240v debate....

[readydave8]

Gas grills don't do it for me. We do barbecue quite a bit, but use charcoal. Home made burgers at the weekend were well received.
If you want to use gas, you might just as well cook in the kitchen - we have a gas stove for that.

Well I'd like to argue about gas grills but don't want to cause this thread to wind up with a large number of posts.

 

[mivey]

Then you have mis-read my postings. In every case, my questions have been in relation to a 2-wire load.

OK. I guess I was looking too far down the road. Maybe we need to be sure some other fundamentals are clear. How about we burn a few posts covering some basic terminology to see if you & I are on the same page?

Let's start with a single-source, 2-terminal, 120 Vrms, 60 Hz, sinusoidal voltage to see if we can agree on currents and voltage forces, and directions for the simplest case before we cover multiple sources, etc.

Let the single, two-terminal voltage be between terminal 1 and terminal 2. Let's take a snap shot in time when current is flowing out from the source at terminal 1, through a resistive load, back into the source at terminal 2. Let that also be when the voltage is at a maximum between terminal 1 & 2. Also, we started plotting the voltage of terminal 1 relative to terminal 2 at a point much earlier in time (much longer than one cycle earlier).

1) Would you agree that the curve we have been plotting plot up to that time now rests at what we call the positive peak?

2) Would you agree that the peak voltage from the source that we are currently plotting is a real voltage force pushing current from terminal 1 to terminal 2?

3) Would you agree that 1/2 cycle before (180? earlier on the waveform), the peak voltage from the source that we were plotting (terminal 1 relative to terminal 2) was a real voltage force, was in the opposite direction from the voltage in item #2, and since the force was in the opposite direction, was pushing current from terminal 2 to terminal 1 through the resistive load?

If we can agree on these, I think we are off to a good start. But I then have a few more basic terminology questions.

 

[mivey]

Your previous example in post 290 was for generators that are physically out of phase.

If you can agree that the generator voltages referenced to Earth were 180? out of phase, perhaps we are not too far from reaching common ground. If I recall the discussion from years back, some posters (must not have been you) said that a 120? phase difference in voltages was real, as well as 121?, 122?, ..., up to 179+++? but as soon as you made the final microscopic, fractional degree change to exactly 180?, that the voltages were no longer out of phase.

This isn't applicable to this discussion. We are discussing a single-core center-tapped transformer.

Lenz's Law does dictate direction, and you are violating it. Not all Laws are based on an equation. Faraday was not proficient in mathematics, so you will not find any equations in his original laws either.

Hold that thought, as I would like to cover some basic terminology with Jim to make sure we are speaking the same language.

 

[mivey]

The point of reference can easily change, but the compass heading for the lane of traffic is fixed. When you move your reference point to the other side of the freeway, the cars don't change their direction to be heading South to North.

Stand at the North pole and let the cars travel towards the North pole on a path that passes directly over it. Consider when they cross the pole: At one instant they were headed North, and the next instant they were headed South. No U-turn required.

 

[Rick Christopherson]

Hold that thought, as I would like to cover some basic terminology with Jim to make sure we are speaking the same language.

Fine with me, but I will make a minor comment before sitting back for your discussion.

If you can agree that the generator voltages referenced to Earth were 180? out of phase, perhaps we are not too far from reaching common ground. If I recall the discussion from years back, some posters (must not have been you) said that a 120? phase difference in voltages was real, as well as 121?, 122?, ..., up to 179+++? but as soon as you made the final microscopic, fractional degree change to exactly 180?, that the voltages were no longer out of phase.

You make it sound like I am disputing phase angles, all phase angles, and that is not correct. I am simply disputing this particular one. I am not disputing the mathematical insertion of a phase angle as a tool, but when you state that it is a real phase angle present in one half of the windings of a common core transformer, that point I dispute.

 

[mivey]

Fine with me, but I will make a minor comment before sitting back for your discussion.

You make it sound like I am disputing phase angles, all phase angles, and that is not correct. I am simply disputing this particular one. I am not disputing the mathematical insertion of a phase angle as a tool, but when you state that it is a real phase angle present in one half of the windings of a common core transformer, that point I dispute.

Duly noted. And I apologize if I got your position mixed up with some others and if I did, I did not do it on purpose.

 

[Rick Christopherson]

Duly noted. And I apologize if I got your position mixed up with some others and if I did, I did not do it on purpose.

