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

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

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!

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



On Sunday 06 January 2002 11:54 pm, Tesla list wrote:
> Original poster: "John H. Couture by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
>
>
> Richard -
>
> Ed is correct and the system is single phase not two phase. To understand
> electrical phasing you have to use vectors. The two phase 220 volt you are
> referring to would be zero volts not 220 volts. Note that the oposite
> vector "trough?" at 180 degrees is also at the oposite polarity and would
> be subtracting not adding to the voltage. Note also that the three vectors
> "hots?" are at 208 volts not 220 volts if the Y vectors are 120 volts and
> arranged correctly. You can check this out and a lot more by reading any
> electrical engineering book on AC circuits.
>
> In the past 15 years this subject has been discussed several times on the
> List and it appears coilers are still having trouble understanding the
> voltages and vectors involved with AC circuits.
>
> John Couture
>
> -----------------------------------------
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Saturday, January 05, 2002 10:12 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Single vs Two Phase (was - Spark gap erosion resistance)
>
>
> Original poster: "Wall Richard Wayne by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>
>
> Ed,
>
> Sorry about the phase illusions you seem to be operating under. 8>)  120
> vac is
> single phase varying around the neutral.  220 two phase vac has two hot
> wires,
> each varying around neutral and their phases are 180 electrical degrees
> apart.
> As one peaks the other is at the opposite trough 180 electrical degrees
> away at
> the same instant.  Of course, 220 three phase vac has three hots all 120
> electrical degrees apart.
>
> If you're interested any electrical utility would be happy to explain it to
> you.  As an aside, I have had all three three types at one time or another.
>
> RWW
>
> > > John.
> > >
> > > Sorry, but standard 220 vac comes in both two and three phases from the
> > > electrical utilities.  The two phase system is 180 degrees apart and
>
> three
>
> > > phase of course is 120 degrees apart in phase.
> > >
> > > RWW
> >
> > WRONG AGAIN.  The normal resedential installation is a three-wire,
> > SINGLE-PHASE system.  (In effect, a center-tapped single-phase system.)
> > A true two-phase system has voltages which are 90 degrees apart. This
> > definition has used since at least Tesla's time, and probably earlier.
> >
> > Ed