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Re: Isotropic Capacity

Subject:  Re: Isotropic Capacity
  Date:  Wed, 28 May 1997 20:29:27 -0400 (EDT)
  From: richard hull <rhull-at-richmond.infi-dot-net>
    To: Tesla List <tesla-at-pupman-dot-com>


At 11:44 PM 5/27/97 -0500, you wrote:
>Subject:  Re: Isotropic Capacity
>  Date:   Tue, 27 May 1997 09:29:10 -0500
>  From:   David Huffman <huffman-at-FNAL.GOV>
>    To:   Tesla List <tesla-at-pupman-dot-com>
>
>
>> Subject:  Re: Isotropic Capacity
>>   Date:  Mon, 26 May 1997 13:47:40 -0400 (EDT)
>>   From:  richard hull <rhull-at-richmond.infi-dot-net>
>>     To:  Tesla List <tesla-at-pupman-dot-com>
>> 
>> 
>> snip
>> 
>> >  A coiler would be interested in the exact capacitance value of
>the
>> >toroid
>> >when on the top of the secondary coil because with the secondary
>coil
>> >inductance it determines the operating frequency of the TC. 
>> >
>> >The capacitance of the sphere is higher when isolated in space
>than when
>> >on
>> >the TC secondary coil. Do any coilers know why?
>> >
>> >  John Couture
>> >
>> >
>> I have always found that any isolated capacitance when considered
>as a
>> capacitive device and connected to or near enough to another
>capacitive
>> isolated device forms a simple series capacitive circuit.( with
>> reference to
>> gorund)  This makes the large device appear to possess less than
>its
>> full
>> isotropic capacitance with reference to ground, which is where we
>always
>> reference most isolated isotropic capacitive measurements on earth.
>
>> 
>Now I'm really confused. As a sphere is moved away from ground its
>capacitance goes up? As a second sphere is brought closer to one
>being measured, the capacitance goes down? Even a series circuit to
>the second capacitor is in parallel with the first wrt ground.
>Am I reading this wrong? This must be one of those cases where the
>real world teaches us something.
>Dave puzzled Huffman
>
>
>>  These series circuits are subtle and complex in multibody problems
>> especially when close to the earth with relation to the sizes of
>the
>> bodies
>> under study.


David,

The series system in the coil case is the sheet capacitance of the
coil's
secondary windings which are between the toroid and ground. (sort of
like a
floating metallic pole.   The interturn capacitance enters into the
whole
business as well. The proximity of all make any simple measurement
indicate
the terminal to be below calculated value.  Remember that the whole
system
remains a series resonant thing.  Do not misunderstand, for an adroit
observer would realize that if he strictly applied this "simple speak"
that
the limiting capacitance of the system would have nothing to do with the
terminal capacitance but instead the smallest series capacitance value
in
the system! (wherever and whatever that might be)  This is not so, as
the
corona sheath enters the figuring when in operation and interacts in as
yet
only imagined ways.

Large (really large) terminals are rarely 10X their major axis from
ground
and develop parallel "plate capacitance" at some point thus overiding
much
of the "series effect" in huge systems.

Like I said.... complex.


Richard Hull, TCBOR