I appreciate that. As I said above, I believe that a lot of the sub-discussions here can be attributed to miscommunication.

 

[jim dungar]

if you & I are on the same page?

Evidently we will never be on the same page.
I know how to interpret a waveform.
I also know a little more than basic math: If A+B=C and A=C-B, if D=-B, then A=C+D which leads to A-D=C which can also be given an arbitrary direction as well a magnitude yielding A<0+B<0=C<0, and A<0=C<0-B<0, if D<180=-B<0, then A<0=C<0+D<180 which leads to A<0-D<180=C<0, while remembering -D<180=-(-B<0).


This is not a question of 'chicken or the egg'. It is about the laws of physics and the fundamentals of transformers.
Given a single core center tapped transformer feeding a 2-wire resistive load.
There is a voltage across the extreme ends of the windings. Where did this voltage come from, the load, or the flux in the core?
There is a single loop current flowing. Is this current in phase with the voltage across the extreme ends of the coil?

 

[BAHTAH]

240V debate

240V debate

First of all there is no safety issue for the customer with a properly installed 240V circuit vs a 120V circuit.
Other than the advantages of reduced voltage drop, if that is an issue there is a difference in the power
(IsqR) consumption of the circuit itself. The 240V circuit will have a reduction of about 25% as compared with
a 120v circuit for the same equipment. With the higher cost of energy there will be a savings over the life
of the circuit even though the power levels are probably quite low. A reduced voltage drop is a plus as related
to the life of the equipment and it's efficiency.

 

[Besoeker]

I am not contesting a reference point. I apparently can't get that point across. What I am contesting is that some people are taking a chosen reference point and redefining the system with it.

The fact is that Van and Vbn are mutually displaced by 180deg.
No redefining either done or required.

 

[Besoeker]

There is a single loop current flowing. Is this current in phase with the voltage across the extreme ends of the coil?

I don't anyone would or has argued against that (assuming a resistive load).

 

[mivey]

Evidently we will never be on the same page.

If we can't agree on what I consider to be the simplest of things, I don't see how we ever can be either.

I know how to interpret a waveform.
I also know a little more than basic math

I don't doubt that one bit. The question is do we have some common termonology to work from so we can even discuss other things?

This is not a question of 'chicken or the egg'. It is about the laws of physics and the fundamentals of transformers.

And you would think it would be quite simple. I know that, in reality, neither of us is supporting breaking any laws. But somewhere we are having a fundamental mis-communication. The reason I asked the questions in post #402, particularly question #3, is that we have not been in agreement in the past on something that to me seems quite simple.

In our last discussion on the topic of joining two separate transformers with two phase-opposed voltages, you claimed that I was just swapping transformer terminals (the thread from long ago). You said I really did not have phase-opposed voltages but was just playing games with the transformer terminals. I found that statement to be incredible, but unfortunately the thread ended before my questions about why you were thinking that way could be addressed.

The last time, I just used waveforms and terminal numbers in my posts. It is the same scenario I detailed in my post #98 here using a graphic all the way from the source to load. These two generators are exactly the same, have the exact same feeders, have the exact same transformers, serve the exact same load, and everything is connected exactly the same way. The only difference is that I went back to one of the generators and rotated one of the windings 180? relative to the other winding.

To me, it is plain and simple to see that these are two phase-opposed sources that are joined by their connection to Earth. The voltage across both loads is double that of the voltage across a single load. In the prior thread, I found it odd that you would think these voltages were not really phase-opposed. I know you are very smart, and find it hard to believe you would disagree with that, so I am thinking that we are not communicating.

That is why I asked the questions in post #402. If we can not agree on the most basic of concepts, we really can't move any further in our discussion until we reach common ground.

I realize this is an example of two separate cores, but I can't but sure we are are talking the same language and we must be able to communicate if we are going to discuss the issue of two wind halves in a single transformer.

 

[mivey]

You make it sound like I am disputing phase angles, all phase angles, and that is not correct.

I'm not sure where Jim is at, and I see no point in waiting further if he & I can't agree on common termonology.

I don't want to assume anything so I will re-state what I think your position is and you can correct any errors:

#1) You agree that we can supply your example circuit with two voltages that have a common Earth connection and we will have a voltage from input terminal #1 (fed by one of the un-grounded source conductors) to the neutral point that is a real voltage, plus we will have a voltage from input terminal #2 (fed by one of the un-grounded source conductors) to the neutral point that is a real voltage, and these two voltages have a 180? displacement?

