maybe the motor windings kept the reference point implied?

My understanding is that a system with 4 legs 90 degrees apart is called a 2 phase system, in the same way that 2 legs 180 degrees apart is called a single phase system.

According to Fitzgerald's "Electric Machinery", 4 legs with a 90 degree displacement is a 4-phase system. It is also called 4-phase in Wagner & Evans' "Symmetrical Components" (Wagner calls them multi-phase systems instead of poly-phase like Fitzgerald though both refer to an n-phase system as having a 360/n displacement). Fitzgerald & Wagner both refer to 1/2 of the 4-phase system as constituting the two-phase system. Wagner did mention that the 4-phase system without a neutral connection was also commonly called a 2-phase system (see? This mixing of names/terms/definitions was evident as far back as 1933). Maybe the neutral point connection made the distinction between it being called 2-phase or 4-phase. Wagner did call the 3-wire 2-phase an irregular system because the phase angle of the generated emf (90 degrees) did not meet the characteristic angle of the system (360/n or 180 degrees).

Wagner also notes the 1-phase 3-wire with the characteristic angle of 180 degrees (n=2). Once again, there is a conflict in terminology. With the polyphase system definition, two legs with a 180 degree displacement is a 2-phase system. He uses a canonical system definition like I posted earlier:

In terms of polyphase systems, an "n" phase system will have "n" voltages of essentially equal magnitude displaced by 360/"n" degrees.

I'm pretty sure I've seen this elsewhere as well but can't find it right now. The problem is that this conflicts with common terminology. I would be inclined to stick with the common terminology of single phase, which is what I think the majority of people use today. Along those same lines, when you use 2-phase, most people are going to think of the old 2 & 4 phase 90-degree displaced systems.

I think the majority of people would call 3-wire 120/240 single phase. Every reference I can put my hands on uses this terminology. I'm not sure if we have a consensus on the 3-wire 120/208 as I have references that call it single phase and some that call it 3-wire network service. I think we have about exhausted all points on this matter, but I wouldn't hold my breath.

As far as hemi-phases, that is something new to me. Were they talking about poles or sets of poles?

 

[mivey]

Concerning phase/time shift:
I think we hashed this over ad nauseam in another thread. A phase difference does not necessarily mean a time shift. To the audio guys, a phase shift means a time shift. This matters when performing transient analysis, especially at the beginning and at the end of the signal. In steady-state you may not be able to see the difference.

In the other thread we posted references that also show a phase shift like we are talking about does not mean a time shift like with transient analysis. We are definitely not talking about time shifting here, as far as stopping and starting a signal.

But, I think you can call these differences in the waveforms time differences or phase differences (see post #347), depending on what you are calling your reference point. If you think about it, the 3-phase waveforms that we like to say have a time-shift, all began their life at the same time. I just don't see that it matters with a steady-state analysis.

 

[dwcaveney]

single phase (modulation)

single phase (modulation)

Insert the word "modulation" after "single phase"
i.e. both legs (modes) are 60HZ, 120Vac
Hence, single phase.

Could someone explain a wye connection?

The law of phases states that a phase model has one more phase than the total number of components in the model, the extra phase being the overall system.

A 120v/240v "single phase" service in a scientific phase model is actually 120, 120, 120&120, 240, 0, system= 6 operational phases, so we call it single phase. Easy eh?

delta system?
L1-L2, L1-L3, L2-L3, L1-N, L2-N, L3-N, L1&L2-N , L1&L3-N, L2&L3-N ,L1&L2&L3-N,
208V, 208V, 208V, 120V, 120V, 120V,120V&120V,120&120V, 120V&120V, 120V&120V&120V, 0, SYSTEM= 12 operational phases, so we call that 3 phase. Even easier right?

Final question: Whats so complicated about electricity? lol

I'm not rich, but I am dumb. If you think I'm thick, check out the thread about why we call a three way switch a 3-way switch.

 

[mivey]

dwcaveney, put down the beer and step away from the cooler. :grin:

I did not follow your discussion. I guess I'm going to have to read it when I have more time/patience. I read some on the law of phases, equilibrium with n components in n+1 phases, or n components in equilibrium at n+2 phases under certain conditions...what? I can't go there right now. Maybe I need to raid your cooler 1st.

