Battle of the Phases

[quogueelectric]

The sarchasm has come to a halt on my part. I can only express my opinion I cannot force someone who is claiming to be an engineer and is completely eluding the fact that a 4 wire delta delivery system does commonly exist. That same person was the one who in fact brought it up. The original post was on what I percieved to be a pole mount single phase center tapped transformer which cannot possibly be out of phase with itself that is why it is called a SINGLE phase transformer. If you are measuring voltage from different points in the winding and reversing the leads of course you can get the tester to read anything you want to. I believe the problem is that he is getting voltage vectors confused with actual phase angles of the transformer. None of the arguments that I have seen to the contrary hold any water in my opinion. This is about as professional as I can say it.

 

[dbuckley]

Not quite. There must be a time difference between positive (or negative) peaks. There are two zero crossings per cycle which may lead one to a false conclusion.

Negation of a sinusoid is equivalent to a 180 degree phase shift.

One doesn't use peaks for this, as if one does there is an assumption that there is only one peak per halfcycle. Phase and polarity both have application outside of sine waves. Hence the use of the zero crossing. Albeit it did omit to point out the zero crosses must be in the same direction...

But, once again, if there is no time difference between the point at which the waveforms cross zero, then there is no phase difference, and without phase difference you cant have any degrees of shift.

You're turning the argument upside down, by saying there is polarity inversion, and then by magic that can be converted into 180 degrees of phase shift. It can't, as by definition, there is no phase shift, so you cant make 180 degrees of it appear.

We did all this stuff in the audio world eons ago, I thought everyone knew this stuff...

 

[mivey]

This must be the 99th time I have tried to get this point across.

Now Don, I know your thoughts, but no one is claiming this to be a two phase system. It is simply a matter of the reference point. Put a scope on L1 and L2 and you see one sinusoid is the negative of the other. That does not constitute a 2-phase system. What you see is what you get--a phase difference.

V1n and V2n are NOT the same voltage even if they appear on a common, center tapped winding. In computer simulations one would model them as separate AC sources.

100 and counting

 

[mivey]

One doesn't use peaks for this, as if one does there is an assumption that there is only one peak per halfcycle. Phase and polarity both have application outside of sine waves. Hence the use of the zero crossing. Albeit it did omit to point out the zero crosses must be in the same direction...

But, once again, if there is no time difference between the point at which the waveforms cross zero, then there is no phase difference, and without phase difference you cant have any degrees of shift.

You're turning the argument upside down, by saying there is polarity inversion, and then by magic that can be converted into 180 degrees of phase shift. It can't, as by definition, there is no phase shift, so you cant make 180 degrees of it appear.

We did all this stuff in the audio world eons ago, I thought everyone knew this stuff...

Refresh my memory as I can't find it right now but, by convention, isn't the phase angle defined to be zero at the point in time where the wave goes from negative to positive? If so, don't the two voltages V1 and V2 (relative to the neutral) have a 180 degree difference?

 

[rattus]

But there is:

But there is:

One doesn't use peaks for this, as if one does there is an assumption that there is only one peak per halfcycle. Phase and polarity both have application outside of sine waves. Hence the use of the zero crossing. Albeit it did omit to point out the zero crosses must be in the same direction...

But, once again, if there is no time difference between the point at which the waveforms cross zero, then there is no phase difference, and without phase difference you cant have any degrees of shift.

You're turning the argument upside down, by saying there is polarity inversion, and then by magic that can be converted into 180 degrees of phase shift. It can't, as by definition, there is no phase shift, so you cant make 180 degrees of it appear.

We did all this stuff in the audio world eons ago, I thought everyone knew this stuff...

I can't follow this argument at all because there IS a time difference between the + zero crossings. That time is T/2, and that looks like 180 degrees to me. This applies to any like points on the waves--peaks, valleys, + crossings, - crossings, etc., etc., etc.

Furthermore, it can be shown by trigonometric identities that

sin(wt +/- 180) = - sin(wt)

But, we already knew that.

Nope, that dog won't hunt!

 

[mivey]

Charlie B.

Thanks for the reality check. I don't see what personal attacks have to do with anything. I would rather listen to what someone has to say than spend time reading the credentials lining their walls. If what someone says reveals that they are a dummy, it is not good form to call them a dummy. The smart ones will know who is who. We can't all be geniuses.

The dumbest of us (include me if you like) can be right and the smartest can be wrong. It may not even be right or wrong but like you said earlier, a matter of viewpoint.

