Electric Fences (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 24 Oct 2003 21:45:57 +0930
From: Matthew Smith <matt@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Electric Fences

Greetings All

Some "applied HV" questions for you today.

1) I need to feed power to an electric fence through an underground
cable.  The solid core, triple-insulated cable sold for the purpose
seems to have a very short lifespan, with the insulation splitting after
very little time.  I am planning to route the cable through water pipe
to prevent penetration by stones, etc., but was wondering what would be
the best cable to use.  Moisture in the pipe would probably cause
ordinary mains cable to pinhole with the HV pulses.  How about some sort
of coax?

[Solid-core polypropylene coax (NOT the foam core) is great for HV, but it
has a fair amount of capacitance so I'm not sure how well it would work
with pulsed or high-frequency HV.  You could always change your driver
circuit and just charge your fence up with straight high voltage DC ;-)
As a side note, you can even use coax cable as a high-voltage capacitor.
SRR]

2) I would like to measure the voltage on the fence at various points,
to calculate losses and trace faults.  (I use a traditional Megger
tester at the moment for fault-finding.)  Since the HV is coming in
pulses, what is the best way to measure?  I was thinking along the lines
of a divider network with the A to D convertor of an AVR microcontroller
sampling at about 1kHz to catch the pulses. Any thoughts?

[You could probably wire up a cap and resistor with a long enough time
constant so you wouldn't have to worry about catching pulses.  SRR]

Cheers

M

-- 
Matthew Smith
Kadina Business Consultancy
South Australia
http://www.kbc.net.au