Just to clarify.

[jim dungar]

I haven't analyzed a circuit as complex as the Teaser.doc since my days in college.

I learned to do basic circuits using slide rules (they were easier to use than punching cards and waiting for the batch program to run). We worried a lot about setting up the problem first rather than just letting the currents work themselves out. When we saw elementary circuits where the current was out of phase with its voltage, we stopped and doubled checked our work to that point.

Saying a 120/240V system was simply (2) 120V sources connected in additive series (like 2 batteries) never resulted in my having to justify my viewpoint. After hundreds of pages of discussion, the only reason I can see to say 120/240V is (2) 120V sources 180? out of phase is to explain the oscilloscope traces that occur when both voltages are viewed with the common point as a reference.

In my work today as a power systems engineer, I can not tell you the last time I "scoped" any neutral information. I work with individual line currents and line-line voltages. I know others are not as fortunate and must see exactly what is on the neutral, but I get to let the software calculate the neutral information so I hardly ever use neutral or ground as a reference point.

 

[rattus]

Easier than you think:

Easier than you think:

Jim, take another look; it is easier than you think.

 

[LarryFine]

The question is, "Are V1n and V2n 180 degrees out of phase?"

I say "no."

Use "n" for the common reference.

Why? To me, a center-tapped secondary is not "two sources."

True, it resembles two sources, just as looking at the two lines from the neutral resembles a 180-degree timing offest.

 

[mivey]

I'm up to date

I'm up to date

Following Rick's advice, I went back to square one.

From post #1:

...There is a single load resistor, so isn't there a single source current either flowing from 1->2 or from 2->1...

No. It is according to your frame of reference.

It is about relativity. See the relative voltages and currents below:

Arguing any different is like arguing power delivered vs power received. It depends which side of the circuit you are standing on. If you say current is only in the positive direction, you MUST have already picked a reference frame or you could not tell what was going on in the circuit.

From post #4

...The point I have tried to make is that what ever method is used to describe the voltages should not require an adjustment in order to describe the currents...

True. The signs are by definition. You haven't started one analysis and then started over with a different analysis when you cross the neutral point.

From post #6

...Draw the single loop current and the two sources. All I can see is that in a 2-wire node analysis what goes in to the node must come out the presence or absence of a voltage source doesn't change anything.

If you were standing on the node it would look different. When the electron was coming in, you would have to face one way to see it. When the electron leaves, you would have to face the other way to see it.

From post #14

Jim, I was wondering, would it help your discussion to look at Power calculations instead of just current?

You will find that there is power entering and leaving a point, even though the electrons did not make a u-turn. Current entering and leaving is analogous power absorbed or power supplied or to positive and negative.

From post #16

...or is it acceptable to have a resistive current "out of phase" with its voltage?...

No. In a correct circuit, it won't be because by definition it is not. See response to #1 above

From post #18:

...One of two things must occur when using your voltage definition, either the current flow through source Vbn suddenly changes direction

Assuming you are talking about a correct circuit, that is EXACTLY what happens when you cross the neutral point. Think about flying over the north pole. Heading in, you are flying in the north direction. When you cross the pole, you are headed south.

HERE IT IS CLASS...PAY ATTENTION: you just changed direction without making a u-turn because of the way north and south are DEFINED.

I'll say it another way: Drive over the North Pole with your GPS on your window and see if it indicates that you have changed direction.

From post #25

With the voltages as defined, there will be no current.

Exactly right. But, I did not catch anyone saying that was a legitimate circuit. If they did, tell me which post so I can review (this may be some of the stuff brought over from another thread).

From post #37:

I have been trying to point out the advantages and disadvantages of different presentations...Making an adjustment (i.e. so that the voltages seem correct) can lead to having to make other adjustments later...

If talking about corner vs neutral, other than the simple case where we could use the easier walk-through analysis instead of the more complex loop analysis, I don't see choosing the corner verses the neutral for a reference as having a permanent advantageous or disadvantageous label. I also don't want to have to keep adjusting things, but I don't see how choosing the neutral as reference makes me do that. I can't believe that's what you were saying so:

If you are talking about rattus trying to fix the sign error in the simple circuit, I agree. He should have fixed it before starting out.

Post #43 (mivey): This guy sounds like a genius :grin:

From Post #44

The +/- signs are like the polarity dots on a transformer, Not easy to change, and this seems to be a common misconception. If we did that, the two voltages would be IN phase, and there would be zero volts between them.

