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

[LarryFine]

No, the reversal IS the cause of the phase angle difference.

:thumbsup:

 

[jumper]

only baffling to those who can't grasp the physics
physical reality

take the 2 sec windings
instead of line-coil-dot-n-coil-dot-line
do line-dot-coil-n-coil-dot-line
what is the line-line v in each case?

:?

Are you referring to the difference between series and parallel connections of the secondary?

Like shown here: https://www.hammfg.com/electronics/transformers/hookup

 

[jumper]

(I do, too, but don't tell anyone!)

:thumbsup:

 

[LarryFine]

I knew this would be raised.
Yes, if you picked any single moment in time.
You can't define a sine wave by a measurement of single point instantaneous values.

No, but you can have a driving voltage and resulting current, and nobody said we must define a sine wave while we're discussing this. We're talking about the physical connection between two AC sources, while you're talking about why it works.

Having said that:

We obviously all can see both sides of this discussion, or we wouldn't be having it. There's no reason for anyone to say that those who refuse to see it their way is stubborn or ignorant. One has to understand an opposing view to argue against it.

Let's keep it fun, if spirited, and not make it personal.

 

[LarryFine]

:happysad:

nope
one dot is common
the other a line
hence out of phase
both lines = in phase = 0 v

To me, when in series, placing the two dots together, or the two lines together, makes them out phase. There would be zero line-to-line output voltage. The two loose ends could be tied together without creating a short circuit; in that case, in parallel, they would be in phase then.

 

[LarryFine]

I found a pair of graphics that I believe present both the fundamental basis of this discussion as well as how trivial the difference really is:

Wish they were bigger, but you can click on them.

The phase-angle camp is saying:




While the polarity camp is saying:




Note the similarity as well as the difference.

 

[jumper]

Good pics Larry.

Shows one debate going on in this thread, but not all of the differences being discussed here.

 

[jumper]

Hmmmm.

Both are types of common single phase services.

Math works both set ups. Two signals combined to create a larger one.:angel:

 

[jaggedben]

only baffling to those who can't grasp the physics
physical reality

take the 2 sec windings
instead of line-coil-dot-n-coil-dot-line
do line-dot-coil-n-coil-dot-line
what is the line-line v in each case?

We all know what the voltage is. That wasn't the question. The question is why you seem to insist that flipping around the first coil is a "180 deg rotation" and not a "reversal". To me, those phrases are synonymous. Either one is as good as the other, and one does not cause the other.

 

[jaggedben]

I found a pair of graphics that I believe present both the fundamental basis of this discussion as well as how trivial the difference really is:

Wish they were bigger, but you can click on them.

The phase-angle camp is saying:

View attachment 20918


While the polarity camp is saying:

View attachment 20919


Note the similarity as well as the difference.

Right. Thanks for posting those.

Now imagine that something disrupts the primary waveform, or the motor shaft rotation, such that there's an assymtrical distortion in the waveform. Which of those graphs is going to better represent what you see in a scope? That was my question in post 241.

 

[winnie]

Going to disagree on this point. Polarity has a very important meaning; it describes the sense of the measurement. While the AC cycle is both + and - over the cycle, you also need to specify the sense that the meter is connected./QUOTE]
Um..
If I connect my Fluke meter to 120Vac will it read any differently if I reverse the leads?

Of course not. Your nice Fluke meter is throwing away all of the phase information to give you a nice true RMS reading.

Say I hand you a pair of two terminal black boxes. Inside each box is a battery and an inverter. Your meter reads 120V when connected to each box. Reverse the leads and you still get 120V for each box. Say you have a fancy meter and can confirm that the boxes are also producing 60Hz.

Now go and predict the voltage you get when you connect the boxes in series. You can't because you don't know the relative phase of these two sources.

If you have some sort of phase sensitive measurement device (say an oscilloscope being triggered by an external phase reference) then reversing the leads will absolutely give you a different reading!

-Jon

 

[SG-1]

To me, if it was two phases, it would be two regardless of the reference point.

I think you will have the same issue with 2-Phase (90 degree displacement) & the scope.

 

[jaggedben]

I think you will have the same issue with 2-Phase (90 degree displacement) & the scope.

I'm doubtful of that. Please explain.

 

[LarryFine]

I think you will have the same issue with 2-Phase (90 degree displacement) & the scope.

No issue with 2-phase, whether 3-wire or 5-wire, and I would never refer to 5-wire as 4-phase.

 

[jumper]

I think you will have the same issue with 2-Phase (90 degree displacement) & the scope.

I'm doubtful of that. Please explain.

No issue with 2-phase, whether 3-wire or 5-wire, and I would never refer to 5-wire as 4-phase.

Oh jeez, do we gotta bring that Two Phase into this mess.:rant:

We got enough problems with the two phases in Single Phase!

 

[SG-1]

I'm doubtful of that. Please explain.

On a 3-Phase delta you will the same number of waveforms with equal magnitudes no matter the reference.

A 3-Phase wye:

If you use the neutral point as the reference you can see 3 waveforms of equal magnitude 120 degrees apart.

If you use a phase as reference you can see 2 waveforms of equal magnitude 120 degrees apart, plus one smaller waveform at zero.

The two phase (90degree) has two ungrounded & one grounded conductor similar to the 240/120 single phase service. No matter where one moves the reference you see two wave forms.

.

 

[SG-1]

Oh jeez, do we gotta bring that Two Phase into this mess.:rant:

We got enough problems with the two phases in Single Phase!

Sorry bout that, but I'm trying to understand why the phase displacement of 180 degrees disqualifies the 240/120 from being 2-Phase.

 

[jumper]

Sorry bout that, but I'm trying to understand why the phase displacement of 180 degrees disqualifies the 240/120 from being 2-Phase.

Ya got a code book handy?

 

[jumper]

Sorry bout that, but I'm trying to understand why the phase displacement of 180 degrees disqualifies the 240/120 from being 2-Phase.

Ya got a code book handy?

I went and snagged the section I wanted from a 2017. Makes two points for me.

Seems like the NEC calls it single phase. 120/208V also.......

310.15(B)(7) Single-Phase Dwelling Services and Feeders. For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted to be sized in accordance with 310.15(B)(7)(1) through (4).

For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, single-phase feeder conductors consisting of 2 ungrounded conductors and the neutral conductor from a 208Y/120 volt system shall be permitted to be sized in accordance with 310.15(B)(7)(1) through (3).

 

[Besoeker]

I am answering the question, but not speaking to you. You know the following.

From an earlier posted link:

“The Center-tap Transformer

center tap transformer

Nicely shows the two output waveforms out of phase.