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Re: Toroid breakout power requirements



At 01:01 PM 4/8/96 +0700, Skip Greiner wrote:

Hi Skip, et al:

>I wonder if anyone has ever attempted to determine the amount of power 
>required to cause a given size toroid to discharge in an arc. The way I 

I believe TESLAC II has a chart that has some approximate figures for
various given toroid sizes, although I do not know if they are based on the
actual breakdown voltage (arc) of the toroid's physical characteristics.

>see it, a toroid has a physical shape which limits the amount of voltage 
>which it can withstand before a breakdown in air. Since the voltage is, I 
>believe, directly related to the charge on the toroid and the charge is 
>limited by the power available, then doesn't it follow that there is some 
>minimum power required to cause a specific sized toroid to discharge?
>This all assumes, of course, that some standard set of conditions prevail 
>such as humidity, temperature, etc. Several recent posts have alluded to 
>a relationship between the geometry of the sphere, oblate, toroid, or 
>whatever and the maximum voltage it will stand off. 

The maxiumum voltage a toroid can withstand is mainly dependent on the size
and symmetry of the electric field produced by the toroid when it is being
charged. (basically)

For a simple analogy, a toroidal discharge terminal is a single terminal
capacitor (read "isolated" capacitor).  If one looks at say a parallel plate
capacitor, it's breakdown voltage is mainly determined by the amount of
energy the electric field is able to store before an arc forms between the
plates.  The electric field is dependent mostly, thought not soley, on:

     (a)  Geometry of the plates 
           (square, circular, ect...)
     (b)  Size of the plates
           (more specifically surface area)
     (c)  Seperation between the plates 
           (thickness of the dielectric medium)
     (e)  Type of dielectric medium 
           (polyethylene, air, ect..)
     (f)  Quality of dielectric medium
           (high, medium, low density)
     (g)  Type of current applied to plates
           (AC or DC)
     (h)  Effects exterior to the capacitor's electric field
           (such as high-intensity magnetic fields in the
            vacinity of the capacitor)

This is standard for the electric fields of all capacitor geometries,
whether they be plate, spherical, cylindrical, or toroidal.  Thus if one
removes one of the plates of the capacitor, such as is the case in an
isolated capacitor, one is actually only increasing the plate spacing to
some distance out to infinity.
Which in turn increases the size of the electric field, which then allows
more energy to be stored in that electric field.  This applies to the
toroidal discharge terminal as well, by allowing the distance seperating the
inner plate (inner torus shell) from the outer plate (outer torus shell) of
the toroidal capacitor to progress to infinity, one increases the magnitude
(size) of the toroid's electric field.  Increasing the electric field allows
more energy to be stored, before eventually the air surrounding the toroid
breaks down and arcs are produced.

Thus for toroidal discharge terminals, the main determining factors for
voltage (arc) breakdown are:  (a)  surface area of the toroid, (b)
quality(Index) of the air/gas surrounding the toroid, and (c)  fields and
objects external to the electric field of the toroid.  Thus the voltage
breakdown point is based on the voltage component of power.

Now as far as the current component of power, it does relate to the amount
and distribution of charge on the toroid.  Which basically determines at
what position(s) and the manner in which the arc discharges from the
toroidal discharge termainal.  The discharge of the energy stored in the
electric field of the toroid (read "arcs" or "sparks") is dependent on the
charge magnitude and charge distribution on the toroid (where it discharges
from, how it discharges, what the discharge looks like, ect...).  Thus the
arc or discharge configuration is based on the current component of power.

Therefore, the charge (read current) determines the configuration of the
discharge while the electric field (read voltage) determines when the
discharge will take place.