Why is residential wiring known as single phase?

[Rick Christopherson]

Adding or subtracting as the case may be yields a phasor (complex number) with the correct magnitude and phase angle. It is nonsense to claim otherwise.

I see that you blew off the answer. So which is it, C or D?

Please explain how your method of subtracting vectors tail-to-tail provides a direction? You stated it. You defend it.

You keep on making false statements, and then never defend them when they are contended. That is dishonest. It would be refreshing to have an honest debate.

 

[Rick Christopherson]

Maybe you could demonstrate by telling us how we get 208V from a 120V wye? Do we reverse one of the phasor arrows, no we can't do that because that would amount to subtraction!

Duh! It does require subtraction using your common node reference. Please show us how it doesn't? Please show us how the two vectors drawn tail-to-tail provide an answer with direction? I already gave you the picture. Instead of the vectors being 90 degrees apart, treat them as 120 degrees apart.

Please tell us how this voodoo vector math of yours works with a tail-to-tail vector?

 

[rattus]

No one has told me yet how sin(wt) can be in phase with [-sin(wt)]. We can plot the two sinusoids and the same sheet of graph paper, and the plots will be perfect inverses of each other.

I don't see how anyone who has passed trig can claim that these two waves are in phase.

Their positive peaks do not coincide and that is one of the criteria to be in phase. If they were in phase the plots would follow the same locus. They do not. I have already posted this requirement.

I am waiting.

 

[Rick Christopherson]

I am waiting.

I see that you are back in "Deflection Mode". Weren't you talking about phasors and vectors just 8 minutes ago?

When someone contests something you say and you have no response for it, you quickly change the subject to something else to deflect away from the topic.

It would be refreshing to have an honest debate.

 

[rattus]

Duh! It does require subtraction using your common node reference. Please show us how it doesn't? Please show us how the two vectors drawn tail-to-tail provide an answer with direction? I already gave you the picture. Instead of the vectors being 90 degrees apart, treat them as 120 degrees apart.

Please tell us how this voodoo vector math of yours works with a tail-to-tail vector?

Glad you asked.

Let Van = 120Vrms @ 0 = 120V + j0
Let Vbn = 120Vrms @ -120 = -60 -j104
Subtracting Vbn 60 +J104
Vab = 180 +j104 = 208V @ 30

 

[Rick Christopherson]

Glad you asked.

Let Van = 120Vrms @ 0 = 120V + j0
Let Vbn = 120Vrms @ -120 = -60 -j104
Subtracting Vbn 60 +J104
Vab = 180 +j104 = 208V @ 30

How does that support your "tail-to-tail" vector math? :dunce:

 

[Rick Christopherson]

Rattus, You are apparently an expert in this tail-to-tail voodoo vector math, so it should be a simple question for someone with your great wisdom. What is the resultant vector of the tail-to-tail subtraction for A and B? Is it C or is it D?

 

[gar]

120319-2012 EDT

In the "Analysis of A-C Circuits", by M. B. Stout, 1952, on page 121 he draws the phasor diagram for a three phase Y generator and uses all tails at the neutral for the three line to neutral voltages. Then separately phase rotation is used to determine the direction of the line-to-line voltage.

It does make sense to have all the line-to-neutral vectors originating from a single point, and then everything fits in a nice symmetrical pattern. A priori knowledge is used to know how to process the vectors.

In another book I looked at the the same procedure is used as Stout used.

.

 

[rattus]

How does that support your "tail-to-tail" vector math? :dunce:

Well, the two phasors are taken from the usual wye diagram, three arrows, joined at their tails. As far as the direction, that should be evident from the expression:

Vab = 208Vrms @ 30 degrees

I could have subtracted Va from Vb to obtain:

Vba = 208Vrms @ -150 degrees

 

[roger]

Ok guys, you've got competition now.

http://now.msn.com/entertainment/0319-funny-mph-video.aspx



BTW Iwire, you weren't even close.

Roger

 

[Rick Christopherson]

A priori knowledge is used to know how to process the vectors.

Gar, my question above did not have your name in it, did it? If you insist on poking your nose into this, then either answer the question posed to Rattus, or get out of the way. Your obfuscation of the topic at hand is not welcome. Rattus is more than capable of deflecting the topic on his own. He brought the topic up. He can defend it.

 

[roger]

Gar, my question above did not have your name in it, did it? If you insist on poking your nose into this, then either answer the question posed to Rattus, or get out of the way. Your obfuscation of the topic at hand is not welcome. Rattus is more than capable of deflecting the topic on his own. He brought the topic up. He can defend it.

Rick, in case you haven't noticed let me point out that this is an open forum, loose the attitude.

