Two phases or not?

"Bob AZ"

( snip tedious drivel)

But in no case, with the information presented here, is there any method or device utilized to give any additional phases. One or two or more. The hot legs are simply the same phase, transformed as needed, added within the transformer, with the resultant two hot legs, 180 degrees out of phase with each other.

** A really beautiful example of "double think" if I ever saw one.

Three phase distribution starts with a generator with 3 sets of windings that is distributed as three phase and utuilzed as needed.

** And if it had only 2 windings instead of 3 ??

Two AC waves would be produced simultaneously, remaining always 180 degrees apart in phase and be completely * indistinguishable * from any other means of creating the same situation.

..... Phil

I bow to your superior logic and wit.

Jeff

Big JOKE!

You fail.

Formally, yes, there exist two phases set apart 180º. But formally also that is never called a "two-phase system".

Reasons:

1.- In polyphase system there is an usual understanding that phases are different when you can not get the other phase by simple means other than using transformers (or transformer arrays). In a 3 Phase system, there is no way to get a phase 120º away by adding, subtracting or switching cable ends of one phase. In a true two phase system, be it a three wire part of a 3 phase system or the Niagara example, there is no way to get the other phase (120º or 90º) by playing with the connections. In a "split phase" system, the 180º phase is equal (in a balanced system) to the other one by just exchanging the "hot" and "ground" wires.

2.- The phase supplying the power to the "split-phase" winding in the secondary of home transformers is only ONE, there is no way to get more than ONE phase out, even if formally the secondary winding could be measured reversing the leads and appear as the negative value (hence the 180º figure) Those two windings of the "split-phase system" are connected in such a way as to provide a total voltage of 240V but could have been connected in parallel to provide the double of current in one phase at 120V. Such parallel connection would produce a "short" and high currents if in fact the two windings were being driven by two distinct phases no matter what games you play with the wire ends.

So, that's why any power engineer will raise an eyebrow if you address such system with the clearly incorrect term of "two-phase system".

--
Mark Cross
If Linux doesn't have the solution, you have the wrong problem.

Look at his website before you concede.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

If the generator had two windings, they would be 90 degrees out of phase. It makes zero sense to have them at 180 degrees, since the windings would have to share the slots, reducing the availible current by half.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

These comments are logical and correct representations of the power system that most of us use. For single phase motors, a 120VAC motor is a single-phase motor, just as a 240VAC motor is referred to as a single-phase motor, not a 2-phase motor because it's using 2 hot lines.

This issue is one that just gets argued endlessly by amateurs and intellects to no end.. essentially a waste of useful time on an issue that's widely misunderstood for all the wrong reasons.

Pick the issue apart just for sport, if you like, but the majority of domestic power supplies are single-phase.. period.

Look anywhere you can for a New 2-phase motor. The only individuals that would be describing a new motor as a 2-phase motor will be some misguided trainee or someone taking advantage of your stupidity of asking for one.

-- Cheers, WB .............

On 1/23/2011 4:44 PM Wild_Bill spake thus:

I disagree entirely. Yes, in this case it's a semantic debate--what I contend is actually 2-phase power (120-0-120 derived from a center-tapped transformer) is not *called* that by the electric power industry. It is, nonetheless, truly two phase power.

I think it's important because the idea of phases in electrical power is an important one, even to a simpleton like the average electrician, never mind the EE.

Example: if you're going to wire an Edison circuit (where two hots from different phases, meaning different sides of the distribution panel, are wired with a common neutral), you ought to understand electrical phases, especially the consequences of two phases 180° apart. After all, that's how the currents from the two sides cancel each other. Failure to grasp such principles can, and do, lead to real-world consequences like building fires.

Who said anything about a 2-phase motor? Nobody, so far as I can tell.

I'm saying that the ENTIRE DOMESTIC POWER SUPPLY FROM THE SECONDARY OF THE POWER COMPANY'S TRANFORMER is 2-phase. Once you plug in a 120 volt anything, or even many 240 volt anythings, you're only using one phase. Sheesh.

Again, where did this straw man come from?

Please notice that because of your non-standard top posting, any previous replies have been cut off. Please do what 99% of others do here and bottom post.

--
Comment on quaint Usenet customs, from Usenet:

   To me, the *plonk...* reminds me of the old man at the public hearing
   who stands to make his point, then removes his hearing aid as a sign
   that he is not going to hear any rebuttals.

Don't waste your breath. it's not worth the effort.