#2) These voltages, even while being phase-opposed, still produce currents in the circuit that, if look at any instantaneous point in time, are flowing exactly the same way as the currents that would flow if we fed the circuit with a center-tapped transformer source?

#3) Your issue is not that the two-generator source has phase-opposed voltages that we joined together, but that we can't have real phase-opposed voltages in the secondary of a single center-tapped transformer?

 

[weressl]

May I ask you a simple question or two?

If I am standing in the middle of a street: Are the cars coming at me or away from me?

If I am in the median between two streets: same question.

This analogy is probably the simplest way to try to understand how flux in a coil wound in a given direction induces voltage. One point needs to be made; it is a two way street, but with only one car(flux)!

 

[jim dungar]

I don't anyone would or has argued against that (assuming a resistive load).

It appears we agree on, a single core (i.e. flux path), a single coil, a single current, and a single voltage in phase with the current?

Now, if we add 2 node points only, about 2.5% in from both ends of the transformer winding, we will still have a single current, and a single flux path. Are the three resultant series voltages still in phase with the single current? Why or why not?

 

[cowboyjwc]

I laughed too but not until tomorrow
since that's when I was at the time

 

[Rick Christopherson]

I'm not sure where Jim is at, and I see no point in waiting further if he & I can't agree on common termonology.

I don't want to assume anything so I will re-state what I think your position is and you can correct any errors:

#1) You agree that we can supply your example circuit with two voltages that have a common Earth connection and we will have a voltage from input terminal #1 (fed by one of the un-grounded source conductors) to the neutral point that is a real voltage, plus we will have a voltage from input terminal #2 (fed by one of the un-grounded source conductors) to the neutral point that is a real voltage, and these two voltages have a 180? displacement?

This isn't exactly my stance, but it is not highly objectionable either. The only objection is that I had to read it a couple of times to make sure it says what it says. I'll come back to this below.

#2) These voltages, even while being phase-opposed, still produce currents in the circuit that, if look at any instantaneous point in time, are flowing exactly the same way as the currents that would flow if we fed the circuit with a center-tapped transformer source?

#3) Your issue is not that the two-generator source has phase-opposed voltages that we joined together, but that we can't have real phase-opposed voltages in the secondary of a single center-tapped transformer?

Number 3 is correct. Number 1 and 2 have minor technical points.

Let's say we have a voltage source V_s that is a black box with 2 wires coming out of it, S₁ and S₂. It has feet on the bottom, so it is always oriented with S₁ at the bottom and S₂ at the top, and it can be stacked on top of another V_s supply. The voltage from S₁ to S₂ is defined to be V_s = V_m sin(ωt), or V_m<0?

Now we have this big rack or frame that we can bolt our power supplies into that comes pre-wired with 3 bus bars: A, N, B with A at the top, B at the bottom, and N in the middle. N is also connected to our chassis frame/ground. The power supplies bolt straight in without turning them upside down. On the lower supply, S₁ bolts to the B-bus and S₂ bolts to the N-bus. Similarly, on the upper supply, S₁ bolts to the N-bus and S₂ bolts to the A-bus.

Now that our supplies are bolted into their frame, we can put on some labels: V_AN = V_s and V_BN = -V_s or if we prefer no negative signs, V_AN = V_s<0 and V_BN = V_s<180. We now have our external voltage designations V_AN and V_BN that appear to be 180? out of phase, but we did not change the definition of V_s in the process. The two V_s supplies are equal in magnitude and in phase with each other, but our external references can be labeled as being 180? out of phase.

My issue has been that with the way some people have been wording their discussions, they are taking the lower V_s power supply and physically rotating it so the feet are pointing upward. I think I have been pretty careful in my discussion to not object to those discussions that designated V_an and V_bn (unless it was an oversight on my part). I don't object to saying V_an and V_bn are 180? out of phase. I do object to saying the two power supplies (transformer windings, etc.) are 180? out of phase.

This is an industry where precision in communication is critical. Saying one thing while meaning another can be very disastrous. Some of the posters may not have realized that their wording was or was not communicating what they really intended it to convey.

In the diagram below, I didn't feel like redrawing a power supply, so I extracted it from the Hayt/Kemmerly text book.

