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130kW Coil -- Oh No!


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From:  - [SMTP:randy-at-gte-dot-net]
Sent:  Friday, February 06, 1998 3:57 PM
To:  Tesla List
Subject:  Re: 130kW Coil -- Oh No!

Tesla List wrote:
> 
> ----------
> From:  Greg Leyh [SMTP:lod-at-pacbell-dot-net]
> Sent:  Sunday, February 01, 1998 4:47 PM
> To:  Tesla List
> Subject:  130kW Coil -- Oh No!
> 
> Hi All,
> 
> The final development and testing efforts of the coil during the
> last few weeks have brought considerable progress, and a few setbacks
> as well.  Most of the major problems so far have had to do with the
> dynamics of the rotary gap system.
> 
> The latest setback on the rotary gap system has to do with
> the sharp pulsations of air pressure exerted on the stationary
> electrode holders by the quickly moving rotating electrodes.  As the
> moving electrode passes the stationary one (at 420 km/h with a
> clearance of 0.9mm), the shock wave tends to hammer the stationary
> electrode supports, which are supported by an array of large porcelain
> insulators.  These shockwaves are strong enough even at half speed
> that hearing protection is required anywhere near the gap.
> Although the porcelain insulators are quite massive, they appear to
> be susceptable to vibrational fatigue, and during power tests
> last Friday one of these insulators failed completely, resulting in
> a rather impressive spray of porcelain shards, ejected out of the
> vault through the access door.  T. Leonard was far enough away, and
> I was behind my favorite steel plate, so no one caught any action.
> 
> On a positive note -- at the time of the insulator failure, the coil
> was generating 22 ft long discharges into the air from the top sphere,
> with the mains at one-fourth of full power!  Electrically speaking
> at least, the coil appears to be doing quite well.

Wow....!

<snip> 
> Also, we were able to bring the primary voltage to 55kV in the
> single-shot mode (~1PPS), at which point the top sphere issues
> 7' to 8' streamers, and the RF current at the base of the coil
> is 60A pk.
> 
> Our plan for the electrode support insulators involves replacing
> all 8 of the porcelain posts with 3.5" x 6" x 27" solid slabs of G-10.
> The material is already in hand; however the machining efforts,
> modifications to the rotary gap frame and testing will probably
> set our schedule back another two weeks.
> 
> I'll report on our progress again when the G-10 is installed.
> 
> -GL

My $.02 along with my usual disclaimer;
I am completely unqualified in any field relating to the following:

A few thoughts: maybe it would be worth considering making each of the
supports a different lengh, with appropriate mods to thier mounting-
points, in order to prevent them from being "sympathetic" to each
other in their vibrational modes. It seems unlikely to my unqualified
mind that a 4"x6"x27" chunk of G10 would have a physical tendency to
wobble around to self-destruction, but, ***I gather*** we are talkng
about mini-thunder shockwaves at Mach 1, and not the considerable but
smaller shockwave of the rotary pushing air around...???????
Does the problem manifest itself w/o the juice applied, but at the
same speeds?

I haven't had time to keep up with the various lists, and I currently
have 572 unread messages in my 'inbox' that are doomed never to be
read, so I hope I am not making too big or an arse of myself here.
I have seen some of the photos of the construction, but can't visualise
the gap construction, so maybe I am way off base.

I read once of an early supersonic fighter prototype that would not
go supersonic; they had to give it a "coke bottle" fuselage, with the
wing roots attached at the waist, apparently to give the shock-wave
somewhere to go. Maybe this is part of the problem here; too much
Mach 1 oomph being confined? 

Hope this is at least food for thought towards the fix,
and thanks for putting up with me.

Randy