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

[winnie]

That is two different phase angles. It is entirely reasonable to say two different phase angles from a single phase supply.[/QUOTE.] They are not in phase so they are different phases.

We'll keep going in circles as long as we are using the term 'phase' to mean multiple things.

This is defined as a 'single phase' supply. There are two 'hot' output legs, they have two different phase angles. In some usages people would say that the two legs are two phases, but others argue against that because they don't like having two phases coming out of a 'single phase' supply.

You can't logically argue that it isn't a 'single phase' supply because that is what it is called. One could as easily call it Betsy. (Residential service in the UK, single phase plus ground I'll call Sam. 90 degree two phase I'll call Donald. 120 degree three phase I'll call Timothy. Residential center tap single phase in the US I'll call Betsy, and two legs 120 degrees apart, which is also called 'single phase' in the US I will call Norbert.)

Because we use the same word to name different aspects of systems, we get tied up in knots either trying to change the name, or trying to explain why the aspects that don't quite match the name are not really there. I absolutely agree that there are two phase angles present. I'm not uncomfortable calling the two 'hot' legs two different phases. But the name is still a 'single phase' service, and there are things that a true 'two phase' service can do that a two hot leg single phase service cannot do.

-Jon

 

[LarryFine]

For 120-0-120 isn't the neutral the obvious and logical choice?
That makes L1-N and L2-N 180deg apart. This two different phases.

Food for thought: if you were measuring the voltage of a pair of batteries in a 2-battery holder, would you place the black probe on the center point and move only the red probe? If you did, you would observe that one of the batteries had a reversed polarity.

If I were measuring the voltage of a pair of batteries in a 2-battery holder, I would move both meter probes and observe that both batteries have the correct polarity. In other words, you're observing L1-N and L2-N, while I would be observing L1-N ans N-L2.

The two 120v secondary halves (or two separate secondaries) must be connected in phase in order for their series connection to add to 240v. If one was out of phase with the other, there would be a difference that creates a subtraction, resulting in zero volts.

 

[mivey]

Food for thought: if you were measuring the voltage of a pair of batteries in a 2-battery holder, would you place the black probe on the center point and move only the red probe? If you did, you would observe that one of the batteries had a reversed polarity.

Think about this: If the batteries were cycling, the time when the probe actually landed would matter. With a battery stack, it does not matter when the probes land which is why the battery analogy is weak.

With the 180d case, the probe timing is such that you get a positive result both times. In this case the probes landed 8.333 ms apart.

The two 120v secondary halves (or two separate secondaries) must be connected in phase in order for their series connection to add to 240v. If one was out of phase with the other, there would be a difference that creates a subtraction, resulting in zero volts.

Think about this: Consider the case where you don't use the 240 volt signal so adding together to make one larger signal doesn't matter.

With some circuits using the 180d displacement (pulse circuit, two-diode rectifier circuits, etc.) we make use of one signal part of the time and the other signal the other part of the time. The fact that they add is of no use in the circuit because they are not used together but used as two separate phases.

This is similar to what Kersting was alluding to in his paper. In his book on distribution modeling, he recognizes the need to model the signals as separate phases with a 180d difference, not as 0d twins. His paper states:

Distribution engineers have treated the standard “single-phase” distribution transformer connection as single phase because, from the primary side of the transformer, these connections are single phase and, in the case of standard rural distribution, single phase line to ground. However, with the advent of detailed circuit modeling, we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary, which now brings into focus the reality that standard 120-/240-V secondary systems are not single-phase line-to-ground systems, but they are three-wire systems with two phases and one ground wire. Furthermore, the standard 120-/240-V secondary system is different from the two-phase primary system in that the secondary phases are separated by 180° instead of three phases separated by 120°.

 

[jaggedben]

We'll keep going in circles as long as we are using the term 'phase' to mean multiple things.
...

-Jon

:thumbsup:

No one can prove that there is a standard convention for what it means, because there isn't.

 

[GoldDigger]

There was a post earlier today that stated that as with any other pairs of "phases", it is possible to derive arbitrary additional phase angles from 120-0-120 from a ceter tapped transformer winding.
Unless you are allowed to use reactive components too, that is simply impossible.
And if you are allowed to use reactive components you can get arbitrary phase angles from s single untapped winding too.

Sent from my XT1585 using Tapatalk

 

[mivey]

There was a post earlier today that stated that as with any other pairs of "phases", it is possible to derive arbitrary additional phase angles from 120-0-120 from a ceter tapped transformer winding.
Unless you are allowed to use reactive components too, that is simply impossible.
And if you are allowed to use reactive components you can get arbitrary phase angles from s single untapped winding too.

Sent from my XT1585 using Tapatalk

If you are referring to my post, I was talking about using the two winding halves where we actually take away two voltages in opposite directions. Don't mis-understand what was posted.

The open wye-wye bank using two center-tapped transformers is such a case. Using 1/2 of two windings with positive taken to be in one winding direction we have two phases with a 120d displacement. Call them positives in the 0d and 120d angle directions.

We can recognize that for each transformer the unused half has a voltage available that is displaced 180d from the used half. We can use these remaining two voltages as positives in the opposite winding direction. Then we can construct the missing phase angle that is positive in the 240d angle direction.

To get the missing 240d phase as positive, we have to recognize there physically exists a positive direction that is away from center tap. This results in L1-N being positive and L2-N being positive. Yes, two different winding directions being positive voltage references.

