From: Paul
Date: Fri, 03 May 2002 12:05:59 +0100
Subject: Re: [TSSP] Secondary voltage stress factor
[Forwarded from Malcolm]
Hello all,
I've just caught up on reading some 20 or so posts. My new
mail antennae have been directed to other areas lately. I have some
comments and observations which may be useful:
Racing arcs: I have run two coils of considerably different size
built on plexi formers. The first was a 14" coil which arc'ed from
top to bottom internally. This was running with far too much energy
in an untuned system - my very early days. The second was a more
reasonable (though still poor) coil which was spacewound. It was run
tuned and was the resonator for my first real working system. Forget
the lousy (excessively lossy) primary. To boost coupling and primary
Q, I ran a third intermediate coil tuned by a transmitting ceramic
directly above the solitary primary turn, Tesla-style. The e-fields
were pretty high and caused racing arcs to form in random fashion on
the resonator several inches above the top of this winding. On
occasion, a flashover would occur between them. In no case for this
or the many coils I have run since have I seen racing arcs occur
inside the former. I am thinking this may well be due to the
thickness of the former dielectric. Things may be different for a
skeletal coil. It is not hard to deliberately induce racing sparks.
Both running untuned and too high a primary energy will do it.
On the q3 problem: To resolve this may require similar measurements
with a quite dissimilar resonator. There may be a parasitic resonator
lurking somewhere in the vicinity which happens to be just right.
Does q3 itself seem abnormal with regard to expectation? I can detect
rings and energy exchanges between a running coil and various
resonators and other objects in my garage. It takes far less energy
than required for breakout to see the effects. In fact my garage is
rendered totally unsuitable for measurement by this, some nearby
powerful radio stations, and the metal cladding.
Wire stress: Racing arcs if allowed to persist will eventually
puncture the best insulation. I have tested a pristine polyesterimide
coating on a pair of adjacent 1mm wires to around 8kV steady and
pulsed DC without puncture. That is at least 4kV/thickness. There was
corona evident. The damage caused by racing arcs would be primarily
due to heating I think.
Regards,
malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.