Re: SRSG electrode spacing

In a message dated 99-06-20 16:24:31 EDT, you write:

<< 1) How much rounding of the electrodes is desirable?. 
> Since anything from just deburring the edges to a full hemisphere is
> possible, I would appreciate guidance for powerlevel 3 kW:(1/4 "
> electrodes) and 10 kW (3/8 " electrodes) Both 3000 RPM (50Hz) 2 rotating
> electrodes, Amount of stationary electrodes will depend upon breakrate,
> but probably 4 sets for 200 bps, to keep cap size down to manageable
> levels.

Hi Finn,

Most people probably just deburr them and leave them square, at high
or low power.  I like the idea of a hemisphere, or near hemisphere, to 
stop too-early firing.  On my sync rotary, I compromised, I made
the fixed electrodes a near hemisphere, and the spinning electrodes
with square or flat ends.  I suppose at the power goes higher, there's
danger that the hemisphere type will behave as a point, and get too
hot, so the middle of the hemisphere should maybe be flattened. 

 > 2) Which total spacing should i use ?.
> I could space them as close as motor endfloat allowes, so that the gap
> will be very short, this will make the gap fire before the electrodes
> align, making the gap distance decrease during dwell, create a long
> dwell period, and also present a short gap for the transformer to arch
> into, after the primary ringdown. This may not matter, since the cap
> will pull the voltage down. Hmmm.....

Generally for smooth firing, they have to be somewhat close, but with
your extra high voltage, they should fire no matter what.  I suppose 
the gap spacing will affect how much voltage is left on the cap after
ringdown.  There is a rare condition that can occur with wide electrodes,
close spacings, small caps, and too little ballasting, which permits
the gaps to re-fire while they're still aligned, this wastes a lot of power,
and gives poor operation.  You could just try different spacings to see
what works best in your system. 
> Setting the electrodes wide, like creating a breakdown voltage across
> the fully aligned electrodes equal to the desired total breakdown
> voltage would result in a very short dwell period, but the arclength
> would also not get shorter during dwell.

I don't think the mechanical dwell period makes much difference, 
since the gap will stop firing once the energy is gone, even if the
electrodes are still aligned.  I think if you try to make the spacings 
wide enough to try to help the quench or break the spark, etc, you'll
just get unsteady firing.

John Freau
> I suppose something inbetween will be needed, so any experiences on this
> subject will be appreciated.

> Cheers, finn >>