Is it Single or Two Phase?

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websparky said:
EVERYONE PLEASE READ SCOTT'S POST AND STUDY IT
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Oh, big deal. I said everything he said, just with fewer words. He's just showing off. (Kidding! I'm kidding!)

Seriously, it's in line with my and most others' opinions. I don't have an engineering background, so I can't post the math. I just understand how it works.
 
rattus said:
Yes, add any two 120V wye phasors and see what you get. For example, add 120V @ -30 to 120V @ -150. Show a little detail please.
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Okay, but I'm going to have to draw it out and scan and post it. Standby.
 
Ok, there is a 180 degree difference in phase if measuring voltage from the two lines of the 120/240V 1ph-3wire system with reference to the center-tap. (We all know that :)

But, how was the jump made to calling that two-phase? I think some are putting down the 180 degree difference in phase thing, just to defend this being single-phase. Which it is.

Been there, argued that, I'm going home to have a beer...
 
engy said:
Ok, there is a 180 degree difference in phase if measuring voltage from the two lines of the 120/240V 1ph-3wire system with reference to the center-tap. (We all know that :)

But, how was the jump made to calling that two-phase? I think some are putting down the 180 degree difference in phase thing, just to defend this being single-phase. Which it is.

Been there, argued that, I'm going home to have a beer...
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Thank you Engy. We should all know that, but apparently some do not. Now for the umpteenth time, I am NOT calling this a two-phase system. I am merely using phasors to compute the voltage between L1 & L2.
 
You guys still have it wrong. If you are using the center tap as your reference, you have one current coming in, and one going out. Current goes from high voltage to low voltage. Therefore, you have 120V at whatever your reference angle is, and -120V at exactly the same reference angle. There never was, is, or will be a phase shift involved in this.
 
Mathematics Anyone?

Mathematics Anyone?

Maybe if you go at this from the mathematics point of view (I know; seriously warped) it would help.

Single phase is single phase because any voltage available can be made from a linear combination of any other voltage available. A linear combination is a sum of a real constant time each value and summed together. So in the simplest, -120V = -1 * 120V. Hence they can all be formed from the same vector times a real constant.

With two phases of a wye, you cannot create any arbitrary new phase because they are not an orthogonal set. If you have two phases separated by 90 degrees, this is an orthogonal set and you can create any new phasor as a linear sum of the two phasors in the set.

Now take three phases of a wye; lets say 0, 120, and 240 degrees. If we multiply the 120 degree phasor by X/2 and the 240 degree phasor by -X/2 the rusultant phasor is of magnitude X at an angle of 90 degrees (orthogonal to the phasor at 0 degrees). So the 3 phasors can be said to be equivalent to an orthogonal pair.

My point is that things become independent, recognizable phases when they cannot be formed from a linear combination of other existing phases. In rectifier technology, "12 phase" transformers are common, but there are really only 3 phases available, with the others formed as taps (linear combinations) of these 3 phases. This is because the 3 phases form an orthogonal set and any more combinations are nothing new.

If that doesn't give you a headache, nothing will.

Mark
 
scott thompson said:
Time For A Monkey Wrench To Be Tossed in!!!

(this may have been mentioned already, so if it has, I'm sorry for the redundancy!)
Example Secondary Configuration:

3? 4W Wye (3 Phase 4 Wire Wye) - 208Y/120V

3 Ungrounded Conductors - derived from Secondary Terminal Bushings "X1" of each 1 Phase 2 Wire Winding (terminals viewed as "X2" on left, "X1" on right).
Call these Lines "A", "B" and "C".
Common Grounded Conductor derived from tapping into the "Series Jumper" which bonds all 3 of the remaining "X2" terminal bushings together.
Call this "N"

[i[just setting things up for pseudo suspence![/i]

Am I completely out of my mind, if I was to refer to the following loads connections to be supplied by a Polyphase Circuit?:

Load = 12 Ohm Resistor, between Line "A" and "N",
Load = 12 Ohm Resistor, between Line "B" and "N",
Load = 20.8 Ohm Resistor, between Line "A" and Line "B"

Do I have a 3 Phase 3 Wire Circuit here???
Would this be considered an "Open Wye"?

Think this one through a bit before replying!
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OK, I thought about it for a bit, and no other takers (unless someone jumps on it while I'm typing)...

Am I completely out of my mind, if I was to refer to the following loads connections to be supplied by a Polyphase Circuit?
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No, not completely :eek:

For the portion that's still rational, resistors come in many forms and not all go by the name of "resistor". A heating element, an incandescent lamp are two such examples. I have even connected some very large wire-wound Resistors (on 480VAC though; don't ask me the purpose as I didn't design the equipment... but I do know they were in a multi-VFD cabinet).

Anyway, until you specify the purpose of the loads, we cannot determine what portion of your mind is still rational :D

Do I have a 3 Phase 3 Wire Circuit here???
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If you meant by your earlier remark these three loads are to be supplied by three wires: 1) The conventional answer is no. 2) The cosmic answer is yes. In anticipation: I'm definitely not going to explain either remark. If you (i.e. anyone) disagree in part or whole that is your prerogative, and I ask you to reconsider.

