Re: single to three phase conversion

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 07:54 AM 3/31/2004 -0700, you wrote:
>Original poster: eric <hydrogen18-at-hydrogen18-dot-com>
>2 phase 180 degrees out of phase isnt hard to generate. just wind the 
>primary clockwise and the secondary counterclockwise. some isolation 
>transformers might be set up like this.


As discussed at some length a few months back, 180 degrees out of phase 
isn't really considered 2 phase.

One way to think about is that a true polyphase system must have some way 
to generate a rotating field without using reactive components.

A true polyphase system will be able to create any desired phase and 
amplitude of sinusoid at the system frequency by some linear combination of 
the system signals.  For instance, if I have a classic 2 phase 90 degree 
system, I can create an arbitrary phase and amplitude sinusoid by doing:

Output = A*phasecircuit1 + B * phasecircuit2

where A and B are constants (i.e. I could do it with transformers) and
A and B are chosen as A = Desired Amplitude * cos(desired phase)
and B = Desired Amplitude * sin(desired phase)


So, to convert classic 90 degree (quadrature) 2 phase to the 3 phases, we 
plug in desired phases of 0, 120, and 240 degrees

To make quadrature 2 phase from 3 phase, you can do essentially the same..

You can make any weird combination of phases you want once you have at 
least two different phases.


You'll note that with two signals 180 degrees out of phase, you can't do 
this.  There's no clever linear combination of the two signals that can 
generate something at 90 degrees.