How do I make my HV chokes?

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: How do I make my HV chokes?
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 22 Feb 1998 23:56:57 -0600
Approved: tesla-at-stic-dot-net


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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Sunday, February 22, 1998 6:20 PM
To:  Tesla List
Subject:  Re: How do I make my HV chokes?

On NST secondary inductance:

> From:  Bill Lemieux [SMTP:gomez-at-netherworld-dot-com]
> Sent:  Friday, February 20, 1998 12:02 PM
> To:  Tesla List
> Subject:  Re: How do I make my HV chokes?
> 
> > An air core inductor as described above would yield only about 0.14 mH
> 
> Admittedly two 140uH inductors is only 350ohms at 200+ kHz.  But keep
> reading...
> 
> > and there's no need to use wire as large as 18 AWG.
> 
> Agree.
>  
> > More importantly, adding this meager inductor in series with the
> > HV xfmr, whose secondary is hundreds of HENRIES just by itself, can do
> > nothing to keep the high frequencies on the outside of the xfmr. 
> 
> Consider this: the inductance of the NST secondary (which, by the way,
> is almost certainly less than 1H- have you measured it?), will
> effectively block the RF _current_ from travelling through the NST
> secondary.  This means that, barring a protection network, the outer few
> turns of the secondary will see a very high
> voltage at a frequency the insulation was never meant to live with.

It is almost certainly in the 100's of Henries range. I have 
resonated rather small caps with it both at power and in small signal 
tests. The popular "impedance matching" criterion of Xc = V/I is 
actually creating this condition for whatever frequency is chosen in 
the Xc part. If you plot secondary winding Rdc vs Xl at Fmains you 
find that Xl is far and away dominant.

Malcolm
<snip>