Jamie wrote:

bud-- wrote:

David Nebenzahl wrote:

On 1/28/2011 11:28 AM Mark Cross spake thus:

David Nebenzahl wrote:

So what's "special" or magic about 180° that it wouldn't be
considered a
completely separate and distinct phase? Why would phase have a
"hole" at
180°? (And for any wisenheimers who will say "well, you must
consider 0°
to be a separate phase too!" I say nonsense: that's just a phase
"identity" which we can ignore as being identical to the original
phase.)


So you get 2 phases out of a single phase power transformer?
With 2 separate secondary windings there are 2 phases. Winding A is not
the same as winding B.

With 3 separate secondary windings there are 3 separate phases. Winding
A is not the same as winding B. And winding C is not the same as A. And
C is not the same as B.

With 4 separate secondary windings there are 4 phases. ....

Your transformer supplier can furnish a single core transformer with 4
secondary phases?
Your transformer supplier can furnish a single-core transformer with 2
secondary phases?


To understand what is "magical" about that you will need to know
phasors and the math related to that. Once you understand the math
that support phasors, you clearly see why 0º and 180º are the same
phasor.

http://en.wikipedia.org/wiki/Phasor


Sorry, I don't use Wikipedia as a source of credible information.


Then use your own knowledge of phasors. The representation of a 120/240V
service (relative to N) is +120 and -120, both real. There are no
imaginary components. Plus and minus relationships.


But even if 0º and 180º are the same phasor, they're still
completely different waveforms, which is the important thing here,
isn't it?



Completely different waveforms? Plus sine is a completely different
waveform from minus sine. Have you taken trigonometry? On a transformer
secondary the relative relationships are locked at plus or minus. 180
degrees is trivial.

When you are doing calculations on a simple single-phase resistive
system you use phase angles? Most of us use plus and minus signs. With
non-resistive elements phasors are used - see above.

You can, of course, call it whatever you want to. Just expect
communication problems. I remember 2 people here who agree with you. It
is not the only 2 people I would want agreeing with me. Maybe you could
shop around to a different newsgroup - maybe alt.engineering.electrical?


And two-phase does still exist. Some relatively small 3-phase to 3-phase
transformers (like 480/277 to 208/120) connect 2 transformers in a Scott
(T) connection. The transformers are an intermediate 2-phase. That is,
real 2-phase - 90 degrees between the voltages

Yes, 2 phase of 90 degree's still exist, so why is that ok but 180
degree's isn't?

Look at power generators (portables), most of them have 2 circuits
from the generator 180 out from each other.. Why is this any different
from a
generator of 90 degrees out ? You can combine a leg of each output from
a those generators also..

It's argument that you won't win from those that truly understand the
meaning of phase angle supplies and the number of supply legs.

Its clear that the maximum you can obtain is only 2 phase angles from
any combination of CT's on a transformer supplied from a single phase
leg how ever, the number of circuits from a transformer can be endless
but not practical, of course.


This, from an illiterate ham radio junkie?


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.