Re: Single vs Two Phase - both sides are right!

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Alex Crow by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<alexcrow-at-blueyonder.co.uk>
> 
> Hi all,
> 
> I would say from my reading of various ham radio and RF design texts that the
> two 'hots' in a 240v system (with the centre being neutral, and if this is
> really how it works in the US) are 180 degrees out of phase, relative to some
> DC reference voltage, so that at any point in time the voltage between them
> is twice that between each leg and neutral (which is the 'zero crossing' for
> both waveforms). I see it like this (sorry, ASCII art was never my strong
> point)-
> 
>        _      +120
>       / \
> Hot1 |---|-------0
>          \_/  -120
> 
>           _   +120
>          / \
> Hot2 |---|-------0
>       \_/     -120
> 
> Are these two waves not mathmematically 180 degrees phased in time? This also
> reminds me of a "bridge" style amp, eg for a subwoofer, where you must invert
> one signal to produce the doubling of voltage (and x4 in power) for the
> speaker.
> 
> *However*, as far as the load is concerned, it sees a 240V, single-phase
> voltage and current, since the Neutral isn't involved. Hence, both parties
> are right in some way. I think we'll have to agree to differ here guys!

	Sorry.  Single phase is single phase, whether or not you center tap
it.  Single phase is single phase no matter what you do. You can't
create a rotating magnetic field with a single-phase system such as
this.  The quadrature phase relationship is required.  Two-phase signals
can be converted to three-phase signals by a "Scott Tee" transformer
circuit and vice versa.  

> As for the 2-P 90-degree phased old system, I've never heard of it so I won't
> even try to comment!
> 
> Cheers,
> 
> Alex

	The two-phase system is still in use for lots of purposes, for driving
servo motors, for example.  The I & Q signals referred to in
communications and present in just about every modem and digital cable
converter are analogous to two phase.

Ed