Gary Coffman wrote in
:

On Wed, 10 Mar 2004 10:17:09 GMT, Anthony
wrote:
"Leo Lichtman" wrote in
:

"Anthony" wrote: Single phase (110V) is as you describe. 230V
power, is actually 'two phase' power, and they are also out of
phase with each other, so that you get somewhat the same effect as
3 phase. ^^^^^^^^^^^^
Sorry, but that ain't rite. 230 volt power, (in the US) consists of
two hot lines, each 115 v from ground, and 180 degrees out of phase,
so the difference between them adds up to 230 v. Two phase would
require four wires, one pair carrying a voltage that is 90 degrees
out of phase with the other. It is not used. I remember it as
being archaic in my old EE textbook, which, itself, is about 60
years old.

Hrm.....
Two hot feeds 180° out of phase.....does this not make 2 phases? Would
not one phase be a single sine wave? Two phases would be 2 sine waves
shifted by some degree, and three phases would be 3 sine waves shifted
by some degree.......maybe i'm wrong here,......

You're wrong. Phase is defined as the angle between current vectors
in a circuit. So to have polyphase power, there has to be more than
one current vector. For normal residential power, there isn't. There
is only one current vector, produced by one core magnetic flux cutting
one winding in the supply transformer.

Now US residential power center taps the transformer providing
240 volts single phase to the house. The center tap by necessity
gives you half of 240, or 120, from the center tap to either end
of the transformer winding. But the magnetic field of the transformer,
and hence the current flowing through the transformer winding is
only in a single direction at any given instant. If it were otherwise
the two component voltage vectors wouldn't sum to 240 volts.

In other words,

120 + 120 = 240

But if they were actually 180 degrees out of phase you'd get
this:

120 + (-120) = 0

Now we know the latter is not true, as touching the two hot ends
will forcefully demonstrate. So we're left with the conclusion that
the two 120 volt component vectors are both pointing in the same
direction at the same time. In other words, they are in phase, and
in fact are parts of a single phase. Because they are both produced
by a single magnetic flux cutting a single winding in the supply
transformer, they couldn't be otherwise.

To get polyphase power, you need multiple windings, cut by
multiple separate magnetic fluxes which are time delayed with
respect to each other so as to produce the observed phase
angles. That's not the case for US residential power, but it
is the case for US polyphase industrial power.

Gary



I stand corrected. Good explination, thanks for the information.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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