Re: Looking for an 18KV distribution arrester

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FIFTYGUY@xxxxxxx 

In a message dated 5/1/07 12:36:51 A.M. Eastern Daylight Time,
tesla@xxxxxxxxxx writes:

>Fascinating.  Yes, the 3kV ones are by Kearney, but I
>too  broke one open (literally--with a sledgehammer)
>and I didn't see such a  thing.

    I didn't notice it until the end - it was the last  thing I saw after I
had tested it, dissected it, and inspected it. It was a  little unnerving,
since I wasn't wearing eye or ear protection in my crowded  garage.

>  All I saw was a silicon carbide disc about 1.5" long and 1.5"  in
>diameter with spring-loaded contacts to hold it in place.

    Same here!

>  Could have missed something in the rubble, though!  ;-)
> Unfortunately, this was years ago and I didn't take any pictures.

    IIRC it was a Winchester/Olin .22 blank (big "X"  headstamp).

> I played with one using a
>15/30 NST and variac and found  that I could hear a
>faint buzzing when the thing went into  conduction.
>Seemed to work great.

I also checked with a 15/30 NST, hi-volt probe on  DMM, and noted the same.

>I've heard of explosive charges being used in fuses,
>but not  in arresters.

    I've seen some supplemental coordinating  distribution fuses blow (500A
at 32kV rating), but I think they blew in half due  to internal 
pressure alone.
You have to have done something pretty stupid to  blow one of those up,
anyhow!

> That is interesting.  I may
>have to break another one  open now! :-))  Of course, if there's rim-fire
ammunition in there,  a
>sledgehammer may not be the best tool to use this time!!! :-O

It's a blank, but even the lowly .22 LR has a  nominal chamber pressure of
24,000 psi. I've heard that the ones for  powder-actuated tools have 
even higher
pressure ratings. A "little" .22 is  capable of a lot!

>The larger 21kV units are all MOV+gap types, I'm pretty  certain.

I *did* notice some sparks shooting out of my  larger arrestor when I was
running a mis-tuned 6" coil with my pig last week. So  an internal 
gap would make
sense.

-Phil LaBudde




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