Would this be considered an "Open Wye"?
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Well, first off that would depend on who or what body of who's is doing the considering. :rolleyes:

If you're suggesting in some zany manner this to be a wye version of "Open Delta", your remaining rationale is borderline... ;)
 
bcorbin said:
You guys still have it wrong. If you are using the center tap as your reference, you have one current coming in, and one going out. Current goes from high voltage to low voltage. Therefore, you have 120V at whatever your reference angle is, and -120V at exactly the same reference angle. There never was, is, or will be a phase shift involved in this.
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BC,

You have not answered my challenge. Tell me why the inverse of a sinusoid is not equivalent to a 180 degree phase shift. Go ahead, give us a phasor diagram showing V1n and V2n and tell us they are in phase.

Until you provide a reference or some reasoning, your claims are not supportable. If you can't do this, then you lose this argument by default.
 
Me, trying again with different words:

For a _single frequency_ sine function, a phase shift of 180 degrees _cannot_ be distinguished from an inversion of that sine function.

sin(omega + pi) = -sin(omega)

For a _single frequency_ sine function, a phase shift of 180 degrees has zero crossings in exactly the same places as an inversion of that sine function.

For a single center tapped transformer coil, it simply _does not matter_ if you _say_ that you have a sine function and its inverted output, or you _say_ a sine function and its 180 degree phase shifted output; it is still a _single phase_ system because there is no time offset in the zero crossings and no ability to derive any of the other phase angles without some form of energy storage.

However if you extend your analysis to systems that are not limited to pure single frequency sinusoidal output, then you _may_ find differences between a 180 degree phase shift and an inversion. For example: -{sin(omega)+sin(2omega)} != {sin(omega + pi) + sin(2omega + pi)}

-Jon
 
Fighting windmills:

Fighting windmills:

Winnie just said, I think, that inverting a sinusoid results in a 180 degree phase shift. However, BC and others have this hangup about calling it a phase shift.

I have just consulted with four of my peers who agree with me. Four of us are degreed engineers while the fourth has no degree but is the smartest man I know, and he has a stack of patents. The five of us represent over 200 years of experience collectively.

Like Archie Bunker's lawyer said, "You can't argue with a station wagon full of nuns"! You shouldn't argue with a passel of old engineers either.

BC, you are outvoted!

It is still a single-phase system though.
 
Rattus,

I was not quite saying that the inversion of a sine wave _results_ in a phase shift.

What I was saying was that an inverted pure sine wave cannot be _distinguished_ from a 180 degree phase shifted sine wave.

I further added that _inversion_ can be distinguished from 180 degree phase shift when you don't have pure sine waves.

As Scott said, the opposite outputs of a single phase transformer are mutually inverted, _not_ phase shifted.

But if the output is a _pure_ sine function, you couldn't tell the output from one with a phase shift.

-Jon
 
winnie said:
Rattus,

I was not quite saying that the inversion of a sine wave _results_ in a phase shift.

What I was saying was that an inverted pure sine wave cannot be _distinguished_ from a 180 degree phase shifted sine wave.

I further added that _inversion_ can be distinguished from 180 degree phase shift when you don't have pure sine waves.

As Scott said, the opposite outputs of a single phase transformer are mutually inverted, _not_ phase shifted.

But if the output is a _pure_ sine function, you couldn't tell the output from one with a phase shift.

-Jon
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Winnie,

First of all, phase shift is only defined for pure sinusoids, so any other waveform has no bearing on this discussion.

Now, if you can't tell the difference, why is it not a phase shift or phase difference if you like that term better?

Give me some solid reasoning behind this argument. No one else has.

Also remember that a cubicle full of old engineers says it is a phase shift!
 
Gentlemen,

First off, I have to say that I agree with all of you for the better part. However, I propose to you that no one can win an argument based on how one perceives and/or describes a single event. You can perceive it and/or describe it any way you wish, but it doesn't change the event. It is what it is.
 
I win!

I win!

iwire said:
LOL :D

All I asked was a simple question. ;)
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The simple answer is that your residential service is single-phase as you already knew, and this single phase service comprises two legs where the phase angle of one voltage differs from that of the other by 180 degrees.

I claim victory by default in this argument because no one has answered my challenges:

1. Larry has not added two wye phasors to obtain the line voltage.

2. BC has not proven that what appears to be a phase difference isn't.

Furthermore, I have the consensus of a minivan full of old engineers that I am right, and I can round up a busload if needed.
 
Silence:

Silence:

The silence on this topic is deafening! I had expected someone to make a stab at proving his point. Now, let me add another fundamental point:

A phasor, like a vector consists of a magnitude--no sign--and an angle. It is therefore improper to attach a negative sign to the value of a phasor.

Very few of our members have any need to work with phasors. I only do it to keep my brain from icing up in my old age. Still, it is beneficial to all to understand the concept and to be able to solve problems graphically even if they don't know the math.
 
Johnny,

I am sure. Since the periods of the harmonics are less than the period of the fundamental, a delay of one millisecond would translate to different delay angles in the various harmonics.

That is a moot point though since we are assuming a pure sinusoid.
 
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