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Re: getting three phase power



Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

Actually, if I were running a DC coil, I'd much rather run it off a
unfiltered 3 phase rectifier, or with a bit of clever transformer wiring, a
6 phase rectifier, than off a big single phase with a monster filter.  The
stored energy in the filter is a real problem: one flashover and your
primary circuit just became a electroforming apparatus or an exploding wire
or both, none of which is particularly pleasant.  Polyphase rectifiers are
neat, because you get low ripple with no stored energy.  Turn the switch
off, and it's dead.

3 phase doesn't necessarily imply high power (although higher powers do
imply three phase, or extreme annoyance from the power company for screwing
up the balance)

If I had three phase power here, particularly 120/208Y, I'd definitely run
three NSTs in parallel on separate phases as a DC coil, rather than running
them all on one phase.

Likewise, if one is running, say, 5-10 kVA (and there are a fair number of
folks on the list doing just that), it's a lot easier to find componentry to
handle the 15-20 amps per phase, rather than handling the 50 amps you'd need
for single phase.  When you start getting over 20-25 amps, everything gets a
LOT more expensive: switches, variacs, fuses, fuseholders, plugs and
sockets, etc.  There's a good reason why three phase is popular for loads
over a few kW, especially if you start pricing good  plugs and receptacles
to handle 10 kVA, (i.e. not stove/dryer plugs which are really designed to
be plugged or unplugged a few dozen times, at most).

And, it's not necessarily thousands of dollars to get three phase power
installed.  It depends on the rules, what services are already available,
etc. In my case, the (3 phase) distribution transformer is about 10 feet
from my service entrance panel on a concrete pad.  It might be a few hundred
dollars, or even a thousand, but probably not ten thousand dollars. It
wouldn't be the first thousand dollars I had frittered away on something
seemingly pointless (at least, so my wife would claim).

 The point is to not reject out of hand the possibility of three phase power
(which comes up every few months on the list).  Also, one shouldn't just
blindly take the word of the weenie who answers the customer service phone
and tells you "it can't be done".  These days, it's easy to actually go look
up the rules (an advantage of regulated utilities) and find out what the
REAL requirements are.  Then, when you call, and the customer service rep
says, it's against the rules, you can ask, "which rule, specifically?" and
maybe you can work out a way to do it, if it is sufficiently valuable or
important.


Note also that a TC doesn't inherently require any particular type of power.
Sure, most folks start with single phase AC power, because it is easy. But,
there is a lot of interest in DC, or rectified AC, and, in fact, prior to
electromagnetic accelerators, one of the ways to generate high energy X rays
(1 MeV) was with a "resonance transformer" which used 3 phase power and some
clever saturating inductors to excite the inductors and capacitors at 180
Hz.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, January 19, 2001 5:21 PM
Subject: Re: getting three phase power


> Original poster: "Eric Davidson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <edavidson-at-icva.gov>
>
> Hi All,
>
> Can anyone give me ONE good reason why you would need/want to power a
Tesla
> coil with 3-phase?? All this talk of trying to get 3 phase service to your
> home, telling the power company you have a 10 hp motor you need to
power...
> stuff like that...gimme a break....a Tesla coil is a decidedly SINGLE
phase
> device.   You may argue that creating the DC for a VTTC might be a little
> better using 3 phase, but even that would hardly justify the $THOUSANDS$
of
> dollars needed to bring 3 phase service to the average home.  IMHO we
should
> let the 3 phase discussion thread die on the vine, there is ample fodder
for
> discussion in tweaking, optimizing and theorizing about our single phase
> coils.  Coil safe
>
> Eric
> edavidson-at-icva.gov
>
>
>
>
>