[Prev][Next][Index][Thread]

Thyratron pair (was DC Drive)



---------- Forwarded message ----------
Date: Sat, 11 Oct 1997 08:26:45 -0700
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Thyratron pair (was DC Drive)

Tesla List wrote:
> 
> ---------- Forwarded message ----------
> Date: Thu, 09 Oct 1997 22:31:27 +0000
> From: Greg Leyh <lod-at-pacbell-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: DC drive
> 
> Larry Robertson wrote:
> 
> > I still think Cpri will remain charged as the gaps comutate, resulting
> > in Lpri seeing 30kV on each discharge except for the very first one.
> 
> You are correct.  I misunderstood the ASCII schematic.  The primary
> waveform will decay to zero, leaving a DC component of 15kV on the
> resonance caps.  If the next gap connect is reverse polarity, the
> primary will see a 30kV peak waveform.
> 
> -GL

Greg, Larry, and all,

If we assume that the tank cap is initially charged to -15 KV from the
previous bang, the next bang will disruptively charge it to +15 KV.
However, because of the primary inductance, the cap voltage will
actually overshoot by half the overall change in capacitor voltage, or
ANOTHER 15 KV, and then ring down to the steady-state level of +15 KV.
So, when the gap initially fires, the capacitor voltage excursion will
actually be 45 KV on the first 1/4 cycle, with a 30 KV peak-to-peak
ringing amplitude (less gap losses). While the primary voltage amplitude
is only 30 KV, the capacitor must be conservatively rated to withstand
at least the 45 KV transition seen at the start of each bang. 

After studying this circuit a bit more, it appears that a this may also
be a very good way to use a pair of thyratrons for performing quenching
experiments or for building an electronic disruptive coil. With this
circuit, a conducting thyratron should never see potentially damaging
voltage reversals because of the DC offsets. If we design the circuit so
that Vpeak of the thyratron is greater than 2xVin, and design it in such
a fashion that we ONLY alternately trigger T1 and T2, the approach
should work. By varying the trigger pulse width, triggering on any notch
could be controlled. It may even be possible to "quench" at any primary
current zero crossing. A pair of 4C35's should be able to handle Vin of
up to 4 KV, and a pair of 5C22's, up to 8 KV.

The circuit below does, unfortunately, require filament transformers
with high breakdown voltage ratings, but one (with two secondaries)
could easily be fabricated from a stripped-down neon transformer.
Removing the HV secondary windings and the shunt plates, and winding
required number of turns of high voltage wire for two LV secondaries
should do it. Note: accidental simultaneous triggering of both
thyratrons might make for some unfortunate pyrotechnics... :^(  

                       
                      T1
                Anode   |
     -----------------| | <------------  
             |          |             |
        +    |                        | 
           -----                      | 
       Vin -----                      |
        -    |       Cp               |
             |      | |      Lp       | 
     ---------------| |----OOOOOOO----- 
             |      | |               | 
        +    |                        |
           -----                      |
       Vin -----                      |
        -    |                        |
             |          |             |
     -----------------> | |------------
                        |  Anode
                      T2
                 
-- Bert H --