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Why is residential wiring known as single phase?
- Thread starter TimWA
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Here we go again, trying to apply electronics to prove this point again.
I said this 5 years ago and I'll say it again it is the people with a strong education in electronics causing this
confusion about single Phase power being two phase. This was never a problem before the internet became
popular and Electronic techs. and Electricians started talking together about it.
I studied Electronics also 40 plus years ago. I have for gotten most of it.
But I do remember studying phase inverters for Class C or push pull Amplifiers.
And if you Techs are honest enough and are willing to eat some crow you would admit that the so called
Phase inverter rather it be a transformer with a center tap or amplifier element such as a triode vacuum tube
or a transistor, it does no more than invert the input signal or reverses its polarity.
The output of the so called phase inverter in a audio amplifier does not shift the phase it reverses the polarity.
There is no phase shift it is inverted.
I realize you where and are being taught this.But it is a polarity inverter ,but please give it some serious thought.
And have enough nerve to admit single phase is just that ?single phase?.
I need to make a correction in this sentence above,I realize you where and are being taught it is a phase inverter .
Well it is a Phase inverter, but I think most who read that think they are implying it is shifting the phase in time by
180 degrees, but they are teaching it inverts the polarity.
Think about it, if it shifted 180 degrees the Audio coming from the speakers would sound like garble.
Rick Christopherson
Senior Member
Wait? Are you suggesting that this is .......not possible? ......Are you saying that a voltage can't change phase in the middle of a wire.....any wire.............like the wire used to wind a transformer? :jawdrop:
In the immortal words of someone I forgot, "Oh the irony....." :angel:
You can't show them simultaneously on the scope and show their relative positions. That would short out the 120V supply and knacker the scope probes so you simply can't demonstrate what you're asking in any meaningful way. Not that it has a lot of meaning anyway.
You can, of course, measure them in sequence. Tells you not a lot.
However, your wish etc.
I'm at home at the moment and don't have my scope with the removable media. So I I had to resort to using a camera to get shots and I think the scope LCD screen fooled the camera autofocus and there's no manual over ride.
L1-N:
N-L1:
Now what do you glean from that?
Not by me. I have consistently used Van and Vbn or V1-n and V2-n
A real time measurement of those for you:
Nope. My point was about the conductor from the transformer to the load. TM's post appeared to be claiming that the voltages at the transformer had a different phase relationship to those at the load. Now, if your were pedantic, the current and conductors would change that a little. But not at all likely to produce a phase reversal.
Do you think otherwise?
I'm measuring both wrt neutral.
Rick Christopherson
Senior Member
Yeah. If the phase can't change across one wire, then it can't change across any wire. So yes, you contradicted yourself.
Fallacious logic there, Ricky.
Like these wires are red so all wires must be red.
Rattus:Thats cute, you should have been a Lawyer.
But don't forget inversion means to change the polarity not shift it in time.
No difference Ronald. Mathematically, -V @ 0 is indistinguishable from V @ 180. Be reminded also that phase angle only applies to pure sinusoids.
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Check any reliable math book for trigonometric identities.
The site I linked to indicates sin(u ? v) = sin(u) cos(v) ? cos(u) sin(v) [1]
Take any arbitrary point of reference for a 120/240V system.
The general voltage function with respect to time will be:
Let u = (t + φ) and v = (? 180?)
Displace the phase of the general voltage function [2] by ? 180?
The site I linked to indicates sin(u ? v) = sin(u) cos(v) ? cos(u) sin(v) [1]
Take any arbitrary point of reference for a 120/240V system.
The general voltage function with respect to time will be:
V(t) = Vmax sin (t + φ) [2]
Where Vmax , and φ are constants and the phase value of the function is t + φ.
Let u = (t + φ) and v = (? 180?)
Displace the phase of the general voltage function [2] by ? 180?
V(t) = Vmax sin (t + φ ? 180?) [3]
By substitution into [1]
= Vmax ((sin (t + φ) cos (?180?) ? cos ((t + φ) sin (? 180?))
Which reduces to:
= Vmax (sin ((t + φ) x (?1)) ? cos ((t + φ) x0))
Which further reduces to:
= ?Vmax sin (t + φ) [2]
The single relevant phase is still t + φ.
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Agreed indistinguishable in most applacations.
But in a single phase power transformer if you shifted 180 on one of the secondary windings
you would have zero volts between L1 and L2.
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Compare Besoeker's current directions to the ones I used, when there is no conductor between the neutral point of the source and the neutral point of the loads, what do you notice?
No so Ronald. We take the DIFFERENCE in potential between L1 and L2. Remember we are measuring the voltage on L1 relative to the neutral and the voltage on L2 relative to the neutral. The phasor diagram looks like this:
V2 = -V1 @ 0 = V1 @ 180 <------N------> V1 @ 0
then
V12 = V1 -(-V1) = 2V1
We are NOT measuring the voltage on the neutral relative to V2.
No Rattus
I'm measuring the voltage between L1 and L2 on the secondary side.
If I flip the polarity or shift 180 degrees of either one of the secondary
windings it would null and there would be no voltage between the lines.
And both lines would read a 120 volts to neutral.
I'm measuring the voltage between L1 and L2 on the secondary side.
If I flip the polarity or shift 180 degrees of either one of the secondary
windings it would null and there would be no voltage between the lines.
And both lines would read a 120 volts to neutral.
Are you measuring with a voltmeter or a scope?
Rick Christopherson
Senior Member
This is exactly the reason why I keep harping on people for making absolute statements that should actually be relative statements. Relative to their chosen analysis method, not the definition of the system. As your posting points out, absolute statements redefine the system, and you get zero volts from V1 to V2.
When some of the posters have stated "the windings are out of phase", this is an absolute statement, and redefines the system.
Has anyone stated that?
I guess with a voltmeter so we want see those stupid opposing sine waves.
That is just the point Ronald. The DIFFERENCE in those stupid opposing sine waves is 240Vrms or 340Vpp. That is where the term "potential difference" comes from. With a properly synched scope you can visualize this difference.
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