No! phi0 = 0 and phi0 = PI for the two waves.
If phi = wt for both V1 and V2, they would both start at 0 and be in phase. They could be paralleled! Don't try this at home kiddies!
Why is residential wiring known as single phase?
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No! phi0 = 0 and phi0 = PI for the two waves.
If phi = wt for both V1 and V2, they would both start at 0 and be in phase. They could be paralleled! Don't try this at home kiddies!
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Need I say it again :KEEP YOUR APPLICATIONS STRAIGHT!!!
Quote Originally Posted by rattus
No! phi0 = 0 and phi0 = PI for the two waves.
And sin(0) = -sin (PI) = 0 So what?
If phi = wt for both V1 and V2, they would both start at 0 and be in phase.
Maybe not "in phase" but they certainly have an identical phase.
They start at the same time, then they would be 'in-phase'
They could be paralleled! Don't try this at home kiddies!
rbalex: red
rattus: blue
Still don't know what you mean by keeping my applications straight.
No! phi0 = 0 and phi0 = PI for the two waves.
And sin(0) = -sin (PI) = 0 So what?
If phi = wt for both V1 and V2, they would both start at 0 and be in phase.
Maybe not "in phase" but they certainly have an identical phase.
They start at the same time, then they would be 'in-phase'
They could be paralleled! Don't try this at home kiddies!
rbalex: red
rattus: blue
Still don't know what you mean by keeping my applications straight.
Exactly which part did I not understand? Was it not inserting the SIN function? or missing the +0? or was it using != instead of NE?
You don't get the fact that there is no reason to use trig identities in the first place. There are no references although we have asked many times. The phases are wt and wt + PI. It is that simple.
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Are the trig functions being used improperly?
Glad you asked. Yes, they are. Simply put, there is no need, nor justification in using the trig identities in the first place. Not taught in any AC Circuits course, not mentioned in any textbook. For that matter we already know that V1 and V2 are inverses.
There is certainly no justification in dumping the phase constant PI in order to claim the the phase of V2 is (wt) instead of (wt + PI). Then we would have to write,
V1n = Vm*sin(wt)
V2n = Vm*sin(wt)
That makes them equal. I don't think so!
Are we to believe that we should apply this identity to all phase problems, or only one very specific case, or not at all???
Where is the proof?
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No, you would write V2n = - Vm*sin(wt); i.e., one phase
gar
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Jim:
Yes there is a problem. The use of the word "phase" or plus a modifier must have a useful meaning, and is supported by general use that applies in many different applications where it is used.
To say that two sine waves that have a phase difference of 180 degrees have the same phase is of no useful value in many applications, including electrical.
Two sine waves that have a 180 degree difference in phase are not the same sine wave. If they were the same, then you would not get interference that would reduce intensity.
Unfortunately I can not use Google books to present this quote. Thus, I have to type it. The reference is "introduction to Physical Optics", by John Robertson, 1941. P 231
All sorts of discussions in optics, acoustics, and radio frequencies are concerned with a phase difference of 180 degrees being something different than a shift of 0 degrees.
Robertson goes on describe what and why a 180 degree phase shift occurs at the closed end of an organ pipe. Basically cancellation is required at the closed end to produce no particle motion. For cancellation a 180 degree phase shift is necessary. This is the necessary boundary condition.
Why do I bring up optics? Because it predates AC electrical circuit theory and for definitions to work well they should apply to all comparable subjects.
.
Jim:
Yes there is a problem. The use of the word "phase" or plus a modifier must have a useful meaning, and is supported by general use that applies in many different applications where it is used.
To say that two sine waves that have a phase difference of 180 degrees have the same phase is of no useful value in many applications, including electrical.
Two sine waves that have a 180 degree difference in phase are not the same sine wave. If they were the same, then you would not get interference that would reduce intensity.
Unfortunately I can not use Google books to present this quote. Thus, I have to type it. The reference is "introduction to Physical Optics", by John Robertson, 1941. P 231
He goes on the describe why the 180 degree shift.
All sorts of discussions in optics, acoustics, and radio frequencies are concerned with a phase difference of 180 degrees being something different than a shift of 0 degrees.
Robertson goes on describe what and why a 180 degree phase shift occurs at the closed end of an organ pipe. Basically cancellation is required at the closed end to produce no particle motion. For cancellation a 180 degree phase shift is necessary. This is the necessary boundary condition.
Why do I bring up optics? Because it predates AC electrical circuit theory and for definitions to work well they should apply to all comparable subjects.
.
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Except the fact that they reveal that both "phases" may be written in terms of a common phase. I find it interesting that you insist that YOU may choose anything you want, but others are restricted to whatever you allow.
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No they aren't; identities are universally applicable - or they wouldn't be identities.
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Well then I think you should review 'mathematical substitutions', so that you can use them correctly.
Simplified.
-Y[wt] = Y[wt-PI]
If Vbn = -Vnb and if Van=Vnb then -Vbn=Van. Their waveforms must start at the same point in time: t0. A simple inversion does not create a time delay, Vbn 'is created' at the exact same time as is Vnb.
Your PI is not a direct part of the phase constant: rather it is simply a modifier to it.
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I get that you want to argue trig with Rbalex when you think it supports your points. I get that you want to claim they're not relevant when they don't support your points. I get that most people don't revert to mathematics beyond addition and subtraction when debating single phase power. And I get that you want to mark a ruler in the middle with 0cm and at the ends as 6cm<0 and 6cm<180. I get that you want to draw your phasors for the ruler one to the left and one to the right. And I get that you want to perform the math as (since the phasors are tail to tail):
6cm<0 - 6cm<180 = 12cm
I get that you don't want to perform the math identity from the math discipline called trigonometry to apply sin(n+180) = -sin(n+0) because that means
6cm<0 + 6cm<0 = 12cm
and it shows they have the same phase by a definition YOU provided earlier in this thread.
http://www.3phasepower.org/3phasepowercalculation.htm
http://www.electronics-tutorials.ws/accircuits/phasors.html
Why can't I write simply V2n = Vm*sin(wt + PI)? Everyone else does.
You still don't get it. Why don't you provide some justification for using the identity which merely shows V1n is the inverse of V2n? We've always known that.
A textbook, an Internet reference, anything valid? Where is the references?
Jim, it doesn't matter how the waves are generated. They are written as having a phase difference of PI radians.
Nope.
Post #1004 was an attempt to provide a cogent, almost self-evident, explanation of why more more than one phase exists in a 120-0-120 system.
It shows exactly why it is more than one phase.
I specifically chose the SCR arrangement.
It requires firing pulses at 180 degrees intervals. That is two per cycle.
The circuit wouldn't require phase displaced pulses if there was just one phase.
I've yet to see a cogent explanation that reasonably refutes this.
All engineering is applied physics. All physics is applied mathematics. There's never any justification required to use physics or math to describe an engineering problem. The burden is on YOU to prove there isn't a justification for it. Without the math there are no phases. Phases are a mathematical construct. As such, math is ALWAYS a valid method of description.
Any and all math books that include trigonometry. I'm sure you can access some.
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