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SG questions explained Was Re: epoxy/adhesive/SG woes



Hi Stan,

> Original Poster: Stan <sdarling-at-columbus.rr-dot-com>
snipple
> >From my own obvservations it appears that most of
>SG heating is due to the electrical arc through the air,
>not the actual current being 'switched' through the
>conductor.  Is this true?  If so, has anyone tried a SRSG
>using brushes like motors have to completely eliminate air
> arcing?

Well the heating actually is caused by the plasma (flame)
temperature of the arc. This is in turn (in some way)
proportional to the amount of pulse current flowing through
the gap. Iīm not quite sure, but I would guess it would follow
the square rule (4x the current, 2x the temp). The pulse
temperatures of such a plasma can be VERY high. In case
you have had a look at my dadīs plasma lab, which can be
found on my webpage at:
http://rwbuchner.future.easyspace-dot-com/
you would be surprised at the temp, which a simple arc
can achieve. A piece of burning Mg is nothing in comparison.
This is why you need heavy materials and/or air flow in the
gap (to help quench and cool the gap). My coil is running at
around 600A peak and if I run the coil for more than 45sec -
1 min, youīll get bad burns, if you touch the CU pipes. Your
idea of using slip rings and brushes wonīt work, because of
two reasons:

- You would need hefty equipment to losslessly (!) commutate
that amount of power.

- In order for there to be no air gaps (sparks), you would need
to use a continuous ring, which means the power is never
switched off, which, in turn, means the whole TC idea wonīt
work.

The spark gap has been around over 100 years and to date,
there are no semiconductors (that I know of), that can switch
that high a voltage AND that high a current in THAT short
amount of time. Sometimes simplicity simply rules ;o)

> The other thing about SG's that I don't understand is
>the general theory.  Does quenching refer solely to the
>desire to remove heat/ionized air to be sure that the
>breakdown voltage of the gap(s) remains relatively
>constant or does it refer to more than that?

No. not quite. Quenching refers to the gapīs possibility to
switch the current on and off at the *proper* moment. I say
proper here, because a while ago there was a discussion
about the necessity of 1st notch quenching. As you can
imagine, it is next to impossible for a RSG to overquench.
This would imply using super high rotary speeds and big disk
diameters. A static gap (if pressure quenched for example)
can INDEED overquench, simply because it is not a force
triggered mechanism, but relies solely on air breakdown (the
ionization) to fire. Think of a simple lighter in a windy area. It
is a pain to keep the flame going as it gets windier. Pretty
much the same can happen, if you use a high volume, high
pressure air flow to aid quenching. Your *flame* can actually
be blown out, long before your TC has a chance of transferring
all itīs power from the primary into the secondary circuit.

>I also don't understand how increasing the BPS of a
>SRSG increases stress on system components.

Consider the following (okay it is a far fetched analogy, but you
will get the idea): What is harder? Walking (low bps) or running
(high bps) a certain distance?  The higher your bps is, the more
instantaneous power you have (provided your setup can supply
it, that is). The more often your gap fires, the more often your
cap will have to charge and recharge. You wouldnīt believe what
kind of (purely mechanical) stress the dielectrica is subjected to,
when you simply charge and discharge a cap. Try taking a piece
of sheet metal and slowly bending it back and forth. You will
notice it doesnīt get warm and you can do this quite a few times,
before it actually breaks. Now take a piece of the same metal
and bend it back and forth really fast. It gets hot and will fatigue
quite a bit sooner. Pretty much the same in a cap.The dielectrica
will only take so much stress and warmth before it dies. Same
goes for the metal foil used in the cap. As a matter of fact, if you
discharge a big (but not super heavy) cap into a direct short, you
can actually feel it jump inside. It is pure mechanical stress that
will kill your equipment at very high bps rates. Sort of like
over-exercising your heart or over- overclocking your computerīs
CPU.

Coiler greets from Germany,
Reinhard