May I ask a question about the single vs two phase stuff

[jumper]

In the analog audio world when we use a transformer to create a balanced signal pair from an unbalanced signal we use the same transformer, only it's a whole lot smaller. There is no question that the balanced waveforms thus generated are each the inversion of the other.

Gunny, I ain’t doing audio signal analysis, I is modeling the available voltages supplied by a standard POCO tranny.

 

[ggunn]

Gunny, I ain’t doing audio signal analysis, I is modeling the available voltages supplied by a standard POCO tranny.

And I agree that from a modeling standpoint when you restrict your analysis to a single frequency sine wave, it makes no difference.

 

[jaggedben]

Gunny, I ain’t doing audio signal analysis, I is modeling the available voltages supplied by a standard POCO tranny.

But it's conceivable you might have a wave distortion that you need to analyze on that, and that you'd need to make a decision about what kind of math to use to analyze it.

 

[jumper]

And I agree that from a modeling standpoint when you restrict your analysis to a single frequency sine wave, it makes no difference.

See, I knew I liked you Gunny, and yeah in traditional power analysis of a 120/240 Single Phase tranny that is what we do.

I am open to other views,but at some point ya gotta choose a model and reference and go from there.

 

[jumper]

But it's conceivable you might have a wave distortion that you need to analyze on that, and that you'd need to make a decision about what kind of math to use to analyze it.

Wave distortion on the primary side?

Why am I looking at the primary side? POCOs problem.

 

[jaggedben]

Wave distortion on the primary side?

Why am I looking at the primary side? POCOs problem.

I didn't say primary side. And I didn't necessarily limit it to a POCO transformer. Not sure why you're insisting on limiting the conversation, when other examples are illustrative of the underlying issues.

We've been over this, but if there's an asymmetrical distortion on the primary side, do the secondary waveforms look like an inversion or a 180deg shift?

If you have a generator, and the scope has a distortion that looks like an inversion, what does that tell you?
If you another generator of the same model, and the scope has a distortion that looks like a phase shift, what does that tell you?

 

[mivey]

That's what I'm trying to get you engineers to do! Seems it's not simple, no one can just quote a book.

We can. It just seems to make so little difference.

Phase: The distance, usually in angular measure, of the base of any ordinate of an alternating wave from any chosen point on
the time axis, is called the phase of this ordinate with respect to this point.

 

[mivey]

And if there's no neutral?

If there is no neutral, you have only two terminals and can only have one waveform and only one phase is present. It takes at least three terminals to get two different waveforms.

 

[mivey]

I mean what's electricity got to do with geometry? Nothing, other than the convention we have invented to tie them together.

They correlate.

Case 1:

Take three identical windings on a generator shaft. Rotate the shaft and the output signals will rise and fall together with their positive peaks together and return to the beginning voltage as the generator completes a 360 degree rotation.

Rotate the windings 120 degrees relative to each other and the voltages will rise and fall in sync but the positive peaks will be displaced by 120 degrees but will still return to their beginning voltage as the generator completes a 360 degree rotation.



also,

Case 2:
Take two identical windings on a generator shaft. Rotate the shaft and the output signals will rise and fall together with their positive peaks together and return to the beginning voltage as the generator completes a 360 degree rotation.

Rotate the windings 180 degrees relative to each other and the voltages will rise and fall in sync but the positive peaks will be displaced by 180 degrees but will still return to their beginning voltage as the generator completes a 360 degree rotation (sound familiar?).

 

[mivey]

One 'debate' in this thread is about using inversion vs. 180deg shift. In the ideal situation, they produce the same mathematical result so it really doesn't matter. But I think that when it comes to assymtrical distortion of the voltage waveform, there's a right answer as to which maintains greater accuracy. There are other variations from ideal waveforms about which that would not necessarily be true. I find it interesting how many engineers on this thread seemingly don't want to go there.

You keep thinking there is a time shift for some reason and thus you keep thinking it makes a difference.

There is no time shift. Both signals start at the same time. One just happens to reach a positive peak 180 degrees after the other.

 

[mivey]

I truely do not like the term split phase.

How can one “split” a phase?

The term phase-splitter is commonly used anyway.

 

[mivey]

Well there are times where we do use a center tapped transformer to “split phases”. We are looking to have, on one secondary winding, the original waveform, and on the other one the same exact waveform with polarity inversion.

There is not one original waveform. There are two original waveforms.

We certainly don’t want something displaced in time by 180 degrees. Doesn’t matter that this isn’t electrical distribution as transformers don’t know and obey the same laws regardless.

No one has said there is a time displacement. That requires a different type circuit. Both waveforms start at the same time.

