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Re: cap explosions
Tesla List wrote:
>
> >From pierson-at-msd26.enet.dec-dot-comFri Oct 18 22:12:56 1996
> Date: Fri, 18 Oct 96 13:21:44 EDT
> From: pierson-at-msd26.enet.dec-dot-com
> To: mail11: ;
> Cc: pierson-at-msd26.enet.dec-dot-com
> Subject: cap explosions
>
> In general (yeah, there are exceptions) a fuel and an oxidizer are needed
> to get a chemical explosion. The caps being (nominally) sealed, there is
> little air in there. Which brings up:
>
> ...air inside... sloshing....
>
> Has the manufacturer said there is air? Is it air, or something else?
> (and air is motly not_oxygen anyway...) I'm not arguing, just wondering.
>
> Has anyone asked about "why no balancing resistors?", that information, if
> available, would be verrrrrry interesting. Again, just wondering...
>
> My first suspicion, even of a fairly vigorous event, would not be of a chemical
> explosion, per se, but of catastophic electrical induced failure.
>
> As to the possibility of case puncture, wood is a fairish conductor (unless
> treated), at tesla-type voltages. (Pix of hv labs show caps, etc, mounted on
> explicit insulators.) Even if the 'power circuit' is 'floating' (not explicitly
> ground referenced) everything has stray capacity to something, leading to
> voltages in unaticipated places... And tesla primary circuits are notorious
> for odd resonant voltages showing up in 'the wrong place'.
>
> regards
> dwp
DWP,
The only real reason for balancing resistors would be to compensate for
variations in leakage currents when the series string has a steady-state
high voltage DC voltage applied. In Tesla coil use, we normally never
run at a steady DC potential - in this instance its more critical that
the series string have fairly closely matched inductances, capacitances,
and "equivalent series resistance" or ESR - the resistive loss during
high current discharge. Since the separate cap rolls are all physically
identical, and were probably built at the same time using identical
material lots, CP has no need to further match them - they're inherently
balanced.
I agree with your view of an electrically-induced failure, and not a
chemical/oxidation event. I'm thinking that an interconnection to the
tin strapping may have been defective, leading to a high-current failure
and flashover in the oil, causing rapid vaporization or a shock wave.
Since the cap was on a sheet of HDPE, there shouldn't have been any
problems with the cap housing. I'm really looking forward to getting any
autopsy info from CP!
-- Bert --