I personally like the cerebral stimulation. It may even make me smarter.

 

[mivey]

I can't follow this argument at all because there IS a time difference between the + zero crossings. That time is T/2, and that looks like 180 degrees to me. This applies to any like points on the waves--peaks, valleys, + crossings, - crossings, etc., etc., etc.

Furthermore, it can be shown by trigonometric identities that

sin(wt +/- 180) = - sin(wt)

But, we already knew that.

Nope, that dog won't hunt!

I agree. I see the time difference as well which leads to the 180 degree difference when using the neutral as the reference. The math shows it. The circuit simulator shows it. The graph shows it.

The degree difference is in the math and math is the universal language. Maybe it is the english wording that is causing the problem.

 

[mivey]

I agree. I see the time difference as well which leads to the 180 degree difference when using the neutral as the reference. The math shows it. The circuit simulator shows it. The graph shows it.

The degree difference is in the math and math is the universal language. Maybe it is the english wording that is causing the problem.

As seen here: [edit: The graphs are SinΘ, -SinΘ, and Sin(Θ+pi)]

View attachment 1278

and here: [edit: The graphs are SinΘ+Sin3Θ, -SinΘ-Sin3Θ, and Sin(Θ+pi)+Sin(3Θ+pi)]
[edit AGAIN: this should have read SinΘ+Sin2Θ, -SinΘ-Sin2Θ, and Sin(Θ+pi)+Sin(2Θ+pi)]

View attachment 1279

 

[rattus]

101 and counting:

101 and counting:

The sarchasm has come to a halt on my part. I can only express my opinion I cannot force someone who is claiming to be an engineer and is completely eluding the fact that a 4 wire delta delivery system does commonly exist. That same person was the one who in fact brought it up. The original post was on what I percieved to be a pole mount single phase center tapped transformer which cannot possibly be out of phase with itself that is why it is called a SINGLE phase transformer. If you are measuring voltage from different points in the winding and reversing the leads of course you can get the tester to read anything you want to. I believe the problem is that he is getting voltage vectors confused with actual phase angles of the transformer. None of the arguments that I have seen to the contrary hold any water in my opinion. This is about as professional as I can say it.

quogue,

First, I can't see that a 4-wire delta system has anything to do with this discussion.

Second, it is well established that we are talking single phase.

Third, I am glad you mentioned "vectors", although that term is obsolete. The preference today is "phasors".

Fourth, forget the transformer and just measure V1n and V2n at the single phase panel. We measure V1n from lug L1 to the neutral bus, and we measure V2n from lug L2 to the neutral bus. We would use a scope so we can visualize the phase difference.

We can describe these two voltages with static phasors,

V1n = 120 @ 0
V2n = 120 @ 180

Clearly there is a 180 degree phase difference.

In summary,

V1n and V2n are NOT the same voltage, they may even differ in magnitude a bit. It matters not that they come from the same transformer.

These two voltages, being defined relative to the neutral bus, exhibit a phase difference of 180 degrees. It is absolutely correct to describe them this way.

 

[mivey]

I just noticed these two graphs of:

SinΘ+Sin2Θ,-SinΘ-Sin2Θ,Sin(Θ+pi)+Sin(2Θ+2pi)
View attachment 1280

and

SinΘ+Sin3Θ,-SinΘ-Sin3Θ,Sin(Θ+pi)+Sin(3Θ+3pi)
View attachment 1281

Now what is this telling me? I'm not sure yet.

 

[mivey]

My post #48 had the graph labeled wrong, as I actually plotted 2Θ instead of 3Θ. I edited the post.

 

[rattus]

101 and counting:

101 and counting:

The sarchasm has come to a halt on my part. I can only express my opinion I cannot force someone who is claiming to be an engineer and is completely eluding the fact that a 4 wire delta delivery system does commonly exist. That same person was the one who in fact brought it up. The original post was on what I percieved to be a pole mount single phase center tapped transformer which cannot possibly be out of phase with itself that is why it is called a SINGLE phase transformer. If you are measuring voltage from different points in the winding and reversing the leads of course you can get the tester to read anything you want to. I believe the problem is that he is getting voltage vectors confused with actual phase angles of the transformer. None of the arguments that I have seen to the contrary hold any water in my opinion. This is about as professional as I can say it.

quogue,

First, I can't see that a 4-wire delta system has anything to do with this discussion.

