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Re: Explain 3 Phase



Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <jasonp-at-btinternet-dot-com>
 
> > 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 tesla 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?

	If so, its not three phase (usually...)
	Ob Tesla:
	Nikola Tesla invented the polyphase systems.  Initially
	two phase, later three phase.  He ran his HV coils off single phase.

> 3 phase is an industrial power supply that runs to large places like school,
> industries and down your road.

	And some homes....  large air-conditioning loads, ferinstance.

> If you look at a normal outlet on a oscilliscope you will se that it is
> a 50Hz sine wave.

	Or 60 Hz, depending on local practice.   8)>>
	(Tesla picked 60...)

> However, if you look at a 3-phase supply on a 3 channel oscilliscope you
> will see that there are

	Three wires, usually plus neutral & safety ground/  The line
	wires will have:

> 3 sine waves, all offset from each other by 1/3 of a division.

	1/3 of a cycle.

> Thus, the p.d. is greater because where you have a peak, you have a rise
> of a slope instead of nothing. 3 phase is used to transmit power, but
> normal home outlets are single phase

> >also, 240 runs into the home, how do we derive only 120 from that?

	What is typically supplied is 120 to neutral, on each of
	two lines.  They are so phased as to add to 240 for loads
	as need it (water heaters, air conditioners, dryers....)

>> i've noticed that the 240 outlet is 4 pronged.

	120, neutral, 120 and safety earth (ground).

>> i think i once came accross a post that described how to get 240 using
>> 2 120 outlets. could i get an explanation on how to do that?

	Would need two appropriately wired outlets next to each other.
	Nearly as simple (and less risky) to wire in a 240 v outlet...

> If you are talking about a normal supply, to get 240 from a 120 outlet, you
> would need a step up tranny. to do the other way round, use a step down.

	In the US the nominal is 60 Hz 120/240.

> simple. If you are talking about 3-phase, then the same thing, but you need
> to split up the phases using a splitter (dont ask me how it works) then feed
> it into 3 trannies (or 3 separate coils on the same core) and then join it
> back together (I think)

	Wellllllll.  It gets complicated.

> > lastly, when a person gets 3 phase power to their house, doesn't most
> > equipment run on single phase?

	Yep.
	Its quite easy to connect single phase loads from any leg of the
	three to neutral.

>> i'm just not fully clear on it. is there a second phase also?

	All manner of combinations can be used.  I believe getting
	real comfortable with a good single phase rig would be
	advisable before diving into 3 phase...
 
> If you get 3-phase to your home, (eg. for a kiln or some seriously power
> hungry device) they just run a 3-phase cable straight of the street into
> your distributor board

	yep...

> Jason
> "If it doesn't work, Increase the voltage!"

	best
	dwp