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

[Gary Glaenzer]

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/single-phase-power-systems/

"I suppose it is because I learned far more about transformers building tube audio amps. There it is quite common to use a center tapped transformer to either.....output two identical signals, 180 degrees apart......or to sum to signals 180 degrees apart into one "phase"."

At the risk of starting a semantics war............

You do NOT get 'two identical signals, 180 degrees apart' with a center-tapped transformer. To do that, the transformer would have to shift one signal in TIME, uniformly, across the audio spectrum.

What you DO get is two signals OF OPPOSITE POLARITY. Which, if you are looking at a perfect sine wave, is INDISTINGUISHABLE from one '180 degrees apart' from the other.

Thank you, soapbox is now available, let the fun begin !

 

[ggunn]

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/single-phase-power-systems/

The following may be at the heart of what he was going on about. Note that the author admits it can just as easily be depicted as two sources 180 degrees apart. After reading the article I am finding it hard to call him dead wrong, but I would have before.

I suppose it is because I learned far more about transformers building tube audio amps. There it is quite common to use a center tapped transformer to either.....output two identical signals, 180 degrees apart......or to sum to signals 180 degrees apart into one "phase".

If you have been dealing with audio signals, then you know that with any waveform more complex than a pure sine wave, inversion and phase shift do not look the same.

 

[Russs57]

Point taken. Historical names are “phase splitter/inverter”. One could also get into a semantics battle regarding polarity of AC waveform.

 

[jaggedben]

...One could also get into a semantics battle regarding polarity of AC waveform.

I think what is confusing for many people on a standard split-phase system is that if you scope L1 to neutral and L2 to neutral, with neutral as the common reference, you get opposite 'polarity'. However, if you view them as two sections of transformer winding in series, and you scope L1-L2, L1-N, N-L2, you see all three waveforms with the same polarity in sync, because you have measured them all with the same orientation to the primary source.

The beginner may intuitively think that using neutral as the common reference is the way one should look at it. But the more advanced person realizes that this is just a choice, among other possible choices, depending on what you're trying to demonstrate or achieve.

 

[ActionDave]

I think what is confusing for many people on a standard split-phase system is that if you scope L1 to neutral and L2 to neutral, with neutral as the common reference, you get opposite 'polarity'. However, if you view them as two sections of transformer winding in series, and you scope L1-L2, L1-N, N-L2, you see all three waveforms with the same polarity in sync, because you have measured them all with the same orientation to the primary source.

The beginner may intuitively think that using neutral as the common reference is the way one should look at it. But the more advanced person realizes that this is just a choice, among other possible choices, depending on what you're trying to demonstrate or achieve.

And there is where the discussion breaks down every time.

 

[K8MHZ]

If you don't reverse the leads, there is no 180 degree shift. If you 'keep the red on the right' the scope will show both 120's and the 240 'in phase', will it not?

If you keep the same lead on the neutral and move the other lead from one side to the other to measure 120 volts, then to be accurate you should also be switching them to read 240 volts, which will give you your 180 shift not on just the 120 volt sides, but the 240 volt side as well, would it not?

 

[ActionDave]

Careful - this topic is probably more likely to end up closed than a topic with "gun" in the title. :lol:

It's not the topic that ends up closing these threads, it's the way the opposing sides end up being so nasty to each other.

The smartest guy in the room is usually a solo act. Here at the Mike Holt Forum we are blessed with having all the smartest guys in the room at the same time. Some are better at sharing the room than others.

 

[electrofelon]

It's not the topic that ends up closing these threads, it's the way the opposing sides end up being so nasty to each other.

The smartest guy in the room is usually a solo act. Here at the Mike Holt Forum we are blessed with having all the smartest guys in the room at the same time. Some are better at sharing the room than others.

Well said

 

[LarryFine]

You do NOT get 'two identical signals, 180 degrees apart' with a center-tapped transformer. To do that, the transformer would have to shift one signal in TIME, uniformly, across the audio spectrum.

What you DO get is two signals OF OPPOSITE POLARITY. Which, if you are looking at a perfect sine wave, is INDISTINGUISHABLE from one '180 degrees apart' from the other.

:thumbsup:

 

[winnie]

I agree, this is a thread about terminology, and 'phase' has many meanings.

One of the points made in the other thread was about the 'hexaphase' transformer. This is a set of 3 single phase coils, all with center taps, with the center taps joined to make a 'star'. Each of the output terminals of such a transformer is 60 degrees out of phase from the adjacent ones.

In the literature on high phase order motors they came up with a term to distinguish phase counting when you had 'phases' that were 180 degrees apart. They used 'hemi-phase'. So using that terminology the hexaphase transformer is a 3 phase transformer with 6 hemi-phases brought out.

Similarly a center tapped transformer is single phase with 2 hemiphases brought out.

Don't know if this helps or is just an extra word to be pedantic with

-Jon

 

[LarryFine]

Don't know if this helps or is just an extra word to be pedantic with

"Couldn't hoit!" ~ Bugs Bunny

 

[buffalonymann]

I guess I'll post it again - one person upload a picture depicting his two phase theory and a few others claiming to be engineers agreed with him. You can see the picture in the Zero Sequence CT thread.

