Re: Lightning Arrestors (was Geek Pig)

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Rick and all,

Another even better reference is "Electronic Ceramics, Properties,
Devices, and Applications", by Lionel M. Levinson, Marcel Dekker, Inc.,
1988, 533pp. While silicon carbide varistors are mentioned, the focus is
really on the more modern Zinc Oxide varistors, due to their performance
advantage and lower leakage current. A very in-depth discussion of
theory of operation for ZnO MOV's is presented. It concludes that the
model which seems to best correspond with observation involves hole
creation and triggered tunneling across the grain boundary once the
inter-grain voltage rises above a critical value. So it appears that the
reason is indeed related to a combination of tunneling and semiconductor
effects. 

Because of their lower leakage currents and sharper "turn-on"
characteristics, simple ZnO MOV's (with NO spark gaps) have pretty much
supplanted the older, more complex (and expensive!) spark gap and SiC
arrestors for power distribution arrestors.

-- Bert -- 
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Richard Wayne Wall by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>
> 
> Hi Bert,
> 
> Excellent pictures of the lightning arrestor.
> 
> I have a question about the silicon carbide "MOV".  What is the
> architecture and composition of the MOV.  Is it classified as a true MOV?
> Years ago I was told that the MOVs in question were innumerable random PN
> junctions and both the forward and reverse voltage drops across the MOV
> were due to the cumulative PN voltage drops.  Does anyone know how they're
> constructed and how they function?
> 
> RWW