How does a typical residential utility transformer work?

[LarryFine]

. . . the phase angle of a sinusoid can be shifted 180 degrees by changing the reference of the voltage measurement or sense of the current measurement.

Well, to be more accurate (I hope), the apparent, or relative (to the universe), angle changes, but the actual phase angle of the voltage between any two points doesn't change in any way. That would be like saying that a positive DC voltage is now a negative voltage, because you decided to swap the test leads of your voltmeter.

Using a bi-polar supply is a better comparison, anyway. Of course, with a split power supply, if you connect one lead of your voltmeter to the circuit common, one pole of the supply will appear positive and the other negative, but the two halves of the supply are clearly "in phase", in the sense that the voltages add, like two batteries in series.


Here's a little (elementary) ditty I posted a while back: http://forums.mikeholt.com/showpost.php?p=708650&postcount=4

 

[rattus]

Nope:

Nope:

Well, to be more accurate (I hope), the apparent, or relative (to the universe), angle changes, but the actual phase angle of the voltage between any two points doesn't change in any way. That would be like saying that a positive DC voltage is now a negative voltage, because you decided to swap the test leads of your voltmeter.

Using a bi-polar supply is a better comparison, anyway. Of course, with a split power supply, if you connect one lead of your voltmeter to the circuit common, one pole of the supply will appear positive and the other negative, but the two halves of the supply are clearly "in phase", in the sense that the voltages add, like two batteries in series.

Here's a little (elementary) ditty I posted a while back: http://forums.mikeholt.com/showpost.php?p=708650&postcount=4

Larry, you are bending the definition! You should say,

V1n - V2n = V12 = V1n + Vn2

The first half of this expression uses out of phase voltages; the second half uses in-phase voltages. This is what I have been claiming all along. Matter of fact, we do reverse V2n and then add just like in algebra, but that does not change the phase angles of V1n and V2n!

Some 50 years ago I learned that the voltages at the end points of a CT secondary are 180 degrees out from each other (re the CT of course). I don't think that has changed.

 

[LarryFine]

Some 50 years ago I learned that the voltages at the end points of a CT secondary are 180 degrees out from each other (re the CT of course).

Yes, they are. The anti-Rattus side is merely pointing out that using the CT (neutral) as the reference is a sort of "artificial" way of justifying the argument.

It depends on whether you want to look at a CT'ed winding as two windings that are connected end-to-end or a single winding that happens to have a center tap.

Electrically, of course, they are the same. Obviously, both sides are correct as seen from their respective points of view.

 

[roger]

Electrically, of course, they are the same. Obviously, both sides are correct as seen from their respective points of view.

And there you have it, Larry has provided the perfect answer. :grin:

Roger

 

[rattus]

Rattus,

Do you agree that using your circuit analysis for current I12 in post #109, a 2-Wire only load would have the source current in coil 2 (your IV2) with a different sense or direction than your reference voltage V2n?

And to remind you again, I am not debating that V2n = -Vn2. I am saying that it is not common practice to say that in a resistive circuit the voltage and current are "opposite" each other.

The convention is to assume the sense of the current as leaving the "hot" node of the source irrespective of its phase angle. The resultant current will be in phase with V2n, i.e., 180 degrees--they are not opposite. It may be confusing to those untrained in phasors, but it is correct. It just depends on the way you write your loop equations. This is the general approach. ANd BTW, did I get the right answers?

Most likely the practitioner will develop his own procedures, and most likely he will avoid the use of phasors insofar as possible. I would too, but for more complex problems, I would use the general approach.

Now, if you refuse to answer my question on the in phase/out of phase question, I will claim victory by default.

BTW, do you want to start a thorough discussion of phasors? There is quite a muddle out there, and I fear we can never straighten it out completely.

 

[roger]

BTW, do you want to start a thorough discussion of phasors? There is quite a muddle out there, and I fear we can never straighten it out completely.

I think it would be best for all if a new thread were started, this one is to drawn out as it is and with every post it is harder to go back and review what has taken place so with that said I'm closing this one.

I will reopen it if someone really wants me to, but I think a new thread will be the best and this one be here for reference.

Thanks

Roger