Re: capacitance formula

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <teslalist-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
 >
 > Original poster: "Crow Leader by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>
 >
 > ----- Original Message -----
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Wednesday, June 04, 2003 8:34 PM
 > Subject: Re: capacitance formula
 >
 > [cut]
 >
 >  > The voltage across each material will be inversely proportional to the
 >  > reciprocal of its dielectric constant.  Partially filling a space with
 >  > high deiectric constant material can lead to voltage breakdown which
 >  > wouldn't otherwise occur.
 >  >
 >  > Ed
 >
 > This sounds backwards. Materials with a lower dielectric constant (assuming
 > same thicknesses) will develop a higher voltage when charged than higher k
 > materials mixed with them. Take for instance potting in HV stuff with air
 > bubbles or voids. They break down first, same issue with high voltage cable
 > with dielectric cores, the idea with them is to make sure there voids
 > between the strands of wire and insulation don't develop high voltages and
 > get destroyed from corona. Same with liquid filled capacitors. Air bubbles
 > will develop corona and eventually destroy the solid dielectric, not the
 > other way around.
 >
 > KEN

	Suppose you take two plates with almost enough voltage for breakdown
and stick a high-dielectric constant material between them.  Most of the
voltage drop will be across the air, which will then break down.  All
depends on the numbers of course.  Bubbles or voids in HV AC insulation
introduce failures if they are the sites of corona which degrades the
insulation around them.  A standard test for corona is to apply a
high-voltage AC across the test specimen and listen for radio noise from
the corona.

Ed