Knowing that you understand it should be enough..

And by the way, I was looking at a 3 wire motor today, 2 phases of 180 apart with CT to operate it (3 wire motor). It was attached to a gear box and only ran one direction, but you could use it as a stepper (servo) or full out run. Most likely some custom motor for an application.

Jamie

Jamie, what info is included on the motor's data plate/label? Is there a capacitance included, with a low value of 25uF or less?

I think you may have been looking at a PSC permanent split capacitor motor.. although I haven't seen any rated at 180V. Most 3-wire motors are PSC types.

BTW, PSC motors aren't defined or referred to as 2-phase motors. They may be specified for some particular rating as single-direction motors, but they are reversible, in fact, fast stopping/reversing is one of the features of PSC motors. The gearheads, and especially the right-angle gearheads with encoders attached are very versatile.

-- Cheers, WB .............

Ack! I almost went blind after seeing that pic on the right.

I should've included in the "Most 3-wire motors are PSC types" statement: if the motors are not for 3-phase.

Just to be more specific (although 3-phase wasn't being included in the topic).

-- Cheers, WB .............

Now you know not to listen to him.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

And you have started another arguement here. haha..

Honestly this is a question that I have always had, and can't understand why it isnt called 2 phase. Unless there is something to the picture I am unaware of.

This qustion will enevetably be debated to the end of time. It is kind of like discussing poloitcs or religion..

On 1/24/2011 7:40 PM Michael Kennedy spake thus:

Well, it really shouldn't be like that. I mean, look, we're discussing a well-known, measurable phenomenon. The output of the center-tapped transformer can be demonstrated to supply two separate and distinct phases. Hell, hook up two 'scopes and see what they show.

It's just that the 'lectric-heads--the lunks who install distribution panels and such--won't let us *call* it "2-phase" for several dubious reasons. Doesn't change the fact that it IS two-phase power. That's what I'm getting at. I'm not trying to force anyone to change their terminology or give up their superstitious beliefs; I know that that's futile.

--
Comment on quaint Usenet customs, from Usenet:

   To me, the *plonk...* reminds me of the old man at the public hearing
   who stands to make his point, then removes his hearing aid as a sign
   that he is not going to hear any rebuttals.

Unfortunately. Maybe we should more generic terminology to describe this. There is a difference in the phase of the two legs off of a center tapped transformer. This can not be argued. Anyone who argues so can go hook up a couple scopes for themselves as you suggested.

Maybe the confusion exsists because of the nature of two seperate phase (split phase) power vs 3. Correct me if I am wrong, but any device requiring

240V could be powered by 2 legs of a center tapped 7200V==>120V N 120V transformer or could be powered by a 7200V==>240V transformer with the same results.

That said Im sure someone will tell me why my theory of why this is a confusion is wrong..

- Mike

Hmm.. I must have not drank my coffee yet when I wrote this.. 3 phase would operate the same way therefore making this all bunk.

|Hmm.. I must have not drank my coffee yet when I wrote this.. 3 phase would |operate the same way therefore making this all bunk.

Actually three phase service from the power company with the phases 120 degrees apart, would work differently. In a 'Y' connection if the voltage between the phases were X volts, the voltage from one phase to neutral would be x/sqrt(3) rather than x/2 as is the case with a center tapped transformer.

David

You're free to call it whatever you like.. and everyone that hears you call single-phase items 2-phase instead, is free to find humor in it, or suspect that you're uninformed, or lesser of you (without giving you any indications). Kinda like referring to an item with a perfectly practical/widely familar name "a thingy", or a (something) thingy.

Superstitious would be applicable in the early years of the last century when folks actually believed that distributed electricity was "fire on a wire". It was a mysterious power to be feared by many folks in backwoods/mountain places in Appalachia for a significant portion of last century, and that same term can be heard in documentary films of that area of the country.

Think what you like, but if you present yourself as being wiser or more reasonable wrt the subject, it's essentially just trolling.. and since you study proper usenet protocol, you know that's the equivalent to numerous simultaneously performed deadly sins.

It's likely no one gives a FRA what you prefer to call single-phase, however, many usenet folks will likely continue to attempt to correct you at your use of the term 2-phase, primarily because it's not applicable to the subject matter.. and just because 2-phase power is essentially non-existent.

As I suggested in my first reply in this thread.. essentially debated to hell'n back, and still, there are still those defending the use of the term

2-phase.

-- Cheers, WB .............