creeping sparks on surfaces (fwd)

---------- Forwarded message ----------
Date: Fri, 24 Apr 1998 07:52:19 -0700
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: creeping sparks on surfaces

> ---------- Forwarded message ----------
> Date: Thu, 23 Apr 1998 18:42:57 EDT
> From: ESchulz531 <ESchulz531-at-aol-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Capacitor check : about tracking sparks on surface of
> 	I had 30kv track across 3 inches on clean PVC in one of my capacitors. 
> cleaned the material and used gloves as not to get oil from my hands on
> PVC is a real bad material for tesla coil capacitors so I guess I should
> suspected this.

Oddly enough, one can get really long sparks on a thin insulating film
backed by a metal plate without much voltage.Bazelyan and Raizer refer to
this as a "creeping discharge". They have a photograph and data on a 1
meter long discharge on a 4mm thick piece of glass on a grounded surface at
a voltage of only 100 kV. They attribute this to the dramatically lower
energy requirements to propagate the spark compared to air.

In view of this, when fabricating your capacitors, you should make sure
that you don't have large areas of plate on one side of the dielectric
without a matching plate on the other.