No. They were drawn in phase to start with (see post #9). It is not a useful circuit. The correct circuit would be to swap the + and - and leave the 180 degrees as shown.

also
From post #60

(discussing the meaning in the diagram way back in post #9)
...Thus the diagram is not self consistent.

Winnie caught that there was a problem. with the circuit diagram as labeled.

From Post #56

True,

Van = Vnb = 115V @ 0.

You are using different references for the two sources. Use "n" for the common

reference.

Agreed. What if your circuit needed +-1.5 volts and you could not find a negative battery (I'll sell you one for $50)? Tie two 1.5 volt batteries in series and use the midpoint as the reference = +- 1.5 volts (I believe Rick addresses this later and shows a nice battery graphic from another thread).

Post #59 (mivey): This guy sounds like an idiot :grin:

Post #62 (winnie): Loved it

From post #64

...
For the single resistor circuit you should have gotten:
Vbn = -115@180 = 115@0
Van = 115@0
vab = 0

That's correct. This circuit is not drawn to be a useful circuit. See my response to post #44.

...
For the complex circuit you should have gotten:
Vbn = -115@0 = 115@180
van = 115@0
vab = 230@0
...

Again Rick is correct. The polarity and angles are drawn correctly for this circuit.

From post #69

...That is clearly the intent of the originator of that sketch...

But instead of trying to make an incorrect diagram work, you should have fixed the diagram first. We are not going to cut anyone any slack here :grin:

From post #70Rick Christopherson) The simple diagram was flawed to start with. Trying to re-define it on the fly was a mistake. Rick said: "You, on the other hand, are trying to redefine the battery itself..." If that is what Rattus said in the other thread, he is wrong. The batteries on the left are yummy, the ones on the right are yucky.

From post #79

I believe this contradicts what you have stated previously, so I am reluctant to comment on this until a few other members have a chance to comment as well.

Without reading an entire other thread, it sounds like rattus got mixed up in a sign problem and didn't realize it. From his other statements here it would appear he knew what he INTENDED to say and tried to take a stand on what he THOUGHT he said instead of just fixing the original error.

 

[jim dungar]

Jim, take another look; it is easier than you think.

I didn't say it was hard to solve, just that it is a more complex circuit than I have done in years. I usually deal with currents, sometimes with voltages, and almost never with actual load elements (i.e. resistors).

When I deal with relaying CT's, using a fixed reference point rather than a fixed "signing" convention would make my life very complicated.

 

[mivey]

One man's East is another man's West

One man's East is another man's West

After hundreds of pages of discussion, the only reason I can see to say 120/240V is (2) 120V sources 180? out of phase is to explain the oscilloscope traces that occur when both voltages are viewed with the common point as a reference.

I'll be kind enough to tell you what happens. When you look on the scope and walk through the circuit, you will see the change in phase when you cross the neutral point. This is by definition, not some stroke of magic.

In the 12/24/48 ohm circuit you will notice 2 different voltages at the common point of the series resistors (call this point C). When there is a wire from n to C, C is forced to use the neutral point of the transformer. Without the wire, the neutral point backs up into the 24 ohm resistor. If you were to probe inside the resistor, you would find the current changes phase when you cross the neutral point. Again, this is by definition.

For those who did not read my previous post where Jim was talking about current changing direction, here is the most important part:

Assuming you are talking about a correct circuit, that is EXACTLY what happens when you cross the neutral point. Think about flying over the north pole. Heading in, you are flying in the north direction. When you cross the pole, you are headed south.

HERE IT IS CLASS...PAY ATTENTION: you just changed direction without making a u-turn because of the way north and south are DEFINED.

I'll say it another way: Drive over the North Pole with your GPS on your window and see if it indicates that you have changed direction.

 

[mivey]

I say "no."


Why? To me, a center-tapped secondary is not "two sources."

True, it resembles two sources, just as looking at the two lines from the neutral resembles a 180-degree timing offest.

No one is taking about a time difference. We've already mowed that grass.

They are, by definition, 180 degrees out of phase.

Why not use the neutral? If it can't be demonstrated that one method has VALUE over the other, then it is just a preference. Using a neutral for a reference is just as valid as using phase-phase. There are uses for both.

I see arguing over that is like arguing which phase of the lighting leg on the delta is the true reference point. It makes no difference.

