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Strike Rails: The Big Question
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From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent: Saturday, March 14, 1998 8:23 PM
To: Tesla List
Subject: Re: Strike Rails: The Big Question
Jeff and all,
Guys in the power industry do get a kick out of Tesla Coils! However,
while that was an interesting story from the guy at the power company,
your original supposition was indeed correct - the REAL reason the wires
are there IS soley to provide lightning protection. Putting a grounded
wire above the lines has virtually no impact on the E-field between the
high tension lines and the ground immediately below.
Fortunately, while the lightning bolts we need to worry about pack a lot
less energy, they are certainly not harmless to our tank caps or HV
supplies. However, by using a combination of safety gaps across the tank
cap, and from each high voltage bushing of the supply transformer to
ground, it is possible to safely run your coil without a strikerail,
thereby gaining a bit more clearance between the top terminal and the
primary. When the toroid outer diameter is at least the diameter of the
outer turn of the primary, the resulting E-field shaping tends to throw
streamers mostly outward and upward. Part of this balancing act also
involves sizing the length of the secondary to at least match the
highest expected power level of the coil.
If the field shaping is done properly, relatively few strikes will
actually hit the primary or a protective strikerail. Streamers which do
head downward tend to follow relatively long curved paths outward, then
back down to the outermost turn of the primary. If a strikerail IS used,
it should be made from smooth round tubing to minimize corona coming
upwards from the strikrail. The safest route is the above sparkgaps PLUS
a strikerail... that way you can safely dissipate direct streamer hits
to the primary circuit or to the HV feeds. Cheap insurance...
Safe coilin' to you!
-- Bert --
Tesla List wrote:
>
> ----------
> From: Jeff W. Parisse [SMTP:jparisse-at-teslacoil-dot-com]
> Sent: Saturday, March 14, 1998 10:31 AM
> To: Tesla List
> Subject: Strike Rails: The Big Question
>
> All
>
> I've been wondering about this for a few months now and
> I think it's time to bring it up for discussion.
>
> Mark Bean and I did a demonstration for the Nevada Power
> Company and after we finished we were given a king's tour
> of the facilities and had every question we could think of
> answered. We asked about the thin wires that ride above
> most if not all high power lines (you know, those huge metal
> towers that usually have two sets of three cables). Before
> the question was answered, I believed them to be ground
> wires for lightning protection. I was wrong. What we were
> told was that these wires ARE ground wires but not for
> lightning protection. The ground wires are flown above the
> HV cables to "bleed up" the electrical field that would
> otherwise "bleed down" to ground interfering with
> communications, etc. In other words, the wires serve to
> shape and drain the em-field that propagates from the HV
> lines.
>
> QUESTIONS: So why do so many use grounded strike rails
> above their primaries? Wouldn't a safety gap placed on
> the tank circuit serve to protect the primary components from
> the effects of a secondary strike to the primary coil? Doesn't
> a strike rail give a charged toroid a nice juicy grounded target
> to hunt for, thereby INCITING strikes in the proximity of the
> primary coil? Does a strike rail "drain, distort and weaken"
> the EM field created by the primary coil?
>
> I've never used a strike rail and have always given my coils
> a place to go (a grounded target) so as to avoid primary
> coil strikes. But, Big Red's gonna need a new primary coil
> and I was just mulling over this issue. Guys?...
>
> Jeff W. Parisse, Director
> kVA Effects
> www.teslacoil-dot-com