On Saturday, November 23, 2013 7:34:33 PM UTC-5, John G wrote:
wrote on 24/11/2013 :
On Saturday, November 23, 2013 5:37:59 PM UTC-5, John G wrote:
nestork has brought this to us :
What needs to happen in here is for people to realize that talk about
three phase delta and wye circuits may be interesting, but it's noise in
here. We DIY'ers recognize that there is three phase power available
for equipment that uses it, but it's not something that we need to know
about, interesting though it may be. And, while I appreciate the input
from the professional electricians in here, we all know that our brains
are excellent housekeepers and that what we don't use will soon be
thrown out to make room for stuff we will use. Three phase power, and
how to wire it is something my brain is just itching to throw out. It
needs the space for stuff it will use, like how to fix a fridge or
spread drywall joint compound smoother.
You are of course correct but lots of people who know very little or
just enough to confuse themselves keep dragging PHASE into discussions
about houshold electrics.
The normal houshold supply in the USA is ONE phase with a centre tap
grounded to produce 120 volts above ground and 120 volts below ground
or 240 volts between the ENDS :/
--
John G
I guess the IEEE and it's power engineer members must
be among those knowing very little or just enough to confuse,
because they clearly speak in terms of two phases being present.
From a paper presented at a recent IEEE power engineering conference:
http://ieeexplore.ieee.org/xpl/artic...number=4520128
"Distribution engineers have treated the standard "singlephase" distribution
transformer connection as single phase because from the primary side of the
transformer these connections are single phase and in the case of standard
rural distribution single phase line to ground. However, with the advent of
detailed circuit modeling we are beginning to see distribution modeling and
analysis being accomplished past the transformer to the secondary. Which now
brings into focus the reality that standard 120/240 secondary systems are not
single phase line to ground systems, instead they are three wire systems with
two phases and one ground wires. Further, the standard 120/240 secondary is
different from the two phase primary system in that the secondary phases are
separated by 180 degrees instead of three phases separated by 120 degrees. "
It could not be any more direct and to the point.
Further, the standard 120/240 secondary is different from the two phase
primary system in that the secondary phases are separated by 180
degrees instead of three phases separated by 120 degrees.
What all of this means is that analysis software and methods must now
deal with an electrical system requiring a different set of algorithms
than those used to model and analyze the primary system. This paper
will describe the modeling and analysis of the SINGLE-PHASE center tap
transformer serving 120 Volt and 240 Volt SINGLE PHASE loads from a
three-wire secondary.
It is interesting that you snipped the last Paragraph which says SINGLE
PHASE twice.
How clear is that? :-?
It's not a paragraph, it's part of the same paragraph.
And the part you referring to says:
"This paper will describe the modeling and analysis of the single-phase center tap transformer serving 120 Volt and 240 Volt single-phase loads from a three-wire secondary."
The transformer is single phase on the primary side. The loads it drives are
single phase 120v and 240v loads. No one is saying anything different. How can you ignore the elephant in the room where the author immediately before
explicitly addresses the exact core of the issue:
"Which now brings into focus the reality that standard 120/240 secondary systems are not single phase line to ground systems, instead they are three wire systems with two phases and one ground wires. Further, the standard 120/240 secondary is different from the two phase primary system in that the secondary phases are separated by 180 degrees instead of three phases separated by 120 degrees. "
He explicitly says that TWO PHASES ARE PRESENT and they differ by 180 deg.
That from an IEEE engineer presenting a peer reviewed paper at a power
engineering conference.
Or an app note from an electrical eqpt manufacturer:
http://www.behlman.com/applications/AC%20basics.pdf
"The two legs, represented by Phase A and Phase B, are
180 deg apart.
Or this white paper from another electrical eqpt manufacturer:
http://www.samlexamerica.com/support...Circuit s.pdf
Note the reference to Phase A and Phase B in the foot note to
the diagram and that they are 180 deg apart. And that the diagram
is clearly labeled Phase A and Phase B.
Are all of them among the confused, who know very little?
I have a degree in Electrical Engineering. Other than this
disagreement, is anything I've posted in these two threads
incorrect? Good grief.
What exactly is your definition of phase? Because it's derived
from one primary phase, you can never have more than one phase?
In electrical engineering, science, math, the most basic meaning of
the word phase is to express the relationship
between two periodic waveforms. In this case, in a split-phase 240/120V
service you have two different waveforms, they are 180 deg out of phase with
each other and you can see it on an oscilloscope. It's every bit as real as
seeing 3 phase waveforms on a scope. The 3 phases are seperated by
120 deg, the split phases service is seperated by 180 deg. That is EXACTLY
what the IEEE engineer is saying.