Suppose you are reading the voltage on a 120/240 panel. There is value in reading L-G. There is value reading L-L. Read the buss to buss voltage and show me the value of using the black lead on the left vs the black lead on the right. That's the value of this argument.

 

[jim dungar]

Following Rick's advice, I went back to square one.

From post #1:
No. It is according to your frame of reference.

It is about relativity. See the relative voltages and currents below:

I think you are missing my point. How many currents flow through a 2-wire resistor?

At what point do your Coming and Going currents change direction? At what point do they become different currents?

What I see is: Coming is pointed to the right and Going is pointed to the right, so they are both in the same direction which means they are like my single source current flowing from 1->n->2 or from 2->n->1.

Also, you have changed the polarity markings on the voltage sources in your right hand column - not fair that is not the connection Rattus started with.

edit just noted issue with voltage

 

[mivey]

correction

correction

Also, you have changed the polarity markings on the voltage sources in your right hand column - not fair that is not the connection Rattus started with.

I just noticed as well and I had to fix the diagram, I had the polarity of the bottom right voltage backward.

 

[mivey]

Ol Blue

Ol Blue

I think you are missing my point. How many currents flow through a 2-wire resistor?

At what point do your Coming and Going currents change direction? At what point do they become different currents?

What I see is: Coming is pointed to the right and Going is pointed to the right, so they are both in the same direction which means they are like my single source current flowing from 1->n->2 or from 2->n->1.

I think you missed my point. There is only one current. There is only one airplane flying over the north pole.

They will change direction when they cross the neutral point because of the way we have defined direction.

The way you are seeing it is as if you were removed from the node of the neutral point. Think about the definition for a minute, I know you can get this. Let me give another illustration.

An old southern boy is sitting on his porch watching the cars go by. So is his neighbor down the street. He sees the headlights of a car approaching. He thinks "that car is coming". When the car passes by, and he sees the tail-lights he thinks "that car is going".

The neighbor has been watching the car too but the car hasn't quite reached their house yet. The neighbor down the street thinks "that car was coming, and its still coming". The car has not done anything different, we just have two different definitions of direction.

Ol Blue thinks we are stupid for watching the cars when we could be chasing them.

Now I'm just a dumb old southern boy but that's about a plain of a definition of direction as it gets.

[edit: spelling]

 

[jim dungar]

I think you missed my point. There is only one current. There is only one airplane flying over the north pole.

They will change direction when they cross the neutral point because of the way we have defined direction.

The way you are seeing it is as if you were removed from the node of the neutral point. Think about the definition for a minute, I know you can get this.[edit: spelling]

This has been a civil discussion, please do not get condescending.

If you are standing at the north pole and see an airplane coming towards you, you would say it is moving foward. Once the plane passes over you and is headed away, do you say the plane has changed directions and is now moving backwards?

 

[rattus]

With the voltages as defined, there will be no current. Write the loop equation:

115V@180? + 115V@0? = I2?100ohm

115V@180? = -115V@0?

-115V@0? + 115V@0? = I2?100ohm

0V = I2?100ohm

I2 = 0A

jgrhist, Perhaps I seen your reasoning here. The original diagram specified 115V @ 0 for each source which clearly indicates voltage at + relative to -. Now since these marks are tantamount to polarity marks, they cannot change. It is a matter of wiring.

The sources are assumed to be identical, especially since they represent two halves of a CT secondary. But now one is labeled, 115V @ 180 which I take to mean Vbn. If you assume it means Vnb, then Vab would indeed be zero.

Blame it on an incomplete diagram which should clearly specify the reference point.

 

[mivey]

This has been a civil discussion, please do not get condescending.

If you are standing at the north pole and see an airplane coming towards you, you would say it is moving foward. Once the plane passes over you and is headed away, do you say the plane has changed directions and is now moving backwards?

Did not mean to be, although it sounds like it. Too bad what we type can read different.

Let me re-phrase: I know you are very knowledgeable. I have read a lot of your posts and you are no dummy. As a matter of fact, I think you are among the smartest here. You seem to be a level-headed individual. If I could express what I'm trying to say in the right way, I know you could see where I'm coming from. Your response indicated you did not get what I said at all. I am trying to think of a better way to put it but I ask that you try to think about what I'm saying to see if you can understand my point. From the posts I've read, I don't ever recall you being stubborn.

