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Re: Rotaries and Neons (fwd)



---------- Forwarded message ----------
Date: Fri, 7 Aug 98 10:14:53 EDT
From: Gary Lau  07-Aug-1998 0935 <lau-at-hdecad.ENET.dec-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: Rotaries and Neons (fwd)

>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Re: Rotaries and Neons (fwd)
>
>Hi Gary,
>         I should have elaborated a bit:
>
>> Date: Wed, 5 Aug 98 08:44:14 EDT
>> From: Gary Lau  05-Aug-1998 0817 <lau-at-hdecad.ENET.dec-dot-com>
>> To: tesla-at-pupman-dot-com
>> Subject: Rotaries and Neons (fwd)
>> 
>> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>> >To: tesla-at-pupman-dot-com
>> >Subject: Rotaries and Neons
>> >
>> >Terry, Gary Lau and all,
>> >                          I'm seeking an opinion here: if one uses a
>> >good RC filter with a NST, is there any remaining hurdle to using an
>> >async rotary gap?
>> >
>> >Malcolm
>> 
>> As I understand it, the reason that async rotary gaps are not recommended
>> for use with neons is not related to filterable high frequency transients.
>> The same kinds of high voltage, high frequency resonances should occur
>> regardless of sync or async, or static or rotary gaps.
>> 
>> The problem with async RSG's and NST's has due to the fact that mains
>> resonance between the NST and primary cap will exceed the NST's breakdown
>> voltage if and when a mains voltage peak does not coincide with a gap
>> presentation.  Using a sync RSG guarantees this cannot happen.  Pole pigs
>> are more robust and can survive a mains ring-up.
>
>I quite understand this and for a long time have advocated planting a 
>static gap firmly across the rotary to catch misses. If this is done,
>do you still see any objections?
>
>Thanks,
>Malcolm 

Hi Malcolm:

I was sure you already knew this and I posted my reply largely for the
benefit of list members that may not be aware of these subtle hazards,
thanks for clarifying.

As you suggest, a static gap shunt across an async RSG should protect
against mains-resonance peaks.  It may however be counterproductive in
that it will limit Vpri to the same value as if you were using just the
static gap.

As to whether the combination of the static shunt and RC filters will
eliminate all NST hazards, I wouldn't bet on it, ever.  It wasn't long
ago that most of us thought the main hazard was at the tank Fres and we
strived to filter that out.  Now we know about the Igap zero-crossing
bursts.  Who knows what will be discovered tomorrow?  It's been suggested
that NST's were never designed to even run at their rated voltages, that
neon tubes clamp the output voltage to something far less, so it could
even be that running an NST open circuit with nothing attached is bad for
it!

Additionally, the question you posed as to why safety gaps fire
differently than the main gaps has yet to be definatively answered.
There is the strong possibility that some unrecognized mechanism exists
to boost the NST output voltage enough to fire the safety gaps, despite
RC filters between the safety and main gaps.  I could speculate and
simulate until the cows come home, but unfortunately lack the test
equipment to observe this.

Regards, Gary