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

[mivey]

Larry,

Here is another way to think of the larger and smaller waveforms considering a 120/208 system.

If the "direction" of the larger waveform dictates the direction for the smaller waveforms and that in turn directs the positive direction in the coils then what do you get? You get one voltage at 180d and one at 120d that sum to get a larger voltage at 150d.

In other words, the larger voltage dictating "coil direction" would show two 60d displaced voltages. These voltages do exist but we normally define them the other way.

FWIW, we can actually make use of the voltage that does exist in the other direction because it is a physical reality, not just some math construct. We actually make use of the voltages in the winding halves in opposite directions in transformer banking and it works just like the math shows.

 

[jumper]

I agree the lower voltage source is upsidedown in Post 616. Better upsize that neutral !

Spice uses +/- to indicate instantaneous polarity of the voltage sources as shown below.

It is not upside down!

I use a spice based software. Multisim.

 

[mivey]

but as two series-connected sources that form a single source, in order to add, must be in phase.

"in order to add". That, I believe, is where you fail.

Can't you see that the two windings in a 120/208 system are also in series? While perfectly happy to subtract those series voltages in a 120/208 system you are convinced you must sum the voltages in a 120/240 system. Don't you see that you are making the use of different reference choices already and that both are valid?

Even with the instantaneous voltages the difference in reference choice is obvious. Or should be.

The 208 voltage "direction" does not define the direction for the 120 voltages and neither does the 240 voltage "direction" define the direction for the 120 voltages.

 

[ggunn]

If and only if you choose YOUR reference of an endpoint. And it is only "just like two batteries" if you want to use the markings and terminal caps someone else chose and if you think a static system can equate to a dynamic system.

Or if you have AC batteries.

 

[kingpb]

Has anybody posted vector diagams? If not, wouldn't that be prudent to the discussion.

 

[jaggedben]

Has anybody posted vector diagams? If not, wouldn't that be prudent to the discussion.

I don't think it changes the discussion. The vector diagram for L1-N would be 180 deg different than the one for L2-N and the same as for N-L2 and we'd still be arguing over whether one of the latter two is the only 'correct' diagram.

Also, one of the points I've been making is that for many types of work the 120/240 system is unique in that you don't need vector diagrams or anything similar.

 

[jumper]

Has anybody posted vector diagams? If not, wouldn't that be prudent to the discussion.

I do not think so, it does not change the discussion nor really help.

 

[jumper]

I don't think it changes the discussion. The vector diagram for L1-N would be 180 deg different than the one for L2-N and the same as for N-L2 and we'd still be arguing over whether one of the latter two is the only 'correct' diagram.

Also, one of the points I've been making is that for many types of work the 120/240 system is unique in that you don't need vector diagrams or anything similar.

Agree.

 

[Russs57]

It was mentioned earlier in this thread that a 180 degree shift (in time) was indistinguishable from a polarity reversal (multiplied by -1) provided we restricted things to a pure sine wave.

So what happens differently between the two when we have a distorted waveform? Wouldn’t that provide a conclusive answer? Frankly I think we a conclusive answer but disagree on naming conventions. I admitted in my first post that I had called them two sources 180 degrees out of phase.

Another reason I ask is related to a power source I use to and how it works with noise and/ or distorted waveforms. It is a split-phase 60-0-60 single phase source derived from a transformer with dual secondary windings.

 

[buffalonymann]

I do not think that failure to grasp the physics is the basis of this discussion. The argument isn't over what is happening, it's over what to call it.

Well, the original discussion is some people mistakenly call a single phase xfmr "two phase" when the winding is tapped in the center. I further asserted if it really was two phase, one could start an induction motor without the use of starting apparatus as a proof that people are mistaken if they think it is two phase. Those who mistakenly called it two phase were schooled in xfmr theory, and then they began offering other excuses as to why they call it two phase.

They failed to grasp the physics because they lack understanding of electrical xfmr theory.

It's one primary winding producing a single sine wave in the secondary, and this doesn't change just because it is center tapped

 

[buffalonymann]

Which means that it's the "way you hook up two of them" that is what accounts for the difference.

SPOT-ON :thumbsup:

 

[jumper]

It is a split-phase 60-0-60 single phase source derived from a transformer with dual secondary windings.

That set up is really no different than our 120/240.

Per NEC, that is single phase by naming convention in Art.647.


