Re: [TCML] Corona Supression

[jimlux <jimlux@xxxxxxxxxxxxx>]

Brandon Hendershot wrote:
> I got a few bolts used as terminals I'd like to cover up. Some other 
> structural nuts and bolts running close to wires I'd like to get some 
> extra assurance on as well. I figured a round cap nut ought to suffice, 
> but I prefer the idea of sticking on some rubber insulation.
> Any kind of rubber caps good for HV? I remember seeing something pretty 
> fitting of the description in the hardware section down at home depot. 
> It looked way too thin though...
rubber caps will be worthless... if there's any air gap at all between 
the metal surface and the rubber, you'll get corona in there, and it 
will rapidly degrade the rubber into dust/mush.

Corona is all about radius of curvature.

If you want to cover it with an insulator, you need something that 
conformally coats it.  Corona Dope or Glyptal are the classic century 
old approaches.. kind of a runny plastic dissolved in a volatile 
solvent, so it coats well, without leaving gaps.  SIlicone is popular 
today, but tricky, because you really have to do it under a vacuum, so 
that tiny air bubbles don't form.  Bubbles create field concentrations, 
which cause corona inside the bubbles, which causes dielectric 
"treeing", which results in breakdown (mechanical and electrical, both).

You begin to see why liquid or gas insulators are so nice... plunk it in 
the tank of oil, pull a bit of a vacuum to get the bubbles out, and 
you're done.



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