A single phase transformer is powered by a single phase primary, when the primary current is flowing in one direction, the secondary current flows in the opposite direction. Polarity is as follows L1 is positive L2 is negative simultaneously N is negative with respective to L1 and positive with respect to L2. A sine wave would show L1 to N starting positive and N to L2 starting positive at the same time; in phase.


There is only one current flowing through the transformer. If L1-N was 180 degrees out of phase with L2-N the currents would buck, they don't. The reason the N carries the imbalance between L1-N and L2-N is because the remaining loads are now a series circuit and their currents flow from L1 to L2

 

[LarryFine]

It's analogous (in one frozen moment in time) to two batteries in series supplying both 1.5v and 3v loads. The DC is additive because of the polarity of each cell (in phase); if you reversed one, you'd still have two 1.5v sources, but no 3v source (out of phase).

What's the real point of the discussion is polarity, plain and simple. A secondary comprised of two 120v windings must be connected "in phase" to provide 240v, and at the same time, mimic a center-tapped 240v secondary, and provide two 120v sources.

 

[jumper]

I think what is confusing for many people on a standard split-phase system is that if you scope L1 to neutral and L2 to neutral, with neutral as the common reference, you get opposite 'polarity'. However, if you view them as two sections of transformer winding in series, and you scope L1-L2, L1-N, N-L2, you see all three waveforms with the same polarity in sync, because you have measured them all with the same orientation to the primary source.

The beginner may intuitively think that using neutral as the common reference is the way one should look at it. But the more advanced person realizes that this is just a choice, among other possible choices, depending on what you're trying to demonstrate or achieve.

I agree, this is a thread about terminology, and 'phase' has many meanings.

One of the points made in the other thread was about the 'hexaphase' transformer. This is a set of 3 single phase coils, all with center taps, with the center taps joined to make a 'star'. Each of the output terminals of such a transformer is 60 degrees out of phase from the adjacent ones.

In the literature on high phase order motors they came up with a term to distinguish phase counting when you had 'phases' that were 180 degrees apart. They used 'hemi-phase'. So using that terminology the hexaphase transformer is a 3 phase transformer with 6 hemi-phases brought out.

Similarly a center tapped transformer is single phase with 2 hemiphases brought out.

Don't know if this helps or is just an extra word to be pedantic with

-Jon

:thumbsup:

 

[jumper]

It's not the topic that ends up closing these threads, it's the way the opposing sides end up being so nasty to each other.
.

:happyyes:

 

[GoldDigger]

If you have been dealing with audio signals, then you know that with any waveform more complex than a pure sine wave, inversion and phase shift do not look the same.

And, although it may seem obvious, it is worth stating that "phase" is *only* applicable when looking at a periodic waveform. Both polarity inversion and *time* delay can be applied to any waveform.
As long as a waveform can be represented as a single sine/cosine wave and its harmonics only, phase shift makes sense.

Sent from my XT1585 using Tapatalk

 

[Besoeker]

There is only one current flowing through the transformer. If L1-N was 180 degrees out of phase with L2-N the currents would buck, they don't.

They do if by buck you mean cancel.
As the N is the common point it is usual/logical to reference the L1 and L2 alternating voltages with respect to that. And they are most certainly 180° out of phase.

 

[jwelectric]

I have two lanes of traffic going from south to north and two going from north to south. In reality all four lanes of traffic is going in the same direction. Stand in the median and look at the south bound traffic. It is going from right to left. Now turn around and look at the north bound traffic, low and behold it is going from right to left, therefore all traffic is going in the same direction.

Now someone prove me wrong. :jawdrop:

Current flows in one large circle so it all depends where we are looking at it that determines what we see. That scope that confuses so many people we are stand on a bridge looking down on those four lanes of traffic so we can see all of them at the same time therefore we see two lanes coming from under us and two going under us but in reality all four are going from right to left.

 

[GoldDigger]

I have two lanes of traffic going from south to north and two going from north to south. In reality all four lanes of traffic is going in the same direction. Stand in the median and look at the south bound traffic. It is going from right to left. Now turn around and look at the north bound traffic, low and behold it is going from right to left, therefore all traffic is going in the same direction.

Now someone prove me wrong. :jawdrop:

Current flows in one large circle so it all depends where we are looking at it that determines what we see. That scope that confuses so many people we are stand on a bridge looking down on those four lanes of traffic so we can see all of them at the same time therefore we see two lanes coming from under us and two going under us but in reality all four are going from right to left.

It is all relative. If I stand on one shoulder of the roadway I see the nearest lanes going from left to right and the farthest going from right to left. If I cross to the other side I again see the nearest lanes going from left to right and the farthest lanes going from right to left. The only possible explanation is that the cars are not really moving at all.
There, I have disproved your assertion. They cannot all be going in the same direction because they are in fact standing still.

 

[mivey]

There is no north or south. There is no right or left. There is no coming or going.

Until you decide which direction you like.

You get to decide these once you stand in the spot you like. It is your world in which to create voltages. You create the reference point wherever you like.