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How do I make my HV chokes




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From:  Gary Lau  24-Feb-1998 0739 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent:  Tuesday, February 24, 1998 6:59 AM
To:  tesla-at-pupman-dot-com
Cc:  lau-at-hdecad.ENET.dec-dot-com
Subject:  How do I make my HV chokes

>>Gary Lau wrote:
>> I have seen advice advocating L-and/or-R-only protection networks posted
>> to this list many times but have not seen any rationale for using these
>> configurations beyond anecdotal "I've been using this and had no failures
>> yet".  Can anyone defend series-only protection networks in a more
>> analytical manor?

>>Having ranted on this topic now, I must confess that despite following my
>>professed beliefs and meticulously constructing an L-R-C-safety gap
>>network, and measuring and confirming that my chokes aren't saturating, I
>>still killed a 15KV/60mA NST, later reviving it by depotting and
>>repotting in Vasoline.  Could it be that NST's in tar are doomed
>>regardless, but detarred, rebuilt ones have better survival rates?
>>Sorry for this anecdotal theory ;-)

>From:  Rick Myers [SMTP:rcm-at-chile.cs.itc.hp-dot-com]
>One thing nobody has mentioned here is the need to prevent 60Hz resonance
>in the NST.  This is probably what killed the above-mentioned transformer.
>The LRC network not only keeps RF from getting into the NST, it must
>also protect the NST from 60Hz resonance.  Brent Turner has some good info
>on this in his book.
>
>Rick

Whether 60 Hz resonance contributes to NST death, though probable, is
still open to debate.  Clearly it enables more power to be pulled through
the transformer, and a transformer "maxed out" through resonance is
probably more likely to toast, although the exact mechanism of failure
still isn't clear.  Could be too much current through the tiny secondary
windings, or excessive voltage rise and carbon tracking.  In the case of
my revived NST, it clearly was carbon tracking.

I don't however think that any of the protective L-C-R circuits discussed
could be contributing to or used to avoid 60 Hz resonance.  The values of
these protective components are very tiny when compared with the L-C
values of the transformer secondary (100's of H) and tank capacitor.  The
damping resistors used are typically in the 500-2K realm while NST
secondary resistances are 5K-10K, and using additional series R's to
supress 60 Hz resonance would require unreasonably high R values.

Gary Lau
Waltham, MA USA