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Re: Corona Loss? AAaaahhhh!!!
Yuri Markov wrote:
> I'm confused, to say the least.
> I recently posted a message asking about capacitors, and what is and
> is not workable. About half the responces I got mentioned corona
> loss. What is corona loss? What causes it? Why is it a problem? And,
> of course, how do I prevent it?
At any point where the electric field exceeds about 30 kV/cm in air,
the air gets ionized and conductive. If there are no nearby conductors,
what is observed is a blue glow that indicates that electrons are
jumping from atom to atom around the conductor, draining current in the
process. Charged ions move too, and it is even possible to feel a
"wind" coming from points charged with high DC voltages ("electric
wind").
If there is a conductor at close enough distance, a spark may form.
The streamers seen in a Tesla coil are just high-current RF corona,
where the glow gives way to spark-like ramifications.
As corona is caused by high electric fields, and the fields are more
intense at points, corners, or edges, high-voltage conductors in air
must have all the surfaces with the large radius of curvature, in
order to do not produce electric fields of more than the air breakdown
limit.
In the case of corona losses in primary capacitors, as frequently
mentioned in this list, corona occurs mainly at the edges of the
capacitor plates, creating conductive pathes that can lead to
catastrophic failure if a high-energy spark forms. The ionized air
also produces chemical reactions that progressively damage the
dielectric material of the capacitor, eventually leading to failure.
The solution is to put all the capacitor not in air, but immersed in
a substance that supports higher electric fields without ionization,
as several types of insulating oil.
Antonio Carlos M. de Queiroz