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0.5*C*V*V vaild? (Was Output Voltages and Voltage/Length)




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From:  Mark S. Rzeszotarski, Ph.D. [SMTP:msr7-at-po.cwru.edu]
Sent:  Tuesday, February 10, 1998 1:08 AM
To:  Tesla List
Subject:  Re: 0.5*C*V*V vaild?  (Was Output Voltages and Voltage/Length)

Hello All,
I said:
>> 2.  Adding a toroid or sphere to the top tends to linearize the voltage rise
>> somewhat, so that the turn-to-turn voltage stress is lessened especially
>> near the top of the coil.
to which Greg Leyh replied:

>I have also noticed in PSPICE that the voltage dist 
>along the sec becomes much more linear when a large
>topload is added.
>If the voltage dist along the sec is mostly linear, 
>then is it reasonable to treat the sec ckt as lumped
>elements, and forget the 'antenna theory' treatment?
        Regrettably, I think the answer is yes.  The math is really
interesting but in the long run the system sure acts like a lumped circuit.
The voltage rise along the secondary is nearly a sine wave from 0 to 90
degrees along the length of the wire if no toroid is added (typical tube
coil).  With a large toroid on top, the phase angle may only go through 0 -
60 degrees or less, and the voltage distribution is much more uniform, since
sine(theta) is approximately linear for small theta.  There is also an
electrostatic shield effect brought on by the toroid which helps prevent
breakout from the turns near the top, where potentials are several orders of
magnitude greater than the breakdown voltage of the insulation.
        The antenna theory stuff works out better if you build systems like
Sloan did - coil in a can stuff which behaves more like a waveguide.
Regards,
Mark S. Rzeszotarski, Ph.D.