647.3 General. Use of a separately derived 120-volt single-phase 3-wire system with 60 volts on each of two ungrounded conductors to a grounded neutral conductor shall be permitted for the purpose of reducing objectionable noise in sensitive electronic equipment locations, provided the following conditions apply:
(1) The system is installed only in commercial or industrial occupancies.
(2) The system’s use is restricted to areas under close su- pervision by qualified personnel.
(3) All of the requirements in 647.4 through 647.8 are met.

 

[buffalonymann]

xfmr.

OK, crazy question for the thread.

Instead of using meters and scopes to determine a 'direction' of flow, why not use a compass? The compass won't need to pick a spot on the coil for a reference.

Of course, this would take a slow version of AC to see the compass needle move.

If we put a compass on each side of the 240 volt coil, one for each 120 volt section, would the compasses point in the same direction as they went from one cycle to the next, or would they be 'out of phase' and point at opposite directions?

How about somebody just reading how a transformer works? Somebody provided a fairly accurate description of the coils and their additive property producing just one current, first in one direction, and then the opposite direction. Physics preclude the existence of opposing currents in a single phase xfmr

 

[jumper]

xfmr.

How about somebody just reading how a transformer works? Somebody provided a fairly accurate description of the coils and their additive property producing just one current, first in one direction, and then the opposite direction. Physics preclude the existence of opposing currents in a single phase xfmr

:roll:

 

[jumper]

It's one primary winding producing a single sine wave in the secondary, and this doesn't change just because it is center tapped

Nope.:happysad:

 

[Russs57]

Jumper, could you ever installed or tried such a distribution system?

I find it makes a noticeable difference.

 

[drktmplr12]

Well, the original discussion is some people mistakenly call a single phase xfmr "two phase" when the winding is tapped in the center.

no one called a single phase transformer "two phase". we have identified that the two waveforms (L1-N and L2-N) observed on the center tapped secondary have a phase difference of 180 degrees, relative to the center tap.

someone did claim that current = work, factually incorrect.

Those who mistakenly called it two phase were schooled in xfmr theory, and then they began offering other excuses as to why they call two phase

no one schooled anyone in transformer theory or offered excuses.

They failed to grasp the physics because they lack understanding of electrical xfmr theory.

everyone participating in this thread grasps the physics. not every grasps how to make their point with respect for their peers

buff, please explain what is wrong with my understanding:

the power source (HV) is single phase and the transformer is a 120/240 center tapped secondary. there are two current loops on the center tapped secondary and in nearly all cases, the waveforms are independent from each other. if i introduce an inductive load to L1-N, the imbalance will be observed on the neutral because current wave form on L1-N will be lagging more as a result. by balancing inductive loads a series circuit was not created, as you claim. if that was true, the voltage drop across loads on L1-N would be observed on L2-N. also, the current does not travel through loads on L1-N to get to the loads on L2-N. in order to create a series circuit would have to either disconnect the center tap or disconnect one leg and turn on a 240V appliance. instead we have two circuits in parallel with different phase angles and a common reference and return path to the source.

 

[jumper]

Jumper, could you ever installed or tried such a distribution system?

I find it makes a noticeable difference.

Which system? The 60-0-60?

 

[jaggedben]

buff, please explain what is wrong with my understanding:

the power source (HV) is single phase and the transformer is a 120/240 center tapped secondary. there are two current loops on the center tapped secondary and in nearly all cases, the waveforms are independent from each other. if i introduce an inductive load to L1-N, the imbalance will be observed on the neutral because current wave form on L1-N will be lagging more as a result. by balancing inductive loads a series circuit was not created, as you claim. if that was true, the voltage drop across loads on L1-N would be observed on L2-N. also, the current does not travel through loads on L1-N to get to the loads on L2-N. in order to create a series circuit would have to either disconnect the center tap or disconnect one leg and turn on a 240V appliance. instead we have two circuits in parallel with different phase angles and a common reference and return path to the source.

"Independent from each other" strikes me as a poor choice of words. I think your point is that they differ. But as long as they are derived from the same HV primary phase (or as gar pointed out, the same generator shaft), then they aren't entirely independent.

I also disagree with you about the L1 and L2 loads not being in series. It is only on the assumption that the resistance of the N conductor is negligible that you can ignore how they are in series. But I'm also not sure how that relates to the larger topic of this thread, which is about how we name waveforms.

 

[Russs57]

Yes Jumper, 60-0-60 system. You can make one on the cheap with a 480/240 X 240/120 single phase transformer. I run both sides in series and use 240 on primary. It is alot like isolated power system used in hospitals.

Still looking for dialogue on what would be different with distorted waveform on true 180 vs -1.