You can take both directions away from center tap to be positive. You don't have to say one direction is positive and the opposite is negative. The above is one such circuit that shows it is a physical truth. Other circuits demonstrate that as well. Basic physics tells you that also.

We have one signal that goes positive and then a second signal that goes positive 8.333 ms later. If you never use this fact, you don't recognize that option exists. Some of us do.

Much like standing on the north pole where every direction is south. But if you are not on the north or south pole, one direction is north and the opposite direction is south. If you never think about it, you get in a rut where you think it is impossible to have both your front and back directed south at the same time.

None of this discussion will change anything. It is just fun to talk about. Each can limit their thinking to one positive winding direction or not. That is a choice and each to his own.

A voltage reference is a choice, not something that is pre-defined. That is the way it works both mathematically and physically.

But each can play in their own sandbox and define things like they want and surround themselves with as many caveats as they want. That is also a choice.

 

[ggunn]

We'll keep going in circles as long as we are using the term 'phase' to mean multiple things.

This is defined as a 'single phase' supply. There are two 'hot' output legs, they have two different phase angles. In some usages people would say that the two legs are two phases, but others argue against that because they don't like having two phases coming out of a 'single phase' supply.

You can't logically argue that it isn't a 'single phase' supply because that is what it is called. One could as easily call it Betsy. (Residential service in the UK, single phase plus ground I'll call Sam. 90 degree two phase I'll call Donald. 120 degree three phase I'll call Timothy. Residential center tap single phase in the US I'll call Betsy, and two legs 120 degrees apart, which is also called 'single phase' in the US I will call Norbert.)

Because we use the same word to name different aspects of systems, we get tied up in knots either trying to change the name, or trying to explain why the aspects that don't quite match the name are not really there. I absolutely agree that there are two phase angles present. I'm not uncomfortable calling the two 'hot' legs two different phases. But the name is still a 'single phase' service, and there are things that a true 'two phase' service can do that a two hot leg single phase service cannot do.

-Jon

Betsy has two hot legs 120 degrees apart? Um...

 

[winnie]

Betsy has two hot legs 120 degrees apart? Um...

*ouch*

No, Betsy has legs 180 degrees apart. Norbert has legs 120 degrees apart ....

Seriously, I came up with the names as follows:
Simple two wire _s_ingle phase: Sam
Three wire single phase (which someone else called '_B_iphase'): Betsy
True 90 degree 2 phase (_d_uo phases): Donald
_N_etwork single phase (two legs of a three phase wye, used in some apartment buildings):Norbert
_T_hree phase: Tim

 

[Besoeker3]

If I were measuring the voltage of a pair of batteries in a 2-battery holder, I would move both meter probes and observe that both batteries have the correct polarity. In other words, you're observing L1-N and L2-N, while I would be observing L1-N ans N-L2.

The two 120v secondary halves (or two separate secondaries) must be connected in phase in order for their series connection to add to 240v. If one was out of phase with the other, there would be a difference that creates a subtraction, resulting in zero volts.

They are out of phase. That's the whole point of the 120-0-120 configuration.

 

[jaggedben]

They are out of phase. ...

I think it's time for this.

 

[Besoeker3]

I think it's time for this.

View attachment 22083

It isn't a matter of opinion. They are 180deg out of phase.

 

[jaggedben]

It isn't a matter of opinion. They are 180deg out of phase.

No, one is the inverse of the other. :lol::lol::lol: (Well, you know, that's just, like, my opinion, man.)

-sin(x)=sin (x+180)

What you are arguing is like arguing that zero is 1 minus 1. And when someone points out that zero can also be gotten with 10 minus 10, you keep insisting it must be 1 minus 1. It's both, man.

 

[Besoeker3]

What you are arguing is like arguing that zero is 1 minus 1. And when someone points out that zero can also be gotten with 10 minus 10, you keep insisting it must be 1 minus 1. It's both, man.

Nope.
They are 180° out of phase with each other.
No ifs, no buts.

 

[ggunn]

Nope.
They are 180° out of phase with each other.
No ifs, no buts.

If you think that "No ifs, no buts" puts an end to discussion, you are mistaken.

 

[jaggedben]

If you think that "No ifs, no buts" puts an end to discussion, you are mistaken.

:thumbsup:
The only way it puts an end to things is if we just get tired of bothering (again).

 

[LarryFine]

Please, please, please, can anyone locate "that" thread? I've tried and failed.

 

[Besoeker3]

If you think that "No ifs, no buts" puts an end to discussion, you are mistaken.

I don't think that at all.
That they are 180 deg apart is irrefutable as a two channel scope will irrefutably show. That's their raison d'être however much it's disputed.

 

[LarryFine]

I don't think that at all.
That they are 180 deg apart is irrefutable as a two channel scope will irrefutably show. That's their raison d'être however much it's disputed.

As I've said, a scope shows what you're talking about because you "artificially" reverse the polarity when you keep one probe on the neutral. If you keep them in the same juxtaposition, or orientation, when comparing, you wouldn't see the opposition.

Of course, we're ignoring the issue that scopes generally don't have isolated negative inputs.

 

[jaggedben]

If discussing scopes didn't end the discussion 800 posts ago, it's not going to now.

 

[LarryFine]

Dennis was kind enough to bring this thread out of hibernation, in the hopes of not repeating it, and allow me to post the link to it here. Please read it:
https://forums.mikeholt.com/showthread.php?t=142765