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Re: Question about ballasting and VA

At 03:11 AM 03/05/2000 +1300, you wrote:
>At 05:40 PM 3/3/00 -0700, you wrote:
snip...
>Terry
>
>I'm not sure that the behaviour of the tank charging circuit is neccesarily
>non-linear.
>
>Something I've always wondered about is if one can consider an inductively
>ballasted tank charging system to be a simple low-pass filter? e.g. if you
>reflect the primary side L to the secondary side of the HV transformer and
>consider it with the tank C, don't you just get a L-section type filter?
>
>If this idea is correct, then the charging circuit will have a linear
>response over the region we are interested in. When the inductance is lower
>than a critical value, the current will only flow in short pulses and the
>total power entering the tank will be small. Clearly the behaviour will be
>non-linear in this region. But when the critical inductance is exceeded,
>the flywheel effect of the inductance will cause the current to flow
>continuously and the output voltage will only change slightly with changes
>in the load resistance. Assuming the impedance matching point is greater
>than the critical inductance, then predicting the filtering action under
>this condition is straightforward.
>
>Alternatively, since we are feeding linear components from a linear source,
>shouldn't we expect to get a linear response?
>
>Thinking out loud,
>
>Gavin Hubbard
>

The spark gap fires and presents basically a step function to the system.
This takes the circuit's analysis out of simple frequency domain LRC
analysis.  While one "could" use series expansions and all, the computer
becomes the tool of choice...

Often you can "fake" the impedances and use an equivalent impedance.  This
has to be measured or calculated.  This equivalent impedance is roughly the
"average" impedance of the nonlinear portions of the circuit.  I do this
for the output arc impedance when I say it is 220K ohms plus 1pF per foot
of arc.  The actual impedance is dramatically time varying but this
"average impedance" allows models to match the output arc fairly well. 

Also, the 120 BPS firing of the gap will probably make the "sweet spot"
more critical as a number of people have observed.  A static gap will just
fire when the voltage reaches the firing level.  However, a rotary gap will
only fire at a specific point in time.  Thus the rest of the system will
have to match that timing making the sweet spot that much sweeter...

Cheers,

	Terry
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