You keep thinking the larger waveform defines a direction for the smaller waveforms. It does not. By that logic, 120/208 would have to be defined L2->N and N->L1. Then you would have 120<180d and 120<120d. Can't you see the problem with the inconsistent logic? Here is the problem:


For the 120/240 system you want to have 120<0d + 120<0d = 240<0d. You should recognize that you can also have 120<0d - 120<180d = 240<0d.

For the 120/208 system you want to have 120<0d - 120<120d = 208<-30d. You should recognize that you can also have 120<0d + 120<300d = 208<-30d.


Both methods are valid ways to take waveforms and is not about inverting an "original" but defining the original the way you are taking the waveforms to start with. There is no pre-determined "original".

The logic of using only one fails because if you recognize that you can take the difference waveforms for the 120/208 system then you should recognize you can take the difference waveforms for the 120/240 system. That is the way voltages work. You define the voltages. It is really that simple.

 

[mivey]

But that's what you've got with 120-0-120

No, it is not. Both signals start at the same time. The only time difference is between the times of positive peaks.

The problem is in the thinking that the larger voltage defines the smaller voltages (I know you don't think that). Please see my prior post about the inconsistency this creates for the 120/208 vs 120/240 systems.

 

[mivey]

I agree with you on this 100% in the observation/measurement sense.

In the "causation" sense, it's the former; it's polarity, plain and simple.

Polarity is strictly the case if you have only two terminals. With two terminals there is only one waveform. The current leaving L1 is EXACTLY the reverse of the current entering L2.

With three terminals, you can have three waveforms. The smaller waveforms do not have to be defined in any particular winding orientation. For the 120/208 system, you want to define them the way the 180d group says is ALSO valid. For the 120/240 system, you want to say only the opposite way is valid.

Either one way is valid or it is not. Your argument is inconsistent.

The fact is that both observed sine waves begin simultaneously.

But there is nothing, physics or otherwise, that says they can only be defined one way. You can have one start negative and one start positive rather than both positive. That is the way voltages work, plain and simple.

 

[jaggedben]

If there is no neutral, you have only two terminals and can only have one waveform and only one phase is present. It takes at least three terminals to get two different waveforms.

That bit of the thread was in the context of discussing the broader meaning of 'phase' within the industry. IOW, if you have an ungrounded or corner grounded delta, you still have three phases even though there's no neutral. If you have a high-leg delta, in my opinion, you still have three phases even though there is a 'neutral' on one of them. I realize that the last point is controversial in the context of this this thread (but not in standard industry terminology). But I think the high-leg delta is illustrative of how it doesn't make sense to insist that the 'neutral' must be the reference, since it doesn't illuminate the three line-line phases.

 

[jaggedben]

We can. It just seems to make so little difference.

Phase: The distance, usually in angular measure, of the base of any ordinate of an alternating wave from any chosen point on
the time axis, is called the phase of this ordinate with respect to this point.

I'm happy to allow that there's a mathematical definition for purposes larger than electrical engineering. But I think 'phase' means something different in the electrical industry, and there's a reason that the 120/240 service is call 'single phase' and the high-leg delta is called 'three phase.'

 

[mivey]

Still using inversion internally

No sir.

Inversion assumes that one has already selected a positive direction from say L2->N->L1. You may also define positive to be away from neutral in which case nothing is inverted.

The voltage does not grow from one end to the other but is a separation of charges that creates an electric field. We define the direction.

You can say this is more positive than that or this is more negative than that. You define the reference point. It is not defined for you by a polarity mark, L1 vs L2, or anything else.

 

[mivey]

If the 120/240 service was the only kind of electrical service that existed, and if power factor and three-phase power weren't things needing to be analyzed, no one would ever have bothered to make phasor math part of electrical engineering education. I know that's a lot of 'ifs', but the point is, inversion really is all the math you need to analyze this service with resistive loads.

Yeah, that's a lot of ifs. And will practically never be the case.

Now, I totally respect the position that says 'well, I'm trained to do phasor math for all these other applications so it's just natural for me to employ it here as well.' But there is nothing ontologically privileged about phasor math. It doesn't represent what the waveforms 'are'. The 'time delay' discussion pretty much proves that.

The "time delay" discussion has nothing to do with it. Time delay is something else altogether.

 

[jaggedben]

You keep thinking there is a time shift for some reason and thus you keep thinking it makes a difference.

There is no time shift. Both signals start at the same time. One just happens to reach a positive peak 180 degrees after the other.

Actually, I've been one of those pointing out that there isn't a time shift with ideal sine waves. And I also keep pointing out that if you don't have ideal waves, then there's a practical difference between using math that reproduces a time shift and math that doesn't.

 

[mivey]

Now someone made a comment about there not actually being any "time shift" with three phase. I'm picturing a rotating generator shaft and having a little problem with that comment. Might be a chance for me to learn something more out of this thread.

See my post 989. I have a graphic but don't feel like digging it up at the moment.