🚀 go-pugleaf

In article <1913@frog.UUCP>, die@frog.UUCP (Dave Emery) writes:
> >you could do what a buddy of mine did...
> >(his barn was overshot by high voltage lines)
> >wrap the rafters with coils, and make off with some free power!!
> >his barn had "infinite" lighting this way!!!

	One minor point: no way, EVER will an electric utility company run
power lines OVER a customer structure (the liability factors and other reasons
for this should be obvious).

> 	I have heard a similar story about farmers in the Midwest using
> long stretches of barbed wire fence near long distance power lines for the
> same "free" power gambit.  As I understand it the power companies were able
> to sucessfully prosecute some of them for stealing power.

	The above situations sound like rural (as opposed to urban) legends
to me.  I suppose if I keep this up, someone is going to confer upon me the
title of "Net Skeptic"... :-)  [This remark, which I couldn't help, makes
more sense if you have been following my postings in another newsgroup,
which shall remain unnamed :-).]

	Now, let's look at this situation and apply a bit of electrical
engineering.  Let's assume the following:

1.	There is a high-voltage electrical transmission line operating at
	128 to 356 kV; the actual voltage is immaterial since all we care
	about is current flow.  A typical single conductor current for such
	a transmission line using 1200 MCM ACSR conductor is 1,000 amperes
	(somewhat on the high side).

2.	There is a distance of 40 feet from the power conductor to a
	"receiving coil"; this figure is pretty conservative, since under
	most circumstances, I don't believe it is possible to get that
	close.

	Since this amounts to a one-turn primary, the flux density (B) 
40 feet away will be given by: B = (4.52)(I)/(h), where B is flux density
in lines/sq inch, I is current in amperes, and (h) is "air gap" distance
in inches.  Plugging in 1,000 amperes and 40 feet makes B = 9.4 lines/sq in
(1.5 Gauss for you Gauss fans).  As a point of comparison, this magnetic
field is roughly 3 times that of the earth's natural magnetic field.

	Now, let's make the following assumptions about a "receiving coil": 

1.	The coil is rectangular, 40 feet long and 4 feet wide, and optimally
	oriented below the transmission line conductor.

2.	There is an iron "core" (pretty damn big piece of metal!); the
	resultant value below will be more than for an air core.

	Let's see what open-circuit sinusoidal voltage will appear in ONE
turn of the above "receiving coil". E = (4.44x10^-8)(a)(B)(f)(N), where
E is induced voltage, a is cross-sectional area of core, B is peak flux
density in lines/sq in, f is frequency in Hertz, and N is number of turns
(1 for now).  Plugging in 9.4 lines/sq in of flux density and the area of
the example "receiving coil" gives us an induced voltage of 0.58 volts per
turn of receiving coil.  Since 1/2 volt won't be very useful, we will need
120/0.58 = 206 turns to give us 120 volts.
	Let's use # 12 AWG wire.  (206 turns)(40 ft + 40 ft + 4 ft + 4 ft)
= 18,128 feet.  Hmmm...  That's OVER THREE MILES of wire to give us 120 volts.
	Let's see how much power we can derive: 18,128 feet of # 12 AWG
wire gives us a DC resistance of 30 ohms, which means that by virtue of DC
resistance alone, we will be limited to a power transfer of roughly 240
watts (assuming load impedance = source impedance).  The power transfer
will really be less, but I don't feel like doing the AC-side calculations
to provide an exact figure.
	The above assumes an iron core in the "receiving coil", which at
4 x 40 feet in dimensions is pretty impracticable.  Without actually doing
the calculations, an air core would be at least an order of magnitude less
efficient.
	Of course, we do have THREE conductors, each of which contributes
to the magnetic field.  On the other hand, no way will there be a 40 foot
air gap between each conductor and the receiving coil.
	At BEST, with over 3 miles of # 12 AWG wire one may get enough free
energy to light a 40-watt light bulb.  Hardly seems worth the effort...
At a cost of around $ 1,000.00 for the copper wire alone, I doubt that anyone
has really tried it.

	[P.S. to Ed Hall: I will not be offended if you view this article
with "suspicion" and doubt.]

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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