Re: HV wire

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

There is another failier system, the reflected current pulse sees a
capacitor with zero reactance at the first moment of time. the current
source will deliver 100+ amps of peak current into fine wire before
inductive reactance has time to form and drop the current. This is a problem
in LCR circuits that can punch a hole through insulation of wires.
   Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Sun, 13 Jan 2002 11:46:41 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: HV wire
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Sun, 13 Jan 2002 16:25:59 -0700
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
> 
> I'd worry about dielectric "treeing", which is the usual failure mode in HV
> wire (some colleagues of mine at work are having all sorts of trouble
> running 18-20 kV through a (small) wire potted in silicone, so I've been
> hearing a lot about it)...
> 
> The basic theory is this:
> A small void in between the insulation and the conductor creates a field
> concentration because of low dielectric constant.
> Corona forms in the void, dissipating some heat.
> The heat breaks down the insulation, enlarging the void.
> Charge deposits on the edges of the void, allowing a "creeping spark" to get
> to the "end of the void", etc...
> 
> If you look at thin sections of the failed wire, you see many little
> microscopic voids.  Over time, the number of voids increases, and
> eventually, one gets to the outside.  Now you have a pin hole through the
> insulation, a nice current path, and bang, the wire's is useless.
> 
> The problem is that in a reasonable length of wire, it's impossible to
> guarantee there are no voids, etc., they don't show up ahead of time (and
> all it takes is one), so it's not like inspection helps.
> 
> About the only strategy to find the problem seems to be using partial
> discharge testing, which looks for the corona starting as the voltage comes
> up, but the testing in itself tends to degrade the insulation, which, in a
> one of a kind space probe is considered an unacceptable risk.
> 
> If you can hear corona hissing in your conduit, your insulation is doomed...
> Of course, it might take 5-10 years for it to degrade to the point where
> it's a problem, by which time you'll have likely replaced it. And, of
> course, the "cost" of insulation failure in your situation is not that high
> (inconvenience, etc.).
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Sunday, January 13, 2002 6:47 AM
> Subject: Re: HV wire
> 
> 
>> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <Tesla729-at-cs-dot-com>
>> 
>> In a message dated 1/12/02 8:49:43 AM Central Standard Time,
> tesla-at-pupman-dot-com
>> writes:
>> 
>> Jim Lux wrote:
>> 
>>> 
>>> ).  Vinyl tubing (e.g Tygon) is another
>>> possibility, but I don't know how good an insulator vinyl is.
>>> 
>>> 
>>> 
>> 
>> 
>> 
>> Jim,all,
>> 
>> I have personally found the transparent vinyl 1/8" thick walled
>> tubing to work quite well to hold off > 15 kVAC when used as
>> an outer sheathing around a # 10 AWG standard insulated
>> stranded wire. Then I insert the vinyl cover "hot" wire thru an
>> equal length of RF grounded aluminum, flex Romex conduit
>> (sort of like a big homemade coax cable). I know there has to
>> be some corona losses in this setup though, because when
>> I energize the "hot"wire inside with my overdriven 14.4 kV pole
>> pig with up to about 17 kV out, without any load from being con-
>> nected to my coil, I hear a considerable amount of corona
>> "hiss" inside the Romex conduit. I know the field is pretty
>> even though and I'm not overly concerned about power losses
>> from the corona since I'm running a 10 kVA pole pig. In about
>> a year, this setup hasn't failed me yet.
>> 
>> Sparkin' in Memphis,
>> David Rieben
>> 
>> 
> 
> 
>