 

[rattus]

Surprise, surprise:

Surprise, surprise:

Please open the attachment for the surprise ending to this saga.

 

[mivey]

Please open the attachment for the surprise ending to this saga.

That is too rich:grin:

Fighting against the enemy for several months?
Hundreds of posts.
Finding out the enemy is you?
Priceless.

[edit: I love this quote from the link: "I have carefully verified the information presented here" . I can't quit laughing. You two are making my sides hurt. :smile:]

 

[coulter]

I won?t waste time responding to frivolous arguments, ...

Interesting - strange you put so many out here. And that's the TRUMTH.

carl

 

[Rick Christopherson]

Please open the attachment for the surprise ending to this saga.

There is no surprise there Rattus, and you have proven nothing. You are trying to use your patented "misdirection" technique again.

I have been saying from the beginning that there is nothing wrong with stating that the phases can be viewed as out of phase. As a matter of fact, I know I already preempted your above quote in the "Battle of the Phases" thread. It took a little bit of searching, but here is the quote that fully acknowledged my article.

Actually, it does matter. However, this is an argument that I couldn't care less about. I have personally stated in public print, in one of the most commonly referenced electrical articles on the internet, that the two sources are out of phase. I stated it as a matter of convenience for the audience so they could better understand the concept. However, in a circuit analysis situation, it is not what I would ever state, and I would not change the phase of one half of a center-tapped transformer.

As is typical with you, you are trying to redirect the discussion off the topic when ever you get backed into a corner.

Just to remind you, the issue at hand is that you said they cannot be inverses. You claimed that my demonstration of them being inverses was only a mathematical solution, and yours was an electrical solution. This is the backward statement that got you backed into a corner. If you are having trouble getting your mind back on topic, then I suggest you go back and reread the discussion.

 

[mivey]

It took a little bit of searching, but here is the quote that fully acknowledged my article.

I did not even remember you saying that, I guess because I wasn't aware of the article at the time. I guess you were covering your tracks earlier than we realized.

I did like the article on the phase converter. It it still functioning? Have you run across any issues?

[edit: how big do you think the rotary converter could get? I have a friend with some tools he would like to run in his shop behind his house. He is on a 1-phase EMC line with little hope of getting a second phase pulled in.]

 

[JohnJ0906]

And I'll bet the OP thought he was asking a simple question.....

 

[rattus]

Did I say that?

Did I say that?

duplicate deleted

 

[Rick Christopherson]

I did not even remember you saying that, I guess because I wasn't aware of the article at the time. I guess you were covering your tracks earlier than we realized.

Someone that is as shallow and predictable as Rattus is, yeah, I expected it. I'm just surprised it took him so long to research it. It is a very popular article. Sometimes it even surprises me to find out how diverse the websites are that hyperlink to it. The most surprising link I found came from a "Battered Womens Support Group". It took me a while to figure out why they would link to an article like this.

I did like the article on the phase converter. It it still functioning? Have you run across any issues?

Yeah, my phase converter article has been so popular over the years that it would come up as the 1st or 2nd google hit on the topic (varies almost daily). The article is getting old (10 years old I think), and I am in the middle of rewriting it completely. The new version will be more informative and also cover VFDs too. A phase converter manufacturer gave me all of the parts necessary to rebuild the original converter because they want to advertise on my website, so I'll be rebuilding it for the sake of the article. The original converter is still running, but I recently replaced it with a VFD. After I rebuild it with the new parts, I'll probably just sell it.

 

[rattus]

Did I say that?

Did I say that?

Just to remind you, the issue at hand is that you said they cannot be inverses. You claimed that my demonstration of them being inverses was only a mathematical solution, and yours was an electrical solution. This is the backward statement that got you backed into a corner. If you are having trouble getting your mind back on topic, then I suggest you go back and reread the discussion.

Never, ever said that. In a nutshell, I am claiming V1n and V2n are inverses of each other which is equivalent to a 180 degree phase difference. You have said as much in another website, so I don't understand why you continue to make these false, frivolous arguments unless you are trying to embarrass me which certainly seems to be the case. Highly unprofessional! Violates Forum rules as well.

 

[rattus]

Interesting - strange you put so many out here. And that's the TRUMTH.

carl

Carl, you shouldn't make these insinuations unless you can support them with facts. Can you?

If I am in error, I will admit it. Won't be the first time--or the last either!