 

[mivey]

This isn't exactly my stance, but it is not highly objectionable either. The only objection is that I had to read it a couple of times to make sure it says what it says. I'll come back to this below.

I'm sure it could be wordsmithed into something not so hard to read but I did not put that much time into it. Sorry it makes it hard to read, but we should be able to figure out what each other is saying with a little back-and-forth.

Number 3 is correct. Number 1 and 2 have minor technical points.

Let's say we have a voltage source V_s that is a black box with 2 wires coming out of it, S₁ and S₂. It has feet on the bottom, so it is always oriented with S₁ at the bottom and S₂ at the top, and it can be stacked on top of another V_s supply. The voltage from S₁ to S₂ is defined to be V_s = V_m sin(ωt), or V_m<0?

Now we have this big rack or frame that we can bolt our power supplies into that comes pre-wired with 3 bus bars: A, N, B with A at the top, B at the bottom, and N in the middle. N is also connected to our chassis frame/ground. The power supplies bolt straight in without turning them upside down. On the lower supply, S₁ bolts to the B-bus and S₂ bolts to the N-bus. Similarly, on the upper supply, S₁ bolts to the N-bus and S₂ bolts to the A-bus.

Now that our supplies are bolted into their frame, we can put on some labels: V_AN = V_s and V_BN = -V_s or if we prefer no negative signs, V_AN = V_s<0 and V_BN = V_s<180. We now have our external voltage designations V_AN and V_BN that appear to be 180? out of phase, but we did not change the definition of V_s in the process. The two V_s supplies are equal in magnitude and in phase with each other, but our external references can be labeled as being 180? out of phase.

My issue has been that with the way some people have been wording their discussions, they are taking the lower V_s power supply and physically rotating it so the feet are pointing upward. I think I have been pretty careful in my discussion to not object to those discussions that designated V_an and V_bn (unless it was an oversight on my part). I don't object to saying V_an and V_bn are 180? out of phase. I do object to saying the two power supplies (transformer windings, etc.) are 180? out of phase.

Then I think we are on the same page. I agree that both of voltages labeled Vs in your diagram are in phase. Looking at your diagram, I also agree that the supplies are in phase.

I also understand that if, instead of using two Vs sources, you used one Vs source and then also used one Vx source with a 180? phase displacement from Vs, that you would say you have two supplies that are 180? out of phase. You would also say that the voltages to the load were exactly the same as those we get by using the two in-phase supplies. Correct?

Add: with Vs and Vx connected so we get double the voltage across the circuit.

 

[Rick Christopherson]

I also understand that if, instead of using two Vs sources, you used one Vs source and then also used one Vx source with a 180? phase displacement from Vs, that you would say you have two supplies that are 180? out of phase. You would also say that the voltages to the load were exactly the same as those we get by using the two in-phase supplies. Correct?

P.S. I was already half way through writing this posting before you edited your posting, so please pay attention to the blue text. That is where your edit was made while I was typing.

I was anticipating that this would be your next comment. However, you did leave out a very critical fact. You forgot to include polarity (or dot convention) with your 180? difference. Without this polarity designation, you have in effect, turned one of the V_s power supplies upside down. If you were to do this, then your voltage from B to A (or A to B) would be zero volts.

As much as I (personally) hate to say this, if you moved your dot from S₂ to S₁ and then labeled the V_x supply as V_M<180?, that would be correct. The reason why I "personally" don't like to say that is because it leads to confusion, and results in the faux-paus that you just made in your quotation above.

The fact that you made this faux paus is great. It would have been harder for me to respond if you hadn't accidentally omitted this detail. (Ahhh! As I suspected, you fixed your faux paus after I had already quoted your original posting.) It is the ease with which this can be overlooked, that is behind my reason for not "personally" condoning it.

So with your new correction (edit) made, I will return to the response that I was already anticipating that I would need to make. What you have in effect done is placed a new label over the top of the original label and reversed the dot-convention at the same time. If we peel back your label, we will see the original label and dot-convention. It didn't change the original power supply, it only gave it a new label that may lead to confusion (yes, I was planning on pointing out "lead to confusion" before you made your faux paus. That is why I was happy to see your faux paus.).

 

[Lady Engineer]

*sneaking in AGAIN*

Wow at this thread!

*sneaking out AGAIN*

I can't believe it's still going. Mike Holt is going to have to add extra storage, before all is said and done. LOL!!!