Re: pole pig question (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 23 May 2007 21:00:35 +0930
From: Frosty <frosty90@xxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: pole pig question (fwd)

here in australia, some rural locations are powered by a SWER system (single
wire earth return) and the ground wire does carry the high voltage return
current, maybe it was a system like this that he hit with his lawnmower.

On 5/22/07, Tesla list <tesla@xxxxxxxxxx> wrote:
>
> Original poster: List moderator <mod1@xxxxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Mon, 21 May 2007 11:34:35 -0400
> From: Jonathon Reinhart <jonathon.reinhart@xxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: pole pig question (fwd)
>
> How is that possible? There is a neutral/grounded wire that runs along
> with
> the three phase wires from pole to pole.  It is the neutral conductor that
> carries the return current back to the substation transformer.  That wire
> running down the pole is one of many hundreds of similar wires that run
> down
> (just about) every other pole that the wires travel along.  It simply
> keeps
> the grounded neutral conductor at ground potential (~0V).  If it were to
> break, there shouldn't be much problem, as the current is still traveling
> down that neutral conductor back to the substation.
>
> Grounded circuits, such as the 120/240V in your house, and the 7.2/14.4kV
> systems in your neighborhood do not use the earth as a return path.  In a
> fault condition in the wiring in your home (say a hot conductor comes lose
> and touches a grounded metal box in the wall), that current is NOT seeking
> to return to "ground", meaning the earth.  This is a common misconception
> due to the fact that the third wire ground system is connect to an earth
> grounding rod. However, the third wire ground is bonded to the neutral
> conductor in your panel box (in many installations, they simply use the
> same
> terminal bar).  Thus, the fault current returns to the transformer then
> via
> the grounded neutral conductor.  The reason this point on the system is
> grounded is again, to keep the whole system's "ground" voltage level at
> the
> same voltage level we are in constant contact with ( ~0V, the earth).  If
> your house's ground/neutral were allowed to float at any 0V (relative) it
> wishes, the fault system would still work. However, a "grounded" metal
> box,
> could be considerably higher potential than the earth, and a human could
> receive a shock.
>
> Imagine if there were no neutral conductor running along the poles. How
> would you ever get electricity?  The current would have to travel
> tens/hundreds of miles along the utility lines to your transformer. Then
> how
> would the current return to the substation? Through the earth? Imagine the
> voltage drop over miles and miles of earth!  Does anyone have any rough
> guesses to the ohms/foot of earth at 8' depth? It would not work.
>
> It is a terrible thing that happened to that poor kid, but something else
> had to have gone wrong. Perhaps the connection to the neutral line up on
> the
> pole was weak at some point, and there was fault current traveling to
> earth.
>
> Jonathon Reinhart
>
>
>
>
> > That innocuous looking wire that runs down the pole into the ground (it
> > often ends in a spiral coil stapled to the bottom end of the utility
> > pole) plays a critical function.  A teenager around here was killed a
> > few years ago when he scraped a utility pole with a lawn mower, breaking
> > the down wire, and essentially running 14.4 KV into the mower deck.
> >
> >
> >
>
>
>


-- 
Frosty