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FW: Jennings vacuum interupter


From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: 	Saturday, November 08, 1997 11:19 PM
To: 	Tesla List
Subject: 	Re: Jennings vacuum interupter

At 12:05 PM 11/8/97 +0000, you wrote:
>
>From: 	Esondrmn[SMTP:Esondrmn-at-aol-dot-com]
>Sent: 	Friday, November 07, 1997 2:57 PM
>To: 	tesla-at-pupman-dot-com
>Subject: 	Re: Dump the RSG!
>
>In a message dated 97-11-07 07:35:08 EST, you write:
>
><< We have replaced an RSG with a Jennings vacuum interrupter and it is
> giving superior performance. They are tricky to adjust but once adjusted
> require no further attention. There are no moving parts so there is no
> maintenance. These are standard electric utility switches and are sometimes
>
>   John Couture  >>
>
>John,
>
>Can you give some details as to how these are built?  Have you taken them
>apart?  How do they work in a Tesla coil application?
>
>Ed Sonderman
>
>----------------------------------------------------------

   Ed & All -

  The Jennings vacuum interrupter we used is a relatively simple electrical
switch consisting of two electrodes (one movable) in a vacuum. The
electrodes are huge, 1 1/4 inch dia. made of a special alloy. The secret of
operation is that the movable electrode is adjusted to a very small gap
(about 5 millinches) and used as a fixed gap. This adjustment is very
critical and difficult to make but once optimized can be left alone. It has
been in operation for over a year and is still working fine. However, we
believe more research for use with Tesla coils is needed. A short
description and drawing of the vacuum interrupter is shown in my Tesla Coil
Design Manual. 

  The vacuum interrupter is capable of a limited number of operations. We do
not know what this limit is when used with Tesla coils. The device is in a
sealed vacuum so taking it apart would not be wise. It is now being used
with a 2500 watt Tesla coil giving 5 ft sparks. This was better than what
the RSG was doing.

  The circuit opening action of this type of vacuum interrupter is
interesting. It prevents an undesireable type of circuit interruption called
chopping. With an inductive circuit (TC primary) opening the circuit too
quickly causes large transient voltages that can damage the insulations in
the circuit (like neon transformers). The vacuum interrupter gives what is
called a soft interruption which does not produce damaging transients.

  The typical fixed and rotary spark gaps can cause chopping because they
operate at atmospheric pressure. The prevention of chopping with these
devices is timing. They must interrupt at zero current which is difficult to
maintain. Chopping may account for those rare extra long sparks because of
the higher voltages in the primary and secondary? But they can also mean
damaging voltages. Is this why so many secondaries are ruined?

  We believe the vacuum interrupter has possibilities but requires more
research. More information can be obtained from Jennings, a Lear Siegler
Company at 970 McLaughlin Ave. San Jose, CA 95122. Note that Jennings also
makes vacuum interrupters for RF transmitters (smaller electrodes). These
are made of glass and not ceramic like the electric utility devices and are
less rugged. At one time Robert Golka was selling the utility type for about
$300. I have not heard from him for over two years.

  Gary Weaver - These devices look like high current fuses, diodes, SCRs.
They are ceramic tubes with large connectors at each end. One connector has
a screw and nut. By loosening the nut you can tell when the contacts close.
I do not have a scanner for postings.

  Charles Bush - The vacuum interrupter will replace the RSG on a small coil
because they will operate at voltages as low as 7 KV. the 10 KA rating is a
momentary rating and the catalog shows many other ratings. However, these
ratings have little to do with Tesla coils. We have the 600 RMS amp
continuous rating unit.

   John Couture