Re: Explain 3 Phase

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

Original poster: "Matt Skidmore by way of Terry Fritz <twftesla-at-uswest-dot-net>" <fox-at-woozle-dot-org>

thanks for your very helpful answers thus far. ive actually found a good
deal of additional info at a website called electrician's toolbox (dont
have the url handy). it explains the differernt transformers and how their
primaries and secondaries work and how to use a couple single phase
transformers to make a 3 phase.

im assuming that you can also hook 120 into the 2 outside terminals of a
transformer to energize the primary for tesla use. if a variac is used to
regulate voltage running into the pig, will that also help ballast/limit
current running into it, or can/will it still draw 15+ amps or act as a
short when the variac is giving out 10 volts. i thought i heard on here
that voltage and amperage is proportional  when using something like a
variac. so i guess im asking if variacs limit current as well as voltage.

thanks again for the help


-fox

On Mon, 23 Apr 2001, Tesla list wrote:

> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jlnance-at-intrex-dot-net>
> 
> On Sun, Apr 22, 2001 at 08:07:47AM -0600, Tesla list wrote:
> > Original poster: "Matt Skidmore by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <fox-at-woozle-dot-org>
> > 
> > Hi all,
> > Could someone please explain 3 phase power to me and the hooks up
> > configurations that go with that? i've heard of it here on the ttesla list
> > and also been looking at some substations that has labels on them
> > indicating 3 phase power. looking over some of the pictures of coilers
> > using pigs i have seen 3 hookups on the low voltage side of the pig. i was
> > wondering how these are hooked up. is the middle post ground?
> 
> Three phase power is used primarily when you are driving large motors, and it
> uses 3 non-ground (and possiably 1 grounded) conductors to deliver it.  If
> transformers are involved there will typically be 3 of them, though you can
> get by with 2 if you do some magic.  Three phase power is not something you
> are likely to find in your house, at least not in the united states.
> 
> > also, 240 runs into the home, how do we derive only 120 from that? ive
> > noticed that the 240 outlet is 4 pronged. i think i once came accross a
> > post that described how to get 240 using 2 120 outlets. could i get an
> > explination on how to do that?
> 
> You mentioned seeing 3 hookups on the low voltage side of the pig.  You are
> correct about the center one being ground.  Typically there is 120V from
> either of the other hookups to the center, and 240 volts between the outside
> posts.  When your house is wired, half of your 120 volts outlets will be
> hooked up between one outside post and ground, and the other half between the
> other outside post and ground.  If you find two outlets which are connected
> to opposite outside posts, there will be 240V between the "hot" sides of
> the outlets.  If the outlets are connected to the same side, there will be
> 0V between the two hot sides.
> 
> > lastly, when a person gets 3 phase power to their house, doesnt most
> > equipment run on single phase? im just not fully clear on it. is there a
> > second phase also? thanks
> 
> The single phase power you have at your house is actually 1 phase of the
> three phase power that runs down the street.  Assuming that you have above
> ground power lines, go outside and look at the wires on the pole that has
> your house transformer on it.  You should see 3 high voltage wires on the
> pole, and perhaps a fourth ground wire that runs along the top of the pole.
> If you look at your transformer, it will either be connected between 2 of the
> 3 high voltage wires, or between 1 high voltage wire and the ground wire.  If
> you wanted three phase power in your house, you would have to hange two
> additional transformers on the pole and run two additional wires into your
> house.  A machine that requires three phase power will have a plug that
> has 3 prongs for "hot" connections and another prong for ground.  The last
> time I looked at one, the 3 hot prongs were aranged in a circle and the
ground
> was in the center.  The plug sort of rotated and locked into the socket.
> Anyway, if you have 3 phase power and you need to power something that just
> needs single phase power, you would connect it between one of the hot wires
> and ground.
> 
> There is such a thing as two phase power where you have two sine waves 90
> degrees out of phase.  You can actually have as many phases as you want,
> however three phase power and single phase power are all that you will ever
> find used.  Single phase power is used when the power requirements are low
> and the cost of the extra transformers and wiring would be significant.
> Three phase power is used when large motors are involved, when a lot of
> power is required, or when power must be transmitted over long distances.
> 
> Hope this helps,
> 
> Jim
> 
> 
> 
>