Re: insulation testing

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

> Any suggestions as to an "apparatus" that can be made easily? I have various
> NSTs, variacs and transformer oil at hand along with a scope and several
> multimeters.

I have used two methods for testing of insulators (for the construction
of
electrostatic devices):

To test if a material is a sufficiently good insulator, I charge an
electroscope and touch it with a sample of the material held in my
hand. A good insulator doesn't discharge the electroscope immediately.

To test for breakdown voltage, I connect the sample between two
high-voltage capacitors of a few tens of pF (Leyden jars), in
parallel with a high-voltage, high resistance material (a piece
of wood). The other ends of the capacitors go to a calibrated
spark gap and a high-voltage source (static machine, NST, etc.).
The power supply charges the capacitors to the gap voltage, and
when the gap sparks, almost the the same voltage is suddenly applied 
to the sample. I can then measure how much voltage the sample 
supports by adjusting the gap spacing.

Corona is caused by air ionization, and have little influence
of the material. If you see corona over the material, it's 
actually a good sign, since the electric current is passing
through the air and not through the material.
See also if the material "draws" corona. This is a bad sign.

Antonio Carlos M. de Queiroz