# RE: Explain 3 Phase

```Original poster: "Tuite, Tom by way of Terry Fritz <twftesla-at-uswest-dot-net>" <TTuite-at-ALLEGROMICRO-dot-com>

BE WARNED!!!! VERY CHEASY GRAPHICS/EXPLANATIONS BELOW!!!! :)

Hmmmmm, mayhap we have a terminology conglict here.  I would call either of
the below 180 degrees out of phase (or inverted):

|---|   |---|   |---|
----------------------
0    |   |   |   |   |   |
---|   |---|   |---|   |---				0

OR
---|   |---|   |---|   |---
0    |   |   |   |   |   |
|---|   |---|   |---|				0

----------------------

This comes from the following, for the sake of simplicity lets look at the
right most signals above.  Here we have one at a constant positive value and
the other at a constant negative value.
Generally we would go to the imaginary plane to really look at this stuff so
lets do that:

Imaginary axis
.
.
.
.................... Real axis
.
.
.

Now if we plot the signals we get;

The top signal yields this:

Imaginary axis
.
.
.
.............----------....  Real axis
.
.
.

Where the magnitude is some purely real positive value.

The botom signal yields this:

Imaginary axis
.
.
.
...---------........  Real axis
.
.
.
Where the magnitude is some purely real negative value.

NOW, the angle between these two vectors is 180 degrees.  So we say they are
out of phase by 180 degrees.  Hehe now I thik I have confused myself, but
for better or worse thats what I think of when I hear 180 degrees out of
phase, or am I completely crazy? :)

Tom T.

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Monday, April 30, 2001 10:29 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Explain 3 Phase
>
>
> Original poster: "davep by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>
>
> Tesla list wrote:
>
> > Original poster: "Peter Lawrence by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>
>
> > >       (on the 'phase' of the 110/240v:
> > >               This seems to ALWAYS lead to confusion, usually
> > >               due to semantics, rather than facts.
> > >
> > >               FACT:
> > >                       The two legs are in phase.
> > >                       (think about it:  If they were not, there
> > >                       would be 0v, not 220v, across the outside...
>
> > then why is it that in Op-Amps they use the term "common
> mode rejection"
> > to refer to the "[difference from the expected] zero output
> voltage" from
> > two inputs that are "common" IE "have the same phase" IE "in phase".
>
> 	Op amps are not power circuits.
> 	(hint:
> 	I have been designing with both for 30 years.
> 	Commercially....)
>
> > We coilers also use "in phase" to refer to two (or more)
> NSTs connected
> > in parallel such that the voltage between outputs of any
> two of them is ZERO
> > (not the two output terminals of one NST, rather two output
> terminals of
> > different NSTs that you are about to tie together to
> parallel the NSTs).
>
> 	I am aware of this.
>
> > You seem to have it backwards from the common use of the
> term "in phase".
>
> 	I don't.
> 	If they are out of phase, how do they sum to 240 across the
> 	outside?
>
> > What the two legs have in common is 60-Hz, other than that
> they are 180-
> > degrees out of phase.
>
> 	Depends on how one interprets the measurement.
> 	(hint:
> 	The 110/240 derives from a center tap & two ends from
> 	ONE TRANSFORMER.  work it out.
>
> > I think you are confusing frequency with phase.
>
> 	I'm not....
>
> 	Ascii graphics are rough, but:
> 		________(+110)
> 		(
> 		(
> 		(
> 		(________neutral
> 		(
> 		(
> 		(
> 		(________ (-110)
>
> 	(secondary only)
>
> 	Since the neutral is grounded, the scope reads relative to the
> 	center, which makes one side LOOK inverted (180 out of phase)
>
> 	Again:
> 	If the two were out of phase, the sum across the outside
> 	would be 0.
>
> 	Hmmmmmmm.  How many here know dot notation, for phasing?
> 	dot (i'll use a * for visibility) is used to formally show
> 	instantaneous phase.  Its set by winding direction.:
> 			*_____________
> 	________*	(
> 		)	(
> 		)	(*____________ (imagine
> coinnected...asciii graphics)
> 		)	(
> 	________)	(
> 			(______________
>
> 	I've omitted cores in all cases....
>
> 	best
> 	dwp
>
>
>

```