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Re: QUENCH TIMES

Hi Marco, All,
    The fastest quenching gas switch is hydrogen at high pressure.
There is an alternative.  A powder filled switch.  Try calcium
carbonate (or powdered limestone) and space your electrodes close
together.  A large surface area helps also.  see the following:

    +ACI-Novel Short Recovery Time High Voltage Switch+ACI-, M. Dufour et.
al., Institute of applied Physics, Berne Switzerland.

Quench times down to a few microseconds have been achieved with 0.02
uF charged to 25 kV at 3 Hz.  You should be able to go faster with a
larger surface area.

This is all I can say about this subject.


-----Original Message-----
From: Tesla List +ADw-tesla+AEA-pupman-dot-com+AD4-
To: tesla+AEA-pupman-dot-com +ADw-tesla+AEA-pupman-dot-com+AD4-
Date: Monday, January 04, 1999 4:49 PM
Subject: QUENCH TIMES


Original Poster: +ACI-Marco Denicolai+ACI-
+ADw-Marco.Denicolai+AEA-tellabs.fi+AD4-

I am designing a TC with a 62 kHz oscillating frequency. As I would
like to
quench at the first notch with a rotary gap, I supposed I can set my
coupling coeff. so that the first notch will come after about 5
oscillations at 62 kHz. That makes about 80 us to reach the first
notch.

So the quest is how to achieve such a short quenching time.

+AD4-From available literature I found that a spark can possibly form when
the
electric field exeeds 40 kV/cm and surely forms when it exeeds 70
kV/cm.
So, if you write down how the stationary and rotating electrode
distance
evolves with time, and calculate the time the electric field is
greater
than 40 kV/cm, you should get a rough figure of your quench time.

I did that and for a peak voltage of 60 kV, rotating speed of 6000
rpm,
rotor diameter of 12+ACI- I got a quench time of over 500 us (+ACE-). Because
I
cannot reasonably increase either speed or rotor diameter, I took the
book's solution and designed to insert a static spark gap in series
with
the rotary one.

By doing that I plan to decrease the voltage at the RSG down to 15 kV:
that
way the theoretical quench time drops down to 100 us, that gives at
least
some hope to achieve the required 80 us.

I was thinking to use a high resistance voltage divider to have 15 kV
on
the RSG and 45 kV on the static gap. The static gap would be a series
of
sections, to easily set its trigger voltage. The voltage divider
should
also remove a part of the randomness involved in air gap trigger
voltage.

Any suggestions or comments about the above story?

Thanks to everybody.