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240VAC single phase from three-phase? - Page 4

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Posted by amdx on April 1, 2010, 7:26 pm
 




  Thanks Bruce,

 Things get dificult to explain when the depend on a reference point.

This website shows a graph showing the phase of the two lines 1808 out of
phase.
See the second graph about half way down on this page, and
description.
http://www.tpub.com/content/construction/14027/css/14027_75.htm
                             Mike
 PS. I still have interest in a graph that shows 3 phase ac where I can
accurately extraopolate 208 V.



Posted by Bruce in alaska on April 2, 2010, 5:07 pm
 




Yea, Mike's thinking is kind of "Out there" electrically speaking. You
don't compare DC and AC when trying to explain AC and Power & Phase
Relationships. As another commenter pointed out Vectors don't work in AC
very well, because they lack the Time Element, and that time element is
a critical part of AC evaluations. You need to know just where in the
cycle you are talking about, when looking at instantaneous Phase and
Power with the vector analysis.

I still remember the quiz in EE 102 that dealt with all this... and I
got 95%, but not without some heavy bookwork, the night before and lots
of scrap paper.... back in my college days...  many decades ago....

--
Bruce in alaska
add <path> after <fast> to reply

Posted by amdx on April 2, 2010, 6:07 pm
 



  I think all our difference with mike boils down to the reference point and
maybe
some semantics. I kinda gave up on the argument.
 I did get some understanding on the 3 phase power problem I had.
I was looking at the wrong point in the waveform, I was 30 degrees of peak.
So using .707 x peak didn't work. Now that I have found the real peak and a
nice graph it all came together.
http://forums.mikeholt.com/showthread.php?t 1543
Note: the dotted line is the voltage that results from adding the voltages
from two of
120 volt lines.
                          Mike (amdx)



Posted by m II on April 2, 2010, 11:33 pm
 

amdx wrote:


I don't feel semantics have place in battery, or AC polarity
terminology. We're not discussing poetry or interpretation of prose.
Either the terms are correct or not. It's not open to 'feelings'.

I'll give this one more shot before dropping the topic.


Imagine a bicycle rolling down a hill.

The wheels are both turning together and at the same speed. They are in
phase.

Look at the very tops of the tires. They are moving in unison..same
speed, same direction. The road surface contacting the tires guarantees
that.

If you now look at the tires where they are closest together, under the
rider, you see something different. The rear tire's periphery is moving
DOWN while that of the front tire is moving up.

This is where you confusion comes from and it IS a reference point
issue. Look at the right side of the bike. *Both* wheels are turning
clockwise. One is NOT 180 degrees out of phase with the other.

Same thing with this three wire, two source, two load single phase
circuit. (AC or DC). Both loops of current are going clockwise. The
neutral wire is the same as looking at the two tires really close up.

If we had different size tires on that bicycle, the relative motion
between the wheels would also be different. That is they wouldn't add up
to a vectorial zero anymore. There is only a vectorial result of zero
when the diameters (or amperages) are identical.

I don't know any other way to describe this and I am not going to try
anymore. It's getting frustrating. I hope you find a reference somewhere
that will clear things up.

mike

Posted by Josepi on April 3, 2010, 2:36 am
 

People are trying to politely explain to you your vectors analogy is
incorrect.

amdx wrote:

I don't feel semantics have place in battery, or AC polarity
terminology. We're not discussing poetry or interpretation of prose.
Either the terms are correct or not. It's not open to 'feelings'.

I'll give this one more shot before dropping the topic.


mike



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