Re: Pole Pig Question: (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 25 May 2007 08:24:11 -0400
From: Jonathon Reinhart <jonathon.reinhart@xxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Cc: rrreinhart@xxxxxxxxx
Subject: Re: Pole Pig Question: (fwd)

I always thought it was best to look at it first as just what you said: 1
Primary (HV) = 1 Secondary.

X1            X2
O             O
|                |
vvvvvvvvvvvvvv   HV
=========
^^^^^^^^^^^^^^   LV
|        |       |
O      O     O
L1     N     L2
  \     / \     /
   120   120

Remember the secondary coil is center-tapped, so for now, just think about
the secondary coil as a whole. The voltage waveform across L1 and L2 will
look exactly like the waveform across X1 and X2, just as one would expect.
The tricky part comes in when you add that centertap, and the confusion is
this:  Voltage is relative.  Now without any grounds connected, all of these
voltages on the LV side are simply relative to each other (I think they
might float at whatever actual voltage they wish).  But L1-L2 is 240VAC,
L1-N is 120VAC and L2-N is 120VAC.

Now, we ground one of the terminals so that the voltage is stable and has a
reference point. We COULD (but don't), decide to ground L1.  In this case,
we could get 120V to ground at N, and 240V to ground at L2.  In this case,
when N was at +120V, L2 would be at +240V (and same for the negative side).

However, it makes much more sense to ground that centertap.  Now the
difference between L1-N is 120VAC and L2-N is 120VAC, but at a given instant
when L1 is at +120V to ground, and L2 is at -120V to ground, because they
are wound the same direction, but on opposite sides of the centertap.  We
ground this center tap, because now, we can still get 240VAC by connecting
to L1 and L2, but we can never get more than 120V to ground, which is safer.
The only way to get a 240V shock is to touch both L1 and L2, which is well,
pretty unlucky.

Hope this helped,

Jonathon

On 5/24/07, Tesla list <tesla@xxxxxxxxxx> wrote:
>
> Original poster: List moderator <mod1@xxxxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Thu, 24 May 2007 16:14:32 -0500
> From: Jim < branley1@xxxxxxxxxxx>
> To: tesla-request@xxxxxxxxxx, Tesla list <tesla@xxxxxxxxxx>
> Subject: Pole Pig Question:
>
>
> Hi Folks:
>
> I have received from you a bucket truck load of insightful input on pole
> pigs that has helped me to better understand them, thanks.
> What seems to be evading me is  How can a single primary feed create 2 -
> secondaries that are alternating in current.
> I always assumed that 1 - primary feed equals 1 - secondary wave form
> not 2 - alternating wave forms.
>
> Your help is greatly appreciated,
>
> Jim
>
>
>
>