Re: [TCML] Corona Supression

[nancylavoie@xxxxxxxxxxx]

Yeah,Glyptal works okay and you just brush or spray it on.I bought something like a 20 oz. can several years ago and used on numerous projects.Made a few experimental inductance coils that looked ugly as sin because of the color of the stuff but other than that,seems to work alright.Will probably flake off if you disturb whatever coat too much but you'll most likely have the can the rest of your life.My can of it never seems to diminish!Kind of pricey though (about 50$ through Eastwood automotive).Give it a try.   Wyatt

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-----Original Message-----
From: Brandon Hendershot <brandonhendershot@xxxxxxxxx>
Date: Mon, 17 May 2010 09:03:11 
To: Tesla Coil Mailing List<tesla@xxxxxxxxxx>
Subject: Re: [TCML] Corona Supression

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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