Roger

 

[Rick Christopherson]

Well, the two phasors are taken from the usual wye diagram, three arrows, joined at their tails. As far as the direction, that should be evident from the expression:

Vab = 208Vrms @ 30 degrees

I could have subtracted Va from Vb to obtain:

Vba = 208Vrms @ -150 degrees

But that's not how vector math works. Vector math is a graphical solution, and it stands on its own. Your statement that tail-to-tail represents subtraction is false, and you cannot defend it, can you?

 

[rattus]

Well, the two phasors are taken from the usual wye diagram, three arrows, joined at their tails. As far as the direction, that should be evident from the expression:

Vab = 208Vrms @ 30 degrees

I could have subtracted Va from Vb to obtain:

Vba = 208Vrms @ -150 degrees

BTW, the secondaries in a wye diagram are joined at the neutral, so the tail represents the neutral, and the heads represent the L-N voltages.

 

[rattus]

But that's not how vector math works. Vector math is a graphical solution, and it stands on its own. Your statement that tail-to-tail represents subtraction is false, and you cannot defend it, can you?

Well, it works for me. Phasors are complex numbers with a magnitude and phase angle. One can work through the math without ever drawing a diagram. If one wishes, one can draw a diagram to help the thought process, or one can draw a precise diagram and solve the problem graphically if one does not know the math.

There is nothing to defend. I have already demonstrated how it works. Maybe you should bone up on phasors before you say anything else.

 

[Rick Christopherson]

Well which is it? You originally said "tail-to-tail", which is a graphical representation. Now you're claiming that you don't use a graphical representation? How are we supposed to figure out the truths of what you claim when you aren't even sure of them yourself?

The math you just showed above is not representative of your alleged tail-to-tail subtraction. You actually did an inversion, which negated the very original inversion you created by choosing V_bn over V_nb. As much as you want to claim that you are using V_bn, you are actually using V_nb. If you can't keep this straight, how can we?

 

[__dan]

BTW, how are you coming on proving that a sine and its inverse are of the same phase? Frankly, I don't know how to do it.

You are claiming that two identical windings, wound on the same core, forced by the same shared flux, output voltages that are out of phase.

If the phase shift is not caused by these facts, what does cause the effect you are claiming?

 

[rattus]

You are claiming that two identical windings, wound on the same core, forced by the same shared flux, output voltages that are out of phase.

If the phase shift is not caused by these facts, what does cause the effect you are claiming?

dan, there is no mention of a transformer, windings, flux, or anything else electrical in the question. It is purely mathematical.

Who can prove that sin(wt) and [-sin(wt)] are in phase??

If you can't prove it say so. I can't prove it either.

 

[__dan]

120319-0841 EDT

Jim:

With two terminals (two wires) we have a single phase, call it phase A if you want (the naming use of phase).

Within the waveform of this phase we can make measurements of how far one point on the wave is with respect to another point in phase displacement units along the phase axis.

When there are more than two terminals, then more than one phase exists to provide names to identify these different sources.

Two or more of these phases might be identical and thus their waveforms would exactly coincide with each other. These phases would be described as "in-phase" or "same phase".

By general usage waveforms that are identical except for an amplitude difference are also described as "in-phase". Note amplitude is only a positive number.

When waveforms that share the same period (frequency) are different in shape, then there has to be a definition of what point on each waveform is the reference point for making comparisons between the waveforms. When comparing two sine waves one might pick the positive peak, and a sine wave with a sawtooth also might use the positive peak of each. Also the positive slope zero crossing is a popular choice. A sine wave compared to a square wave would most certainly use a defined slope and zero crossing because there is no unique maximum positive point for the square wave.

In normal usage, as we have shown in many different references, a sine wave and its inverse or 180 degree shifted wave are not "in-phase" or of the "same phase".

Anyone that is really familiar with circuit analysis will not classify V_AN and V_BN of a center tapped secondary as being "in-phase".

.

Gar;

Your analysis subdivides the wave in time. The time division example uses the same reference point for time but uses a different, opposite reference point relative to the winding turn direction, which is homogeneous on the same core. A salient fact to omit.

Take the instantaneous case and subdivide the winding, not the waveform. This analysis yields the fact that a measurement between any two points on the winding is a perfect fractal of the whole, an exact copy that differs only in amplitude. As you state above, any two points on the winding are "in phase". Voltage and current are instantaneous between any two points on the winding or between any three points, or between any infinte sample and combination of points on the winding. The phase does not shift, there is no propagation delay from one part of the winding to the other, in the scale of time used for practical applications, the effect is instantaneous with no time delay.

It is confusing to claim or instruct otherwise.

 

[__dan]

dan, there is no mention of a transformer, windings, flux, or anything else electrical in the question. It is purely mathematical.

Who can prove that sin(wt) and [-sin(wt)] are in phase??

If you can't prove it say so. I can't prove it either.

And where does the -sin(wt) come from. Is it because the leads are reversed relative to the other windings turn direction or is it caused by the magic voltage genie?

No mention of transformer in the last 2300+ posts ... That's hilarious.