Second, it is well established that we are talking single phase.

Third, I am glad you mentioned "vectors", although that term is obsolete. The preference today is "phasors".

Fourth, forget the transformer and just measure V1n and V2n at the single phase panel. We measure V1n from lug L1 to the neutral bus, and we measure V2n from lug L2 to the neutral bus. We would use a scope so we can visualize the phase difference.

We can describe these two voltages with static phasors,

V1n = 120 @ 0
V2n = 120 @ 180

Clearly there is a 180 degree phase difference.

In summary,

V1n and V2n are NOT the same voltage, they may even differ in magnitude a bit. It matters not that they come from the same transformer.

These two voltages, being defined relative to the neutral bus, exhibit a phase difference of 180 degrees. It is absolutely correct to describe them this way.

 

[bcorbin]

Third, I am glad you mentioned "vectors", although that term is obsolete. The preference today is "phasors".

Please stop with the blanket generalizations. Just because you prefer to use phasors (since you have a misguided belief that a phasor can only have a positive magnitude) doesn't mean that's the only legitimate way to approach the problem.

 

[mivey]

rattus,

This may muddy the water and add to your "I've already said we are only talking about single-phase" count (101 being the latest?) but we are in the "battle of the phases" thread (do you think iwire named it that for sport?) so here's the question:

In Fitzgerald's "Electric Machinery" 5th edition appendix A-5 he states: "Four-phase systems are obtained from three-phase systems by means of special transformer connections" . This indicates that an x-phase system can use transformer connections to create an X+1 phase system. He shows a diagram of transformers in the shape of a cross and states that one quadrant is a 2-phase system. Have anyone ever seen the details on how the primary windings are connected and what kind of transformers were use?

Also, for the delta-neutral record, he states in A-1: "In the delta connection (Fig. A-5b), no neutral exists and only a three-wire three-phase system can be formed."

 

[rattus]

What?

What?

Please stop with the blanket generalizations. Just because you prefer to use phasors (since you have a misguided belief that a phasor can only have a positive magnitude) doesn't mean that's the only legitimate way to approach the problem.

Not misguided at all. The word, "magnitude", always indicates a positive value. The polar form of a phasor includes a magnitude and phase angle. If you negate the phasor, the magnitude is still positive, but you have shifted the phase angle by 180 degrees.

I don't see where you got this notion, but no one claims this is the only way to approach the problem, but since quogue brought it up, I thought it would be appropriate. It is however a classy approach.

Now, can you point out any fault in my example??

 

[rattus]

rattus,

This may muddy the water and add to your "I've already said we are only talking about single-phase" count (101 being the latest?) but we are in the "battle of the phases" thread (do you think iwire named it that for sport?) so here's the question:

In Fitzgerald's "Electric Machinery" 5th edition appendix A-5 he states: "Four-phase systems are obtained from three-phase systems by means of special transformer connections" . This indicates that an x-phase system can use transformer connections to create an X+1 phase system. He shows a diagram of transformers in the shape of a cross and states that one quadrant is a 2-phase system. Have anyone ever seen the details on how the primary windings are connected and what kind of transformers were use?

Also, for the delta-neutral record, he states in A-1: "In the delta connection (Fig. A-5b), no neutral exists and only a three-wire three-phase system can be formed."

The Scott T connection provides two phases from three. However, I would still consider this a two-phase system because additional "phases" obtained by inversion do not count as phases. Yes, you may have four phase angles but not four phases.

 

[Rick Christopherson]

.... forget the transformer and just measure V1n and V2n ...

Yeah, let's forget the key facts when they don't fit. Let's forget that both sources are actually coming from the same physical device. Because if we do this, then we can arbitrarily change the phase of one source relative to the other. Afterall, it is common practice by real engineers to arbitrarily change phase instead of using a minus sign.

 

[mivey]

...but not four phases.

Fitzgerald's terminology, not mine but I wouldn't stress over it either way.

I understand what is meant either way, and understanding what is meant is the root of communication.

 

[mivey]

...by real engineers...

How does this add to the value of what you are saying? Saying things like this does not increase one's stature; probably the opposite. Say what YOU believe. Don't try to be a spokesperson for the rest of the world.

 

[mivey]

How does this add to the value of what you are saying? Saying things like this does not increase one's stature; probably the opposite. Say what YOU believe. Don't try to be a spokesperson for the rest of the world.

By the way, who says engineers (real or fake) know everything anyway?