KraakeCrest said:
I appreciate your patience, and I will look at this closely tommorow. Now I need to rest my brain and maybe open a beer, before I take a look at it again.
I got out in the yard for a while and my brain is clarifying too.
My choice of words "voltage divider" seems not ideal, and i stumbled across another site that might help me formulate a better explanation.
I am not satisfied with what I've said and will work on it tonight. Meanwhile, from this link which discusses a tangent to your question,
http://circuitglobe.com/harmonics-in-three-phase-transformers.html
He shows by algebra that third harmonic current cannot flow into a three wire wye (which he calls star).
Then he shows by algebra that the
line to neutral voltages CAN contain third harmonic but without a neutral we cannot detect their presence.
5th and other non-triplens are present and detectable but we're not concerned with them...
Hmmm
so presence or absence of 3rd harmonic in
line to neutral voltage cannot be detected by
line to line measurement
and that means we can't tell from primary side
line to line voltages whether they are present.
Even in absence of third harmonic
current entering your transformer, each
line to neutral voltage can contain a third harmonic.
But it won't show up in the
line to line voltage. (I know I'm repeating - i do it for myself when proofreading for consistency)
It will show up as neutral displacement, because at any instant the third harmonic component adds to one (or two) of the phases and subtracts from the other(s)
and without a fourth wire the neutral is free to gyrate..
Now, adding a delta winding short circuits third harmonic component of phase voltages as i mentioned above.
Any third harmonic component of flux will induce current in those delta windings that, by Lenz's Law, opposes said third harmonic flux. That component of flux will be driven to almost zero, just as in any short circuited transformer.
>>>>It's very backward to our intuition though to think of third harmonic flux as driven
not by a third harmonic component of primary current but instead by the
LACK of one. <<<<
I think that's the thought key i was looking for.
Probably i should have started there, with BH curve That's what underlies the
blue oops- edit - make that
dark green i0 magnetizing current's peakiness in that Warsaw University lab exercise up above
If those mostly 3rd harmonic magnetizing current peaks can't flow , the flux and voltage won't be sinewaves.
Then we get into the three phase trigonometry that hides that distortion from you when looking line to line.
if you can make a coherent presentation out of all this you'd probably do your class a big favor. When our intuition leads us to the formula we're beginning to understand, and that sure beats cramming for exams.
Run this line of thought by professor ? Maybe it'd help him figure a better way to present the subject .
I got to make use of the daylight - yard is a mess . TTFN
old jim