At 08:51 PM 7/12/2006, Red wrote:
>Hi, Gang;
>
>I scribbled a few calculations concerning the temperature rise if a
>copper pipe filled with water conducts a lightning strike.
>
>I assumed a 0.5" OD pipe with 0.050" wall thickness and I assumed a
>30,000 A current for a duration of 1 millisecond. That makes a worse
>than average strike.
<snip>
looks basically sound to me. This is actually not a lot different from the
water resistors used in HV pulse power applications. I've built various
sizes as things like charging resistors for a marx generator, as well as
the load dump.
http://home.earthlink.net/~jimlux/hv/rwater.htm has some similar
calculations to yours.
I would suspect that electromagnetic forces might have a bigger effect. The
fast pulse at high current can put pretty high forces on the pipe. It's a
real design issue for bus bars in electrical substations for instance: you
don't want things breaking during a fault. Heck, even the regular 60 Hz
current at several thousand amps puts a pretty impressive force on the bus
bars.
F = 2E-7 * I1*I2/r
Put, say, 10 kA on the two buss bars, and have them 50 cm apart, and you're
looking at 1000 N (about 200 pounds). Put a 100 kA transient from a fault
into the system, and you're looking at 100kN. (and therein lies the secret
of shrinking a quarter to smaller than dime size...)
Jim
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