Re: [TCML] Corona Supression

[Brandon Hendershot <brandonhendershot@xxxxxxxxx>]

Alright,
So is there anything like "corona dope" inexpensive enough to be  
applied and removed whenever I need to take things off the terminals?  
Does corona dope or glyptal need to under vacuum to be applied?
Thanks Guys,
Brandon

On May 16, 2010, at 9:12 PM, jimlux <jimlux@xxxxxxxxxxxxx> wrote:

> 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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