I don't think you missed my point because you are dumb or stubborn. I just can't seem to figure out a way to explain myself so you can see it. Don't just take what I'm saying in words and say it isn't right. Think about what I'm saying and see if you can see where I'm coming from. I know you have this ability.

[edit: typo]

 

[mivey]

seat belts please

seat belts please

If you are standing at the north pole and see an airplane coming towards you, you would say it is moving foward. Once the plane passes over you and is headed away, do you say the plane has changed directions and is now moving backwards?

When the plane is coming towards me, I would say it is coming towards me. Once it passes by, I would say it is heading away.

A person standing futher away would either say the plane has been coming towards them the whole time, or has been heading away the whole time, depending on their location.

 

[mivey]

Tail no tails

Tail no tails

Let me try this way. Suppose an electron had some kind of tail-wind, like a comet. If we stand at a point and see the leading side of the electron, we are going to call that positive flow. If we see the tail of the electron, we are going to say that is negative flow.

When the electron flies by us, it by definition, has changed from a positve flow electron to a negative flow electron.

The electron notices no change. The person standing way away from us notices no change.

I see it as a relativity issue.

 

[mivey]

Do you hear what I hear

Do you hear what I hear

How about an engineering example (train engineer that is). I hope this is a good example.

The doppler effect: The train horns blows. The sound wave is different depending on whether the train is coming or going. It all sounds the same to the conductor.

 

[Rick Christopherson]

I'm kind of disappointed with this turn of events today. This discussion has been moving forward in a logical and progressive fashion, but suddenly we need to rehash previously resolved issues because someone returns from out of town. The waters have gotten so muddy all of a sudden that it isn't even clear what the discussion is supposed to be about. We've gone from almost having this resolved, to suddenly talking about the North Pole.

In one fell swoop, we lost the continuity of this discussion. I don't know about anyone else, but I feel we have just wasted 3 days worth of work and are starting all over again, throwing away any progress previously made.

 

[LarryFine]

Why not use the neutral? If it can't be demonstrated that one method has VALUE over the other, then it is just a preference. Using a neutral for a reference is just as valid as using phase-phase. There are uses for both.

I see arguing over that is like arguing which phase of the lighting leg on the delta is the true reference point. It makes no difference.

Suppose you are reading the voltage on a 120/240 panel. There is value in reading L-G. There is value reading L-L. Read the buss to buss voltage and show me the value of using the black lead on the left vs the black lead on the right. That's the value of this argument.

I absolutely agree with all of this.

 

[mivey]

muddy waters

muddy waters

...The waters have gotten so muddy all of a sudden that it isn't even clear what the discussion is supposed to be about...

The idea that the current all of a sudden becomes "out of phase" with the voltage was part of the OP.

From post #1:

...are you saying that the current flowing into a source is always out of phase with the source?

There is a single load resistor, so isn't there a single source current either flowing from 1->2 or from 2->1...

As far as I can tell, it appears to be one of the only remaining unresolved issues. As far as I can tell (it is hard to understand what someone knows), rattus understands that the phase shift happens when crossing the neutral point (the midpoint of the resistor), Jim does not. The north pole was an attempt at explaining that.

...previously resolved issues...almost having this resolved...starting all over again, throwing away any progress previously made...

rattus appears to have made progress and he & Jim were the original players in this thread. He now realizes the mistake pointed out in post #25 (2 days earlier). This was not "resolved" until now.

from post #92

jgrhist, Perhaps I seen your reasoning here. The original diagram specified 115V @ 0 for each source which clearly indicates voltage at + relative to -. Now since these marks are tantamount to polarity marks, they cannot change. It is a matter of wiring.

The sources are assumed to be identical, especially since they represent two halves of a CT secondary. But now one is labeled, 115V @ 180 which I take to mean Vbn. If you assume it means Vnb, then Vab would indeed be zero.

Blame it on an incomplete diagram which should clearly specify the reference point.

[edit: spelling]

 

[Rick Christopherson]

... rattus understands that the phase shift happens when crossing the neutral point (the midpoint of the resistor), Jim does not.

The respondents in this thread include some of the best minds that this forum has to offer. I think a little more humility is in order here. You walked into this discussion after 3 days absence, and by your own admission, you hadn't fully read it until tonight, but you want to suggest that the existing participants don't understand what we have already discussed in your absence?

I think it is extremely short sighted on your part to suggest that Jim does not understand power systems, when this is his primary area of focus.