mivey
Senior Member
Original and related: 938 1180 1213 1237 1263 1266 1294/1295
Why is residential wiring known as single phase?
- Thread starter TimWA
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mivey
Senior Member
They can cause a minor phase shift between the output voltages. I made that point to show that the two voltages were not exact reversals of each other like you have when reversing a two-wire voltage. The other point about load was that it shows how the voltages are being used (in phase or phase opposed). No different than identifying the use like when we say we are using it as a 120 volt source or using it as a 240 volt source.
I didn't make the point that the load characteristics are irrelevant to the phase of transformer secondary voltages.
The point I made is that, with a resistive load, the voltage and current will be in phase. That's the case whether or not there is a rectifier in circuit.
If the currents are not in phase, and clearly they are not, then the voltages can't be in phase.
It's simple. I like simple.
I made no such assertion.
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I like simple too. So either the load's characteristics are relevant to the transformer secondary voltages or they aren't. That's how I'm trying to simplify the discussion.
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- PE (Retired) - Power Systems
Finally a definitive answer - the two output voltages of a standard 120/240V (two reconnectable windings) transformer are in-phase.
All the way back to the basic math of Vnb * -1 = Vbn
To make Besoeker's circuit work, absolutely nothing is changed (the windings are physically connected Vx1x2+Vx3x4) except our reference point, which moved from the windings' ends to a common node. The rectifier circuit, actually, functions regardless of which reference point we choose to connect our measurement device (scope) to, therefore the visible waveform directions do not define the 'phasing' of the transformer output voltages.
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- Wisconsin
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- PE (Retired) - Power Systems
I have been very specific in keeping my discussion to the real world, 'run of the mill', installed in millions of locations, single winding center-tapped transformer with its extrememly common customer owned cousin (a two winding reconnectable version).
There has been consisten agreement that other combinations of sources are both theoretically and physically possible. But the OP mention utility transformers and residential 120/240V services.
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- PE (Retired) - Power Systems
My apologies on the quote, I meant to say you asserted that V12 and V34 are in-phase or they could not be paralleled.
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The load will affect the voltage some, of course. But, within the rating, not to any great extent as a rule.
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Are Ia and Ib in phase?
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There is nothing you have posted that cannot be explained using the single-phase point of view.
Your circuits work because of the way they are wired. Not because of what you see on your scope.
I have posted at least one edited copy of one of your diagrams showing the circuit analysis based on V12 and V34 being in phase.
I know of no one that is disputing the basic math of V34 * -1 = V43. But you are developing V43 from math, not from a re-orientation of the two output voltages of V12 and V34. We have previouslly agreed that a physical reconnection will cause your circuit to no longer function as intended.
gar
Senior Member
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jim:
In my post 1293 you ignored responding to the first and main part of the post. The last part of the post was only an aside to point out that because the secondary was only one long continuous wire that that fact did not define phasing of the two sides of the center tap.
How do you respond to the first part of my post 1293? Keep in mind that the purpose of that part of the post does not have anything to do with whether the secondary of a standard distribution transformer is a continuous winding or not, but rather to get across the point that the end points of the center tapped secondary are not "in-phase" using the center tap as the reference point.
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jim:
In my post 1293 you ignored responding to the first and main part of the post. The last part of the post was only an aside to point out that because the secondary was only one long continuous wire that that fact did not define phasing of the two sides of the center tap.
How do you respond to the first part of my post 1293? Keep in mind that the purpose of that part of the post does not have anything to do with whether the secondary of a standard distribution transformer is a continuous winding or not, but rather to get across the point that the end points of the center tapped secondary are not "in-phase" using the center tap as the reference point.
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For the rectifier circuit shown in #1004, are Ia and Ib in phase?
You can look at it any way you wish Jim, but it is very logical to define both terminal voltages relative to N--in a consistent fashion. It would be inconsistent to use more than one reference in a circuit, and V2 is just as important as is V1. It would be wrong to define V2 as Vx3x4. The circuit would still work of course, but our analysis would show that we have a half wave rectifier, and we would be puzzled when the scope actually showed a full wave rectifier.
I have seen more than one reference which describes the voltages on the two legs as being out of phase, but it is just a matter of definition whether the voltages are in phase or not in a transformer. You say tomato, I say tomahto. That's it..
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- Mission Viejo, CA
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- Professional Electrical Engineer
Do the load's characteristics define the phase of the transformer secondary voltages?
Of course not.
mivey
Senior Member
Well, he did say V12 was in phase with V34. But he also said V12 was phase-opposed to V43.
Nothing will change the POLARITY. Regardless of the connection, V12 will stay in-phase with V34 and phase-opposed to V43.
Most all of the single-phase transformers we use can be connected A-B&C-D for series additive or A&C-B&D for parallel using the internal terminal board (using the ANSI internal terminal notation). Most of the transformers only have the three external bushings that are tied to the four internal A,B,C,D terminal points. The larger single-phase transformers do come with four external bushings that give external acces to the four internal terminal points.
No one is saying that V12 and V34 are not in phase. What has been said is that it is also true that V12 and V43 are phase-opposed. My open-wye example shows that usage is physically valid because we make use of a
"real world, 'run of the mill', installed in millions of locations, single winding center-tapped transformer "
with its phase-opposed voltages to create the missing third phase. The transformer in the "a" phase is the 'run of the mill' 3-bushing type and the one in the "b" phase is the 4-bushing type. Why is it so hard for you to accept that the created third phase has a voltage that has a physical phase angle that is displaced from the other two because we made use of the 180? displaced output voltages from the single-phase transformer?
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- Mission Viejo, CA
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- Professional Electrical Engineer
May we ignore them then?
You can if you wish but how they flow in terms of phase and magnitude is a consequence of of the applied voltage and load characteristics.
Hanging my hat on it? No. It just had a simple explanation which as we say here, was good enough for government work. And saved a lot of typing.
[ur]http://en.wikipedia.org/wiki/Skin_effect[/url]
emphasis added
And the area surrounding the residential wires would be called ... ... INSULATION! Alternating current flows INSIDE the copper to a depth determined by it's frequency. Not outside. Otherwise insulation would be the most worthless material in the world. It would burn/melt as the power passed through it and you'd get shocked/burned just touching it.
:rotflmao:
Maybe you should read some of those materials instead of just collecting them.
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