tom wrote:
On 7/23/2010 4:23 PM, Jim Lux wrote:

If the ball is wet, especially with distinct droplets, then you can get
corona forming much earlier. The electrostatic forces tend to make the
droplets fly off.


Non-rhetorical question(s).

I must be missing something then. Why don't I see corona on the tips of
leaves at the tops of my trees? Trees are pretty conductive when
hundreds of kilovolts are involved.

In the clear air field (the 100V/meter sort of thing), you're not going
to see corona, because the voltages aren't high enough.

In thunderstorm type fields, you would see corona, if you look closely.
There's an interesting paper (which I can't find right now, but I'll
look) where someone measured the current from a field of wheat.

Not all breakdown will produce visible corona.

If you have a resistive thing (i.e. a tree), covered with sharp points,
then the object tends to adopt the overall voltage profile surrounding
it, so there's not much net difference in voltage between the
leaf/needle and the surrounding, so the field isn't locally high, so
there isn't any breakdown.



Or my antenna masts for that matter, 'cause they are grounded, too.

You probably DO have corona breakdown, it's just not noticeable. It's
kind of a challenge to measure microamp currents in a 100 foot tower.
And if that milliamp or microamp is spread over a large area (i.e. your
tower isn't a smooth machined surface with only the one point having
small radius of curvature) then it would be less noticeable.