Re: [TCML] Re: Position of baffle inside secondary

[Paul Nicholson <tcml88@xxxxxxxxxxx>]

Dex wrote:

> Thanks for the graphs.Very useful!

Several years ago I posted a list of all the possible causes
of racing arcs I could think of...

 http://www.pupman.com/listarchives/2002/July/msg00429.html

I don't think any progress has been made to narrow down the
list since then.  Probably it is not too great an issue,
reduction of coupling always (I think) cures the problem.
It's just that, to our embarrassment, we don't know why.

I mentioned an animation which shows the effect of a sudden
discharge from the topload - I found it,

 http://abelian.org/tmp/thor.anim1.gif

It's a normal waveform until 40uS, when a sudden discharge is
applied to the topload and a large transient passes down the
coil as a result, reflecting back and forth a couple of times
before dispersion spreads it out.  The instantaneous
secondary voltages are very high in this extreme case.

Here's the discharge part of the event with the timebase
reduced so that we can see the transient more clearly,

 http://abelian.org/tmp/thor.anim2.gif

This is not a typical breakout, but a sudden and almost
complete discharge of the topload to ground, so it doesn't
represent normal operation, but serves to illustrate one way
that abnormal voltages can develop on the secondary.

Perhaps during normal breakout, the stepwise advancement
of the streamers produces step changes in top voltage,
injecting a series of rapid transients into the coil.
Measurement of base current waveform would show the presence
or not of these.  If transients can be detected in the base
current and their amplitude measured, we can go some way
towards estimating the voltage gradients involved.

It is not clear how k adjustment would affect this scenario,
except perhaps that high k might mean the breakout advances
in larger steps.

> But nobody answered your question if racing sparks can
> appear in the case of a coil without streamers from
> topload -(.

Indeed.   It may not be a simple answer - there could be
different types of secondary breakdown that are casually
lumped together under the name 'racing arcs'.   Attempting
to classify different types of breakdown would be a
useful step.

--
Paul Nicholson
--
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