RE: [Fwd: Spark gap not firing]

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi John,

At 04:43 PM 2/9/2001 -0800, you wrote:
>
>Ralph -
>
>I have built and tested several TC's with the capacitor across the NST and
>never lost a NST. I always used a protective spark gap across the NST output
>as I show in my books. These protective gaps would operate once in awhile
>during tests so a high voltage was never across the NST output. I do not
>believe Terry's NST tests prove that the cap across the NST is more of a
>risk than the gap across the NST.

Those test indeed do not "prove" anything.  They only strongly suggest :-))
 One would have to do a bunch of statistical destructive test to really
prove anything with some confidence factor...  I also advocate that, at the
very least, a safety gap should be used.

>
>Terry's test setup does show current spikes in the test circuit but high
>voltage is what damages the windings and the curves  show only normal
>voltages across the NST output. According to the List there have been many
>NSTs destroyed that had the operating gap across the output. The TC primary
>regardless of where the gap is located can have destructive voltages created
>during operation and a protective gap across the output will keep these
>voltages from shorting the windings.

The voltages levels by themselves are within the NST's rated maximum.
However, what worries me is the frequency.  If and NST gets hit with 15kV
at 60 Hz it is happy.  But think of what happens when the output terminals
are hit with 15kV at 400kHz!  The secondary coils of the NST are not going
to look like nice inductors anymore but rather complex L's and C's.  I
suspect that instead of the high voltage being evenly distributed across
the output windings, as they are at low frequency, much of the voltage is
spread across just a few windings at high frequency.  At 400kHz, the high
frequency voltage is just not going to get very far in the output windings
and that high voltage my hit only a few layers and BLAMMO!  Since trying to
figure out how the high frequency voltage distributes in the output winding
of an NST is rather messy.  I figure it is best to simply stop it from ever
going there...

Reports like yours of NSTs taking this high frequency voltage are
encouraging.  However, I suspect that is an exceptional case.  Since the
strong emphasis on using protection filters, and putting the gap across the
NST began, the number of NST failures has dropped dramatically...

Cheers,

	Terry


>
>John Couture
>
>---------------------------------------
>
>
>-----Original Message-----
>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>Sent: Thursday, February 08, 2001 5:13 PM
>To: tesla-at-pupman-dot-com
>Subject: Re: [Fwd: Spark gap not firing]
>
>
>Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
><Parpp807-at-aol-dot-com>
>
>Hi Bart,
>Every text and pamphlet in my Tesla collection, including Circular 74, shows
>the TC schematic with the capacitor connected in parallel with the NST. Now,
>it suddenly
>registers that these older schematics do not pertain to an NST. Until now, I
>was unaware of Terry's paper on the subject. Thanks for calling this to my
>flickering attention span.
>There is learning taking place but it is very sloooow.
>
>Cheers,
>Ralph Zekelman
>
>
>
>